Patent Publication Number: US-2021178175-A1

Title: Illuminating device implantable in a living being

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an illuminating device intended to be at least partially implanted in a living being with a view to illuminating, locally, at least one region of the living being. 
     PRIOR ART 
     To treat certain pathologies of a living being, it has been imagined to optically stimulate an internal region of the living being. To this end, devices have been proposed that comprise a light source and that are at least partially or completely implanted in the living being with a view to illuminating the desired region. 
     The advantageousness of optically irradiating/illuminating certain regions of the human brain with such devices has notably been observed. 
     However, on account of the risks related to the implantation of such a device in the brain, it will be understood that such a device must be perfectly designed. 
     Patent application US2017281928A1 and patent application U.S. Pat. No. 10,213,596B2 describe implantable illuminating devices comprising an IPG (acronym of implantable pulse generator) that powers a light source, and a probe comprising a light guide tasked with delivering a light beam to the region to be treated. 
     Other solutions have also been proposed in the documents referenced US2019/168022A1, EP3539449A1 and WO2017/103380A1. 
     These solutions do not meet some or all of the following criteria: 
     illumination at a wavelength tunable from 2 to 50 mm; 
     compatibility of an illumination source with IPGs available on the market (i.e. without hardware modification); 
     modularity (ability to stimulate electrically and/or optically, choice of a plurality of illumination wavelengths, etc.). 
     Moreover, it is known that the curve of treatment effectiveness is a bell-shaped curve depending on the duration of the treatment and on the injected optical power. 
     At the present time, there are no simple and compact solutions allowing the effectiveness of such a treatment to be measured. 
     The aim of the invention is to provide an implantable, optically stimulating device configured to meet one or more of the aforementioned objectives, i.e.: 
     compactness and suitability for deep brain stimulation (DBS); 
     compatibility with existing IPGs; 
     modularity and adaptability (electrical and/or optical stimulation and choice of the illumination wavelength); 
     therapeutic effectiveness, achieved by tracking biological parameters via characterization of the surrounding medium (optical, thermal, electrical method); 
     ability to monitor correct operation of the probe. 
     Moreover, the solution of the invention will possibly allow the following objectives to be met: 
     evaluation of the penetration of the light into the tissues, in order to adjust the dose applied to the patient; 
     multi-wavelength stimulation; 
     assistance with surgical placement, by recording absorption/scattering parameters during the insertion of the probe into the biological tissues; 
     surveillance of the variation in the optical parameters of surrounding tissues via various methods (DRS for diffuse reflectance spectroscopy, fluorescence, absorption peaks of biological molecules, and/or thermal tracking). 
     The solution of the invention will be implemented based on materials recognized to be biocompatible. 
     DISCLOSURE OF THE INVENTION 
     This aim is achieved via an optically stimulating module to be integrated into a probe that is implantable into a living being with a view to locally illuminating a region of said living being, said module comprising:
         a casing that is at least partially transparent,   a hermetic electronic unit that is placed in said casing and that comprises an internal volume housing a light source, a processing and control unit, a first photodetector and a second photodetector, an opaque screen separating its internal volume into a first space containing the light source and the second photodetector, and a second space containing the first photodetector,   a connecting device for connecting said module to a central control and power unit.       

     According to one particularity, the module comprises an optical filter for selecting wavelengths applied to said first photodetector. 
     According to another particularity, the module may comprise at least one waveguide arranged on the first photodetector with a view to limiting any parasitic light and to optimizing a capture of photons. 
     According to another particularity, the module comprises a transparent porthole, chosen to capture signals of wavelength longer than  4  μm. 
     According to another particularity, the electronic unit comprises at least one substrate comprising two opposite faces, said two light sources being mounted on a single of the two faces of said substrate. 
     According to another particularity, the electronic unit may comprise a suitable hermetic cover on the substrate and forming said internal volume of the electronic unit. 
     According to another particularity, the casing of the module may comprise a ring that is closed at its two ends by two plugs, said two plugs bearing means for holding the electronic unit housed in the casing. 
     According to another particularity, the module may comprise electrically stimulating electrodes on the lateral surface of its ring. 
     According to another particularity, the module may comprise a coating material injected into its casing around the hermetic electronic unit. 
     The invention also relates to a probe that is implantable into a living being, said probe being intended to be electrically connected to an electrical power source and having an elongate architecture, said probe comprising a plurality of optically stimulating modules such as defined above, said modules being juxtaposed along the probe and separated from one another by a nonzero distance, said probe comprising a coating material filling the space between two adjacent modules. 
     The invention also relates to an implantable illuminating device intended to be implanted into a living being with a view to locally illuminating a region of said being, said device comprising an electrical power source comprising a plurality of parallel electrical supply paths and a probe that is electrically connected to the electrical power source and that has an elongate architecture between a proximal end and a distal end, said device comprising a probe such as defined above 
     According to one particularity, the power source is an implantable pulse generator. 
     According to another particularity, the device comprises means for determining a light dose to be applied depending on received signals coming from one or more first photodetectors of the modules. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Other features and advantages will become apparent in the following detailed description that is provided with reference to the appended drawings, in which: 
         FIG. 1  shows an example of an embodiment of the device according to the invention; 
         FIGS. 2A and 2B  illustrate various types of stimulation current or voltage signals able to be generated by the generator employed in the device of the invention;  FIG. 2C  illustrates an example of pulsed signals serving for implementation of impedance monitoring; 
         FIGS. 3 and 4  schematically show the architecture of the device according to the invention,  FIG. 4  being a close-up of the probe of the device; 
         FIGS. 5A to 5C and 6A to 6C  schematically show a module according to the invention seen from the side, seen from above and seen along its axis, respectively, according to two different particular embodiments; 
         FIGS. 7A to 7G  show a plurality of embodiments of the module, seen from the side and seen along its axis; 
         FIGS. 8A, 8B and 8C  schematically show a scheme of connection of a module according to the invention to a cable, seen from the side, seen from above and seen in cross section, respectively; 
         FIG. 9  schematically shows the functional architecture of a module according to the invention; 
         FIG. 10  illustrates the scheme by which a module is addressed by the IPG; 
         FIG. 11  shows the electronic architecture of the module and the scheme by which the module is electrically connected and addressed; 
         FIG. 12A  shows timing diagrams illustrating the principle of a first mode of operation of the device, corresponding to a stimulation achieved by turning on luminous diodes; 
         FIG. 12B  shows timing diagrams illustrating the principle of a second mode of operation of the device, corresponding to signals measured by a photodetector of the module being read after turn-on of the luminous diodes; 
         FIG. 13  illustrates the measuring principle employed to adjust the optical dose using the device of the invention; 
         FIGS. 14A and 14B  illustrate various illuminating configurations permitted by the device of the invention. 
     
    
    
     DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT 
     The invention relates to an implantable illuminating DBS device  1  (DBS being the acronym of deep brain stimulation). This device notably allows localized illumination (for example in the near infrared or with any other wavelength depending on the envisioned treatment—neuroprotective treatment, optogenetic treatment, etc.) of target tissues (for example the SNc, hippocampus, striatum, etc.) to be carried out while minimizing the medical risks of the implantation. This device may in particular be used to treat neurodegenerative diseases such as Parkinson&#39;s disease, Alzheimer&#39;s disease, Huntington&#39;s disease, etc. 
     It will be seen that the device  1  may optionally incorporate solutions enabling other modes of stimulation (notably electrical stimulation). 
     The illumination of the tissues may have various objectives depending on the application: neuroprotection, optogenetics, stimulation, etc. A number of targets are concerned, for example: the substantia nigra pars compacta (SNc), which degenerates in Parkinson&#39;s disease; the hippocampus, main center implicated in the start of Alzheimer&#39;s disease; and the striatum for Huntington&#39;s disease. The illumination may be delivered directly to the tissues (bidirectional illuminator, this surgical strategy involves risks of additional lesions) or via routes passing through the ventricles (cavities allowing cerebrospinal fluid (CSF) to circulate) and making contact with the structures to be treated (directional illuminators). 
     Moreover, the device also allows measurements to be taken with a view to performing various diagnostics on and monitoring the surrounding tissues. The device allows correct individual operation of the light sources to be monitored with a view to guaranteeing correct treatment. 
     The device  1  of the invention comprises an electrical power source. This power source is advantageously composed of an implantable pulse generator (commonly called an IPG) referenced IPG in the drawings. 
     As known, an implantable pulse generator mainly comprises a circuit board and a battery, which may or may not be rechargeable. The circuit board comprises a microcontroller that is responsible for managing the operation of the generator. The IPG may especially be programmed to deliver what are referred to as bipolar pulses, such as those shown in  FIGS. 2A and 2B . In  FIGS. 2A and 2B , the waveform thus comprises a positive square pulse I+ and a negative square pulse I−, which are separated from each other by a dead time. To balance the electrical charges injected into the tissues, the two pulses may be symmetric (as illustrated in  FIG. 2A ) or modulated in amplitude and in duration (as illustrated in  FIG. 2B ) with the same amount of charge injected during both pulses (t×i×V with t the duration of the pulse, i current and V voltage). The generator comprises n paths, with n higher than or equal to 2, and for example between 4 and 12 paths. 
       FIG. 2C  shows the IPG-generated signals that allow the impedance of the probe  10  that is connected thereto to be monitored. These signals may be coded in order to individually address each function of each of the electronic units  3 . 
     The device  1  then comprises an implantable probe  10  connected to the generator. 
     This implantable probe  10  takes the form of a supple elongate stem. The probe  10  advantageously has a circular cross section. By way of example, the diameter of the cross section of the probe may range from 1 to 3 mm, and is preferably 1.3 mm in order to be compatible with the standard tools used in DBS. 
     The device  1  comprises electrically connecting means allowing the probe  10  to be connected to the IPG via its proximal end, by way of a connector  15  and an extension  16 . At the distal end, the probe  10  advantageously has an atraumatic shape  100  (for example an oblong or spherical shape). 
     According to the invention, over at least some of its length, the probe  10  incorporates a plurality of juxtaposed optically stimulating modules M forming a strip. This strip is advantageously located in proximity to the distal end of the probe  10 . 
     The number of modules of the probe  10  may be tailored to the pathology to be treated and to the size of the region of tissue to be treated (which may for example range from 5 to 50 mm in length). 
     With reference to  FIGS. 3 and 4 , the modules M are connected to one another so as to form a daisy chain and are held together by a coating material  12  such as silicone, polyurethane or epoxy, the material possibly being chosen notably depending on the rigidity required for the application. Each module M Is connected to the IPG by a point-to-point link. It will be seen below that the point-to-point link incorporates a plurality of conductors, which are required for the module to operate. 
     With reference to  FIGS. 5A to 5C and 6A to 6C , each optically stimulating module M may comprise a casing  2 . The casing  2  may comprise a ring made of a transparent and biocompatible material such as sapphire or silica and closed at its two ends by plugs (not shown), so as to form a hollow cylinder incorporating an electronic unit notably equipped with an optical unit. The cylinder may have an outside diameter of 1300 μm. 
     The two plugs are used to correctly position the electronic unit and to facilitate filling of the cavity with a coating material  22 , which may be a transparent or scattering material depending on the sought-after uniformity objective (silicone, polyurethane or epoxy). An epoxy adhesive with a refractive index limiting losses by reflection will possibly be selected, and will possibly be combined with a filler in order to improve heat transfer and seal-tightness, and to meet constraints on expansion during production. In the probe, each module M is thus independent of each other module and has its own electronic architecture, i.e. its electronic unit and its connecting electrical contacts, and its own mechanical architecture, the latter being composed of the ring and plugs. It should be noted that each module of the electronic unit is hermetic, making each module easy to integrate into a probe during its manufacture. 
     The electronic unit comprises means for storing electrical energy such as a micro-battery or an MOS capacitance or capacitor C 1 , C 2 , with a view to supplying the electronic unit  3  with electricity between two supply pulses delivered by the IPG. 
     The electronic unit of each module M comprises one or more light sources. The light sources may be LEDs, OLEDs, μLEDs, VCSELs, lasers, QCLs, etc. The light sources may be monolithic (such as LEDs) or have a matrix-array arrangement (hybridization of a matrix array of μLEDs the various wavelengths). 
     The light sources may operate at a voltage lower than a few volts (2 V for example for LEDs), with currents possibly ranging from 2 mA to 25 mA. The IPG may, for its part, deliver a voltage of 15 V and currents ranging from 25 to 50 mA, this for example allowing a plurality of components in series (for example up to seven diodes of 2 V) to be powered. 
     Nonlimitingly, as shown in the appended figures, each module M comprises two luminous diodes D 1 , D 2 . The two luminous diodes D 1 , D 2  may be identical and emit the same wavelength. However, it is also possible to make provision to use two diodes that emit at two separate wavelengths, for example 670 nm for one and 810 nm for the other, with the objective of achieving neuroprotection. 
     In each module M, light sources other than those used for the optical stimulation and of suitable wavelength may be incorporated in order to allow measurements of surrounding tissues to be taken by measuring backscattered light (DRS, absorption peaks specific to a biological molecule (hemoglobin versus oxyhemoglobin, glucose, etc.). The detectors incorporated into the modules must be able to detect the emission wavelengths of sources. 
     In each module M, a temperature sensor (for example in CMOS technology) will possibly be incorporated into the electronic module in order to allow the operation of the device to be monitored (thermal safety, in case of heating) and to allow the local temperature of the surrounding tissue to be monitored (this temperature being dependent on the amount of tau protein in the case of Alzheimer&#39;s disease for example). A thermally conductive element (for example a finger made of conductive material arranged between the sensor and the casing of the module) may be integrated into the module M to facilitate the measurement of temperature and to make it more reliable. 
     The illumination is carried out in a plurality of directions that are transverse (and notably radial in a probe of circular cross section) to the axis of the probe. Depending on the modules employed, it is possible to illuminate in various directions, over the entire periphery of the probe or in a narrower defined angular range. It will notably be possible to employ bidirectional illuminating modules (for example 2×110°, standard emission angle of LEDs) or more directional illuminating modules (for example 1×110°). 
     The electronic unit  3  may comprise a first photodetector PhD 1 . This first photodetector PhD 1  is fastened to the substrate  30  of the electronic unit  3  and is positioned to detect the optical signals transmitted by the surrounding tissues. This first photodetector PhD 1  may for example be a hybridized large-area photodiode or a matrix array of CMOS detectors. 
     The electronic unit  3  may comprise a second photodetector PhD 2 . This second photodetector PhD 2  is fastened to the substrate  30  of the electronic unit and is positioned to monitor correct operation of the luminous diodes. This second photodetector PhD 2  may for example be a photodiode in CMOS technology or a hybridized photodiode. 
     Nonlimitingly, the electronic unit  3  may also comprise any other physical sensor able to participate in biological and physiological monitoring of surrounding tissues, for example a temperature sensor, optical sensor and/or electrical sensor, with the aim of monitoring changes in the surrounding tissue, adjusting the treatment to each patient in each region of illumination (depth of penetration of the light locally into the surrounding tissue) and ensuring the safety of the device. 
     Nonlimitingly, the electronic unit  3  may comprise a substrate  30  having a holding first face (top face) to which the two luminous diodes are fastened. On its top face, the substrate  30  bears the second photodiode PhD 2 , juxtaposed with the two diodes D 1 , D 2 . The latter must be positioned so as to capture some of the radiation emitted by each of the two luminous diodes. The first photodetector PhD 1  is separated from the two luminous diodes by a screen in order not to capture the signal emitted by the luminous diodes directly but only the signal transmitted by the surrounding tissues. In the variant of  FIGS. 5A to 5C , the first photodetector PhD 1  may thus be fastened to said first face, and separated from the two luminous diodes by an opaque screen  32 . In the variant of  FIGS. 6A to 6C , the first photodetector PhD 1  is fastened to the opposite face (bottom face) of the substrate  30 , the screen then being formed by the substrate itself. 
     To make the electronic unit hermetic, a cover  31  is placed on the substrate; this cover  31  will be completely (or locally) transparent. 
     In the case where the first photodetector PhD 1  is fastened to the bottom face of the substrate  30 , a second cover  310  may be used to cover the photodiode. As a variant, it is also possible to replace the cover with a conformal deposition deposited, by ALD, on all of the electronic unit, with the exception of the electrical contact-redistribution pads. 
     Depending on the configuration, nonlimitingly, each substrate  30  may be opaque or at least partially transparent in order to let the light emitted by the luminous diodes pass without inappropriate masking. The layout of the masking due to the conductive tracks and the extent of the transparency of the ring will possibly be tailored to the orientation of the luminous diodes D 1 , D 2  and to the degree of scattering of the light. Each module may thus be configured to create a directional or isotropic illumination. 
       FIGS. 14A and 14B  illustrate various possible illumination configurations. In  FIG. 14A , the module comprises two diodes fastened to the same face of the opaque substrate  30 . The cover  31  is chosen to be transparent. The illumination is thus produced only on a single side. In  FIG. 14B , the substrate  30  is transparent and the cover  31  is also transparent, allowing light to be emitted from both sides. 
     The two luminous diodes D 1 , D 2  are assembled (via conductive adhesive or soldering) and integrated into the hermetic electronic unit  3 . 
     With reference to  FIG. 9 , in addition to the components described above, the electronic unit  3  incorporates a control and processing unit UC. This control and processing unit UC may be a CMOS module. It is configured to perform at least the following functions:
         managing the electrical power supply of the components of the electronic unit  3 ;   decoding received input signals;   regulating the power supplied to the light sources of the module;   addressing components of the electronic unit  3  and managing the functions;   conditioning the signals delivered by the photodetectors PhD 1 , PhD 2 , the temperature sensor, electrocorticogram (ECoG) electrodes if present, of the electronic unit  3  (integration function, amplification function, current-voltage conversion function, etc.);   protecting against electrostatic discharges.       

     The IPG to which the probe  10  is connected is capable of delivering: 
     low-voltage pulses (for example 0.1 V, 40 μsec) in order, for example, to manage the addresses of the modules M and to synchronize the measurements if required; 
     “power” pulses (for example 15 V, 50 mA, 250 μsec) for powering the diodes D 1 , D 2 , the capacitors C 1  and C 2  and the electronic unit  3  of each module M. 
     The IPG incorporates a microcontroller that may perform various functions: 
     managing the power supply of the electronic unit  3  of each module M of the probe  10 ; 
     daily programming of the various functions (illumination, type of measurements, signal transfer); 
     converting (analog to digital datum corresponding to physical values); 
     storing the measurements carried out; 
     transferring the data on request. 
     The IPG will possibly perform a test on each module M, at regular intervals (i.e. programmed intervals or on request), to check it is operating correctly. 
     With reference to  FIGS. 7A to 7F , the module may perform various additional functions, these additional functions possibly of course being combinable with one another. 
       FIG. 7A : 
     The module of the invention may be of hybrid type, i.e. comprise optically stimulating means and electrically stimulating means. In this case, as shown in  FIG. 7A , the module M, in addition to comprising the luminous diodes D 1 , D 2 , also comprises electrodes  20  allowing surrounding tissues to be stimulated electrically. These electrical contacts  20  may be arranged on at least one portion of the surface of the side wall of the cylindrical casing  2  of the module M. The electrodes  20  may be connected to the same IPG as that employed to power the luminous diodes and occupy certain of the specific paths of the generator. The electrodes, which are deposited locally in order to let the optical beam pass, may for example be made of bulk or sputtered platinum-iridium or of IrO2. In  FIG. 7A , by way of example, the electrodes  20  are circularly arcuate in cross section and extend over an angular segment of the ring. 
     When a module is hybrid, i.e. when it possesses both optically stimulating means and electrically stimulating means, it should be noted that it may operate in either of the two stimulating modes or in both stimulating modes simultaneously. 
       FIGS. 7B and 7C : 
     The first photodetector PhD 1  may be equipped with selective filters  21  (for example dielectric filters) in order to allow measurement of fluorescence (for example amyloid plaques marked with a fluorophore such as “CRANAD-xxx”). 
       FIGS. 7D and 7E : 
     The first photodetector PhD 1  may be equipped with an optical waveguide  25  to limit parasitic light and to optimize the capture of photons. 
       FIGS. 7F and 7G : 
     The module M may comprise a porthole  23  that is transparent to sources of wavelengths longer than 4 μm. This porthole is made of a material (silicon for example) different from that of its casing  2  (which is for example made of sapphire). The electronic unit may then incorporate a far-infrared (FIR) module  24  for measuring the absorption of the tissues in the wavelength range 4-13 μm. 
     The control and processing unit UC may comprise analog and/or digital components. 
     The electronic unit may also incorporate a circuit  40  for driving the two luminous diodes and a circuit  41  for processing the signals delivered by the two photodetectors PhD 1 , PhD 2  and the temperature sensor. 
     A plurality of paths of the IPG may be reserved for management of the functionalities provided by each module M. 
     To generate the functionalities of a single module, four conductors (for example) or paths Vx (x ranging from 1 to N paths of the generator) of the IPG are required. With reference to  FIG. 10 , for each module, the following architecture may be employed:
         a first path V 1  is intended for the supply of power to the module: The generator is able to deliver a voltage of about 15 V;   a second path V 2  is intended for addressing the module;   a third path V 3  allows the measurement signals delivered by the module to be collected;   a fourth path V 4  serves as a voltage reference.       

     All of the paths of the IPG may be passed through a multistrand cable  11  (4 to 12 paths for example).  FIGS. 8A to 8C  illustrate a scheme of connection of a module to a multistrand cable  11 . The cable  11  may pass through each module M, under the substrate  30 , and each electronic component of the module M may be connected to one conductor of the cable using a via  34  produced through the substrate  30 . 
     By way of example,  FIG. 11  shows the electronic and operational architecture of an electronic unit employed in the module of the invention.  FIG. 11  thus shows:
         the first path V 1  and the fourth path V 4 , which are intended to power all of the electronic unit  3  by delivering supply voltages VDD and VSS: the IPG applies a supply voltage (for example 15 V) to this path;   the second path V 2 , to which the control and processing unit UC is connected and to which control signals may be applied; the control and processing unit UC may comprise a decoder intended to decode the received input control signals. Depending on the received input signals, the control and processing unit UC is configured to generate, as output, with a view to driving the luminous diodes D 1 , D 2 , a drive signal Vc intended for the driving circuit  40 ; the driving circuit  40  may comprise two transistors T 1 , T 2  (MOSFETs for example) that are connected in series with the LEDs, one of these transistors being p-type and the other n-type. Depending on the state of the drive signal Vc (polarity +/−) delivered by the control (IPG) and processing unit UC, and on the positive or negative alternation of the voltage delivered by the supply, the drive circuit  40  turns on the first luminous diode D 1  or the second luminous diode D 2 ;   the third path V 3 , to which is connected at least one photodetector PhD 1 , which is forward- or reverse-biased depending on the measurement electronics (photovoltaic or photoconductive mode) of the electronic unit  3  and on the processing circuit  41  used to process the signals delivered by this photodetector PhD 1 ; the processing circuit  41  may for example comprise an integrator, a converter or any other component conventionally employed in signal processing. It should be noted that the signals generated by the photodetector PhD 2  are processed in the same way. These measurements may be carried out on request, or regularly according to a preestablished protocol stored in the memory incorporated into the generator (IPG). These measurement points may be taken outside of the therapeutic illumination phase.       

       FIG. 12A  shows timing diagrams illustrating the operation of the device in a stimulating mode, i.e. in a tissue-treating mode.  FIG. 12A  thus shows:
         the supply signals delivered by the generator on its first path V 1 . First signals S 1  are dedicated to supplying power to components of the electronic unit and allow the voltage VDD (VDD+, VDD−) to be delivered. Second signals S 2  are dedicated to supplying power to the luminous diodes D 1 , D 2 . This supply is driven depending on the state of the drive signal Vc delivered by the control and processing unit UC;   the addressing and control signals S 3  delivered by the IPG on its second path. These signals S 3  are intended for the control and processing unit UC of the module M. When the module M is addressed, its control and processing unit UC generates drive signals Vc intended for the circuit  40  for driving the luminous diodes;   the current level I_D 1 , I_D 2  passing through each of the two luminous diodes D 1 , D 2 , after control thereof.       

       FIG. 12B  shows control and measurement timing diagrams illustrating the operating principle of the device in a measuring mode.  FIG. 12B  thus shows:
         the supply signals delivered by the generator on its first path V 1 . First signals S 10  are dedicated to supplying power to components of the electronic unit and allow the voltage VDD (VDD+, VDD−) to be delivered. Second signals S 20  are dedicated to supplying power to the luminous diodes D 1 , D 2 . This supply is driven depending on the state of the drive signal Vc delivered by the control and processing unit UC;   the addressing and control signals S 30  delivered by the IPG on its second path. These signals S 30  are intended for the control and processing unit UC of the module M. When the module M is addressed, its control and processing unit UC generates drive signals Vc (Vc 1 , Vc 2  and Vc 3  in our example) intended for the driving circuit  40  of the luminous diodes D 1 , D 2 ;   the current level Id passing through each of the luminous diodes D 1 , D 2 , after control thereof with Vc 1 ;   the current signal Ipd measured on the output of the photodetector PhD 1  after command thereof with Vc 2 ;   the voltage signal Vpd obtained on the output of the processing circuit  41 ;   the voltage signal that is read on the third path V 3  by the IPG;   the reset of the photodetector and of the integrator after reception of the control signal Vc 3 .       

     It should be noted that the device according to the invention, equipped with a plurality of modules such as described above, will be able to perform various treatments or various functions:
         adjustment of the optical dose: A treatment sequence comprises controlling a first module of the probe into optically stimulating mode so as to cause emission of a light beam F and measuring the signals transmitted by the tissues to the other modules of the probe (see  FIG. 13 ). This sequence may be repeated for each module of the probe. Such measurements allow the generator to determine the depth of penetration of the light and thus the absorption/scattering coefficients of the surrounding tissues, with a view to adjusting the dose of light to be emitted depending on the results of the measurements. Such measurements may be carried out at regular intervals or in real-time, via use of an automatic-control loop. The measurement taken by the first photodetector PhD 1  of each module is proportional to the depth of light penetration;   various biological effects to be monitored:
           micro-vascularization, with a view to evaluating the level of scarring and/or changes in surrounding tissues;   temperature, notably useful in case of Alzheimer&#39;s disease;   monitoring of the density of amyloid plaques in the hippocampus; DRS measurement with suitable wavelengths allows any changes in the surrounding tissues to be observed;   monitoring of StO2 (cerebral tissue oxygen saturation);   detection of amyloid plaques via measurement of fluorescence induced by a fluorophore such as CRANAD-xxx.   
               

     The invention thus has many advantages. An implantable optically stimulating device that is “multiplexable” by virtue of its control and processing unit UC and that allows surrounding tissues to be monitored by virtue of the use of a photodetector, is provided. 
     The advantage of providing an illuminating probe that is directly implanted into or that makes contact with the structures to be treated is that it allows changes in biological parameters to be observed directly in the tissues in question via an optical measurement (DRS, amplitude pulsation, StO2, etc.). Various 650 to 1070 nm light sources are known to be effective in the treatment of neurodegenerative diseases. The same wavelengths are perfectly suitable for measuring vascularization, O2 saturation, and absorption and scattering in cerebral tissues. 
     This device moreover allows the optical parameters of the tissues to be recorded during the placement of the probe. In particular: 
     optical parameters may be measured (absorption and scattering by DRS measurement) at various wavelengths in order to optimize the dose applied to the patient during stimulation; 
     tissues may be located, via a simple measurement of reflectivity, in order to assist with deep placement of the probe (for example, in the case of Parkinson&#39;s disease, electrodes are placed in the STN to compensate for the lack of dopamine and the probe extends 5 to 10 mm to illuminate the SNc, center targeted by NIR treatment); 
     micro-hemorrhages may be monitored during the descent of the probe. 
     The device is compatible with the use of a conventional IPG. It is moreover particularly compact, suitable for deep surgery and may prove to be particularly adaptable because of the ability to stimulate both optically and electrically. 
     Furthermore, it should be noted that the device may be manufactured using standard technologies:
         CMOS technology as regards the electronic unit;   LED, OLED, μLED, VCSEL or other laser technology as regards the diodes;   photodetector made of silicon or a matrix array of CMOS photodiodes;   ring- or strip-shaped metal electrodes;   hermeticity by laser welding of the cover and/or atomic layer deposition (ALD) on components of the electronic unit.