Patent Application
20180117309
The present application relates to electrophysiologic recording and/or stimulation of brain tissue using electrode arrays.
Several common disorders of the brain, spinal cord, and peripheral nervous system arise due to abnormal electrical activity in biological (neural) circuits. In general terms, these conditions may be classified into:
When the electrical lesion is focal and relatively discrete, as is very often the case, effective diagnosis and treatment of such conditions depends on precise localization of the lesion and, when possible, restoration of normal electrophysiologic function to the affected region.
A variety of well-established techniques exist for localizing electrical lesions in the brain, each of which has specific limitations.
While the foregoing list is not exhaustive, it provides a general overview of the range of techniques presently available for electrical recording and stimulation of the living human brain.
In practice, all neural recording and stimulation techniques involve design trade-offs among a number of primary factors:
An ideal electrophysiologic neural probe, should simultaneously provide optimal performance in all four of the above categories. Exemplary existing solutions for lesions of particular types, in particular brain regions are as follows:
Diagnosis and treatment of functional electrophysiologic lesions in brain regions remain challenging or intractable. In particular, deep brain regions are frequent sites of functional lesions, yet remain difficult to access systematically and minimally invasively. For example, the medical temporal lobe is a common site for seizure foci and the substantia nigra is the site of neuronal degeneration causing Parkinson's disease; both regions are several centimeters deep to the cortical surface.
The present application discloses an electrode array for neural recording and stimulation, which can be deployed using minimally invasive techniques, to electrophysiologically localize and stimulate targets within wide regions deep within the brain.
In one aspect, the present application discloses an implantable medical device with a flexible substrate, an array of electrodes mounted on the flexible substrate for recording and stimulating neurological activities within ventricles of a brain, and a conformal scaffolding supporting the flexible substrate.
In some embodiments, the array of electrodes can be periodic. In some embodiments, the conformal scaffolding can be continuous. In some embodiments, the conformal scaffolding can be a plurality of flat panels oriented parallel to each other, and a continuous loop of metal wire, wound in a helical pattern across the plurality of parallel panels and longitudinally along the length of the plurality of parallel panels. In some embodiments, the metal wire can be made of a shape memory alloy, such as nitinol. In a some embodiments, the flexible substrate can be a flexible printed circuit board made of polyimide. In some embodiments, the plurality of electrodes can be made of platinum, iridium, or gold. In some embodiments, the implantable medical device further includes a power source and a microprocessor, each electrically coupled to the array of electrodes.
In another aspect, the present application discloses a method for electrically interacting with a neural tissue using an electrode array located within a ventricular compartment of a brain, the method can include selecting a portion of neural tissue for electrical interaction, accessing previously stored registration information regarding a location of the electrode array within the ventricular compartment of the brain, selecting one or more electrodes in the electrode array for electrical interaction based on the registration information, and interacting with the neural tissue with the selected electrodes.
In some embodiments, the method can include stimulating neural activities of the neural tissue, or recording neural activities of the neural tissue, or simultaneously stimulating and recording neural activities of the neural tissue. In some embodiments, the method can include forming an electrical field beam distributed in a three-dimensional space using the selected electrodes. In some embodiments, the method can include localizing electrical activity in the brain using the selected electrode distributed in a three-dimensional space. In some embodiments, the method can include localizing electrical activities from epileptogenic foci within a hippocampus for the management of epilepsy. In some embodiments, the method can include stimulating the brain in response to epileptogenic activity within the hippocampus for the management of epilepsy. In some embodiments, the method can include interacting with motor pathways by an electrical field generated by the electrode array at a distance to assist in restoring mobility and limb control. In some embodiments, the method can include stimulating visual pathways to generate visual perception. In some embodiments, the method can include stimulating sensory cortex or sensory thalamus to deliver sensory stimulation to the brain for a neurosensory prosthesis or for the treatment of thalamic pain. In some embodiments, the method can include stimulating hypothalamic nuclei for the management of neuroendocrine disorders, circadian rhythm disorders, physiologic response to fever or hypothermia, or obesity. In some embodiments, the method can include registering the electrode array to obtain its orientation and position within the ventricular compartment of a brain via neuroimaging. In some embodiments, the method can include placing the electrode array into the ventricular compartment of a brain via a minimally invasive insertion technique, such as a cannula or catheter.
The device described herein can be used with minimally invasive techniques for precise spatial and temporal localization of electrical activity within the brain, and for precise electrical stimulation of brain tissue, to diagnose and restore function in conditions caused by abnormal electrical activity in the brain.
An exemplary electrophysiologic neural probe provides maximal spatial and temporal resolution, enables three dimensional electrical recording and stimulation, and can be deployed noninvasively, without disrupting normal brain tissue.
In particular, the present disclosure describes a flexible and collapsible array of electrodes, and a minimally invasive method of delivering such an array into the cerebral ventricles, the fluid-filled cavities at the center of the brain. The walls of the cerebral ventricles are formed by the inner surfaces of several deep brain structures that are difficult to access from the cortical surface, including the hippocampus and medial temporal lobe (frequently involved in seizure disorders), the hypothalamus (which is involved in hormonal regulation, circadian rhythm, and the modulation of cravings related to a range of factors, including sleep, food, salt and water, warmth, and sex), the thalamus and basal ganglia (involved in movement disorders such as Parkinson's disease), and the internal capsule (frequently damaged in hemorrhagic stroke). By arraying electrodes along the inner walls of the cerebral ventricles, deep brain targets can be accessed electrically for precise electrical recording and stimulation.
In summary, electrode arrays positioned within the ventricles can interface with structures deep within the brain, without traumatizing brain tissue, in ways that conventional depth electrodes and surface electrodes cannot. The ability of these electrodes to more extensively interface with deep brain structures is due to two principal properties. First, during initial placement, ventricular arrays can be navigated within a purely fluidic compartment that provides extensive access to deep brain structures. By navigating within this fluidic compartment (the cerebral ventricular system), ventricular electrode arrays avoid traumatizing delicate brain tissue. Second, multiple neural structures that are difficult to access electrically using conventional techniques are situated in close proximity to the surface of the ventricular system. The ventricular system of the brain can be accessed and navigated using techniques of minimally invasive neurosurgery, including neuro-endoscopy.
Conformal electrode arrays can be clinically useful in mapping and targeted ablation of cardiac lesions causing heart arrhythmias. For example, conformal electrode arrays can be used for electrophysiologic mapping in real-time in the heart. Exemplary techniques for treating conditions such as atrial fibrillation can use conformal electrode arrays, delivered through the major blood vessels, to record from the electrical system of the heart (De Ponti et al. (2004) Europace 6:97-108); (Yamada (2007) Indian Pacing Electrophysiol. J. 7:97-109). However, there is extremely limited precedent for intraventricular electrode recording in the brain (Konrad et al. (2003) J. Neurol. Neurosurg. Psychiatry 74:561-565), and prior work has been conducted only with linear electrode configurations, not with conformal arrays. Additionally, there is limited precedent for stimulation of brain regions surrounding the ventricles from within the ventricles, (Benabid et al. (2016) Neurosurgery 79:806-815) and prior work has been limited to conventional deep brain stimulation electrodes, not conformal electrode arrays.
In some embodiments, array 200 can include a mechanism for expanding skeleton member 201 from the axial configuration used for initial implantation, to an expanded, deployed configuration that conforms (based on measurements obtained, for example, from patient-specific medical imaging) to the inner shape of the intracranial ventricular compartment. Certain general geometric characteristics are appropriate for implantation within the cerebral ventricles, but shape-memory materials permit skeleton member 201to be sized and shaped in a patient-specific manner. Ovoid and cylindrical shapes provide useful approximations to the shapes of certain parts of the cerebral ventricular system.
In some embodiments, panels 202, 203 can be composed of polyimide or other polymer substrates suitable for fabricating flexible printed circuits. The panels are typically rectangular, but deformable. Typically they measure between about 5 mm and about 50 mm in width, about 20 mm and about 60 mm in length, and about 10 micrometers to about 100 micrometers in thickness.
A non-exclusive list of materials that can be used to make stiffener 204 includes polyimide, polyether ether ketone (PEEK), polycarbonates, polyamides, polyethylene, polypropylene, polyesters, and polyethersulfones. The stiffness of stiffener 204 can be controlled such that it is rigid enough to hold the array in place while it is being unsheathed from a cannula, while stiffener 204 can be flexible enough to conform in a gentle arc per the anatomy inside the cerebral ventricles.
In some embodiments of the present disclosure, stiffener 204 and center panel 203 can be bonded together with a biocompatible adhesive. Exemplary biocompatible adhesives can include, but not limited to, medical grade epoxies, including flexible and high-bond-strength cyanoacrylate epoxies. In some embodiments, stiffener 204 and center panel 203 can be bonded by heat curing under pressure. In some embodiments, stiffener can be molded or etched with trenches, which can be used to hold skeleton member 201 in place. In one embodiment of the present disclosure, the side panels do not have stiffeners, and can wrap upwards to conform to the anatomy. In some embodiments, each side panel 202 also can have a stiffener.
Flexible printed circuit board 207 can be a polymer substrate upon which a series of electronic devices, for example, electrodes 208, can be mounted. In some embodiments, flexible printed circuit board 207 can be polyimide, PEEK, polyacrylic, epoxy, fluoropolymers or a transparent conductive polyester film. Flexible circuit 207 can be mounted on top of skeleton member 201 (not shown in
In order to generate a strong and focused electrical field for stimulation and recording or neural activity, flexible printed circuit board 207 can have a periodic array of electrodes 208. For example, a total of 350 electrodes 208 are shown in
In some embodiments, flexible circuit 207 can be a continuous sheet. In some embodiments, flexible circuit 207 can be slit by laser excision to form center and side panels to allow easier folding of conformable electrode array 200. In the slit configuration, the electrical components can be positioned such that no electrical components span across the fold line.
In some embodiments, electrodes 208 can be composed of a biocompatible and electrically conducting material. Electrodes can be made of materials including, but not limited to, platinum, iridium, or gold. Electrodes 208 also can be further coated with platinum-iridium or gold to improve conduction properties, biocompatibility, and radiopacity.
In some embodiments, the array of electrodes 208 supported on flexible printed circuit board 207 can be used for recording of electrical signals generated by the brain in the regions surrounding the cerebral ventricles, or for electrically stimulating regions of the brain surrounding the cerebral ventricles. In some embodiments, electrodes 208 in the array can be designed and arranged for recording, stimulation, or both. Material and geometric considerations, as well as electrical impedance considerations, apply to optimizing for one mode of operation or the other. Arrays can be configured with recording electrodes alone, stimulation electrodes alone, a combination of types, or electrodes capable of operating in both modes. Electrode surfaces can be treated, for example through chemical etching or other roughening techniques, or through polymer coating, to optimize their effective surface area and modify their impedance for recording or stimulation.
In some embodiments, each electrode 208 can have an associated conductor trace 205. In some embodiments, conductor traces 205 can be used to connect electrodes 208 to recording, stimulation, and other computational apparatus outside the ventricular system. Conductor traces 205 can be aligned inside the loops of skeleton member 201, which can be threaded inside the loop and merge into a single signal cable 206. Cable 206 can exit the ventricular system and the skull along the insertion path of the endoscope used to implant the array, as discussed below. In some embodiments, conductor traces 205 can be composed of any suitable biocompatible conductor, for example, gold. In some embodiments, conductor traces 205 can be gold at nine micrometers thick, sandwiched inside flexible printed circuit board 207. Cable 206 can pass through a narrow-diameter tract through the cerebral cortex and cortical white matter, to exit through a small burr hole surgically drilled through the skull at the time of initial implantation. Accordingly, and as discussed in detail below, electrode array 200 can be connected to an implantable power source, implanted microcomputer, and implanted mechanism for data telemetry and communication with external devices. In some embodiments, the power source and microcomputer can be external to the body.
In some embodiments, a biocompatible coating can be conformal coated on to the entire assembly as a moisture barrier and lubricating coating. In some embodiments, the entire assembly can be conformally coated with Parylene C.
The collapsed configuration of the electrode array 200, as shown in the perspective view in
In some embodiments, skeleton member 201 can be calibrated in a patient-specific manner to exert adequate pressure on the walls of the ventricular compartment to remain in fixed position and in contact with the inner ventricular surface, but without disrupting neurologic function and without significantly deforming the anatomic structures forming the boundaries of the ventricular compartment. In some embodiments, the contact pressure may be almost negligible, for example, just adequate to maintain the skeleton member 201 in the shape of the cavity, without exerting a physiologically significant pressure on the surrounding brain. The very minimal residual pressure can be accommodated over time by the brain with negligible clinical physiologic effect.
Prior neural electrical stimulation techniques have been one-dimensional or two-dimensional in nature. For example, some techniques for neural stimulation in the context of electrode arrays have been demonstrated in the context of interleaved stimulation and current steering techniques for cochlear implants (Rubenstein (2004) Curr. Opin. Otolaryngol. Head Neck Surg. 5:444-448); (Choi et al. (2012) Cochlear Implant Research Updates, Chapter 5). The electrode arrays and neural substrates of interest in cochlear implant applications, however, are essentially one-dimensional. Recent developments in the context of deep brain stimulation (Timmermann et al. (2015) Lancet Neurol. 14:693-701) have demonstrated the value of current-steering techniques in deep brain stimulation, but those systems are also limited by being essentially one-dimensional as well. This revised approach to deep brain stimulation, using multiple current-sources, has recently been described and implemented (Timmermann et al. (2015) Lancet Neurol. 14:693-701), but the approach, while effective, remains limited in the sense that the electrode array is effectively linear, and requires intraparenchymal placement. The volume of brain tissue accessible for neural stimulation using deep brain simulation electrodes is extremely limited as compared with the planar intraventricular electrode arrays described here, which can assume three-dimensional shapes. Additionally, the deep brain stimulation electrodes must penetrate deep into the brain, damaging neural tissue along the insertion tract. The device disclosed herein relates to three-dimensional conformal electrode arrays, used to record from or stimulate three-dimensional volumes of neural tissue, which has not been accomplished by the prior art techniques.
An electrode array on a three-dimensional surface enables more versatile shaping of electric fields and more precise spatial targeting than conventional one-dimensional and two-dimensional electrode arrays. The ability to position arrays of many electrodes deep within the brain confers such arrays the further ability to generate tailored electrical fields, designed to stimulate an individual brain region with high spatial and temporal precision. In contrast to depth electrodes (such as those used in deep brain stimulation), for which intraparenchymal position is the primary determinant of the region stimulated, the regions accessible to stimulation by conformal arrays can be programmed with many degrees of freedom after deployment. Accordingly, stimulation by the described conformal electrode array does not require the direct proximity to the region of interest as does stimulation by linear depth electrodes such as those used in deep brain stimulation.
Because of the high volumetric density of neurons within the brain, focused electrical fields are required for effective and precise neural stimulation. In some embodiments, a beam-formed electrical field can be created by the stimulation device. This can require three-dimensional distribution of the electrode contacts inside the brain. The conformable array described in the present disclosure with three-dimensional distribution of electrodes enables beam forming of the electrical field. Beam formation enables a strong and focused stimulation of brain tissue, which is an advantage over existing technologies using one-dimensional electrodes. Further, the relatively large number of electrodes and the conformal design of the device enable a stimulation of three-dimensional volumes of neural tissue.
Several minimally invasive approaches can be used in contemporary neurosurgery for precise placement of devices within the cerebral ventricular system. (Mark M. Souweidane. Intraventricular Neuroendoscopy: A Practical Atlas. B. Braun, Aesculap Neurosurgery, Berlin) The conformal electrode array described herein is designed to integrate with several such techniques.
Following deployment, the conformal electrode array changes from a collapsed state (as shown in
Following array implantation is registration of the array 506. During this step, three-dimensional neuroimaging can be used to establish the final, deployed, spatial and anatomic orientation of an array within the ventricular system. In some embodiments, elements of the conformal electrode arrays are radio-opaque, enabling unambiguous localization of each electrode in three-dimensional space and with respect to neighboring neuroanatomic structures using conventional neuroimaging modalities, such as computed tomography (CT). Registration can allow for precise stimulation and recording of neural tissue.
After deployment, as particular electrodes transmit electrical signals reflecting neuronal activity within the brain, it may be important in many applications to correlate the precise positions of implanted electrodes with their positions in three-dimensional space and with respect to anatomic structures. Such correlations can be established using CT imaging of the brain, provided the position of each electrode can be identified on CT. For this reason, to ensure detectability via CT and fluoroscopic imaging, certain components of the electrodes and the device are radio-opaque. For example, in some embodiments, radio opaqueness can be achieved using platinum titanium alloys. Analysis of such imaging data (typically high-resolution computed tomography, CT) forms the basis of the following:
Following registration, conformal electrode array can operate in a plurality of modes. For example, the device can operate in a recording mode 508, a stimulation mode 512 and a feedback mode 510.
In some embodiments, the device can include a recording mode. In the recording mode, a method of correlating imaging determining the position of the array relative to anatomic structures, with electrophysiologic recording data from which particular neural signals arise, to determine the spatial and neuroanatomic origin of those signals can be performed.
In some embodiments, the method can include a stimulation mode. In the stimulation mode, a method of correlating imaging determining the position of the array relative to anatomic structures, with computationally determined electric field geometry, so as to achieve precise image-guided electrical stimulation of neural structures can be performed. In some embodiments, this method can include a method of shaping the electric fields generated by the electrodes, so as to stimulate precise anatomic regions surrounding the cerebral ventricle; this configuration may be programmed prior to or following array implantation (based on patient-specific imaging, electrode recordings, behavior, response to therapy, or other data). A set of computational models, taking into account patient-specific anatomy based on neuroimaging obtained with the array in place, can be used to compute the anatomic origin of particular electrical signals recorded by the array. Similarly, a related set of such models can be used to shape the electrical fields and steer the electrical currents collectively generated by the array within surrounding neural tissue, in order to stimulate with anatomic and functional precision.
In some embodiments, in a feedback mode, electrical stimulation and recording can be performed simultaneously (by designating certain electrodes for stimulation and others for recording) or in an interleaved manner, in order to confirm efficacy of electrical stimulation in real-time, and in order to adapt electrical stimulation programs to real-time electrophysiologic responses. In some embodiments, the device can switch between modes after implantation. Each individual electrode in the array can be independently controlled. Once the electrode is implanted its geometric configuration and impedance are fixed. But any electrode can theoretically be used at any time for recording or stimulation. In practice, arrays can be fabricated with specific electrodes designed either for recording or for stimulation, and the mode will rarely be changed after implantation. However, the current or voltage settings at each stimulation electrode can be independently controlled, as can stimulation timing; frequency, amplitude, and pulse-width of stimulation; and stimulation pulse shape, among other parameters.
The described conformal electrode array positioned in the cerebral ventricles can be minimally disruptive to normal brain tissue but can have extensive access to deep brain nuclei and fiber tracts that are otherwise difficult to access. Accordingly, the conformal array of ventricular neural electrodes disclosed herein has several major advantages over existing technologies.
As the leads from the recording electrodes exit the brain, they form a bundle that is tunneled through a small-diameter hole surgically drilled in the skull. After exiting the skull, this bundle may be tunneled in a subcutaneous layer to a microcomputer or other device designed to power the electrodes, store recording data, store stimulation parameters, and coordinate wireless data telemetry with external devices. These active electronic components are contained within the hermetic package. In such a configuration, the conformal electrode array permits long-term electroencephalographic monitoring of patients in the ambulatory setting, as there is no fluidic communication between the brain and the outside world, and hence no major risk of intracranial infection. In this configuration, the monitoring capabilities of the conformal, minimally invasive system disclosed here offer an option not available using conventional grid and strip electrodes, which are implanted via craniotomy, tunneled through dura, skull, and skin, and permit leakage of cerebrospinal fluid and a conduit between the brain and the outside world. Epilepsy patients undergoing monitoring using such techniques, which represent the present state of the art, must be monitored in a hospital setting until the recording electrodes are removed. Furthermore, in the current state of the art, removal of the electrodes requires a second operation for electrode removal, repair of the dura membrane, and reaffixing of the removed portion of the skull.
On the other hand, the system disclosed herein does not preclude monitoring using such conventional techniques. Using the system disclosed herein, device leads may also, temporarily, be tunneled through the skin for patient monitoring in a conventional epilepsy monitoring unit.
Epilepsy often but not always arises due to lesions deep in the temporal lobe that are difficult to access electrically and surgically. Medically refractory epilepsy is a condition in which an individual is prone to recurrent seizures that cannot be controlled by antiseizure medications, though the individual may be otherwise neurologically normal between seizures. This class of seizure disorder is often caused by a lesion deep within the temporal lobe of the brain (the associated condition is often referred to as “mesial temporal lobe epilepsy”). Definitive treatment for such lesions has traditionally involved major brain surgery. In recent years, a variety of modern techniques have been developed for ablating such lesions in minimally invasive fashion, once a sufficiently high degree of diagnostic confidence is achieved with regard to lesion location. However, definitive diagnosis remains challenging for the reasons described in the previous section: EEG, MEG, and ECoG provide limited spatial resolution when the lesions of interest are deep within the brain, and only a limited number of exploratory depth electrodes can safely be placed.
Traditional, contemporary approaches to localizing seizure foci within the medial temporal lobe and hippocampus approach these structures from the external cortical surface. However, the surface of the medial temporal lobe and hippocampus form the inner wall of the temporal horn of the lateral ventricle, and are therefore directly accessible to electrode arrays placed within the cerebral ventricles. The system disclosed here provides for highly spatially accurate localization of abnormal electrical activity in these deep structures, without requiring depth electrodes or a traditional craniotomy (a conformal ventricular electrode array can be introduced through a small burr hole, in stereotactic or endoscope-assisted fashion).
One principal application of the conformal intraventricular electrode array is in localization of seizure foci in patients having temporal lobe epilepsy. In such patients, the electrode array is deployed in recording mode, with electrodes arrayed along the ventricular surface of the temporal horn, which is defined by the structures of the medial temporal lobe, including the hippocampus. In this application, the goal is precise spatial and anatomic localization of epileptogenic foci within the hippocampus or medial temporal lobe. The array configuration of the electrodes permits patterns of electrical activity to be localized in three-dimensional space and correlated with three-dimensional anatomic neuroimaging.
Neurologic disorders such as Parkinson's disease and epilepsy can be treated using spatially targeted electrical recording and stimulation of specific neuroanatomic structures. Electrical stimulation of deep brain targets is an important modality in the treatment of Parkinson's disease, essential tremor, and certain (thalamic) pain syndromes. The efficacy of neurostimulation-based therapy is highly dependent on the ability to stimulate the correct target with precision. In certain cases, it is difficult or impossible to introduce a conventional intraparenchymal depth electrode into the target without simultaneously generating a lesion associated with electrode placement.
The conformal electrode array in the present disclosure can be used in deep brain stimulation for Parkinson's disease. A grid of intraventricular electrodes enables highly versatile shaping of electrical fields, with the ability to design and modify the electric field within and surrounding the traditional targets used during deep brain stimulation. In some embodiments, the aggregate electric field and current density function of the implanted array can be configured to stimulate deep brain nuclei associated with the treatment of Parkinson's disease and related movement disorders. These periventricular targets include the subthalamic nucleus, globus pallidus, specific thalamic nuclei, and substantia nigra.
Other applications of the described conformal electrode array can include minimally invasive stimulation of the optic radiations. This technique may provide an approach to delivering visual stimuli to the blind. Several approaches to electrical stimulation of the visual pathways have been experimentally demonstrated and reviewed (Pezaris et al. (2009) Neurosurg. Focus 27:E6), as potential approaches to developing a visual prosthesis for the blind. All such approaches, to date, have used intraparenchymal depth electrodes, which would require introducing lesions into the very tracts or grey matter structures that carry or process visual information, as the depth electrodes would need to penetrate the cortical regions or white matter tracts of interest.
Phosphenes, visual phenomena often described as transient “flashes of light” related to electrical stimulation, are common side effects of deep brain stimulation during initial intraoperative placement and testing of the electrodes, and subsequent programming. In the context of deep brain stimulation targeting the thalamus and subthalamic nucleus, for example, high-amplitude stimulation can give rise to fringe electrical fields that cause depolarization of axons in the optic tracts, giving rise to transient visual sensations. While these effects are unwanted in the context of deep brain stimulation, they confirm that it is possible to generate visual sensations in reproducible manner by controlling the electric field generated by electrodes placed at a distance from the optic pathway, rather than directly into the pathway itself (at the level of the optic tracts, lateral geniculate nuclei, optic radiations, or visual cortex, for example).
The conformal array of intraventricular electrodes disclosed herein enables highly versatile shaping of electrical fields, with the ability to target locations along the visual pathway, including the optic tracts, lateral geniculate nuclei, optic radiations, and visual cortex. An adaptive, computational approach to mapping the visual pathways using electrical stimulation and recording, with or without collaboration from the subject, holds promise for a prosthesis to restore vision to the visually impaired.
Targeted electrical stimulation of white matter tracts transected by hemorrhage or stroke has the potential to restore neurologic function. Several approaches to electrical stimulation of the motor pathways have been experimentally demonstrated and reviewed, as potential approaches to developing a neural prostheses for paralyzed individuals and amputees (Wolpaw et al. (2012) Mayo Clin. Proc. 87:268-279), and as approaches to restoring function in patients paralyzed or partially paralyzed due to stroke (Boyd et al. (2015) Front Neurol. 6:226). Some such major and promising approaches, to date, have used cortical surface electrodes or intraparenchymal depth electrodes, which can only be placed through conventional neurosurgical techniques, and which can require introducing lesions into the very tracts that carry motor information, as the electrodes need to penetrate the cortical regions or white matter tracts of interest.
Involuntary, stimulation-triggered muscular contractions are common side effects of deep brain stimulation during initial intraoperative placement and testing of the electrodes, and subsequent programming. In the context of deep brain stimulation targeting the thalamus or globus pallidus, for example, high-amplitude stimulation can give rise to fringe electrical fields that cause depolarization of axons in the internal capsule, giving rise to transient muscular contractions (often in the face). While these effects are unwanted in the context of deep brain stimulation, they confirm that it is possible to control motor function in reproducible ways by controlling the electric field generated by electrodes placed at a distance from the motor (corticospinal) tracts, rather than directly into the tracts themselves (at the level of the motor cortex or spinal cord).
The internal capsule is of particular interest in the context of this disclosure. Fibers of the internal capsule carry neural signals regarding voluntary movement from the motor cortex to the spinal cord, from where they are transmitted to the skeletal muscles that generate such movement. The internal capsule is a common location for hemorrhagic strokes, particularly those related to high blood pressure; strokes of this type tend to disrupt or destroy some of the internal capsule fibers, leaving stroke victims permanently weak or paralyzed on the side of the body opposite the hemorrhage. Many of the internal capsule fibers travel within millimeters of the ventricular surface, and are therefore amenable to precise stimulation using precisely controlled electrical fields. This disclosure therefore has the potential to be used in the context of neural prosthetics for paralyzed and disabled individuals, as well as for individuals recovering from stroke.
The conformal array of intraventricular electrodes disclosed herein can enable highly versatile shaping of electrical fields, with the ability to target locations along the motor pathway, including multiple targets within the internal capsule. An adaptive, computational approach to mapping the motor pathways using electrical stimulation and recording, with or without collaboration from the subject, holds promise for a prosthesis to assist in restoring mobility and limb control to the paralyzed and disabled.
The conformal electrode array in the present disclosure can be used in deep brain stimulation for thalamic pain syndrome. In some embodiments, the aggregate electric field and current density function of the implanted array is configured to stimulate targets within the thalamus associated with thalamic pain syndrome.
The conformal electrode array in the present disclosure can be used for stimulation of hypothalamic nuclei. In some embodiments, the aggregate electric field and current density function of the implanted array is configured to stimulate targets within specific nuclei of the hypothalamus, in the walls of the third ventricle. Such targeting may be useful in the management of neuroendocrine disorders, circadian rhythm disorders, physiologic responses to fever or hypothermia, and obesity, which are centrally physiologically regulated by specific nuclei in the hypothalamus.
The conformal electrode array in the present disclosure can be used in stimulation of subcortical white matter tracts and internal capsule for stroke rehabilitation and neuromotor prostheses. In some embodiments, the aggregate electric field and current density function of the implanted array can be configured to stimulate a set of targets within the motor pathways of the brain, including targets within the internal capsule or cerebral or elsewhere in the corticospinal tract. In these embodiments, the conformal electrode array can have clear advantages over traditional depth and microelectrode arrays, as the conformal array can be configured to simulate the fields and current densities generated by an array of electrodes implanted anywhere within large volumes of the brain, without damaging or displacing brain tissue, and the configuration can be changed. Implanted electrodes or microelectrode arrays, by contrast, cannot easily be moved after implantation without risk of significant brain injury. Furthermore, the set of targets stimulated can be chosen in a three-dimensional manner that would be difficult or impossible to achieve using any existing depth electrodes or microelectrode array. In some embodiments, feedback control based on sensed electrical activity within the sensory pathways, including neuronal activity within the sensory thalamus, may be used to modulate motor coordination.
The conformal electrode array in the present disclosure can be used in stimulation of the sensory thalamus for neurosensory prostheses. Most of the surface of the thalamus is accessible from the ventricular system. Most of the major sensory pathways of the nervous system ascend through the brainstem and relay within the thalamus before ascending to the cortex. In some embodiments, the aggregate electric field and current density function of the implanted array is configured to stimulate a set of targets within the sensory thalamus, for use in the context of a sensory neuroprosthetic device, delivering sensory stimulation to the brain (from modalities such as touch, pain, temperature, hearing, and vision) in a programmable manner, possibly based on data acquired by external sensors.
In some embodiments, the aggregate electric field and current density function of the implanted array is configured to stimulate a set of targets within the visual pathways of the brain, including targets within the optic tracts, lateral geniculate bodies, and optic radiations. In each of these targets, a topological representation of images projected on the retina is preserved in the organization of neuronal cell layers and corresponding axons, facilitating rational stimulation patterns intended to generate perception of meaningful images.
In these embodiments as well, the conformal array can be configured to simulate the fields and current densities generated by multiple arrays of electrodes implanted at many sites within the optic pathways, without damaging or displacing brain tissue in those pathways, and the configuration can be changed based on individual patient experience over time. Implanted electrodes or microelectrode arrays, by contrast, cannot easily be moved after implantation without risk of significant brain injury, and implantation would damage the optic pathways. Furthermore, the set of targets stimulated can be chosen in a three-dimensional manner that would be difficult or impossible to achieve using any existing depth electrodes or microelectrode array, and difficult-to-access parts of the visual pathways can be targeted noninvasively.
In such visual prosthetic applications, stimulation could be delivered in a programmed manner, based on data acquired by external sensors such as video cameras.
While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the disclosure, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
This application is a continuation of U.S. application Ser. No. 15/585,917 filed on May 3, 2017, which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/395,672 filed on Sep. 16, 2016 and U.S. Provisional Patent Application No. 62/406,623 filed on Oct. 11, 2016, all of the above are incorporated by reference in their entirety. This application is related to U.S. patent application Ser. No. 15/585,746 filed on May 3, 2017, entitled “A Visual Prosthesis Employing Virtual Neural Electrode Arrays”.
| Number | Date | Country | |
|---|---|---|---|
| 62395672 | Sep 2016 | US | |
| 62406623 | Oct 2016 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15585917 | May 2017 | US |
| Child | 15856677 | US |
