WO2017048421A1 - Methods and systems for near-simultaneous measurement of neuron activity and neurotransmitter concentration - Google Patents

Abstract

Methods and systems providing near-simultaneous measurements of neurotransmitter release and neural activity are presented. The system has a voltammetry probe for neurotransmitter recordings and an electrophysiology probe, including a relay switch, for neural ensemble recordings. The electrophysiology circuitry is isolated from the applied voltage of the voltammetry prove when the switch is open. The voltammetry probe features a novel grounding/referencing scheme that applies a voltage to the working electrode and grounds the reference electrode. This configuration may help reduce interference between electrophysiological (voltage/action potential) and voltammetric recordings.

Description

METHODS AND SYSTEMS FOR NEAR-SIMULTANEOUS MEASUREMENT OF NEURON ACTIVITY AND NEUROTRANSMITTER CONCENTRATION

CROSS REFERENCE

[0001] This application claims priority to U.S. Patent Application No. 62/218,994, filed September 15, 2015, the specification(s) of which is/are incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

|0002] The present invention relates to fast-scan cyclic voitammetry and neural ensemble recording, more particularly to methods and systems for measuring neuron activity (action potential) and neurotransmitter (or biogenic amine) concentration nearly simultaneously.

GOVERNMENT SUPPORT

[0003] This invention was made with government support under Grant No. DBS 1450767, awarded by NSF. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

|0004] Complex behaviors such as learning and decision-making depend on coordinate interactions between groups of neurons. These interactions are thought to be regulated by neuromodulators such as dopamine. Understanding the neural basis for such behaviors therefore may depend on measuring chemical signaling and its effects on the coordinated electrical activities of neurons. The present invention features methods and systems that help enable mapping the impact of neurotransmitter release on interactions between neurons during behavior.

[0005] Fast-scan cyclic voitammetry (FSCV) is an electrochemical technology used for acquiring real-time measures of neurotransmitter release. FSCV is able to measure several neurotransmitters (e.g., dopamine, 5-HT/serotonin, norepinephrine, glutamate, etc.) because these substances can be oxidized at low voltages, providing selective electrochemical detection based on voltage-dependent oxidation and reduction processes. Briefly, a voltage that is sufficient to oxidize the neurotransmitter is rapidly cycled across an implanted carbon fiber microeiectrode. The oxidation process results in current flow at the electrode surface, and the amount of current is measured and subsequently converted into concentration of the neurotransmitter in the vicinity of the electrode tip. The voltage that is used may be within a range, for example from -1.1 to +1 .4V. As an example, the voltage range or sweep for dopamine is -0.4V to 1.3V to - 0.4V (at 400 V/s). The voltage sweep for serotonin is 0.2V to 1.0V to -0.1V to 0.2 V (at 1 ,000 V/s). Scans may be, for example, about 5 ms in duration.

[0006] Single-unit neural recording is a method of measuring the action potential of a single neuron. For example, a microeiectrode (e.g., platinum, tungsten, glass, etc.) is implanted into the brain (e.g., in or close to the ceil membrane), and the microeiectrode records changes in voltage (correlated with action potential) with respect to time. Neural ensemble recording is a technology used for detecting action potentials of multiple neurons. Like single-unit recording, neural ensemble recording measures changes in voltage, but ensemble recording utilizes electrode arrays that can record potentials of large numbers of neurons at the same time. In addition to single-unit activity, local field potentials can also be measured.

[0007] Although it is widely agreed that functions such as learning, motor control, and decision making require coordination between the activities of neurons and neuromodulators, the present understanding of this coordination is constrained by the absence of instrumentation for combined measurement of neural-ensemble activity and neuromodulator release, in vivo eiectrophysiology from high-density extracellular electrode arrays and FSCV has been used with great effect to independently measure neural ensemble activity and dopamine release with sub-second temporal resolution in awake and behaving animals. Extracellular electrophysiological measurement is advantageous in its capacity to record the activity of neurons through measurement of voltage fluctuations caused by ion flux induced by neural firing. Furthermore, advances in the miniaturization of head-stage amplifiers and high-density electrode array scan allow simultaneous measurement of over 140 neurons in behaving animals. Extracellular eiectrophysiology, however, cannot measure chemical concentrations and, consequently, cannot directly measure neuromodulator release. Fast-scan cyclic voltammetry at carbon-fiber microelectrodes (CFMEs) is a well-established technique capable of measuring neurotransmitter dynamics in vivo with sub-second resolution, high sensitivity (low nM limit-of-detection), and high spatial (tens of microns) resolution. Yet, FSCV is limited to measurement of eiectroactive neurotransmitters and neurotransmitter release at a small number (1 -3) of localized sites. Thus, combining electrode-array eiectrophysiology and FSCV technologies would provide a much- needed tool for probing previously uninvestigated links between neural ensemble and neuromodulator dynamics.

[0008] Dopamine is known to change neuronal excitability, modulate neural plasticity, and regulate learning and memory. However, the impact of dopamine release on the dynamics of neural networks has not been directly investigated due to an instrumentation void. Previous efforts to combine FSCV and electrophysiological measurements utilized a single carbon fiber electrode for both measurements. While knowledge gained through such studies should not be understated, the single-sensor approach has limitations. For example, electrophysiological and voitammetric measurements can only be acquired within the same brain region and from, typically, a single neuron. Thus, questions regarding the role of neuromodulation in altering between-neuron and between-region interactions cannot be addressed. Further, the single-sensor approach reduces the success rate of experiments due to the difficulty of locating a recording site suitable for both dopamine and single-unit recordings.

[0009] To address these limitations, the present invention features an instrument termed DANA (Dopamine And Neural Activity), which allows combined measurement of dopamine release by FSCV and neural activity from electrophysiological electrode arrays. Two approaches were utilized to allow combined recordings. First, a modified voitammetric headstage that allows for the application of the voitammetric waveform directly to the working electrode similar to that described by Takmakov et al. A second approach integrates a 32-channel solid-state relay (SSR) between the electrophysiological electrode array and amplifiers. The electrophysiological component of the DANA system was first characterized in an artificial cerebral spinal fluid (aCSF) gelatin to assess the system's capacity to measure a known signal. The ability of the DANA to monitor evoked dopamine release and multiple single-unit activity was then established in an anesthetized rat in two distinct brain regions: the hippocampus and the ventral striatum. Finally, SSR was shown to be compact enough to facilitate concurrent monitoring of phasic dopamine changes, single-unit activity, and local-field potentials in a freely moving animal, demonstrating the potential of the DANA system to investigate connections between physiology, chemistry, and behavior. SUfVlfVlARY OF THE INVENTION

[0010] Coordination between the activities of ensembles of neurons and the release of neuromodulators is thought to facilitate neural plasticity and regulate information transfer in neural circuits. Little direct evidence for such coordination exists, however, given a lack of instrumentation for combined monitoring of neuromodulator release and singie- unit/local-field signals, Described herein is a measurement platform that allows for the combined monitoring of eiectrophysioiogy from high-density electrode arrays and dopamine release from carbon-fiber microe!ectrodes. Integration of these two measurement systems was achieved through modification of the voltammetric system to allow application of the voltammetric waveform directly to the carbon-fiber microelectrode and the addition of a solid-state relay array positioned between the electrophysiological electrode array and amplifiers. The integrated measurement platform, DANA, was characterized in vitro (i.e., synthetically, as in a glass) using an artificial cerebral spinal fluid gelatin. Stimulated dopamine release and multiple single- unit and local-field activity were measured in anesthetized rats to demonstrate the capacity of DANA to monitor these events in a time-locked manner. Furthermore, the capacity of DANA to measure activity in freely moving animals was shown through recording of single-unit activity, high-frequency local-field oscillations, and dopamine release,

[0011] For example, the system of the present invention comprises a voltammetry probe for measuring neurotransmitter concentration and an eiectrophysioiogy probe for measuring action potential/neural activity. In one embodiment the voltammetry probe comprises an operational amplifier, coupled to the working electrode, and configured to output a portion of the resulting current in the working electrode when a voltage is applied. Thus voltage is applied to the working electrode while another, reference, electrode is grounded. This grounding/referencing scheme (see FIG 2B) is opposite of traditional FSCV (see FIG. 2A), and may help reduce interference between physiological (voltage/action potential) and voltammetric recordings (current). The electrode array also allows for the measurement of multiple different neurotransmitters requiring different detection waveforms, e.g., both dopamine and serotonin at different sensors.

[0012] The system further comprises a voltage amplifier array, or eiectrophysioiogy probe and a computer-controlled relay switch. The relay switch helps protect the electrophysio!ogy instrumentation by isolating the electrophysioiogy circuitry from the implanted electrodes during voltammetric scans. This helps allow for the near- simultaneous measurement of electrical activity in the brain while the large amplitude voitammetry waveform is applied (note that the measurements are near-simultaneous as no electrical activity can be recorded during the very short (e.g., 5 ms) period when the FSCV scan is delivered). Note that the system of the present invention may feature post-processing systems to remove artifact (since artificial electrophysiological signal may be measurable). The system of the present invention may further comprise a hardware/software synchronization system to help ensure proper synchronization of the voitammetry probe components and the electrophysioiogy components. The hardware/software synchronization system may feature video tracking.

[0013] As illustrated in FIG. 4A-4B, the methods and systems of the present invention allow recordings of both a neurotransmitter (such as dopamine) via more than 1 probe (e.g., 4 probes, 8 probes, etc.) and neuronal activity via multiple recording channels (e.g., 120 recording channels).

[0014] Note that the present invention is not limited to the aforementioned applications. For example, in some embodiments, the methods and systems of the present invention may be used to measure other compounds (e.g., norepinephrine) and neural activity outside the brain (e.g., in model animals such as the pig for heart research).

[0015] The present invention has the unique and inventive technical feature of methods and systems that allow for the near-simultaneous measurement of neurotransmitter concentration and neuronal activity, e.g., methods and systems for integrated and near- simultaneous measurement of the activities of groups of individual neurons and sub- second changes in neurotransmitter concentration. Without wishing to limit the present invention to any theory or mechanism, it is believed that the methods and systems of the present invention are advantageous because they allow for measurements in awake and behaving animals. None of the presently known prior references or work has the unique inventive technical feature of the present invention.

[0016] Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows a schematic representation of the system of the present invention comprising a voltammetry probe and an electrophysiology probe.

|0018] FIG. 2A (prior art) shows a setup of a traditional voltammetry probe (e.g., fast- scan cyclic voltammetry) wherein the potential is applied to the reference electrode and the working electrode (e.g., carbon probe) is grounded.

[0019] FIG. 2B shows a schematic setup of the voltammetry probe of an embodiment of the present invention wherein the potential is applied to the working electrode (e.g., carbon probe) via an operational amplifier and the reference electrode is grounded.

[0020] FIG. 3 shows a detailed version of the schematic setup of FIG. 1 , where the electrophysiology probe is isolated from the voltammetry probe by use of a relay switch.

[0021] FIGs. 4A-4B show a schematic representation of the integrated recording of dopamine, single-unit, and local field activity. FIG. 4A shows dopamine recording (voltammetry) and multi-unit (Intan) recording systems are integrated for recording in behaving animals. FIG. 4B (top) shows triangular pulses (-0.4V- 1.3V) used for dopamine measurement. These pulses in traditional FSCV create artifacts preventing multi-unit recordings. The system of the present invention may rapidly adapt to artifacts and permits spike and local field recordings (LFP) during inter-pulse intervals. White boxes: times when physiological recordings are not acquired.

[0022] FIG. 5A shows firing activity of a group of 15 simultaneously-recorded neurons in the medial prefrontal cortex of a behaving rat (bin size = 100 ms, 0-5 spikes/bin).

[0023] FIG. 5B shows correlation coefficient matrix indicating relationships in action potential timing between neuron-pairs in FIG. 5A. Briefly, FIG. 5B illustrates that interactions between ceils can be measured, e.g., this can be done only with ensemble recordings as opposed to other techniques wherein the FSCV electrode is used as the recording electrode.

[0024] FIG. 5C shows measurement of dopamine (anesthetized rat, striatum). Dopamine released (dashed line) following brain stimulation.

[0025] FIG. 5D shows spontaneous dopamine release (dashed rectangle) in a rat running on a maze. [0026] FIGs. 6A-6C show microarrays for acute and chronic recording. FIG. 6A shows an acute array of the present invention. This array may be modified to house a carbon fiber probe (inset - blue). FIG. 6B shows a 30 tetrode chronic Microdrive (Right: Intan 32ch headstage (top) and voltammetry headstage). FSG. 6C shows striatal targets (blue and red) for acute and chronic experiments.

|0027] FIG. 7 shows a successful test of rapidly adapting amplifier circuitry. Without circuitry that adapts to voltage transients, the 1 V voltammetry pulse would disrupt recording of action potentials for up to 30 seconds. To validate the new capacity of the RHD-2132 to rapidly adapt to a 1V pulse, a train of square-waves (square component being comparable in frequency/amplitude to an action potential) following a 1 V pulse (thick black bar). The RHD-2132 recovered the high-frequency (>400 Hz) component of the square wave (red arrow) within 20 ms following the 1 V transient.

|0028] FIG. 8 shows a flow diagram of the method of the current system.

[0029] FIGs. 9A-9B show a schematic of an instrumental set-up of the present system. FIG, 9A shows a common grounded Ag/AgCI reference (arrow), a 16-stereotrode electrophysiological (Ephys) array, and carbon-fiber microeiectrode (CFME) are inserted into a brain or artificial cerebral spinal fluid. Ephys array is followed by a 32-channei solid-state relay (SSR, perforated box) consisting of eight, four-channel MAX333A precision analog switches which prevent current between the ephys array and amplifiers. This SSR may or may not be required dependent upon experimental conditions. The CF E is interfaced through a custom headstage. An LF356 operational amplifier was used to allow application of the voltammetnc waveform directly to the CFME and facilitate a common grounding scheme. FIG. 9B shows the measurement "time-share" scheme. A timing pulse from the voitammetric system (top) controls the application of the voitammetric waveform (second down) and collection of the voitammetric output (third down). This timing pulse also triggers the SSR to an open-circuit configuration. Thus, the electrophysiological output is not measured during this time as indicated by the grey boxes in the zoomed raw electrophysiological signal (bottom trace).

[0030] FIGs. 10A-10C show an in vitro characterization of the DANA system. FIG. 10A shows artifact measured at the eiectropysioiogical array in artificial cerebral spinal fluid gelatin (aCSF) during voitammetric waveform application with (bottom) or without (top) incorporation of the solid-state relay (SSR). Small traces show the measured signal in the absence of waveform (WF) application. FIG. 10B shows power-spectral-density (PSD) analysis of electrophysiological traces during waveform application. The amplitude of these interferences decrease with increasing frequency. FIG. 10C shows the ability to extract target frequencies was assessed by injecting 500 μν (peak-to-peak) sine waves into the aCSF.

[0031] FIGs. 11A-1 1 D shows simultaneous measurement of single-unit activity and dopamine release. FIG. 1 1A shows a schematic of probe placement. A carbon-fiber microelectrode (CFME) was placed in the nucleus accumbens to measure dopamine evoked via a stimulating electrode in the medial forebrain bundle (MFB). Electrophysiological (Ephys) array was placed in the contralateral hippocampus. FIG. 1 1 B shows simultaneous measurement of single-unit activity and dopamine release. Raster plots of single-trail responses of a neuron upon medial forebrain bundle (MFB) stimulation (indicated by red bar). FIG. 1 1 C shows a Peri-event histogram for five stimulations (left) and the average waveform of cell at each electrode of the stereotrode. FIG, 1 1 D shows simultaneous measurement of single-unit activity and dopamine release. The average change in dopamine concentration in response to MFB stimulation (± SEM). Inset displays a characteristic dopamine voltammogram.

[0032] FIGs. 12A-12C show multi-unit activity measured with dopamine release. FIG. 12A shows average evoked dopamine release (n = 5 stimulations, ± SEM), Inset displays characteristic dopamine waveform. FIG. 12B shows Peri-event histograms from eight simultaneously measured hippocampal neurons. FIG. 12C shows a pie chart displaying fractions of neurons with firing rates that were non-responsive, increasing, or decreasing in following MFB stimulation (n = 3 rats). Responsivity was determined using Student's t-test of the average firing rate five seconds before and after the stimulation (n = 5 stimulations).

[0033] FIGs. 13A-13C shows the DANA system used to measure dopaminergic, single- unit, and local-field potential response to i.p. injection of 20 mg/kg ketamine (t = 0 min) in a freely moving rat. FIG. 13A shows the percent change from average pre-drug peak current of stimulated dopamine release. Inset displays average pre-drug and post-drug current vs. time traces (30 min period, ± SEM). FIG. 13B shows the average firing rate of a hippocampal neuron measured in the time between voltammetric scans. Inset shows average waveform of ceil. Red dashes indicate stimulations. FIG. 13C shows power of high-frequency oscillations (100-160Hz) measured in the time between voltammetric scans. Inset are sample traces of oscillations before (left) and after (right) ketamine injection.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] As previously discussed, the present invention features methods and systems for integrated and near-simultaneous measurement of the activities of groups of individual neurons and sub-second changes in neurotransmitter concentration. The methods and systems integrate electrode array and FSCV technology for acquiring realtime measures of neurotransmitter release (e.g., dopamine release) and multiple single- neuron activity measurements (high-density ensemble recording) (see F!G. 4). For example, the system of the present invention comprises a voitammetry probe (401 ), an electrophysiology probe (405) and a computer (404). The voitammetry probe comprises: a first electrode array (402) consisting of a first working electrode (308) and a grounded common reference electrode (302) as well as a first amplifier (403) operatively connected to the first working electrode (306). Applying a voltage to the input of the amplifier (403) causes a voltage to be applied to the working electrode (308). The amplifier (403) is configured to ouptut a portion of the resulting current in the working electrode (306) when a voltage is applied.

[0035] In some embodiments, a low-noise operational amplifier (201 ) is used as the first amplifier. The operational amplifier (201 ) applies potential to the working electrode (202) of the electrode array; the reference electrode (203) is grounded (see FIG. 2B). This grounding/referencing scheme, which is opposite of traditional FSCV (see FIG. 2A), may help reduce interference between physiological (voltage/action potential) and voltammetric recordings (current).

[0036] As mentioned earlier, the system also comprises an electrophysiology probe (405). This probe consists of a voltage amplifier array (409) and a relay switch (301 ). The voltage amplifier array (409) comprises a second electrode array (406) consisting of a second working electrode (304), operatively connected to a relay switch (301 ), and the common reference electrode (302) found in the voitammetry probe (in other words, the voitammetry probe and the electrophysiology probe share a common ground). A second amplifier (407) is also included in the configuration of the electrophysiology probe (405). This amplifier (407) is operatively connected to the relay switch (301 ), and is configured to output the voltage change at the second working electrode (304) when the relay switch (301 ) is closed, !n an embodiment, the second amplifier (407) is a low-noise operational amplifier (303).

[0037] The voltammetry probe (401 ) outputs a current indicative of a neurotransmitter concentration and the electrophysiology probe (405) outputs a voltage change indicative of the potential of one or more neurons. Output current is induced by the voltammetry probe (401 ) by applying a temporary voltage sweep to the voltage input of the first amplifier (305) resulting in a flow of current indicative of the neurotransmitter concentration. The voltage change acquired by the electrophysiology probe can only be obtained when the relay switch is closed. The opening/closing of the relay switch is computer (404) controlled. As used herein, a computer comprises a microprocessor, wherein the microprocessor effectuates commands and instructions n accordance with the present invention. For example, in some embodiments, the microprocessor receives a signal when a voltage sweep is applied to the first working electrode (306) of the voltammetry probe (401 ). In response, the microprocessor sends a second signal to open the relay switch (301 ), thereby isolating the electrophysiology probe (405) from the voltage applied at the first working electrode. At the conclusion of the voltage sweep, a third signal is sent to the microprocessor which responds by sending a fourth signal to close the relay switch (301 ). Upon closure of the relay switch, the electrophysiology probe (405) outputs a voltage change indicative of the potential of the one or more neurons.

|0038] The electrode array of the voltammetry probe also allows for the measurement of multiple different neurotransmitters, e.g., both dopamine and serotonin.

[0039] In some embodiments, the voltammetry probe comprises a tetrode array. In some embodiments, the voltammetry probe comprises a conducting polymer coating, e.g., a biocompatible conducting polymer. For example, in some embodiments, the voltammetry probe may be constructed using electrochemical polymerization of the monomer 3,4-efhylenedioxythiophene (EDOT) on the electrode. After baking and rinsing, a film with a positively charged polymer backbone balanced by negatively charged tosyiate ions may be formed. PEDOT electrodes may be fabricated by elecfropolymerizing EDOT onto platinum electrodes. In some embodiments, electrodes can then be integrated in mass-producible arrays (like standard tetrodes), allowing for multiple probe recordings. Without wishing to limit the present invention to any theory or mechanism, it is believed that the conducting polymer coating (e.g., PEDOT) is advantageous because the conducting polymer coating (e.g., PEDOT) can help transform robust metal electrodes into voltammetric probes, allowing the probes to be integrated into tetrode arrays. In some embodiments, the voitammetry probe is based on traditional carbon probes.

[0040] In some embodiments, the low-noise operational amplifiers feature high- performance data acquisition cards, !n some embodiments, the eiectrophysioiogy probe is capable of recording from four channels, at least four channels, etc., e.g., 8 channels.

[0041] The system of the present invention may feature flexible and powerful software for recording, controlling, and analyzing voitammetry data.

[0042] In a further embodiment, the relay switch is a computer-controlled solid-state relay (SSR), e.g., a multi-channel SSR, integrated into the eiectrophysioiogy probe. The SSR is a multi-channel SSR (e.g., 32-channel, 36-channel, or other appropriate multichannel SSR). The SSR helps protect the eiectrophysioiogy instrumentation by isolating the eiectrophysioiogy circuitry from the implanted electrodes during voltammetric scans. This helps allow for the near-simultaneous measurement of electrical activity in the brain while the large amplitude voitammetry waveform is applied.

[0043] In some embodiments, the system of the present invention features postprocessing systems to remove artifact (since artificial electrophysiological signal may be measurable). For example, in some embodiments, the amplifier array features integrated real-time saturation rejection circuitry, which allows for rapid artifact rejection.

[0044] In some embodiments, single-unit recording arrays of the eiectrophysioiogy probe comprise a material comprising tungsten or steel single-unit tetrodes and octrodes.

[0045] The system of the present invention may further comprise a hardware/software synchronization system to help ensure proper synchronization of the voitammetry probe components and the eiectrophysioiogy components. For example, in some embodiments, a microcontroller is used to synchronize recordings from the voitammetry probe and the electrophysiology probe (ensemble system). In some embodiments, the microcontroller generates a sync pulse that is split and sent to both probes. In some embodiments, the hardware/software synchronization system may feature video tracking.

[0046] Referring to FIG. 4A-4B, the methods and systems of the present invention allow recordings of both a neurotransmitter (such as dopamine) via more than 1 probe (401 ) (e.g., 4 probes, 8 probes, etc.) and neuronal activity via multiple recording channels (e.g., 120 recording channels) (402).

[0047] Without wishing to limit the present invention to any theory or mechanism, it is believed that phasic release of dopamine in the striatum may coincide with the reactivation of between-neuron correlations associated with recent experience; the methods and systems of the present invention may be used to investigate this hypothesis by measuring ensemble activity immediately following dopamine release. For example, if reactivation increases following dopamine release, it would suggest that dopamine enhances plasticity in networks of neurons.

EXAMPLE 1

[0048] Example 1 describes methods and devices for neurotransmitter and neural activity recordings in anesthetized rats. The present invention is not limited to the components, configurations, or methods described in Example 1 .

[0049] The system in Example 1 involves recordings from arrays of 8 tetrodes (see FIG. 6A) and dopamine probes (n=8) mounted on micro-manipulators (traditional carbon fiber and PEDOT coated metal probes may also be evaluated.) Recordings are acquired from the striatum (see FIG. 6C), given the strong dopaminergic innervation of this region. Dopamine release is triggered by electrically stimulating the medial forebrain bundle. As shown in FIG. 5A-5D, both single-unit and dopamine release in the striatum has been successfully recorded. In some embodiments, the system of the present invention features recovery of action potentials 10 ms after a volfammefric scan (given that voltammetric pulses last 5 ms, this would result in 85% of the signal being available for single-unit analysis).

EXAMPLE 2 [0050] Example 2 describes a device for acute neurotransmitter and neural activity recording in freely behaving animals. The present invention is not limited to the components, configurations, or methods described in Example 2.

[0051] The system in Example 2 features a novel microdrive array (see FIG. 6B) and a behavioral recording system. The array may house 30 tetrodes and 8 dopamine probes. In some embodiments, the methods of the present invention feature evaluating success by comparing single-unit and dopamine recordings acquired from trials in which the system is fully connected and trials in which one system (volfammetry or single-unit) is removed,

[0052] Example 3 describes a successful test of rapidly adapting amplifier circuitry. The present invention is not limited to the components, configurations, or methods described in Example 3.

[0053] FIG. 7 shows a successful test of rapidly adapting amplifier circuitry. Without circuitry that adapts to voltage transients, the 1 V vol tarn metry pulse would disrupt recording of action potentials for up to 30 seconds. To validate the capacity of the RHD- 2132 to rapidly adapt to a 1V pulse, a train of square-waves (square component being comparable in frequency/amplitude to an action potential) following a 1 V pulse (black bar) was tested. The RHD-2132 recovered the high-frequency (>400 Hz) component of the square wave (red arrow) within 20 ms following the 1 V transient. I n some embodiments, the high-frequency component of a simulated signal (square wave pulses) that is on par with the frequency-range of extracellular action potentials (600- 8000 Hz) can be recovered within 20 ms following the offset of the 1V pulse. In some embodiments, lower-frequency components (-10 Hz) require more time to recover. In some embodiments, the methods and systems of the present invention allow for acquiring a signal immediately after each 5 ms voltammetry pulse (see FIG. 4). Given the 100 ms inter-pulse interval, this may allow 95 of 100 ms or 95% of the signal to be used for spike and local field acquisition. In some embodiments, the methods and systems of the present invention allow for acquiring a signal immediately after each 10 ms voltammetry pulse (leaving 85% of the signal available for spike-extraction). [0054] Example 4 describes the animals and surgical procedures used to test the system. The present invention is not limited to the components, configurations, or methods described in Example 4.

[0055] Male Sprague-Dawley rats were pair-housed on a reverse 12-hr light-dark cycle until the time of surgery and provided food and water for ad libitum consumption. Surgeries were performed under isoflurane anesthesia (1.5 - 3.5 %). Stereotaxic coordinates were taken from Paxinos and Watson. Craniotomies were drilled above the nucleus accumbens (NAc, Anterior-Posterior (AP): 1.5 mm, Medial-Lateral (ML): 1.4 mm, Dorsal-Ventral (DV): 6.3 - 6.8 mm from brain surface) and medial forebrain bundle (MFB, AP: -2.5 mm, ML: 1 .7 mm, DV: 7.4 - 8.5 mm from brain surface) to allow implantation of the FSCV recording electrode (NAc) and the bipolar stimulating electrode. A craniotomy was drilled contralateral to the above the hippocampus (AP: -3 mm, ML: 2 mm) for the insertion of the 16-stereotrode (32-channel) electrophysiological array. A final craniotomy was drilled over the cerebral cortex (~ 5mm depth) for placement of the reference electrode. Dopamine release was evoked by injecting a 60- pulse train of 2ms, 300 - 600 μΑ, biphasic, square wave pulses at a frequency of 60 Hz with an optically isolated DS4 biphasic current stimulator. After verifying measurement of evoked dopamine release, the electrophysiological array was lowered slowly, starting at 2.0 mm from brain surface and stopping when multiple single units were identified in the electrophysiological signal. A series of five MFB stimulations spaced by five minutes each were recorded at each depth.

[0056] Implantations of the stimulating and reference electrodes as well as the electrophysiological array were performed as described vide supra. A chronic carbon- fiber microelectrode was implanted info the dorsal striatum (AP: 1 mm, ML: 2 mm, DV: 4.2 mm). The animal was housed individually following surgery and allowed 6 weeks for recovery before performing experiments. Dopamine release was evoked as described above.

EXAMPLE 5

[0057] Example 5 describes the fabrication of the electrodes used in the first and second electrode arrays. The present invention is not limited to the components, configurations, or methods described in Example 5. [0058] Stereotrodes were fabricated using 25 μηι tungsten wire and were inserted into sixteen -1 ,5 cm fused silica capillaries (103 μηι Inner Diameter (I.D.), 170 μηι Outer Diameter (O.D.)) that were pre-loaded into eight stainless steel guide cannulae. Electrodes were connected to a custom 32-channel electrode-interface board (EIB) fitted with a 32-channel connector. Stereotrodes were connected to the EIB by inserting each wire into individual through-holes, each hole corresponding to a single recording channel. Wires were connected to the EIB by pressing gold EIB pins into the through- holes to strip the electrode wire and make contact with the ESB trace.

[0059] A carbon-fiber microeiectrode was prepared as previously described. In short, an AS4 carbon fiber was loaded into a four inch glass capillary then pulled to form a seal using a pipette puller and subsequently cut to - 75 μητι.

[0060] A chronically implantable carbon-fiber microeiectrode was fabricated using the method described by Clark et al. Briefly, an AS4 carbon fiber was loaded into a ~1 .5 cm length of fused silica capillary (75 μπι I.D., 150 μηι O.D). A seal was made between the carbon fiber and capillary using a quick-drying epoxy. Silver epoxy was used to provide contact between the carbon fiber and a silver pin for interfacing. To reduce biofouling and enhance sensitivity, the chronically implanted electrode was coated in a PEDOT: Nafion copolymer. Co-polymer was eiectrodeposited by applying 15 cycles of a triangle waveform (1 .5 V to -0.8 V vs. a silver quasi-reference electrode at 100 mV/s) in a 20 ml_ solution of acetonitriie containing 200 μΜ EDOT and 200 μί. Nafion.

[0061] Ag/AgCi reference electrodes were produced by soaking 0.25 mm silver wire in chlorine bleach for ~ 4 hr.

EXAMPLE 6

[0062] Example 6 describes the data collection and analysis of the FSCV and single-unit and local field acquisition. The present invention is not limited to the components, configurations, or methods described in Example 6,

[0063] A 400 mV/s triangle waveform (-0.4 V to 1.3 V, vs. Ag/AgCI) was applied at a frequency of 5 Hz and data were collected using custom instrumentation and WCCV 3.0 acquisition software. Electrophysiological data (aCSF gelatin simulations and in vivo data) were collected with an !ntan RHD2132 headstage amplifier connected to an RHD2000 USB interface board using version 1 .4.2 RHD2000 interface software for Windows, In one set of experiments, the !ntan RHF2132 headstage amplifier was isolated from the implanted electrode array using a custom 32-channel analog switch. Ail electrophysiological recordings were sampled continuously at 20 or 30 kHz (0.5 - 6000 Hz band-pass filter) and digitized with 16-bit resolution.

[0064] Data analysis was carried out using WCCV 3.0. An average of ten cyclic voltammograms collected in the period preceding stimulation were subtracted from all voltammograms to produce background-subtracted cyclic voltammograms. Dopamine concentration was estimated using within-subject principal component regression using cyclic voltammograms obtained via MFB stimulation and in vitro flow-cell calibration of electrodes fabricated in the same manner (24 ηΑ/μΜ, n = 3 electrodes). Standard Fourier spectral analysis was applied to these data (spectrogram and spectral density) using custom software written using Matlab and the Matlab signal-processing toolbox.

[0065] For spike extraction, recordings between the voltammetric scans were band-pass filtered (300 to 6000 Hz), and spike waveforms were sorted based on waveform templates. Responsiveness of cells was determined using a paired t-test of the average firing rate during a five-second period before and after stimulus application (n = five stimulations). Peri-event histograms were used to visualize total firing response to MFB stimulations (bin size = 100 ms). For local-field extraction, recordings were filtered from 0.5 to 600 Hz, and down-sampled from 20,000 Hz to 2,000 Hz. To reduce the effect of the voltammetric scan on the LFP signal, a 20 ms window (starting at scan-onset) was removed from the LFP trace.

[0066] inter-scan LFP activity was band-pass filtered from 130 to 150Hz and the root mean square (RMS) power was calculated for each segment of local-field activity (180ms). Mean RMS values per segment were smoothed over one-second intervals with a convolution filter (Hanning kernel). A one-minute window following ketamine injection was ignored due to interference from animal handling.

EXAMPLE 7

[0067] Example 7 presents alternate systems to simultaneously measure the neurotransmitter concentration and single/multiple unit potentials. The present invention is not limited to the components, configurations, or methods described in Example 7. [0068] The measurement platform developed herein combines a traditional eiectrophysioiogy array and carbon fiber microeiectrode for measurement of dopamine release at discrete sites utilizing a "time-share" approach (FIG. 9B). That is, eiectrophysioiogy is not measured during the periodic voltammetric scans and vice versa. When combining these two systems, it is necessary to employ a common reference to limit electronic noise. The potential waveform required to measure dopamine dynamics lasts 8.5ms, has a magnitude of 1.7 V, and is applied a frequency of 5 Hz (every 200ms). Commonly, the inverse of the desired voltammetric waveform is applied to the reference electrode. This creates a technical challenge as applying this large potential change to the electrophysiological reference results in saturation of the electrophysiological amplifiers as these amplifiers are designed to measure sub-millivolt changes in extracellular potential. To protect the electrophysiological instrumentation and to enable integration the systems, two separate approaches were taken. The first involved the addition of a digitally controlled 32-channel solid-state relay (SSR, Figure 9A, perforated grey box) between the electrophysiological array and amplifiers. This afforded greater protection of the physiological amplifiers if, for example, the FSCV electrode was in close proximity to the recording array. The second approach utilized a modified version of the voltammetric instrumentation (FIG. 9A, bottom right) that significantly reduce the scan artifact and thus produced less interference with electrophysiological recordings.

[0069] Under the first approach, a SSR, composed of eight, MAX333A quad precision analog switches, was arranged on a dual-sided printed circuit board (image not shown). The SSR array has a compact profile (8 g, 0.5 x 3.5 x 4.5 cm) , allowing for use with freely moving animals. A TTL control pulse from the voltammetric system (FIG 9B, top) was used to put the SSR into an open-circuit configuration for the duration of the 8 ms scan, preventing current flow between the array and protecting the electrophysiological amplifiers (FIG. 9B, middle two traces). Given the "time-share" approach, electrophysiological data was recorded between the voltammetric scan intervals. The capacity to collect single-unit activity during the inter-pulse interval is illustrated in FIG. 9B (bottom trace), which presents recordings of individual single-unit spiking events collected between scans. The SSR-integration approach is advantageous as it allows integration of electrophysiological recordings into existing systems, which use the reference electrode for application of the voltammetric waveform with limited modification. Further, this approach isolates electrophysiological and vo!tamrnetric recordings and could allow for combined recordings in medical applications.

[0070] Under the second approach, a modified variant of the voltammetric instrumentation was created that significantly reduced the FSCV scan artifact on the electrophysiological system. As discussed, a common approach to FSCV recording is to apply the inverse of the desired voltammetric waveform to the reference electrode when making FSCV measurements. Instead, the voltammetric instrumentation (FIG. 9A, bottom right) was modified so that the voltammetric waveform is applied directly to the working electrode. The voltammetric headstage was constructed using a LF356 operation amplifier chosen for its rapid slew rate (12V/p,s), low noise (0.01 pA/Hz), wide unit-gain bandwidth (5 MHz), and low input bias current (30pA). Through application of the 1.7V voltammetric waveform to the working electrode, the voltage change at the reference electrode was now common to both systems, allowing superior cancelation at the electrophysiological amplifiers. The platform used in this work includes an Intan RHD2132 amplifier headstage with a working range of 5 mV. Upon application of the voltammetric waveform in vivo in anesthetized animals, the amplitude of the artifact caused by the application of the voltammetric waveform in the absence of the SSR was 1 - 2 mV. Thus, unwanted saturation of electrophysiological amplifiers was prevented using the novel LF356 voltammetric headstage configuration of the invention. However, it is important to note that if more rapid scan rates or larger working electrode than those tested would be expected to increase the measured artifact. This could necessitate the addition of the SSR even when utilizing the LF356 voltammetric headstage.

EXAMPLE 8

[0071] Example 8 details the synchronization of the FSCV and !ntan systems. The present invention is not limited to the components, configurations, or methods described in Example 8.

[0072] To ensure precise synchronization of the recordings, the waveform frequency TTL pulses described above were sent to a digital input of the Intan electrophysiology recording system. Additionally, an Arduino microcontroller was used to send a unique code to both the voltammetric and electrophysiological systems upon receiving an event TTL sent by the voltammetric system. This TTL can be used to trigger any device with a digital trigger and was used to trigger a stimulation pulse-train in this work.

[0073] To assess the effect of application of the voitammetric waveform as well as addition of the SSR on the electrophysiological recordings, recordings were made in a Tris-buffered artificial cerebral spinal fluid gelatin (aCSF gelatin). Application of the voitammetric waveform causes an artifact in the electrophysiological recordings both with and without the SSR (FIG. 10A). !t should be noted that the amplitude of the observed artifact caused by application of the voitammetric waveform in the absence of the SSR was markedly lower in amplitude than the artifact observed in vivo; however, the shape and duration of this artifact are similar. The artifact created by switching of the SSR in vitro closely resembles that seen in vivo. Additional in vitro characterization was carried out on the data collected in the presence of the SSR to better characterize the SSR-switehing artifact which was greater in amplitude (both in vitro and in vivo) than the artifact observed in the absence of the SSR.

[0074] Power spectral density (PSD) analysis of the local-field trace acquired during FSCV scanning revealed expected narrow-band artifactuai frequency responses occurring at multiples of the waveform application frequency (WAF). These responses decayed in amplitude with increasing multiples of the WAF (FIG. 10B), Because artifacts were narrow-band (full-width half-maximum ~ 0.7 Hz), measurement of physiological oscillatory responses could be acquired for frequencies between artifacts; however, at least at low frequencies, scan artifacts would prevent measurement at precise multiples of the FSCV scan frequency. To illustrate the capacity to extract low frequencies between harmonics of the scan frequency, a 7 Hz sine wave was injected into the gelatin to simulate neural activity (FIG. 10C). The target frequency is visible and well separated from artifactuai peaks and thus could be extracted even in the presence of interference from SSR switching. If the frequency of interest in a particular experiment were a multiple of five, the WAF could be adjusted to 4 or 8 Hz to allow extraction of this frequency.

[0075] A power-spectral-density analysis was performed to determine the earliest time after offset of the voitammetric scan at which each input frequency was recovered as defined by a signal-to-noise ratio (S/N) > 1.5 when comparing the power of the target frequency to that of adjacent frequencies. In general, high-frequency input signals were recovered more rapidly than low-frequency signals. All input frequencies > 2 Hz were recovered within the 191.5 ms between scans. Frequencies above 20 Hz were recovered within 50 ms of voltammetric scan offset resulting in a duty cycle > 70%. Frequencies above 200 Hz were recovered within 10 ms resulting in a duty cycle of 90%. Therefore, gamma, high-frequency oscillations (including ripples), and single-cell spiking activity should be detectable between voltammetric scans.

EXAMPLE 9

|0076] Example 9 illustrates the use of DANA in a behaving rat. The present invention is not limited to the components, configurations, or methods described in Example 9.

[0077] To determine whether the DANA system, with inclusion of the SSR, was suitably compact for use in behavioral experiments, evoked striatal dopamine release as well as hippocampai single-unit activity and local-field potentials were concurrently measured in a freely moving rat (FIGs 13A-13C). Ketamine was injected to induce a well- characterized high-frequency (> 100Hz) local-field potential. Dopamine release was evoked through MFB stimulation at five-minute intervals. Concurrently, single-unit activity and local-field potentials were measured during the periods between voltammetric scans. After a thirty-minute baseline period, ketamine (20 mg/kg, i.p.) was administered to induce high-frequency oscillations and measurement continued for 60 minutes. This proof-of-concept measurement of dopamine release and neural activity in a freely moving animal showcases the distinctive capabilities of the DANA system and its potential to uncover new information regarding the dynamic role of neuromodulators in behaving and adapting animals.

|0078] Computers typically include known components, such as a processor, an operating system, system memory, memory storage devices, input-output controllers, input-output devices, and display devices. It will also be understood by those of ordinary skill in the relevant art that there are many possible configurations and components of a computer and may also include cache memory, a data backup unit, and many other devices. Examples of input devices include a keyboard, a cursor control devices (e.g., a mouse), a microphone, a scanner, and so forth. Examples of output devices include a display device (e.g., a monitor or projector), speakers, a printer, a network card, and so forth. Display devices may include display devices that provide visual information, this information typically may be logically and/or physically organized as an array of pixels. An interface controller may also be included that may comprise any of a variety of known or future software programs for providing input and output interfaces. For example, interfaces may include what are generally referred to as "Graphical User Interfaces" (often referred to as GUI's) that provides one or more graphical representations to a user. Interfaces are typically enabled to accept user inputs using means of selection or input known to those of ordinary skill in the related art. The interface may also be a touch screen device. In the same or alternative embodiments, applications on a computer may employ an interface that includes what are referred to as "command line interfaces" (often referred to as CLI's). CLI's typically provide a text based interaction between an application and a user. Typically, command line interfaces present output and receive input as lines of text through display devices. For example, some implementations may include what are referred to as a "shell" such as Unix Shells known to those of ordinary skill in the related art, or Microsoft Windows Powershell that employs object-oriented type programming architectures such as the Microsoft .NET framework.

[0079] Those of ordinary skill in the related art will appreciate that interfaces may include one or more GUI's, CLI's or a combination thereof. A processor may include a commercially available processor such as a Celeron, Core, or Pentium processor made by Intel Corporation, a SPARC processor made by Sun Microsystems, an Athlon, Sempron, Phenom, or Opteron processor made by AMD Corporation, or it may be one of other processors that are or will become available. Some embodiments of a processor may include what is referred to as multi-core processor and/or be enabled to employ parallel processing technology in a single or multi-core configuration. For example, a multi-core architecture typically comprises two or more processor "execution cores". In the present example, each execution core may perform as an independent processor that enables parallel execution of multiple threads. In addition, those of ordinary skill in the related will appreciate that a processor may be configured in what is generally referred to as 32 or 84 bit architectures, or other architectural configurations now known or that may be developed in the future.

[0080] A processor typically executes an operating system, which may be, for example, a Windows type operating system from the Microsoft Corporation; the Mac OS X operating system from Apple Computer Corp.; a Unix or Linux-type operating system available from many vendors or what is referred to as an open source; another or a future operating system; or some combination thereof. An operating system interfaces with firmware and hardware in a well-known manner, and facilitates the processor in coordinating and executing the functions of various computer programs that may be written in a variety of programming languages. An operating system, typically in cooperation with a processor, coordinates and executes functions of the other components of a computer. An operating system also provides scheduling, input-output control, file and data management, memory management, and communication control and related services, all in accordance with known techniques.

[0081] System memory may include any of a variety of known or future memory storage devices that can be used to store the desired information and that can be accessed by a computer. Computer readable storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules, or other data. Examples include any commonly available random access memory (RAM), read-only memory (ROM), electronically erasable programmable readonly memory (EEPROM), digital versatile disks (DVD), magnetic medium, such as a resident hard disk or tape, an optical medium such as a read and write compact disc, or other memory storage device. Memory storage devices may include any of a variety of known or future devices, including a compact disk drive, a tape drive, a removable hard disk drive, USB or flash drive, or a diskette drive. Such types of memory storage devices typically read from, and/or write to, a program storage medium such as, respectively, a compact disk, magnetic tape, removable hard disk, USB or flash drive, or floppy diskette. Any of these program storage media, or others now in use or that may later be developed, may be considered a computer program product. As will be appreciated, these program storage media typically store a computer software program and/or data. Computer software programs, also called computer control logic, typically are stored in system memory and/or the program storage device used in conjunction with memory storage device. In some embodiments, a computer program product is described comprising a computer usable medium having control logic (computer software program, including program code) stored therein. The control logic, when executed by a processor, causes the processor to perform functions described herein. In other embodiments, some functions are implemented primarily in hardware using, for example, a hardware state machine. Implementation of the hardware state machine so as to perform the functions described herein will be apparent to those skilled in the relevant arts. Input-output controllers could include any of a variety of known devices for accepting and processing information from a user, whether a human or a machine, whether local or remote. Such devices include, for example, modem cards, wireless cards, network interface cards, sound cards, or other types of controllers for any of a variety of known input devices. Output controllers could include controllers for any of a variety of known display devices for presenting information to a user, whether a human or a machine, whether local or remote. In the presently described embodiment, the functional elements of a computer communicate with each other via a system bus. Some embodiments of a computer may communicate with some functional elements using network or other types of remote communications. As will be evident to those skilled in the relevant art, an instrument control and/or a data processing application, if implemented in software, may be loaded into and executed from system memory and/or a memory storage device. AH or portions of the instrument control and/or data processing applications may also reside in a read-only memory or similar device of the memory storage device, such devices not requiring that the instrument control and/or data processing applications first be loaded through input-output controllers. It will be understood by those skilled in the relevant art that the instrument control and/or data processing applications, or portions of it, may be loaded by a processor, in a known manner into system memory, or cache memory, or both, as advantageous for execution. Also, a computer may include one or more library files, experiment data files, and an internet client stored in system memory. For example, experiment data could include data related to one or more experiments or assays, such as detected signal values, or other values associated with one or more sequencing by synthesis (SBS) experiments or processes. Additionally, an internet client may include an application enabled to access a remote service on another computer using a network and may for instance comprise what are generally referred to as "Web Browsers". In the present example, some commonly employed web browsers include Microsoft Internet Explorer available from Microsoft Corporation, Mozilla Firefox from the Mozilla Corporation, Safari from Apple Computer Corp., Google Chrome from the Google Corporation, or other type of web browser currently known in the art or to be developed in the future. Also, in the same or other embodiments an Internet client may include, or could be an element of, specialized software applications enabled to access remote information via a network such as a data processing application for biological applications.

[0082] A network may include one or more of the many various types of networks well known to those of ordinary skill in the art. For example, a network may include a local or wide area network that may employ what is commonly referred to as a TCP/IP protocol suite to communicate. A network may include a network comprising a worldwide system of interconnected computer networks that is commonly referred to as the Internet, or could also include various intranet architectures. Those of ordinary skill in the related arts will also appreciate that some users in networked environments may prefer to employ what are generally referred to as "firewalls" (also sometimes referred to as Packet Filters, or Border Protection Devices) to control information traffic to and from hardware and/or software systems. For example, firewalls may comprise hardware or software elements or some combination thereof and are typically designed to enforce security policies put in place by users, such as for instance network administrators, etc.

[0083] Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference cited in the present application is incorporated herein by reference in its entirety.

[0084] As used herein, the term "about" refers to plus or minus 10% of the referenced number.

[0085] Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. Reference numbers recited in the claims are exemplary and for ease of review by the patent office only, and are not limiting in any way. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase "comprising" includes embodiments that could be described as "consisting of", and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase "consisting of is met.

[0086] The reference numbers recited in the below claims are solely for ease of examination of this patent application, and are exemplary, and are not intended in any way to limit the scope of the claims to the particular features having the corresponding reference numbers in the drawings.

Claims

WHAT IS CLAIMED IS:

1. A system (400) for near-simultaneous measurement of a neurotransmitter concentration and a potential of one or more neurons, said system comprising: a. a vol tarn metry probe (401 ), wherein the vo!tammetry probe (401 ) comprises: i. a first electrode array (402), wherein the first electrode array (402) comprises a first working electrode (306) and a common reference electrode (302), wherein the common reference electrode (302) is grounded; and ii. a first amplifier (403), operatively connected to the first working electrode (306) of the voitammetry probe (401 ) configured to output a portion of the current in the first working electrode (306), wherein applying a voltage to a voltage input of the first amplifier (403) causes a voltage to be applied to the first working electrode (306): b. an eiectrophysiology probe (405), wherein the eiectrophysiology probe (405) comprises a voltage amplifier array (409) and a relay switch (301 ), wherein the voltage amplifier array (409) comprises: i. a second electrode array (406), wherein the second electrode array (406) comprises a second working electrode (304), operatively connected to the relay switch (301 ), and the common reference electrode (302); and ii, a second amplifier (407) operatively connected to the relay switch (301 ), wherein the second amplifier (407) is configured to output the voltage change at the second working electrode (304) when the relay switch (301 ) is closed; and c. a computer (404), operatively connected to the relay switch (301 ); wherein the first amplifier (403) outputs a current indicative of a neurotransmitter concentration, wherein the eiectrophysiology probe (405) outputs a voltage change indicative of the potential of one or more neurons, wherein measurements are taken by the voltammetry probe (401 ) by applying a temporary voltage sweep to the voltage input of the first amplifier (403) resulting in a flow of current indicative of the neurotransmitter concentration, wherein when a voltage sweep is applied, a first trigger is activated sending a first signal to alert the computer (404), where the computer responds by sending a second signal to open the relay switch (301 ), wherein as a result, the voltage amplifier array (409) of the electrophysioiogy probe (405) is isolated from the voltage applied at the voltammetry probe (401 ), wherein the electrophysioiogy probe (405) and the voltammetry probe (401 ) share a grounded common reference electrode (302), wherein when the voltage sweep is ended, a third signal is sent to the computer (404) where the computer (404) responds by sending a fourth signal to dose the relay switch (301 ), whereupon the electrophysioiogy probe (405) outputs the voltage change indicative of the potential of the one or more neurons.

2. The system of claim 1 , wherein the first electrode array (402) comprises two or more electrodes,

3. The system of claim 1 , wherein the first electrode array (402) comprises about 4 to 8 electrodes.

4. The system of claim 1 , wherein the first electrode array (402) comprises a tetrode array.

5. The system of any of claims 1 -4, wherein electrodes of the first electrode array (402) comprise a conducting polymer coating.

6. The system of claim 5, wherein the conducting polymer coating comprises 3,4- efhylenedioxythiophene (EDOT) or platinum 3,4-ethyienedioxythiophene (PEDOT).

7. The system of any of claims 1 -6, wherein system (400) can measure concentrations of two or more neurotransmitters.

8. The system of any of claims 1 -7, wherein the first (403) amplifier and second amplifier (407) are low-noise operational amplifiers (305, 303),

9. The system of claim 8, wherein the non-inverting input of the first operational amplifier (305) is connected to a voltage input, where applying a voltage to the voltage input causes a voltage to be applied to the first working electrode (306).

10. The system of claim of any of claims 1 -9, wherein the relay switch comprises a solid-state relay (SSR, 301 ).

1 1. The system of claim 10, wherein the SSR (301 ) is a multi-channel SSR, wherein the voltage amplifier array (409) comprises a plurality of operational amplifiers operatively connected to each channel of the SSR, wherein the voltage amplifier array (409) outputs voltage changes indicative of the potentials of a plurality of neurons.

12. The system of claim 1 , wherein the voltage amplifier array (409) comprises saturation rejection circuitry for artifact rejection.

13. The system of claim of any of claims 1 -12 further comprising a synchronization system for synchronizing recordings from the voltammetry probe (401 ) and the eiectrophysioiogy probe (405).

14. The system of claim 13, wherein the synchronization system comprises a microcontroller.

15. A method for near-simultaneous measurement of a neurotransmitter concentration and a potential of one or more neurons, said method comprising introducing a system of any of Claims 1 -14 into an animal.

16. The method of claim 15, wherein two software platforms are synchronized to time-lock electrochemical and electrophysiological data.