WO2022079294A1

WO2022079294A1 - Electroencephalographic headset

Info

Publication number: WO2022079294A1
Application number: PCT/EP2021/078703
Authority: WO
Inventors: Cécile GIBERT; Fabrice VAILHEN; Yohan Attal
Original assignee: Mybrain Technologies
Priority date: 2020-10-16
Filing date: 2021-10-15
Publication date: 2022-04-21

Abstract

A headset (100), intended to acquire electroencephalographic signals of a subject comprises a covering support (10) configured to be positioned on at least a portion of the head of the subject, the covering support (110) comprising a plurality of insertion areas (113); a set of electrodes comprising a plurality of measurement electrodes configured to respectively fit into one of the insertion areas (113); an acquisition module connected to the measurement electrodes and configured to acquire signals provided by the measurement electrodes, said signals being representative of an electroencephalographic activity of the subject; wherein the covering support (110) is made of a material having a Young's modulus between 3.2 GPa and 4 GPa; and wherein the covering support (110) has a thickness ranging from 0.5 mm to 2.5 mm.

Description

ELECTROENCEPHALOGRAPHIC HEADSET

FIELD OF INVENTION

The present invention pertains to the field of biological signals acquisition. More particularly, the present invention relates to a headset for acquiring electroencephalographic signals of a subject. In a particularly advantageous but non-limiting manner, such a headset may be used for biofeedback control of body functions influencing the signals acquired in a conscious subject.

BACKGROUND OF INVENTION

It is known to use electroencephalography, most commonly referred to as EEG, to measure the electrical activity of the brain of a subject with high temporal accuracy, for example millisecond per millisecond. Typically, this involves obtaining information on the neurophysiological activity of the brain over time and in particular of the cerebral cortex, in particular for diagnostic purposes in neurology or in cognitive neuroscience research. The subject of the measurements is in a state of consciousness, for example in a lying, relaxed or sitting position.

In a conventional way, brain activity measurements (such as electroencephalography -EEG- or near-infrared spectrometry -NIRS-) are performed using a headset positioned on the head of the subject. Such a headset comprises a covering support configured to be positioned on at least a portion of the head of the subject, typically the scalp of the subject. The covering support comprises a plurality of insertion areas in which brain sensors (electrodes for EEG, optodes for NIRS) are inserted. The measurement electrodes for EEG are in contact with the scalp and are suitable for measuring neurons electrical activity. Similarly, the optodes for NIRS are in contact with the scalp and are suitable for measuring cerebral hemodynamic responses. The respective positions of the sensors, and therefore the positions of the insertion areas, are determined according to a standardized model known to the person skilled in the art, i.e. the 10/20 model. As a result, the covering support generally has a perforated shape, comparable to a mesh, the mechanical strength of the support being provided by elements joining the sensors. These elements can be made with different width configurations, so that the appearance of the covering support may vary, for example from a net to a perforated blanket. Such a headset also comprises an acquisition module connected to the measurement electrodes and configured to acquire signals provided by the measurement electrodes, these signals being representative of the encephalographic activity of the subject.

The success of the use of EEG relies to a large extent on the fact that it is a painless and non-invasive test, capable of providing a significant amount of information relating to the health of the subject. However, once collected, this information has to be analysed in a detailed and precise manner. Therefore, a lot of research work has been carried out in recent years, in conjunction with the development of new technologies, to improve the quality of the measurements as well as their analysis.

While significant progress has been made in these areas, the comfort of the subject wearing such a headset has so far been neglected. In particular, when the subject is submitted to a predefined measurement protocol, which in some cases may be intensive, it is important that the subject feels comfortable so as to be able to focus on the measurement protocol. However, in such conditions of use, current headsets cause discomfort to the subject. In addition, while progress has been made in improving the quality of the measurements post acquisition, i.e. by improving analysis methods of acquired signals, improving the quality of measurements through the development of new measurements tools, such as new types of headsets has seen much less interest and development. Thus, in the solutions known to date, the headset is not configured to be adaptable to different cranial morphologies, which makes its positioning on the head of the subject sometimes difficult, causing bad contact between the electrodes and the skull of said subject. SUMMARY

The purpose of the present invention is to overcome all or some of the limitations of the prior art solutions, particularly those outlined hereabove, by providing a headset for acquiring electroencephalographic signals of a subject which can be easily positioned on the head of the subject, whatever the morphology of the skull of the subject, which is comfortable when worn by a subject, even during intensive measurement sessions e.g. lasting several hours, and which also ensures precise measurements. In particular, precise and enhanced measurements are allowed due to an optimum fit between the headset and the skull of the wearer.

To this end, according to a first aspect, an object of the invention is a headset for acquiring electroencephalographic signals of a subject, said headset comprising: a covering support configured to be positioned on at least a portion of the head of the subject, the covering support comprising a plurality of insertion areas, a set of electrodes comprising a plurality of measurement electrodes configured to respectively fit into one of the insertion areas, an acquisition module connected to the measurement electrodes and configured to acquire signals provided by the measurement electrodes, said signals being representative of an electroencephalographic activity of the subject, wherein the covering support is made of a material having a Young’s modulus between 3.2 GPa and 4 GPa.

The headset of the invention is particularly well suited to be used for long measurement sessions on a conscious subject, for example for biofeedback sessions lasting several hours, since it is specially configured to avoid discomfort for the subject. It has been found that the specific mechanical properties of the covering support, typically a Young’s modulus between 3.2 GPa and 4 GPa, make it possible to position the headset easily on the head of a subject, for any morphology of the skull of the subject, while also ensuring that, once the headset has been placed on the head of the subject, the measurement electrodes remain precisely positioned against the skull of the subject. More precisely, the specific mechanical properties of the covering support provide, on the one hand, sufficient flexibility to allow easy handling and positioning of the headset on the head of a subject and, on the other hand, sufficient strength to hold the measurement electrodes in a precise position when on the head of the subject, even during intensive measurement sessions. In other words, the covering support being made of a material having a Young’s modulus between 3.2 GPa and 4 GPa allows for a snug fit of the headset on an skull morphology. By “intensive measurement sessions”, it is referred here to sessions which may last several hours and/or which are implemented when the subject is in movement, for example during a sport session.

In particular embodiments, the headset may additionally include one or more of the following features, taken in isolation or according to any possible combination.

In one embodiment, the covering support is made of a polymer material. In one embodiment, the covering support is made of a biocompatible polymer material, in particular a polymer material based on nitrile, i.e. a polymer comprising at least one cyano group. Such a biocompatible material is well suited for use of the headset in intensive measurement sessions. In addition, polymer materials, in particular nitrile based polymers, have the advantage that they can be cut very precisely, for example by means of a laser, so that the shape of the covering support can be easily adjusted. Such polymers are also advantageously easy to clean, flexible enough to be adaptable to any skull morphology while rigid enough to allow electrodes insertion.

In one embodiment, the headset comprises: a circumferential part configured to surround the head of the subject, elastic holding means configured to ensure that the covering support is held in place when on the head of the subject, adjustment means configured to cooperate with the elastic holding means in order to adjust the pressure of the measurement electrodes on the head of the subject.

In one embodiment, the circumferential part comprises: two reinforcing elements each intended to cover one temple of the subject, two elastic strips, i.e. a front strip intended to be positioned on the forehead of the subject and a rear strip intended to be positioned on the back of the skull of the subject, the front and rear strips being arranged so as to connect the reinforcing members together, wherein: the elastic holding means comprise an elastic tightening strip, having a first end fixed to a first reinforcing element among the two reinforcing elements, the adjustment means comprise at least one opening arranged on the second reinforcing element among the two reinforcing elements and configured to reversibly hold a second end of the tightening strip.

In one embodiment, the covering support comprises two openings through which the tightening strip passes, said openings being each arranged facing one of the reinforcing elements. Thanks to these openings, the covering support can be reversibly fixed to the circumferential part. Thus, the headset is easy to handle and transport, when all its elements are linked together.

In one embodiment, the number of measurement electrodes is at least six.

In one embodiment, the set of electrodes further comprises a ground electrode connected to the acquisition module. Such a ground electrode makes it possible to define a reference potential.

In one embodiment, each measurement electrode is held by means of at least one fastening member with respect to the covering support.

In one embodiment, each insertion area has a plurality of holes, each measurement electrode having a printed circuit board (PCB) with conductive pins extending therefrom and respectively inserted into the holes of a corresponding insertion area, the PCB being held with respect to the covering support by half shells configured to be arranged on either side of the covering support, and by a fastening member extending between the half shells.

In one embodiment, each insertion area comprises a hole, each measurement electrode having a PCB with conductive pins extending therefrom and inserted into said hole, the PCB being enclosed in a shell having a peripheral groove configured to receive the edge of said hole.

In one embodiment, the shell is over-moulded around the PCB. Such a configuration allows the PCB to be securely and easily attached to the shell, without requiring much handling or any additional fastening means. Moreover, it makes it possible to manufacture and assemble the measurement electrode before it is fixed to the covering support. In this way, the measurement electrode can be inserted more easily relative to the covering support, ensuring a tight assembly.

In one embodiment, the half shells or the shell are made of thermoplastic polymer, preferably polyamide. Polyamide is particularly suitable due to its high impact resistance and ease of use in rapid prototyping by Selective Laser Sintering.

According to another aspect, an object of the invention is an electroencephalographic signal monitoring system, comprising a headset as described above; a signal display module; and transmission means configured to transmit signals acquired by the headset to the signal display module. In one particular embodiment, the transmission means are wireless.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the invention will become apparent from the following description of embodiments of a headset and an electroencephalographic signal monitoring system according to the invention, this description being given merely by way of example and with reference to the appended drawings in which:

Figure 1 is a perspective view of a headset for acquiring electroencephalographic signals of a subject according to an embodiment of the invention, the measurement electrodes having been omitted for better clarity of the figure.

Figure 2 is a perspective view of the covering support of the headset of Figure 1.

Figure 3 is a view of the covering support according to another embodiment. Figure 4 is a view of the covering support according to another embodiment.

Figure 5 is a perspective view of elastic strips and tightening strip according to another embodiment.

Figure 6 is a view at larger scale of a part of the headset of Figure 1 comprising a measurement electrode according to a first embodiment, fitted into a corresponding insertion area of the covering support of the headset.

Figure 7 is a view similar to Figure 6 for a headset comprising a measurement electrode according to a second embodiment, fitted into a corresponding insertion area of the covering support of the headset.

In these figures, references that are identical from one figure to another denote identical or analogous elements. For reasons of clarity, the elements represented are not to scale, unless stated otherwise. Moreover, the figures are not intended to limit the scope of the claims to the embodiments depicted. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims.

DETAILED DESCRIPTION

This invention relates to a headset for acquiring electroencephalographic signals of a subject, said headset comprising: a covering support configured to be positioned on at least a portion of the head of the subject, the covering support comprising a plurality of insertion areas, a set of electrodes comprising a plurality of measurement electrodes configured to respectively fit into one of the insertion areas, an acquisition module connected to the measurement electrodes and configured to acquire signals provided by the measurement electrodes, said signals being representative of an electroencephalographic activity of the subject, wherein the covering support is made of a material having a Young’s modulus between

3.2 GPa and 4 GPa.

The headset according to the invention is configured for the monitoring of the cerebral electrical activity of a subject.

In the following example, the subject is considered to be conscious and in a sitting position, and submitted to a measurement protocol, for example during clinical trials. By way of example, such a measurement protocol may be conducted for diagnostic purposes in neurology, in order to detect pathologies such as epilepsy, disorders of consciousness, brain damage, etc.

It is understood that, according to other examples of the invention that are not detailed here, the subject may be in a position other than a sitting position, such as a standing position or a lying-down position, or the subject may be in movement. The invention may also be implemented in a context other than a diagnostic measurement protocol, in particular the subject may make personal use of the headset of the invention with the purpose of monitoring his/her own cerebral electrical activity.

Figure 1 schematically illustrates a headset 100, according to an embodiment of the invention, for acquiring electroencephalographic signals of a subject, said headset 100 comprising a covering support 110. The headset 100 is part of an electroencephalographic signal monitoring system (not illustrated in the figures). Said system comprises, in addition to the headset 100, a signal display module, and transmission means configured to transmit signals acquired by the headset 100 to the signal display module.

Such a monitoring system allows the subject or a third party, in particular a qualified medical staff, to monitor the acquired signals in real time. It is thus possible to have very rapid access to useful information, for example if the person monitoring the acquired signals knows how to interpret said signals, or if assistance in the interpretation of said signals is provided. For example, such assistance may be provided by an additional electronic module integrated in the monitoring system, which is configured to deliver intelligible information (such as for example written messages on the display module) for a non-specialist person. The signal display module is of any type known per se, such as a computer screen, a tablet, a smartphone, etc. The transmission means are also of any type known per se and allow the transmission of the acquired signals according to a predetermined communication protocol. Said communication protocol may be of any type. For example, the transmission means may be wireless, and the communication protocol may correspond to Wifi or Bluetooth. As a variant, other communication protocols may be selected, and wired transmission means may also be considered.

In a general way, the person skilled in the art knows how to choose and configure a signal display module and transmission means compatible with the headset 100 of the invention, so as to form an electroencephalographic signal monitoring system. Therefore, these aspects are not described in more detail here.

Figure 2 is a view of the covering support 110 of the headset 100 shown in Figure 1, in a configuration in which the covering support 110 is flat. The covering support 110 is configured to be positioned on at least a portion of the head of the subject. According to the shown example, the covering support 110 is intended to be placed on the scalp, at the top of the skull of the subject, in a manner substantially centered with respect to the latter. In other words, with reference to the standardised model known as the 10/20 model for positioning measurement electrodes on a skull, the covering support 110 has a center of inertia intended to be substantially superposed with an electrode location known as Cz.

In this example, as shown in Figures 1 and 2, the covering support 110 substantially has a shape of a figure “eight”, with two loops 111 connected by a central junction zone 112 including the center of inertia of the covering support 110. The two loops 111 of the covering support 110 are configured to be placed on lateral parts of the scalp of the subject, on either side of a line dividing the skull into two equal parts and joining the forehead to the back of the skull.

The selection of a shape of a figure “eight” for the covering support 110 is only an illustrative embodiment of the invention, this embodiment having the advantage of being simple to manufacture while minimizing the need for material with regard to the positioning of the electrodes, this point being detailed later. Figure 3 is a view of the covering support 110 of the headset 100 with a six-branch shape, according to another embodiment.

Figure 4 is a view of the covering support 110 of the headset 100 with two branches intended to be placed on the front and four branches intended to be placed on the back of the head of the subject.

Other shapes are possible for the covering support, such as a disc, a square, etc. Indeed, the shape of the covering support may be selected according to the intended use of signal. For instance, to detect altered mental states induced by respiratory distress, the covering support allows for positioning electrodes in the most suitable positions, i.e. on premotor and supplementary motor areas (corresponding to FC1 and FC2 positions according to the 10/20 standard), higher-level secondary and association (C3 and C4) and pre-parietal (CPI and CP2) cortices. To detect ictal patterns in epilepsy, the covering support allows for positioning electrodes in an advantageous configuration, i.e. in the forehead (Fpl, Fp2, F7, F8) and behind the ears (P7, P8).

In an embodiment, the headset comprises several covering supports, each support comprising a plurality of insertion areas. This embodiment improves versatility of the headset. A covering support corresponding to a first specific monitoring may be joined with another covering support corresponding to a second specific monitoring, yielding multimodal simultaneous measurement systems to improve the spatiotemporal resolution of brain imaging.

The covering support 110 is made of a material, in particular a polymer material, having a Young’s modulus between 3.2 GPa and 4 GPa, preferably between 3.4 GPa and 3.8 GPa preferably between 3.6 GPa and 3.8 GPa. In a preferred configuration, said covering support 110 is made of a material, in particular a polymer material, having a Young’s modulus of 3.7 GPa. Such a range of values gives flexibility to the covering support 110 without reducing its resistance, so that it is suitable for ensuring support of the electrodes and for intensive measurement sessions. Thanks to the specific mechanical properties of the covering support 110, the headset 100 of the invention can be easily manipulated to be positioned on the head of the subject. Indeed, such a range of Young’s moduli allows for an easy and snug fit between the covering support 110 and the skull of the wear, whatever the skull morphology. An easy fit means that the covering support 110 is adaptable to any skull morphology and a snug fit means that the electrodes are in contact with the skull at all times whatever the skull morphology.

The material used to build the covering support 110 may be a homogeneous material or a composite structure, provided that Young’s modulus measured on a length scale longer than the typical length of the composite is still between 3.2 GPa and 4 GPa. For instance, covering support may comprise successive layers of materials laminated one on another. The covering support may be also an assembly of pieces of different materials (like a puzzle, a checkerboard or a glue laminated structure) arranged in a way that Young’s modulus lies in the defined range.

In a preferred embodiment, the covering support 110 is made of a nitrile, more precisely of a material being a nitrile, more precisely of a polymer comprising at least one cyano group. The selection of this biocompatible material makes the headset 100 well suited for use in intensive measurement sessions. In addition, such a polymer material can be cut very precisely, for example by means of a laser, so that the shape of the covering support 110 can be easily adjusted according to desired positions for the measurement electrodes. A “nitrile” refers herein to an organic compound having at least one cyano functional group (also called carbonitrile).

In a specific configuration of this embodiment, the polymer comprising at least one cyano group (also called herein polymer material based on nitrile, also called herein a nitrile) is acrylonitrile butadiene rubber, i.e. a copolymer of acrylonitrile and butadiene.

In a preferred embodiment, the covering support 110 has a thickness ranging from 0.5 mm to 2.5 mm, more preferably from 1 mm to 2 mm, even more preferably from 1.2 mm to 1.8 mm, most preferably from 1.4 mm to 1.6 mm. In a most preferred configuration of this embodiment, the covering support 110 has a thickness equal to 1.5 mm.

In a preferred embodiment, the covering support 110 has a thickness ranging from 0.5 mm to 2.5 mm, more preferably from 1 mm to 2 mm, even more preferably from 1.2 mm to 1.8 mm, most preferably from 1.4 mm to 1.6 mm, and is made of a material having a Young’s modulus between 3.2 GPa and 4 GPa.

In addition, the headset 100 comprises a set of electrodes, which includes measurement electrodes configured to respectively fit into a plurality of insertion areas 113 in the covering support 110. The insertion areas 113 thus ensure that the electrodes are held in place. The expression “measurement electrodes” refers to electrodes configured to measure an electrical signal resulting from brain activity, typically in response to an action of the subject, such as a blink of the eye. The measurement electrodes may be of any type, the person skilled in the art being able to make a selection from electrodes available on the market. According to a preferred embodiment, the measurement electrodes are dry electrodes. Dry electrodes are preferred because they are easier and quicker to set up as compared to wet electrodes, in which a conductive gel has to be applied on the head of the subject. According to a preferred embodiment, the set of electrodes further comprises a ground electrode configured to define a reference potential. For example, such a ground electrode is positioned on mastoid or clavicle.

The headset 100 of the invention may comprise any number of measurement electrodes suitable for its function. In particular, the person skilled in the art knows how to determine the appropriate number of measurement electrodes according to the signals to be acquired, as well as to the geometry of the covering support 110. By way of example, the number of measurement electrodes of the headset 100 is at least equal to six, preferably the number of measurement electrodes of the headset 100 is equal to six. It was found by the inventors that a number of six measurement electrodes is advantageous, because it provides a range of signals representative of brain electrical activity, while limiting the manufacturing cost of the headset 100.

As already mentioned above, the respective positions of the measurement electrodes are according to the 10/20 model. In a particular embodiment, illustrated in a non-limiting way in Figures 1 and 2, the covering support 110 comprises six insertion areas 113 configured to receive six measurement electrodes. Each loop 111 has three insertion areas 113 uniformly spaced so as to form the vertices of an isosceles triangle. The covering support 110 is also dimensioned so that electrodes placed in the six insertion areas 113 occupy the positions known under the labels C3, C4, CPI, CP2, FC1 and FC2.

In a particular embodiment illustrated in Figure 2, the covering support 110 also comprises an insertion area 113 substantially centered in the central junction zone 112 between the two loops 111. In this way, more configurations are available for inserting the measurement electrodes. For example, the insertion area 113 in the central junction zone 112 receives an electrode in the position known as Cz.

In a particular embodiment illustrated in Figure 3, the covering support 110 comprises seven insertion area 113, but without having a loop structure. Positions of electrodes are similar as for covering support of Figure 2.

In a particular embodiment illustrated in Figure 4, the covering support 110 comprises six insertion area 113: two intended to be located on the front of the head of the subject and four intended to be located on the back of the head of the subject. As compared to embodiments of Figure 2 and 3, positions of electrodes are different.

In other embodiments not detailed here, it is possible to have a different positioning of the insertion areas 113. Here again, the skilled person knows how to determine the positions of the insertion areas according to the signals to be acquired.

The measurement electrodes are manufactured in such a way that they can be inserted into the insertion areas 113 and held securely in place.

In a first embodiment, each measurement electrode is held by screwing means with respect to the covering support 110. A measurement electrode according to this first embodiment is referenced in Figure 6 with the label “120”.

Figure 6 schematically illustrates an example of said first embodiment, and shows an exploded view of the electrode 120 assembled with the covering support 110. As shown in Figure 6, each measurement electrode 120 has a PCB 121 with conductive pins 122 extending therefrom and respectively inserted into holes of a corresponding insertion area 113. In this example, the number of pins 122 is equal to eight, and the PCB 121 having a hexagonal shape. It is possible to have a different number of pins, and also a different shape of the PCB .

In the first embodiment shown in Figure 6, the PCB 121 is held with respect to the covering support 110 by means of: half shells 123 arranged on either side of the covering support 110. By “either side of the covering support 110”, it is understood the side intended to be placed on the scalp and the opposite side. Since the pins 122 are to be in contact with the scalp, it is understood that the PCB 121 is inserted towards the insertion area 113 in a movement from the opposite side to the side facing the scalp. In this way, the covering support 110 is clamped between the PCB 121 and a half shell 123 on one side, and the other half shell 123 on the other side. a screw 124 extending between the half shells 123. The screw 124 supplements the holding of the measurement electrode 120 with respect to the covering support 110. Preferably, in order to ensure a well-balanced attachment of the PCB 121, and therefore of the measurement electrode 120, the screw 124 is arranged so as to extend through a central hole 125 of the PCB 121, the pins 122 being uniformly distributed in a circle around this central hole 125.

In a preferred embodiment, the half shells 123 are made of thermoplastic polymer, preferably polyamide. Polyamide is particularly suitable due to its high impact resistance and ease of use in rapid prototyping by Selective Laser Sintering.

Figure 7 schematically illustrates a second embodiment, in which the half-shells are combined into a single shell 132. A measurement electrode according to this second embodiment is referenced in Figure 7 with the label “130”. Figure 7 shows an enlarged partial view of an insertion area 113 in which a measurement electrode 130 corresponding to this second embodiment is arranged (the insertion area 113 being specially configured for this purpose). This view corresponds to a cross section of the covering support 110. In this example, all the features described in reference to the first embodiment, and relating to the material used to manufacture the half shell, as well as the configuration of the PCB (shape, number of pins), are identically reproduced. As illustrated in Figure 7, each insertion area 113 comprises a hole, for example of circular shape, the PCB 131 being enclosed in a shell 132 having a peripheral groove 133 configured to tightly receive the edge of the hole (such a hole being for example also illustrated in Figures 1 and 2). In this way, the edge of the hole is pinched inside the groove 133, which allows the measurement electrode 130 to be held efficiently. By way of a non-limiting example, the depth of the groove 133 is of the order of a few millimeters, for example between 1 and 2 mm.

As shown in a non-limiting way in Figure 7, the shell 132 is over-moulded around the PCB 131. The pins extend through the over- moulding so that they can be positioned in contact with the scalp and thus fulfil their function. This is particularly advantageous in that it allows the PCB 131 to be securely and easily attached to the shell 132, without requiring much handling or additional fastening means. It is also understood that the electrode 130 corresponding to this second embodiment can be completely manufactured and assembled before it is fixed to the covering support 110. Therefore, once manufactured, it only has to be fixed to the covering support 110 by means of its groove 133.

It should be noted that, although the first and second embodiments above have been described separately, in another variant they may also be combined, i.e. in such a way that the set of electrodes comprises, on the one hand, at least one measurement electrode 120 held by screwing means and, on the other hand, at least one measurement electrode 130 having an over- moulded shell.

By way of a non-limiting example, the covering support 110 illustrated in Figure 2 comprises seven insertion areas, six of them being configured to cooperate with a measurement electrode 120 held by screwing means, whereas the last insertion area is configured to cooperate with a measurement electrode 130 comprising an over-moulded shell.

The covering supports 110 illustrated in Figure 3 and 4 comprise insertion areas configured to cooperate with measurement electrodes 130 comprising an over- moulded shell. In some embodiments, the headset 100 of the invention may comprise additional sensors or transductors. These sensors or transductors may be located in insertion areas 113, instead of electrodes, or may be located anywhere else on the headset.

Additional sensors may be optical sensors or optodes. For instance, the near- infrared spectrometry (NIRS) assesses hemodynamic responses as temporal changes in oxyhemoglobin (oxyHb), deoxyhemoglobin (deoxyHb), and total hemoglobin (totalHb) concentrations. Optodes include both the light emitters and detectors allowing for NIRS that are properly arranged to create a predetermined illumination scheme within the cerebral cortex.

Additional sensors may be magnetoencephalographic sensors.

Additional transductors may be direct current stimulation devices. For instance, Transcranial Direct-Current Stimulation (tDCS) electrodes, that can implement a portable, wearable brain stimulation technique that delivers a low electric current to the scalp.

In particular, the coupling of EEG and NIRS is desirable for simultaneous recordings because these two methods can be used to measure brain signals without interfering with one another. The combination of EEG-NIRS systems would be useful for revealing the temporal order of neural activation and has been proven to be more efficient than each individual modality in brain computer interface applications, seizures and epilepsy detection, language studies and the characterization of fatigue to predict driver drowsiness using portable systems.

The headset 100 also comprises an acquisition module (not illustrated in the figures) connected to the measurement electrodes 120, 130 and configured to acquire signals provided by the measurement electrodes 120, 130, said signals being representative of an electroencephalographic activity of the subject. The acquisition module may also be connected to additional sensors or transductors.

The acquisition module comprises, for example, one or more processors and storage means (magnetic hard disk, electronic memory, optical disk, etc.) in which data are stored, as well as a computer program product, in the form of a set of program code instructions to be executed to implement all or part of the signal acquisition. As a variant, or in addition, the acquisition module comprises one or more programmable logic circuits (FPGA, PLD, etc.), and/or one or more specialized integrated circuits (ASIC), and/or a set of discrete electronic components, etc. suitable for implementing all or part of the signal acquisition. In other words, the acquisition module comprises software means (specific computer program product) and/or hardware means (FPGA, PLD, ASIC, etc.) configured to acquire signals provided by the measurement electrodes 120, 130.

The connection between the acquisition module and the measurement electrodes 120, 130 allows transmission of the measurements obtained by said electrodes in real time. In a particular embodiment, the connection between the acquisition module and the measurement electrodes 120, 130 is a wired connection. In particular, each measurement electrode 120, 130 has a connecting wire that is attached to the acquisition module. Preferably, the connection wires are grouped into a connection braid (not shown in the figures) in order to facilitate the handling of the headset 100, especially when the number of measurement electrodes 120, 130 is high, for example higher than ten electrodes. Such a braid also prevents the connecting wires from becoming intertwined.

It is noted that, in general, all the electrodes included in the set of electrodes of the headset 100 are connected to the acquisition module. In particular, this applies to the case where the set of electrodes comprises a ground electrode.

In a particular embodiment of the headset 100, a circumferential part 140 is provided in addition to the covering support 110, this circumferential part 140 being configured to surround the head of the subject. Such a circumferential part 140 makes it easier to hold and center the covering support 110 on the head of the subject.

In a first configuration and referring back to Figure 1, said circumferential part 140 comprises two reinforcing elements 141, each intended to cover one temple of the subject. The reinforcing elements 141 are of a substantially rectangular shape, thus taking the form of strips, and are made of a material that stiffens the structure of the circumferential part 140, and therefore also that of the headset 100.

The circumferential part 140 further comprises two elastic strips, such as a front strip 142 intended to be positioned on the forehead of the subject and a rear strip 143 intended to be positioned on the back of the skull of the subject, said front and rear strips 142, 143 being arranged so as to connect the reinforcing members 141 together. For example, and as illustrated in Figure 1, notches 144 are provided at the ends of the reinforcing members 141, the elastic strips 142, 143 passing through these notches 144 so as to form said circumferential part 140. By way of example, the circumferential part 140 is held in place by folding the elastic strips 142, 143 on themselves once they have passed through the notches 144, with fixing means (not illustrated in Figure 1) being provided for this purpose, for example a Velcro band, two-sided adhesive tape, etc. Advantageously, said fixing means are reversible so as to allow the circumferential part 140 to be adjusted to the size of the skull.

In this way, the circumferential part 140 takes the shape of a headband. The elastic strips 142, 143 thus configured allow flexibility to be provided at the front and back of the skull, which improves the comfort of the subject. The elastic material of the strips 142, 143 may be of any type. For example, the elastic strips 142, 143 are made of neoprene with a tensile strength less than 1 MPa and an elongation at break greater than 150% (minimum tensile strength and minimum elongation at break according to ASTM D412).

In a particular embodiment (not illustrated in the figures), the acquisition module cooperates with the rear strip 143 and is held thereon. For example, the acquisition module has notches through which the rear strip 143 passes. Such a configuration prevents the acquisition module from being away from the other elements of the headset 100, in particular the electrodes, which simplifies the connection between the electrodes and the acquisition module, while limiting discomfort for the subject. However, as a variant, it is possible to have an acquisition module located differently, for example on the front band 142 or in contact with one of the reinforcement elements 141. In the embodiment where a circumferential part 140 is provided, the headset 100 further comprises elastic holding means configured to ensure that the covering support 110 is held in place when on the head of the subject. This ensures that the covering support 110 does not shift from its position when the subject moves his head, for example during a sports session. In addition, the headset 100 comprises adjustment means configured to cooperate with the elastic holding means so as to modify the pressure applied by the electrodes 120, 130 on the head of the subject. The possibility to adjust the pressure of the electrodes 120, 130 makes it possible to improve the comfort of use of the headset 100, according to the sensitivity of the subject.

By way of example, as illustrated in Figure 1, the elastic holding means comprise an elastic tightening strip 145, comprising a first end 146 fixed to one of said reinforcing elements 141. Such a fixation can be of any type, for example by gluing or by means of a notch as described above in the case of the front and rear strips. Thus, according to this configuration, the first end 146 of the tightening strip 145 forms a fixing point through which it is possible to exert a force to adjust the pressure of the electrodes 120, 130 on the skull. As for elastic strips 142, 143, elastic tightening strip 145 is preferably neoprene with a tensile strength less than 1 MPa and an elongation at break greater than 150% (minimum tensile strength and minimum elongation at break according to ASTM D412).

In this configuration, the mechanical properties of elastic strips 142, 143 and elastic tightening strip 145 on one hand and covering support 110 on the other hand allow for a very efficient positioning of the headset. In particular, elastic tightening strip is rigid enough to impose some deformation to the covering support 110 (of higher Young’s modulus), but deformations of covering support 110 are small and prevent a wrong positioning of electrodes. Last, properties of elastic strips 142, 143 and elastic tightening strip 145 provide with a comfortable set-up for the subject as pressure is applied in a very uniform way on the head of the subject.

Preferably, the tightening strip 145 is arranged so as to be along a virtual line dividing the covering support 110 into two substantially equal parts. In other words, the tightening strip 145 is substantially centered with respect to the covering support 110. Such a configuration allows a balanced adjustment of the electrode pressure on the skull.

It is possible to have more than one tightening strip, for example three to six tightening strips, fixedly held with a reinforcing element in a way identical to that described above, so as to optimize the laying of the covering support 110 on the head of the subject.

Figure 5 shows a combination in a single piece of a front strip 142 and tightening strips 145. In this configuration, circumferential part 140 comprises one reinforcing element 141, for instance in the back of the skull (not shown). The reinforcing element 141 has notches 144 in which front strip and tightening strips are passed to ensure positioning of electrodes, as described above. This configuration is particularly suitable to cooperate with covering support 110 shown on Figure 3: tightening strips are fitted with branches of six-branch covering support, providing with a very stable and comfortable positioning of electrodes. Neoprene as described above is a preferred material for this configuration.

The adjustment means comprise at least one opening 147 arranged in the reinforcing element 141 opposite to the one to which the first end 146 of the tightening strip 145 is fixed, and configured to reversibly hold a second end 148 of said tightening strip 145. For example, and as illustrated in Figure 1, the opening 147 is arranged along an edge of a reinforcement element 141. Once the tightening strip 145 is passed through this opening 147, it is folded on itself and held in place with fixing means known per se (Velcro band, adhesive, knot, etc.).

It is possible to have more than one opening arranged in the considered reinforcing element, for example three regularly spaced openings along the same edge of said reinforcing element. Such a configuration makes it possible to have several tightening strips, preferably as many tightening strips as openings, each tightening strip being inserted in one of the openings.

In a particular embodiment, the covering support 110 comprises two openings 114 through which the tightening strip 145 passes, said openings 114 being respectively arranged facing the reinforcing elements 141. More particularly, and as illustrated in a non-limiting way in Figure 1, the openings in the covering support 110 are positioned so that the first and second ends 146, 148 of the tightening strips 145, respectively, pass through them. Thanks to the openings 114, the covering support 110 is reversibly fixed to the circumferential part 140.

In a second configuration (not shown), said circumferential part 140 is an elastic headband (as elastic holding means) without reinforcing elements. The circumferential part 140 further comprises tightening strips intended to be attached to the covering support either by opening 114 or by fixing means known per se (Velcro band, adhesive, knot, etc.). In this configuration, tightening strips are fitted with the branches of covering support, providing with a very stable and comfortable positioning of electrodes. Neoprene as described above is a preferred material for this configuration.

While various embodiments have been described and illustrated, the detailed description is not to be construed as being limited hereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the disclosure as defined by the claims.

REFERENCES

100 - Headset

110 - Covering support

111 - Loop

112 - Junction zone

113 - Insertion areas

114 - Opening

120 - Measurement electrode

121 - PCB

122 - Conductive pin

123 - Half shell

124 - Fastening member

125 - Central hole 130 - Measurement electrode

131 - PCB

132 - Shell

133 - Peripheral groove 140 - Circumferential part

141 - Reinforcing element

142 - Front strip

143 - Rear strip

144 - Notch 145 -Tightening strip

146 - First end of the tightening strip

147 - Opening

148 - Second end of the tightening strip

Claims

23

1. Headset (100) for acquiring electroencephalographic signals of a subject, said headset (100) comprising:

- a covering support (110) configured to be positioned on at least a portion of the head of the subject, the covering support (110) comprising a plurality of insertion areas (113),

- a set of electrodes comprising a plurality of measurement electrodes (120, 130) configured to respectively fit into one of the insertion areas (113),

- an acquisition module connected to the measurement electrodes (120, 130) and configured to acquire signals provided by the measurement electrodes (120, 130), said signals being representative of an electro-encephalographic activity of the subject, wherein the covering support (110) is made of a material having a Young’s modulus between 3.2 GPa and 4 GPa, and wherein the covering support (110) has a thickness ranging from 0.5 mm to 2.5 mm.

2. Headset according to claim 1, wherein the covering support (110) is made of a polymer material, in particular a polymer material based on nitrile.

3. Headset according to claim 1 or claim 2, wherein the polymer material is a copolymer of acrylonitrile and butadiene.

4. Headset according to any one of claims 1 to 3, comprising: a circumferential part (140) configured to surround the head of the subject, elastic holding means configured to ensure that the covering support (110) is held in place when on the head of the subject, adjustment means configured to cooperate with the elastic holding means in order to adjust the pressure of the measurement electrodes (120, 130) on the head of the subject.

5. Headset according to claim 4, wherein the circumferential part (140) comprises: two reinforcing elements (141) each intended to cover one temple of the subject, two elastic strips such as a front strip (142) intended to be positioned on the forehead of the subject and a rear strip (143) intended to be positioned on the back of the skull of the subject, the front and rear strips (142, 143) being arranged so as to connect the reinforcing members (141) together, wherein: the elastic holding means comprise an elastic tightening strip (145), comprising a first end (146) fixed to a first reinforcing element (141) among the two reinforcing elements, the adjustment means comprise at least one opening (147) arranged on the second reinforcing element (141) among the two reinforcing elements and configured to reversibly hold a second end (148) of the tightening strip (145). Headset according to claim 5, wherein the covering support (110) comprises two openings (114) through which the tightening strip (145) passes, the openings (114) being each arranged facing one of the reinforcing elements (141). Headset according to any one of claims 1 to 6, wherein the number of measurement electrodes (120, 130) is at least six. Headset according to any one of claims 1 to 7, wherein the set of electrodes further comprises a ground electrode connected to the acquisition module. Headset according to any one of claims 1 to 8, wherein each measurement electrode (120) is held by means of at least one fastening member with respect to the covering support (110). Headset according to claim 9, wherein each insertion area (113) has a plurality of holes, each measurement electrode (120) having a PCB (121) with conductive pins (122) extending therefrom and intended to be respectively inserted into the holes of a corresponding insertion area (113), the PCB (121) being held with respect to the covering support (110) by half shells (123) configured to be arranged on either side of the covering support (110), and by a fastening member (124) extending between the half shells (123).

11. Headset according to any one of claims 1 to 10, wherein each insertion area (113) comprises a hole, each measurement electrode (130) having a PCB (131) with conductive pins extending therefrom and inserted into said hole, the PCB (131) being enclosed in a shell (132) having a peripheral groove (133) configured to receive the edge of said hole.

12. Headset according to claim 11, wherein the shell (132) is over-moulded around the PCB (131). 13. Headset according to any one of claims 9 to 12, wherein the half shells (123) or the shell (132) are made of a thermoplastic polymer, preferably polyamide.

14. Electroencephalographic signal monitoring system, comprising: a headset (100) according to any one of claims 1 to 13, a signal display module, - transmission means configured to transmit signals acquired by the headset to the signal display module.

15. System according to claim 14, wherein the transmission means are wireless transmission means.