WO2023285360A1

WO2023285360A1 - Device for determining a brain response to a sensory stimulus

Info

Publication number: WO2023285360A1
Application number: PCT/EP2022/069284
Authority: WO
Inventors: Rascle ANGÉLIQUE; Bonnet STÉPHANE; Planat-chretien ANNE
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2021-07-12
Filing date: 2022-07-11
Publication date: 2023-01-19
Also published as: FR3124937A1

Abstract

A device for analysing a brain response generated by a user in response to a sensory stimulation. The device comprises an extended reality system for generating the sensory stimulus as well as electrodes, a light source and at least one photosensor designed to be placed against the user's scalp.

Description

Title: Device for determining a cerebral response to a sensory stimulus

TECHNICAL FIELD The technical field of the invention is a device for collecting, in a non-invasive and synchronized manner, optical and electrical cortical signals, so as to measure a cerebral response to stimuli addressed to a user.

PRIOR ART

There are several ways to estimate, non-invasively, a mental state of a user. Currently, the most common mental state estimation systems are based on electrical measurements of cerebral activity, using “EEG” (ElectroEncephaloGraphy) type electrodes distributed over a user's skull. These measurements provide actionable information about brain activity. Products for the general public, based on EEG electrodes, are now available, particularly in the field of entertainment.

Recently, optical techniques of the functional Near Infrared Spectroscopy (fNIRS) type have been developed, so as to form another modality for analyzing cerebral activity. This type of technique makes it possible to evaluate a local variation in blood oxygenation in the cortex. The principle is based on illumination of the cortex, in a near infrared wavelength, and on detection of an optical signal backscattered by the cortex, a few centimeters from the point of illumination. The signal detected depends on the attenuation induced at the level of the cortex but also at the level of the other tissues crossed.

The wavelengths used exploit the strong absorption of deoxyhemoglobin or oxyhemoglobin in the near infrared. The fact that cerebral activity is correlated with blood oxygenation levels is used to quantify variations in cerebral activity from optical measurements taken at different times. This type of method is for example described in the following publications:

[1] P Pinti, The present and future use of functional near-infrared spectroscopy (f NI RS) for cognitive neuroscience. Ann NY Acad Sci. 2020 Mar;1464(l):5-29; [2] L Lim et al., A Unified Analytical Framework With Multiple fN 1RS Featuresfor Mental Workload Assessment in the Prefrontal Cortex, IEEE Trans.on Neural Systems and Rehabilitation Engineering, vol. 28, no. 11, p. 2367-2376, Nov. 2020.

The use of f NI RS type techniques is currently confined to uses in the field of research or in laboratory environments. The inventors propose an integrated device allowing coupling between electrical and optical methods, analysis of cerebral activity, and a virtual reality, augmented reality or mixed reality system.

DISCLOSURE OF THE INVENTION

A first object of the invention is a device for analyzing the cerebral response of a user, the device being configured to send a sensory stimulus to the user and to record a cerebral response following the stimulus, the device comprising:

- a support, configured to be worn by the user;

- an extended reality system, connected to the support, and intended to emit the sensory stimulus;

- electrodes, intended to be applied to the skin covering the skull of the user, each electrode being configured to record an electrical cortical signal generated by a cortical zone of the user located opposite the electrodes; the device being characterized in that it comprises

- a light source, arranged to illuminate the skin covering the user's skull, forming an illumination zone, the light source being arranged to emit light in a spectral band between 650 nm and 1350 nm;

- at least one photodetector, configured to detect light backscattered by the cortex, under the effect of illumination by the light source, the detected light emanating from a detection zone on the skin covering the skull, the distance between the detection zone and the illumination zone preferably being between 1 mm and 7 cm, the detected light forming an optical cortical signal;

- a processing unit, programmed to establish:

• a variation of an electrical cortical signal detected by at least one electrode following the emission of the sensory stimulus, said variation forming an electrical cerebral response to the sensory stimulus;

• a variation of at least one optical cortical signal detected by at least one photodetector following the emission of the sensory stimulus, said variation forming an optical cerebral response to the sensory stimulus. According to one embodiment, the processing unit is configured to estimate a mental state of the user from the optical and electrical cerebral responses. The processing unit can be configured to adjust the sensory stimulus, at a time, according to the mental state of the user estimated at a previous time. The device may comprise a movement sensor, configured to generate an actimetry signal representative of a movement of the user, the processing unit being configured to take the actimetry signal into account when estimating the mental state of the user.

The light source can be a continuous or frequency modulated light source.

At least two electrodes, at least one light source and at least one photodetector are preferably arranged less than 5 cm from each other, so as to address the same cortical zone.

According to one possibility, the device comprises an illumination optical fiber, extending from an illumination source, to an illumination end, the illumination end being intended to be placed in contact with the user's skull, the illumination optical fiber forming the light source.

According to one possibility, the device comprises a detection optical fiber, extending from a light detector, to a detection end, the detection end being intended to be placed in contact with the skull of the user, the detection optical fiber forming the photodetector.

Advantageously, each electrode, the or each light source, the or each photodetector, is connected to the support, thus forming a monolithic device.

The support can be a frame for a bezel. The bezel may be a virtual reality or augmented reality bezel, forming the extended reality system.

The extended reality system may feature:

- a projection surface, configured to project visual information, forming a visual stimulus;

- And/or a sound generator, configured to generate a sound forming an auditory stimulus. The extended reality system may include:

- a vibration generator, configured to generate a tactile stimulus;

- an electrostimulation generator, configured to generate a muscular stimulus.

A second object of the invention is a method for analyzing a cerebral response of a user following the generation of a sensory stimulus, using a device according to the first object of the invention, the process comprising: a) generation of a sensory stimulus by the extended reality system; b) following step a):

- detection of at least one electrical cortical signal by an electrode of the device;

- activation of at least one light source and detection of an optical cortical signal by a photodetector of the device; c) using the processing unit, taking into account the signals detected during step b) and determining the cerebral response of the user following the sensory stimulus generated in step a).

Steps a) to c) can be carried out iteratively, the method being such that following a first iteration, the sensory stimulus generated during step a) is adapted according to the cerebral response determined during an iteration previous.

The sensory stimulus may be intended to cause the user to perform a cognitive task.

The invention will be better understood on reading the description of the embodiments presented, in the remainder of the description, in connection with the figures listed below.

FIGURES

FIG. 1 represents an example of a device according to the invention.

Figure 2 shows the path of a photon through different structures covering the cortex and through the cortex, between an illumination zone and a detection zone located at a distance from the illumination zone. The illumination zone and the detection zone are located on the skin covering the skull.

Figure 3 schematizes the various sensors of the device described in connection with Figure 1.

FIG. 4 shows the main steps of a method implementing the device.

DESCRIPTION OF PARTICULAR EMBODIMENTS

Figure 1 shows an embodiment of the invention. Device 1 comprises a support 10, intended to be held at the level of a user's head. The support carries an extended reality system 11, here taking the form of a bezel. The term extended reality includes virtual reality, augmented reality and mixed reality. The extended reality bezel 11 comprises a projection surface, intended to display a virtual scene for the attention of the user.

The extended reality bezel is intended to address a sensory stimulus or several sensory stimuli to the user. By sensory stimulus is meant a visual stimulus and/or a stimulus sound. Visual and sound stimuli can be combined. The extended reality bezel may be intended to immerse the user in a virtual environment. The extended reality system 11 can generate other types of stimulus, for example a haptic stimulus or a muscular stimulus, of the electrostimulation type.

The device 1 is intended to capture and analyze a cerebral response of the user to the displayed virtual scene. It comprises electrodes 12, of the electroencephalography (EEG) type, intended to be placed on the skin covering the skull (scalp or forehead). In known manner, EEG-type electrodes make it possible to pick up an electrical activity of the cortex. The signal collected by each electrode forms an electrical cortical signal. The number of electrodes can be between two and a few tens. The diameter of an electrode can be a few millimeters or around 1 cm.

The device 1 comprises at least one light source 13, intended to illuminate an illumination zone 14 on the skin covering the skull. The light source, or each light source, emits in a spectral band between 650 nm and 1350 nm. This spectral band allows a high penetration depth of the light in the tissues, in this case the skin, the skull and the dura mater. The photon absorption properties are mainly governed by the hemoglobin present in the cortex. Each light source can be a light-emitting diode, or one end of an illumination optical fiber connected to an illumination source located on the support 10. In this case, the illumination optical fiber or the end of the illumination optical fiber is equated with the light source. The emission spectral band of a light source is preferably less than 100 nm or less than 50 nm. Preferably, the device comprises: a light source, the emission wavelength of which is less than 800 nm, which corresponds to a spectral band in which the absorption of deoxyhemoglobin is greater than the absorption of oxyhemoglobin; a light source, the emission wavelength of which is greater than 800 nm, which corresponds to a spectral band in which the absorption of oxyhemoglobin is greater than the absorption of deoxyhemoglobin;

Preferably, two light sources emitting in two different spectral bands are close to each other, so that the area of illumination of each of the light sources can be considered as merged. Alternatively, each light source can emit successively in several spectral bands. The device comprises at least one photodetector 15, configured to detect light backscattered by the user's tissues illuminated by the light source. The photodetector 15 can be a photodiode, directly in contact with the user. It may also be one end of a detection optical fiber, the other end of which is connected to a light detector located on the support 10. In this case, the detection optical fiber or the end of the detection fiber is likened to the photodetector 15. This possibility is illustrated in FIG. 2. Each photodetector 15 is configured to collect light emanating from the skin covering the user's skull at the level of a detection zone 16. The detection zone 16 is located at a distance d from the illumination zone 14. The distance d between the illumination zone 14 and the detection zone 16 is called the backscatter distance. Preferably, the device is configured so that for an illumination zone 14, different detection zones 16 are arranged respectively at different backscatter distances. Each backscatter distance is between 1 mm and 30 mm, or even 70 mm.

In FIG. 2, exemplary statistical average paths followed by photons penetrating into the tissue at the level of an illumination zone 14, and emanating, by backscatter, from a detection zone 16 located at a distance of backscatter d from the illumination zone 14. The photons propagate through the skin A, the skull B, the dura mater D and the cortex C. It is considered that the greater the backscatter distance, the greater the light signal collected at the detection zone is representative of deep layers of the user's tissues. In the present case, taking into account the thickness of the skin and the bone, in the case of an adult, the cortex is at a depth of between 1 cm and 2 or 3 cm from the skin. It is better that the backscatter distance is about 3-3.5cm for an adult.

The light source 13 can be continuous or frequency modulated.

Under the effect of a sensory stimulus, generated by the extended reality system 11, certain parts of the user's cortex can react. One objective of the invention is to detect the cerebral response, whether it be an electrical reaction and/or an optical reaction, the latter reflecting hemodynamic effects induced by cortical activity.

The electrical response can be picked up by electrodes placed on the skin covering the user's skull. In a manner known per se, the response of the cortex results in a variation of the electrical activity, the latter being able to be recorded by the electrodes 12. The device comprises a processing unit 20, intended to collect and analyze the signals electric detected by the electrodes or the optical signals from each photodetector. The processing unit 20 comprises various modules.

A first module 21 is programmed to perform an analysis of the electrical signals collected by the electrodes. Usually, the first module 21 can perform an analysis of the spectral power in different spectral bands, for example one or more of the spectral bands known in the field of the frequency analysis of EEG signals: band d, band Q, band a or band b. According to one possibility, the frequency analysis can select a spectral band whose power undergoes a temporal variation considered to be significant under the effect of the sensory stimulus and then quantify the temporal variation of spectral power in the spectral band thus selected. This temporal variation corresponds to the electrical response of the cortex to the stimulus addressed to the user. A second way of analyzing EEG signals is to average several cerebral responses by synchronizing with the time of appearance of the stimuli: this so-called evoked potential analysis technique is particularly robust because the measurement noise will decrease during the process. on average.

A second module 22 is programmed to carry out an analysis of the optical signals emanating from each detection zone 16 and detected by each photodetector 15. Known principles of functional near-infrared spectroscopy f NI RS are then implemented, mentioned in the prior art. The f N I RS modality makes it possible to detect a hemodynamic response of the cortex, following the perception of the sensory stimulus. The use of different wavelengths makes it possible to estimate a variation in the concentration of oxyhemoglobin and deoxyhemoglobin under the effect of the stimulus. Certain stimuli can in fact trigger neuronal activity inducing an increase in the demand for oxygen. This local increase results in an increase, at the level of the cortical zone concerned, in the concentration of oxyhemoglobin, and a decrease in the concentration of deoxyhemoglobin.

The second module 22 is configured to quantify the variations of optical signals detected before and after the stimulus. These variations constitute the user's optical response to the stimulus.

The second module 22 can be configured to estimate a heart rate or a respiratory rate. For this, a photodetector located at a short distance from a light source, typically less than 1 cm, is implemented. With regard to the estimation of the heart rate, one can implement the principles described in the French patent application FR2014157. With regard to the estimation of the respiratory rate, the principles described in Charlton PH, Bonnici T, Tarassenko L, Clifton DA, Beale R, Watkinson PJ can be implemented. An assessment of algorithms to estimate respiratory rate from the electrocardiogram and photoplethysmogram. Physiol Meas. 2016 Apr;37(4):610-26.

The first and second modules are configured to establish a cerebral response, respectively electrical and optical, in the cortical zone considered, resulting from the perception of the stimulus by the user. By cortical zone is meant the zone of the cortex the activation of which forms a response detectable by the electrodes and the photodetectors arranged opposite the latter. In order to address the same cortical zone, at least two electrodes, at least one light source and at least one photodetector, forming two source-detector pairs, are preferably grouped together in a perimeter whose diameter is less than 5 cm.

According to one possibility, the device 1 comprises a movement sensor 17, intended to detect a movement of the user. It may for example be an accelerometer. The movement sensor 17 generates an actimetry signal representative of the movement of the user. The use of such a signal makes it possible to avoid the interpretation of artefacts in the cerebral responses of the user, in particular the electrical response, the analysis by EEG possibly being sensitive to the movements of the user. The movement sensor 17 is connected to an actimetry module, making it possible to record the actimetry signal and to detect any movement liable to cause a disturbance of the electrical or optical response.

The extended reality system 11 can be equipped with an inertial unit. The movement sensor 17 can be one of the sensors of the inertial unit.

According to one possibility, the device comprises an electrodermal activity sensor 18. Such a sensor is configured to estimate a variation in impedance of the skin. Impedance variation can occur when the user is under stress. The electrodermal activity sensor is formed of two electrodes, a current or voltage source, and an impedance measurement circuit.

According to one possibility, the device comprises an eye tracking sensor 19, arranged on the projection surface, so as to follow the eye movement of the user. Such a sensor can comprise one or more infrared cameras aiming to follow the movement of the eye. The electrical and optical cerebral responses, resulting from the modules 21 and 22, are used by the processing unit 20 to estimate a mental state of the user and/or a change in the mental state following the successive emission of different stimulus. The processing unit 20 comprises an analysis module 23, configured to estimate the mental state of the user. The mental state of the user can be a level of stress, fatigue, concentration, or emotion, or, more generally, a cognitive load. The movement 17, electrodermal activity 18 or eye tracking 19 sensors can be connected to the analysis module 23, so that their measurements are taken into account in determining the mental state of the user. This is to remove artifacts that may be related to user movements or eye movements. It may also involve obtaining additional measurements, tending to confirm the estimate of the mental state. This is for example the case when electrodermal activity measurements are used to confirm the occurrence of a state of stress. An example of determining the mental state of a user is described in the publication [2] cited in the prior art.

The processing unit may include one or more microprocessors.

An example of combining optical and cortical EEG measurements is described in the publication Mahmoudzadeh M “Usefulness of stimultaneous EEG-NIRS recording in language studies”, Brain and Language, May 2011.

FIG. 3 illustrates the connection between the various components previously described. Preferably, the device is in one piece, the various components being connected and/or integrated into the support 10.

An interesting aspect of the device is that depending on the mental state estimated by the processing unit 20, feedback can be performed, so as to adapt each stimulus. For example, a visual stimulus, at a time, can be adapted according to the state of the user estimated at a previous time. When the user is immersed in a virtual scene, the content of the virtual scene, which forms the stimulus addressed to the user, can thus vary according to the evolution of the mental state of the user. For example, when the user is requested by the virtual environment to perform tasks, the difficulty of the tasks can vary according to the mental state of the user, for example his state of stress or fatigue.

The processing unit 20 can estimate a score, quantifying the mental state of the user, for example a level of stress or a level of relaxation. The score can be communicated to the user, via the extended reality system, visually or audibly. That allows the user to practice changing their mental state. Such an embodiment is suitable for practicing relaxation activities for the user.

In FIG. 3, the arrows in solid lines illustrate signal transmissions by wired or wireless link. The dotted arrows correspond to the action of the user's cortex, which, under the effect of the scene displayed by the extended reality system 11, generates a cerebral response that can be measured by the electrodes 12 or the photodetectors 15.

The stimulus can be addressed without the user being focused on it. The stimulus can be a part of the virtual scene, not necessarily directly perceptible by the user, and which makes it possible to bring about an evolution of the mental state of the user, for example generating stress or, on the contrary, relaxation . Thus, it is possible to estimate a mental state of the user without the latter being aware of the stimuli applied, the latter being embedded in the virtual environment in which the user is immersed. For example, the user can be placed in a soothing musical atmosphere, while visual stimuli are addressed to him.

One advantage of the device is that it makes it possible to obtain good synchronization between the application of successive stimuli and the measurements of the cerebral responses, and this by using an integrated device.

The mental state of the user can be transmitted to a remote unit 30, so as to carry out temporal monitoring and correlations between the stimuli applied and the evolution of the mental state. It may also involve identifying situations to which the user is sensitive.

During the implementation of the device, the user is for example subjected to a continuous musical atmosphere, of the background music type, and/or to discontinuous noises: in this case, the device comprises a source of sound emission, for example a headset. The discontinuous noise can be a signal given to the user to start or stop the execution of a particular instruction, so as to modulate the cognitive load. The discontinuous noise can also be intended to generate a stress effect on the user, for example a high-pitched noise.

As a complement or alternative to a visual and/or auditory stimulus, the device can subject the user to another sensory stimulus. It may in particular be: a stimulus applied to a part of the user's body: in this case, the device comprises a haptic stimulus generator, for example a vibration generator; a muscular stimulus, applied to a muscle of the user: in this case, the device can comprise for example an electrostimulation module; The user can thus be simultaneously exposed to stimuli of different types: for example visual + auditory, visual + haptic.

According to one possibility, the visual and sound stimulus aims to generate a cognitive task of the user. It may for example be a question of asking the user, audibly or visually, to perform a task involving a cognitive load or a certain state of stress. It may for example be a matter of carrying out an increasing or decreasing count, taking into account a predefined increment (or decrement). For example, the user is visually or audibly asked to count down from a value, for example 1000, by successive decrements of 13. The user performs this cognitive task after the transmission an audible or visual instruction signal. As previously mentioned, the complexity of the cognitive task can be adjusted according to the mental state of the user, in this case the cognitive load of the user.

In one embodiment, the extended reality device is an augmented reality goggle. In this case, the user perceives the real environment in which he finds himself and visual indications are displayed by augmented reality. These indications can constitute a stimulus. For example, the user can engage in physical activity. The indications displayed are instructions addressed to the user to modulate his physical activity: change of movement, acceleration... Depending on the mental state of the user, the instructions, which form the stimuli, are adapted, by adjusting the level of difficulty.

FIG. 4 represents the main steps of a method for estimating a mental state of a user using the device previously described.

Step 100: display of a scene to the user by the extended reality bezel 11. As previously indicated, this may be a virtual scene or a scene comprising information of the augmented reality type.

Step 110: acquisition of electrical measurements by the electrodes 12.

Step 120: acquisition of optical measurements by the photodetectors 15.

Step 130: acquisition of measurements from other sensors: motion sensor 17 and/or electrodermal activity sensor 18 and/or eye tracking sensor 19.

Step 140: quantification, by the first module 21, of the electrical response to the scene displayed, from the electrical measurements resulting from step 110 and from previous electrical measurements. Step 150: quantification, by the second module 22, of the optical response to the scene displayed, from the optical measurements resulting from step 120 and from previous optical measurements.

Step 160: estimation of the mental state of the user from the optical response and the electrical response resulting respectively from steps 140 and 150.

Step 170: from the mental state of the user, forming a feedback signal so as to adjust the observed scene. This step is optional.

Step 180: transmission of the mental state of the user to the remote unit 30. This step is also optional.

Steps 100 to 180 can then be repeated.

A notable advantage of the invention is to facilitate the temporal synchronization between the generation of the sensory stimulus and the determination of the cerebral response of the user following the generation of the stimulus. Synchronization allows better control of the effect of the sensory stimulus on the user. The device is configured to be worn by the user: it is therefore particularly suitable for mobile use.

From the measured cerebral response, the device makes it possible to retroact on the generation of the stimulus, and to adapt the stimulus according to the cerebral response. The stimulus can thus be adapted according to the mental state of the user, in particular the cognitive load of the user.

The device may be used for analyzes carried out for diagnostic purposes, or for functional rehabilitation purposes. For example, it may be a question of piloting a rehabilitation program for the motor skills of the user, the program indicating motor tasks to be carried out by the user The device makes it possible to adapt the rehabilitation program, in particular the frequency and/or or the difficulty of motor tasks, to the mental load of the user.

The device can also be used to test the psychic abilities of users likely to carry out certain operations which may prove to be stressful. The device can for example be used to follow the evolution of the mental load of a pilot subjected to a virtual environment, simulating difficult flight situations. The principle can be extended to any operator required to carry out specific operations in a potentially stressful work environment. Although described in connection with a bezel, the extended reality device can take other forms. It may for example be a visor attached to a support connected to the user's head.

Claims

1. Device (1) for analyzing the cerebral response of a user, the device being configured to send, at a time, a sensory stimulus to the user and to record a cerebral response following the stimulus, the device comprising:

- a support (10), configured to be worn by the user;

- an extended reality system (11), connected to the support, and intended to emit the sensory stimulus;

- electrodes (12), intended to be applied to the skin covering the user's skull, each electrode being configured to record an electrical cortical signal generated by a cortical zone of the user located opposite the electrodes; the device being characterized in that it comprises

- a light source (13), arranged to illuminate the skin covering the skull of the user, forming an illumination zone (14), the light source being arranged to emit light in a spectral band between 650 nm and 1350 nm;

- at least one photodetector (15), configured to detect light backscattered by the cortex, under the effect of illumination by the light source, the detected light emanating from a detection zone (16) on the skin covering the skull, the distance between the detection zone and the illumination zone being between 1 mm and 7 cm, the detected light forming an optical cortical signal;

- a processing unit (20), programmed to establish, in synchronization with the instant at which the sensory stimulus is addressed:

• a variation of at least one optical cortical signal detected by at least one photodetector following the emission of the sensory stimulus, said variation forming an optical cerebral response to the sensory stimulus.

2. Device according to claim 1, in which the processing unit (20) is configured to estimate a mental state of the user from the optical and electrical cerebral responses.

3. Device according to claim 2, in which the processing unit is configured to adjust the sensory stimulus, at a time, according to the mental state of the user estimated at a previous time.

4. Device according to any one of claims 2 or 3, comprising a motion sensor (17), configured to generate an actimetry signal representative of a movement of the user, the processing unit (20) being configured to take into account the actimetry signal when estimating the mental state of the user.

5. Device according to any one of claims 2 to 4, wherein:

- the device comprises an eye tracking sensor (19) and/or an electrodermal activity sensor (18);

- the processing unit (20) is programmed to take into account the measurements resulting from the eye tracking sensor and/or from the electrodermal activity sensor to determine the mental state of the user.

6. Device according to any one of the preceding claims, in which the light source (13) is a continuous or frequency modulated light source.

7. Device according to any one of the preceding claims, in which at least two electrodes, at least one light source and at least one photodetector are arranged less than 5 cm from each other, so as to address the same cortical zone. .

8. Device according to any one of the preceding claims, comprising an illumination optical fiber, extending from an illumination source, to an illumination end, the illumination end being intended to be placed in contact with the user's skull, the illumination optical fiber forming the light source (13).

9. Device according to any one of the preceding claims, comprising a detection optical fiber, extending from a light detector, to a detection end, the detection end being intended to be disposed at the contact with the user's skull, the detection optical fiber forming the photodetector (15).

10. Device according to any one of the preceding claims, in which each electrode, the or each light source, the or each photodetector, is connected to the support (10), forming a monolithic device.

11. Device according to any one of the preceding claims, in which the support (10) comprises a frame for a bezel, the bezel being a virtual reality or augmented reality bezel, forming the extended reality system (11).

12. Device according to any one of the preceding claims, in which the extended reality system (11) comprises:

- And/or a sound generator, configured to generate a sound forming an auditory stimulus.

13. Device according to any one of the preceding claims, in which the extended reality system comprises:

- a vibration generator, configured to generate a tactile stimulus;

- an electrostimulation generator, configured to generate a muscular stimulus.

14. Method for analyzing a cerebral response of a user following the generation of a sensory stimulus, using a device (1) according to any one of the preceding claims, the method comprising: a ) Generation, at a time, of a sensory stimulus by the extended reality system (11); b) following step a):

- detection of at least one electrical cortical signal by an electrode (12) of the device;

- activation of at least one light source and detection of an optical cortical signal by a photodetector (15) of the device; c) using the processing unit, taking into account the signals detected during step b) and determining the cerebral response of the user following the sensory stimulus generated in step a), the response cerebral being determined in synchronization with the instant at which the stimulus is applied.

15. Method according to claim 14, in which steps a) to c) are carried out iteratively, the method being such that following a first iteration, the sensory stimulus generated during step a) is adapted according to the brain response determined in a previous iteration.

16. Method according to any one of claims 13 or 14, in which the sensory stimulus is intended to cause the execution of a cognitive task by the user.