US20130066391A1 - Techniques for selecting signal delivery sites and other parameters for treating depression and other neurological disorders, and associated systems and methods - Google Patents

Abstract

The present disclosure is directed generally to techniques for selecting signal delivery sites and other signal delivery parameters for treating depression and other neurological disorders. A method in accordance with a particular embodiment includes obtaining first imaging information corresponding to a first region of a patient's brain, the first imaging information being based at least in part on functional characteristics of the first region. The method includes obtaining second imaging information corresponding to a second region of the patient's brain, the second region being a subset of the first region, the second imaging information being based at least in part on functional or structural characteristics of the second region. A target neural population is selected based in part on the second imaging information. The method still further includes applying an electromagnetic signal to the target neural population to improve a patient function.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. application Ser. No. 12/395,257, filed Feb. 27, 2009, now U.S. Pat. No. 8,262,714, which claims the benefit of U.S. Provisional Application No. 60/086,199, filed Aug. 5, 2008, the disclosures of which are fully incorporated herein by reference for all purposes.
TECHNICAL BACKGROUND
• Aspects of the present disclosure are directed generally toward techniques for selecting signal delivery sites and other signal delivery parameters for treating depression and other neurological disorders, and associated systems and methods.
BACKGROUND
• A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. For example, the neural functions in some areas of the brain (i.e., the sensory and motor cortices) are organized according to physical or cognitive functions. Several areas of the brain appear to have distinct functions in most individuals. In the majority of people, for example, the areas of the occipital lobes relate to vision, the regions of the left inferior frontal lobes relate to language, and particular regions of the cerebral cortex appear to be consistently involved with conscious awareness, memory, and intellect.
• Many problems or abnormalities can be caused by damage, disease and/or disorders in the brain. Disorders include neuropsychiatric and/or neuropsychological disorders, such as major depression. A person's neuropsychiatric responses may be controlled by a looped signal path between cortical structures, e.g., superficial structures at the prefrontal cortex of the brain, and deeper neural populations.
• Neurological problems or abnormalities are often related to electrical and/or chemical activity in the brain. Neural activity is governed by electrical impulses or “action potentials” generated in neurons and propagated along synaptically connected neurons. When a neuron is in a quiescent state, it is polarized negatively and exhibits a resting membrane potential typically between −70 and −60 mV. Through chemical connections known as synapses, any given neuron receives excitatory and inhibitory input signals or stimuli from other neurons. A neuron integrates the excitatory and inhibitory input signals it receives, and generates or fires an action potential when the integration exceeds a threshold potential. A neural firing threshold, for example, may be approximately −55 mV.
• When electrical activity levels at either the superficial cortical structure or the deep brain structure are irregular, action potentials may not be generated in the normal manner. For example, action potentials may be generated too frequently, or not frequently enough. Such irregularities can result in a neuropsychiatric disorder. It follows, then, that neural activity in the brain can be influenced by electrical energy supplied from an external source, such as a waveform generator. Various neural functions can be promoted or disrupted by applying an electrical current to the cortex or other region of the brain. As a result, researchers have attempted to treat physical damage, disease and disorders in the brain using electrical or magnetic stimulation signals to control or affect brain functions.
• Transcranial electrical stimulation (TES) is one such approach that involves placing an electrode on the exterior of the scalp and delivering an electrical current to the brain through the scalp and skull. Another treatment approach, transcranial magnetic stimulation (TMS), involves producing a magnetic field adjacent to the exterior of the scalp over an area of the cortex. Yet another treatment approach involves direct electrical stimulation of neural tissue using implanted deep brain stimulation electrodes (DBS). However, the foregoing techniques may not consistently produce the desired effect with the desired low impact on the patient. For example, TES may require high currents to be effective, which may cause unwanted patient sensations and/or pain. TMS may not be precise enough to target only specific areas of the brain. Deep brain stimulation is a relatively invasive procedure, and it can be relatively difficult to implant DBS electrodes in tissue located well below the cortex. Accordingly, there exists a need for providing more effective, less invasive treatments for neuropsychiatric and neuropsychological disorders.
BRIEF SUMMARY
• FIG. 1 is a flow diagram illustrating a method for treating a patient in accordance with a particular embodiment of the disclosure.
• FIG. 2 is a schematic illustration of cortical and sub-cortical brain structures, along with regions selected in accordance with embodiments of the disclosure.
• FIG. 3 is a flow diagram illustrating a method for treating a patient's depression in accordance with an embodiment of the disclosure.
• FIG. 4 is a partially schematic illustration of brain and peripheral structures that may be associated with the method shown inFIG. 3.
• FIG. 5 illustrates an electrode device operatively coupled to an external controller in accordance with an embodiment of the disclosure.
• FIG. 6 is a schematic illustration of a pulse system configured in accordance with several embodiments of the disclosure.
• FIG. 7 is an isometric illustration of an electrode device that carries multiple electrodes in accordance with an embodiment of the disclosure.
• FIGS. 8A-8C are partially schematic illustrations of electrode devices implanted at locations selected in accordance with embodiments of the disclosure.
DETAILED DESCRIPTIONIntroduction
• The present disclosure is directed to methods for treating neurologic dysfunction, which may include neuropsychiatric, neuropsychological, neurodevelopmental and/or other disorders, and associated systems for carrying out such methods. As used herein, the phrase “neurologic dysfunction” is used to encompass a variety of conditions or disorders, including neuropsychiatric disorders and neuropsychological disorders. As a further shorthand, the term “neuropsychiatric disorders” is used to include both neuropsychiatric disorders and neuropsychological disorders. Representative types of disorders falling within this definition include major depression, mania and other mood disorders, bipolar disorder, obsessive-compulsive disorder (OCD), Tourette's syndrome, schizophrenia, dissociative disorders, anxiety disorders, phobic disorders, post-traumatic stress disorder (PTSD), borderline personality disorder, as well as others such as Attention Deficit/Hyperactivity Disorder (ADHD) and/or craving or reward driven behaviors (e.g., associated with an addiction to legal or illegal drugs, gambling, sex, or another condition such as obesity).
• In general, various aspects of the methods and systems disclosed herein are directed to treating neurological conditions or states with electromagnetic stimulation, typically electrical stimulation applied to particular cortical structures of the patient's brain, e.g., from an epidural or subdural location. As used herein, “stimulation” refers generally to extrinsic signals directed to the patient to achieve a beneficial result. The signals may have an inhibitory or excitatory effect on particular neural populations. One representative technique includes using at least two sets of imaging information to more particularly identify the neural population to which therapeutic electromagnetic signals are delivered. Another particular method, directed to depressed patients, can include applying electromagnetic signals to one or more patient brain regions expected to correspond to the dorsolateral prefrontal cortex (DLPFC) and identifying a change in a region of the brain other than the DLPFC. Based at least in part upon this information, a practitioner can determine whether or not the patient is a candidate for cortical signal delivery to address depression, and/or the practitioner can select a target neural population to receive cortical signals, and/or the practitioner can update cortical signal delivery parameters. Further particular embodiments are described in greater detail below with reference toFIGS. 1-8C.
Systems and Methods for Patient Selection, Target Neural Population Selection, and Signal Delivery Selection
• FIG. 1 is a flow diagram illustrating aprocess100 for treating a patient in accordance with a particular embodiment of the disclosure. Theprocess100 includes obtaining first imaging information corresponding to a first region of a patient's brain, with the first imaging information being based at least in part on functional characteristics of the first region (process portion101). For example, the first imaging information can be obtained using functional magnetic resonance imaging (fMRI) techniques.Process portion102 can include obtaining second imaging information corresponding to a second region of the patient's brain, with the second region being a subset of the first region. The second imaging information can be based at least in part on functional or structural characteristics of the second region, and can have a resolution greater than that of the first imaging information. Accordingly, the second information can be used to more precisely identify a target neural population that will receive therapeutic electromagnetic signals. For example, a typical fMRI-based process for locating a target neural population has a resolution of about 1-3 centimeters. By adding the second information, (e.g., using diffusion tensor imaging processes described later) the practitioner can achieve a resolution of 3 millimeters or less. In addition to increased resolution, the foregoing technique can be conducted without a surgical procedure and is therefore less invasive than other techniques. Still further, this technique can be readily used to identify target neural populations of “silent” neurons, e.g., cognitive, emotive and/or other neurons that typically do not produce an immediate motor or sensory response.
• The practitioner can use the first and/or second information to identify particular areas of interest, and/or to eliminate from further consideration areas that are not of interest. In any of these cases,process portion103 includes selecting a target neural population based at least in part on the second imaging information, andprocess portion104 includes applying an electromagnetic signal to the target neural population to improve a patient function. For example, this technique can be used to improve the functioning of a patient suffering from depression. A representative example is described in further detail below with reference toFIG. 2.
• FIG. 2 is a schematic illustration of a patient'sbrain220 illustrating cortical structures221 (e.g., superficial or outer structures) located at thecortex223, and sub-cortical structures222 (e.g., deeper, non-superficial structures) located below or within thecortex223. Thecortical structures221 can include the dorsolateral prefrontal cortex (DLPFC)224 which has neuronal tracts (illustrated schematically by doubled-headed arrows inFIG. 2) extending to thesub-cortical structures222. The DLPFC has connections with manysub-cortical structures222 but for purposes of illustration, Brodmann area 10 and Brodmann area 25 are specifically shown inFIG. 2. In a particular embodiment, the practitioner can preferentially focus imaging tasks on one or brain locations expected to form a portion of or correspond to the DLPFC and then preferentially direct electromagnetic signals to portions of the DLPFC. In other embodiments, the practitioner can focus imaging tasks (and electromagnetic signals) on particular neuroanatomical structures, portions of which may be included in the DLPFC, e.g., portions of the patient's middle frontal gyrus, and/or superior frontal gyrus. In still further embodiments, the practitioner can focus imaging tasks (and/or electromagnetic signals) on still other structures, e.g., the patient's inferior frontal gyrus, orbitofrontal cortex, and/or ventrolateral prefrontal cortex. Additional details of techniques for targeting and applying therapy to these structures are included in pending U.S. application Ser. No. 12/330,437, filed Dec. 8, 2008 and incorporated herein by reference.
• TheDLPFC224 can include subareas, for example, acognitive area225 associated with the patient's cognitive functioning, and anemotive area226 associated with the patient's emotional functioning, both shown schematically inFIG. 2. The locations of these areas may in at least some cases vary from patient to patient. In addition, individual patients may have a depression condition that results from dysfunctions in thecognitive area225 or theemotive area226 or both thecognitive area225 and theemotive area226. Using functional imaging techniques (e.g., fMRI), a practitioner can identify which of the two areas is a likely candidate for cortical stimulation. For example, the patient can be exposed to a stimulus (described in further detail later) that triggers an acute depression response, while the patient's brain is imaged. In some cases, only one of theareas225,226 may be a suitable candidate, and in other embodiments, both areas may be suitable candidates. In any of these cases, thecognitive area225 and/or theemotive area226 can correspond to the first region of the patient's brain described above with reference toFIG. 1. In still another embodiment, neither thecognitive area225 nor theemotive area226 may particularly stand out when the first imaging information is obtained, and accordingly, theentire DLPFC224 or some other region of the DLPFC may correspond to the first region described above with reference toFIG. 1.
• As shown inFIG. 2, thecognitive area225 and theemotive area226 may each have many tracts that descend to a variety ofsub-cortical structures222. In certain embodiments, the practitioner may be particularly interested in applying electrical signals to those areas of theDLPFC224 that have a significant number of neuronal fibers or tracts that descend to Brodmann area 10 and/or Brodmann area 25. Accordingly, the practitioner can obtain the second imaging information described above with reference toFIG. 1 to identify a second, more precisely defined region of the patient's brain suitable for receiving cortical stimulation. For example, if thecognitive area225 is of particular interest, the second imaging information can be used to identify asecond region227athat includes tracts (or a greater number of tracts or density of tracts) extending to Brodmann area 25 and/or Brodmann area 10. If theemotive area226 is of particular interest, the practitioner can identify asecond region227bthat has tracts (or a greater number of tracts or density of tracts) descending to Brodmann area 25 and/or Brodmann area 10. Accordingly, the first imaging information described above with reference toFIG. 1 can identify a general region for cortical stimulation with a first level of resolution, and the second imaging information can identify one or more second regions with a higher level of resolution to more precisely identify one or more target neural populations. Further details of suitable techniques for obtaining the first imaging information and the second imaging information are described below.
• In at least some embodiments, the first imaging information is based at least in part on functional characteristics of the first region. For example, the first information can be obtained using correlates that are associated with or indicative of neural functioning levels. Such correlates include blood flow, metabolism, perfusion, glucose levels, water levels, magnetic characteristics, and/or electrical characteristics. Suitable techniques for identifying and/or measuring such correlates can include fMRI, spectroscopy based on MRI, positron emission tomography (PET), single photon emission computed tomography (SPECT), and/or computed tomography (CT). In any of these embodiments, the image or information used to produce the image is correlated with a particular activity related to the patient's depression. For example, in some cases, the patient's working memory is affected by depression and accordingly, the patient can undertake working memory tasks while the first imaging information is collected. In other embodiments, the patient can be exposed to emotion-triggering stimuli (e.g., visual, auditory, tactile and/or olfactory stimuli) so as to identify regions of the brain that are active in response to such stimuli and are correlated with the patient's depression. Further details associated with assessing patient functioning are included in co-pending U.S. Patent Publication No. US 2008/0103548, incorporated herein by reference.
• The second imaging information can be structural or functional in nature and is generally obtained for a smaller region of the brain (e.g., a subset of the first region) than is the first imaging information. In a particular embodiment, diffusion tensor imaging (DTI) techniques are used to identify neuronal tracts or fibers descending to sub-cortical areas that are known or expected to play a role in the patient's depression. More specifically, the practitioner can identify a “seed point” at the DLPFC using the first information. On the basis of the seed point, the practitioner can perform a fiber tracking analysis to identify fibers that connect the DLPFC to specific sub-cortical structures. This technique can be performed for multiple seed points at the DLPFC, and one or more target neural populations can be selected to include the areas of the DLPFC having the highest density of (intact) fiber tracts that descend to the specific sub-cortical area(s) of interest. Accordingly, the foregoing tractography analysis can apply to white matter in the brain, in contrast to techniques that may apply only to gray matter.
• The foregoing approach is expected to produce better (e.g., more efficacious) results than identifying and stimulating a deep brain structure because many deep brain structures have a high density of tracts that extend to many different superficial locations, some of which may be associated with the patient's depression, and many of which are not. As a result, methods that focus on stimulating deep brain areas may be inefficient and/or may create unintended cortical effects because it may be difficult to accurately target the deep brain area(s) of particular interest. Accordingly, in particular embodiments of the present techniques, no deep brain stimulation is applied. In a further particular aspect of this embodiment, simulation is applied only to areas identified based on the second imaging information. Further information relating to the use of DTI for site identification is included in U.S. Patent Publication No. US 2008/0039895, incorporated herein by reference.
• In general terms, DTI techniques identify neuronal tracts by identifying adjacent tissue volumes (voxels) having diffusion tensors aligned in the same direction. In addition to or in lieu of using diffusion characteristics to identify tracts, the practitioner can use diffusion information to identify the level of anisotropy of the brain tissue, typically referred to as fractional anisotropy (FA). In general terms, FA refers to the magnitude of the diffusion tensor, as opposed to its direction. It is expected that in at least some embodiments, the level of anisotropy can be indicative of regions affected by depression. For example, if the FA level for a particular region of the DLPFC is relatively low (e.g., lower than a standard or average value across a general patient population), this can indicate an area associated with the patient's depression. If the FA level is low, yet still above a threshold value, this may indicate an area suitable for cortical stimulation. Accordingly, the FA level can be used to identify patients who are suitable candidates for cortical stimulation therapy, and/or target neural populations in patients who are suitable candidates. Suitable threshold FA values are expected to be different for different brain areas and/or different neuropsychiatric/neuropsychological conditions. FA values may also be used to identify changes (e.g., improvements) in patient condition over time, as a result of the therapeutic treatments described herein. For example, it is expected that the patient's FA values may increase as a result of structural changes, including but not limited to dendritic sprouting and/or the formation of new axons.
• In other embodiments, functional characteristics of the brain may be used to identify the second region described above with reference toFIG. 1. For example, spectroscopy may be used. In a particular aspect of this embodiment, the practitioner can analyze fMRI results on a real-time or nearly real-time basis, and conduct a magnetic resonance spectroscopy (MRS) diagnosis on a subset region of the brain in a single patient visit. When the practitioner uses spectroscopy to obtain the second information, the practitioner can focus the analysis on a smaller area than may be used to obtain the first information, resulting in a higher sensitivity analysis and an expected increase in the precision of the results.
• Techniques other than spectroscopy may also be used to identify the second brain region, based on structural characteristics of the brain. For example, the thickness of the gray matter within the first region can be used to identify the second region. In a particular embodiment, the gray matter thickness is assessed using MRI techniques. In general, the greater the gray matter thickness, the greater the functionality of the tissue. The practitioner can select highly functional tissue as the target neural population in cases for which it is expected that this will be beneficial, e.g., when it is expected that stimulation will encourage the functional tissue to take on additional functionality. The practitioner can select less functional tissue in cases for which it is expected that stimulation can raise the functionality to normal or approximately normal levels. These techniques can be used separately or in combination.
• As described above with reference toFIG. 1, once a suitable second region has been selected, the practitioner can apply an electromagnetic signal to the target neural population to improve a patient function. In a particular embodiment, the practitioner uses a cortical electrode (e.g., an electrode positioned epidurally or subdurally within the cranial cavity of the patient's skull, proximate to the target neural population, and outside a cortical surface of the patient's brain) to apply electrical signals to the target neural population. Depending upon the patient's condition, the electromagnetic signals may be applied in a manner that inhibits the target neural population, or excites or facilitates the target neural population. The frequency and/or polarity (anodal or cathodal) of the signal may be selected to achieve the desired result. The stimulation may be delivered so as to have a direct effect on the target neural population, for example, an effect that lasts as long as or slightly longer than the stimulation itself. In other embodiments, the stimulation may be applied to neural populations that are expected to retain long-lasting changes (e.g., neuroplastic changes) that can last for days, weeks, months or years after the stimulation has ceased. In such cases, the treatment regimen can include an adjunctive therapy in combination with the electrical stimulation. Representative adjunctive therapies include working memory tasks, exposure to emotional triggers, psychological counseling and others.
• In other embodiments, techniques generally similar to the foregoing techniques can be used to perform functions other than identifying suitable target neural populations. For example, such techniques can be used to screen treatment candidates. In a particular embodiment, if the patient's FA level is low, the patient may be a suitable candidate for cortical stimulation treatment. However, if the FA level is too low, the patient may not respond adequately to cortical stimulation and may accordingly be screened out or selected for an alternative treatment.
• In another embodiment, one or more of the foregoing techniques can be used to select a particular treatment modality. For example, if the patient's FA value is within a particular range, the patient may be selected to undergo cortical stimulation. If the FA value is within a different range, the patient may be expected to respond better to transcranial magnetic stimulation (TMS) techniques, or deep brain stimulation (DBS) techniques. Accordingly, the particular technique or modality used to treat the patient can depend upon the patient's FA value.
• In still further embodiments, the FA value may change over the course of time and/or during the course of treatment. Accordingly, the foregoing techniques may be applied at additional points during the patient's treatment regimen to update the signal delivery location and/or the treatment modality used to affect neurons at the target location. Any of the foregoing techniques may also be used to select or update signal delivery parameters other than the target neural population. Such parameters can include the signal frequency, amplitude (voltage and/or current), polarity (anodal or cathodal) and/or delivery mode (e.g., unipolar or bipolar).
• Other techniques may be used in addition to the foregoing techniques to not only identify the target neural population, but identify one or more electrode locations that are expected to deliver signals to the target location in a particular (e.g., efficient) manner. For example, a practitioner can use numerical simulation techniques in combination with structural MRI data to estimate the conductivity of the region around the target neural population. Such techniques typically use the different electrical characteristics of different substances and structures in the brain (e.g., cerebral spinal fluid, neurons, connective tissue, vascular structures and others) to estimate the conductivity of different electrical paths. The practitioner can then select the position of a cortical electrode to be one that results in the shortest and/or lowest conductivity path to the target neural population. It is expected that such an arrangement can reduce the power required to deliver signals to the target neural population, and can accordingly provide stimulation for a greater period of time before it becomes necessary to replace or recharge the power supply that powers the electrodes. This approach can also reduce or eliminate the possibility of misdirected current creating unintended effects at populations other than the target neural population. Similar techniques may also be used to aid the practitioner in aligning the electric field lines generated by one or more electrodes with anatomical features. For example, these techniques can be used to align field lines with the axons of neurons at the target neural population.
• FIG. 3 is a flow diagram illustrating a process300 in accordance with another embodiment of the disclosure. The process300 can make use of naturally occurring connections between the patient's DLPFC and other areas of the patient's brain to provide information that is then used to screen the patient, identify a target neural population, and/or update signal delivery parameters. In a representative example, once a patient is identified as having depression or another neuropsychological/neuropsychiatric disorder (process portion301), the practitioner can identify a baseline level of excitability for a first area of the patient's brain that does not include the patient's DLPFC. For example, the first area of the patient's brain can include the patient's motor cortex or sensory cortex.Process portion303 includes performing several functions for at least one second area of the patient's brain, located at the patient's DLPFC. These functions can include applying stimulation to the patient's DLPFC (process portion305) and, after applying stimulation to the patient's DLPFC, identifying a change in the patient's excitability level at the first area of the brain (process portion306). Based at least in part on the identified change in the patient's excitability level at the first area,process portion307 can include performing any of the following functions: identifying the patient as a candidate for cortical signal delivery (process portion309), selecting a target neural population to receive cortical signals (process portion310), and/or updating cortical signal delivery parameters (process portion311). A representative example implementing an embodiment of the process300 shown inFIG. 3 is described below with reference toFIG. 4.
• FIG. 4 is a partially schematic illustration of a portion of the patient'sbrain220, identifying theDLPFC224 and cortical, non-DLPFC brain areas with which theDLPFC224 communicates. These areas can include themotor cortex230 and thesensory cortex231, among others. Themotor cortex230 communicates with one or more of the patient's muscles233 (e.g., at the patient's arm or hand) via thespinal cord232. Thesensory cortex231 communicates with one or more of the patient's sensory receptors234 (e.g., the patient's olfactory nerve). In some cases, e.g. for tactile sensory receptors at the patients trunk or extremities, this communication also occurs via thespinal cord232. In a representative procedure, the practitioner identifies a baseline level of excitability of the patient's motor cortex, for example, by assessing the patient's response to motor stimuli. The practitioner can then apply excitatory or inhibitory stimuli to theDLPFC224. For example, the practitioner can apply rTMS signals to the patient for a period of about 20 minutes. After stimulating theDLPFC224, the practitioner can again assess the patient's level of motor excitability, for example, by applying single-pulse and/or paired-pulse signals (e.g., TMS signals) to the patient's brain and assessing the response level. Single pulse TMS signals may be used to assess a direct effect of the DLPFC on the patient's level of motor excitability, and paired-pulse TMS signals may be used to isolate the effect of inhibitory and/or excitatory interneurons on the patient's level of motor excitability. In any of these embodiments, the foregoing procedure can be repeated for multiple sites at theDLPFC224, and one or more of these sites can be selected as a target neural population, based upon the effect that stimulation at the site has on the patient's level of motor excitability.
• In particular embodiments, it is expected that locations of theDLPFC224 that have a greater effect on motor excitability than others may be suitable candidates for cortical stimulation. Similar techniques can be used to optimize and/or update the signal delivery parameters used to provide therapy to the patient, after a cortical stimulation device has been implanted in the patient. For example, the effect of the stimulation on the patient's motor excitability at a variety of parameter settings (e.g., stimulation amplitude, polarity, and/or frequency) can be determined and, based upon this determination, particular parameters can be selected or eliminated. The same or a similar technique can be used during the course of the patient's therapy to update signal delivery parameters, for example, as the patient's body adapts to the applied therapy, and/or as the functional level of the target neural population changes as a result of therapy.
• Many aspects of the foregoing process can be automated in certain instances. For example, once the patient has received a cortical implant, the patient can also receive one or more implanted sensors located at the motor cortex or sensory cortex, or at the patient's spine (e.g., at a cervical location), or at a peripheral location (e.g., at the patient's muscle or sensory receptor). The sensor(s) can identify changes in the level of excitability at any of these locations and can be coupled to a controller which is in turn coupled to electrodes implanted at the DLPFC. Accordingly, the controller can automatically adjust the signal delivery parameters applied to the electrodes at the DLPFC as the patient's responses to therapeutic signals (or test signals) provided by the electrodes change. This closed-loop arrangement can operate in a semi-automated or fully automated manner to reduce or eliminate the need for the patient or the practitioner to continuously monitor patient performance and/or response to the therapy.
• In many instances, it is desirable to compare the state of a patient when the patient is acutely depressed, to a baseline state of the patient. This technique can be used to identify areas of the brain that are active or inactive when a patient is depressed. For example, the practitioner can obtain an image of the patient's brain when the patient is acutely depressed, and compare that image with one obtained when the patient is in a stable or baseline condition. This technique can be used to identify the first region of the brain described above with reference toFIG. 1, or, in particular embodiments (assuming a high degree of resolution), this technique can be used to identify the second region. In any of these cases, the practitioner will obtain an image of the patient's brain or the relevant portion of the patient's brain when the patient is in the baseline or first state, then acutely affect the patient's emotional or cognitive functioning, obtain a second image while the patient is in the second state, and compare the images.
• A variety of techniques are expected to be suitable for creating such an effect. For example, rapid tryptophan depletion, which is presently used to identify depression patients suitable for SSRI treatments, can be used to trigger an acute depression condition. Sleep deprivation is another technique that can acutely modulate depression (e.g., it can cause acute remission of depression symptoms), as is hypnosis. In other cases, a patient can be shown sad pictures to induce sadness, depression, or another emotion. In still further cases, multiple sessions of rTMS can acutely modulate the patient's depression response. For example, rTMS can cause a reduction in depression symptoms, or a remission of depression. A variety of imaging/visualization techniques can be used to identify brain areas associated with the acute response. These areas may be hypoactive or hyperactive. Such techniques can include PET scans based on FDG or water analysis, perfusion MRI, connectivity fMRI, and/or task-related fMRI (e.g., in which a patient performs a cognitive or memory task).
• In particular cases, the DLPFC or portions of the DLPFC are expected to be hypoperfused and/or hypometabolic when the patient is depressed, and thus a suitable target neural population can be identified using measures of perfusion/blood flow and/or glucose consumption. In other cases, patients with depression or major depressive disorder (MDD) may have reduced glutamate, and/or reduced glutamate/glutamine peaks, and/or reduced choline levels at the frontal cortex, the DLPFC, and/or other cortical regions or subregions. Magnetic resonance spectroscopy (MRS) is expected to be suitable for identifying such areas as target neural populations and/or identifying indications of recovery after therapeutic treatments in accordance with the present disclosure.
• In still another embodiment, EEG measurements may be used to identify areas with increased and/or otherwise perturbed activity. For example, EEG measurements may be used to detect increased gamma and/or theta wave activity, which is expected to correlate with depression. In particular cases, EEG measurements can detect changes in brain activity induced by rTMS stimulation.
Representative Stimulation System Embodiments
• Many aspects of various techniques or procedures described above can be performed by suitable systems configured to deliver cortical stimulation and, in certain cases, stimulation in accordance with other modalities.FIG. 5 schematically illustrates a representative corticalsignal delivery system250. Thesystem250 can include apulse system260 that is positioned external to the patient's skull. For example, as shown inFIG. 5, thepulse system260 can be placed on the external surface of the patient'sskull235, beneath the scalp. In another arrangement, thepulse system260 can be implanted at a subclavicular location. Thepulse system260 can be controlled internally via pre-programmed instructions that allow thepulse system260 to operate autonomously after implantation. In other embodiments, thepulse system260 can be implanted at other locations, and at least some features of thepulse system260 can be controlled externally. For example,FIG. 5 illustrates anexternal controller265 that controls thepulse system260.
• FIG. 6 schematically illustrates details of an embodiment of thepulse system260 described above. Thepulse system260 generally includes ahousing261 carrying apower supply262, anintegrated controller263, apulse generator266, and apulse transmitter267. In certain embodiments, a portion of thehousing261 may include a signal return electrode. Thepower supply262 can include a primary battery, such as a rechargeable battery, or other suitable device for storing electrical energy (e.g., a capacitor or supercapacitor). In other embodiments, thepower supply262 can include an RF transducer or a magnetic transducer that receives broadcast energy emitted from an external power source and that converts the broadcast energy into power for the electrical components of thepulse system260.
• In one embodiment, theintegrated controller263 can include a processor, a memory, and/or a programmable computer medium. Theintegrated controller263, for example, can be a microcomputer, and the programmable computer medium can include software loaded into the memory of the computer, and/or hardware that performs the requisite control functions. In another embodiment identified by dashed lines inFIG. 6, theintegrated controller263 can include an integrated RF ormagnetic controller264 that communicates with theexternal controller265 via an RF or magnetic link. In such an embodiment, many of the functions performed by theintegrated controller263 may be resident on theexternal controller265 and theintegrated portion264 of theintegrated controller263 may include a wireless communication system.
• Theintegrated controller263 is operatively coupled to, and provides control signals to, thepulse generator266, which may include a plurality of channels that send appropriate electrical pulses to thepulse transmitter267. Thepulse transmitter267 is coupled to asignal delivery device240, e.g., anelectrode device241 that carrieselectrodes242. In one embodiment, each of theseelectrodes242 is configured to be physically connected to a separate lead, allowing eachelectrode242 to communicate with thepulse generator266 via a dedicated channel. Accordingly, thepulse generator266 may have multiple channels, with at least one channel associated with each of theelectrodes242 described above. Suitable components for thepower supply262, theintegrated controller263, theexternal controller265, thepulse generator266, and thepulse transmitter267 are known to persons skilled in the art of implantable medical devices.
• Thepulse system260 can be programmed and operated to adjust a wide variety of stimulation parameters, for example, whichelectrodes242 are active and inactive, whether electrical stimulation is provided in a unipolar or bipolar manner, signal polarity, and/or how stimulation signals are varied. In particular embodiments, thepulse system260 can be used to control the polarity, frequency, duty cycle, amplitude, and/or spatial and/or topographical qualities of the stimulation. Representative signal parameter ranges include a frequency range of from about 0.5 Hz to about 125 Hz, a current range of from about 0.5 mA to about 15 mA, a voltage range of from about 0.25 volts to about 20 volts (e.g., approximately 10 volts), and a first pulse width range of from about 10 psec to about 500 psec The stimulation can be varied to match, approximate, or simulate naturally occurring burst patterns (e.g., theta-burst and/or other types of burst stimulation), and/or the stimulation can be varied in a predetermined, pseudorandom, and/or other aperiodic manner at one or more times and/or locations.
• In particular embodiments, thepulse system260 can receive information from selected sources, with the information being provided to influence the time and/or manner by which the signal delivery parameters are varied. For example, thepulse system260 can communicate with adatabase270 that includes information corresponding to reference or target parameter values. Sensors can be coupled to the patient to provide measured or actual values corresponding to one or more parameters. The measured values of the parameter can be compared with the target value of the same parameter. Accordingly, this arrangement can be used in a closed-loop fashion to control when stimulation is provided and when stimulation may cease. In one embodiment, someelectrodes242 may deliver electromagnetic signals to the patient while others are used to sense the activity level of a neural population. In other embodiments, thesame electrodes242 can alternate between sensing activity levels and delivering electrical signals. In either embodiment, information received from thesignal delivery device240 can be used to determine the effectiveness of a given set of signal parameters and, based upon this information, can be used to update the signal delivery parameters and/or halt the delivery of the signals.
• In other embodiments, other techniques can be used to provide patient-specific feedback. For example, a detection system ordevice280 such as a magnetic resonance chamber can provide information corresponding to the locations at which a particular type of brain activity is occurring and/or the level of functioning at these locations, and can be used to identify additional locations and/or additional parameters in accordance with which electrical signals can be provided to the patient to further increase functionality. Accordingly, the system can include a direction component configured to direct a change in an electromagnetic signal applied to the patient's brain based at least in part on an indication received from one or more sources. These sources can include a detection component (e.g., the signal delivery device and/or the magnetic resonance chamber280).
• FIG. 7 is a top, partially hidden isometric view of an embodiment of asignal delivery device740, configured to carry multiplecortical electrodes742. Theelectrodes742 can be carried by aflexible support member744 to place eachelectrode742 in contact with a stimulation site of the patient when thesupport member744 is implanted. Electrical signals can be transmitted to theelectrodes742 via leads carried in acommunication link745. Thecommunication link745 can include acable746 that is connected to the pulse system260 (FIG. 6) via aconnector747, and is protected with aprotective sleeve748. Coupling apertures or holes749 can facilitate temporary attachment of thesignal delivery device740 to the dura mater at, or at least proximate to, a stimulation site. Theelectrodes742 can be biased cathodally and/or anodally. In an embodiment shown inFIG. 7, thesignal delivery device740 can include sixelectrodes742 arranged in a 2×3 electrode array (i.e., two rows of three electrodes each), and in other embodiments, thesignal delivery device740 can include more orfewer electrodes742 arranged in symmetrical or asymmetrical arrays. The particular arrangement of theelectrodes742 can be selected based on the region of the patient's brain that is to be stimulated, and/or the patient's condition.
• FIG. 8A is a schematic illustration of afirst electrode device841aimplanted above or upon a patient's middlefrontal gyrus236 in accordance with an embodiment of the disclosure. Thefirst electrode device841aincludes afirst electrode842aand asecond electrode842bthat are carried by a substrate orsupport member844. The first andsecond electrodes841a,841bare coupled to a pulse generator (not shown) in a manner understood by one of ordinary skill in the art. In this embodiment, eachelectrode842a,842bis generally circular. Depending upon embodiment details,such electrodes842a,842bcan be approximately 0.5-4.5 mm (e.g., 3.75 mm) in diameter, and can have a center-to-center spacing of approximately 10-40 mm (e.g., 15 mm, 18 mm, or another separation distance). The centers of thefirst electrode842aand thesecond electrode842bcan be positioned to approximately intersect or reside along or proximate to a line or anarc243athat generally bisects at least a portion of the middlefrontal gyrus236 into superior and inferior portions. The particular position alongline243acan be determined by any of the foregoing techniques directed to identifying target neural populations and associated stimulation sites (e.g., electrode placement sites). Such techniques can also be used to place the electrodes at other cortical locations, including, but not limited to, those described below with reference toFIGS. 8B-8C.
• FIG. 8B is a schematic illustration of asecond electrode device841bimplanted above or upon a patient's middlefrontal gyrus236 in accordance with another embodiment of the previously described surgical implantation protocol. Thesecond electrode device841bincludes asupport member844 that carries a first, a second, and athird electrode842a,842b,842cand possibly annth electrode842d,where n is greater than or equal to 4. In several embodiments, thesecond electrode device841bcan be positioned such that as many electrodes842a-842das possible reside above, along, or proximate to a line or anarc243bthat generally bisects at least a portion of the middlefrontal gyrus236 as the line orarc243bextends between the middlefrontal gyrus236 and thecentral sulcus237 in an anterior-posterior direction.
• FIG. 8C is a schematic illustration of athird electrode device841cimplanted above or upon a patient's middlefrontal gyrus236 in accordance with yet another embodiment of the aforementioned surgical implantation protocol. Thethird electrode assembly841cincludes asupport member844 that carries a first and a second row ofelectrodes851,852, where eachelectrode row851,852 includes at least afirst electrode842aand possibly up to an n^thelectrode842d.Thethird electrode device841ccan be positioned such that eachelectrode row851,852 is approximately equidistant from a line orarc243cthat extends anteriorly from thecentral sulcus237 and which approximately bisects a portion of the middlefrontal gyrus236; or such that a superior and aninferior electrode row851,852 are approximately equidistant from the superior frontal sulcus238 and the inferiorfrontal sulcus239, respectively.
• In some embodiments, theelectrode device841ccan include electrodes842a-842dthat are arranged, organized, or positioned in a curvilinear or arcuate manner rather than in a linear manner. An arc along which electrodes842a-842dare positioned can be predefined such that the electrodes carried by an as-manufactured electrode device will conform or approximate conform to the curvature of a particular portion or section of a neuroanatomical structure, such as the crown of the middle frontal gyrus spanning Brodmann areas 9, 46, and/or 9/46.
• A stimulation procedure directed toward the application of extrinsic stimulation signals to treat neuropsychiatric dysfunction can include one or more time periods in which each electrode of a given electrode assembly is electrically active. Additionally or alternatively, a stimulation procedure can include one or more time periods in which particular electrode subsets carried by a given electrode assembly are electrically active. The activation of each electrode and/or one or more electrode subsets can depend upon the type of neurologic dysfunction under consideration and/or the patient's clinical response, imaging response, and/or electrophysiologically measured (e.g., ECoG) response to the applied stimulation signals.
• In a representative example, theelectrode device841bshown inFIG. 8B can have an initially active electrode subset that includes the first, second, and third electrodes841a-841c.Depending upon the nature and/or extent of a patient's response to the extrinsic stimulation signals (for instance, the presence or absence of a noticeable or favorable acute response, and/or the presence or absence of a beneficial or adverse response that arises over the course of a number of weeks (e.g., 2-12 weeks)), additional, one or more anterior electrodes841dcan be activated at one or more times. Moreover, one or more most-posterior electrodes841a,841bcan be deactivated at one or more times, and/or stimulation signals applied to such more-posterior electrodes841a,841bat a reduced intensity or level in the event that clinical, imaging, and/or electrophysiologic data indicates thatsuch electrodes841a,841bprovide relatively less or little contribution to therapeutic efficacy.
• In a representative embodiment, thethird electrode device841cshown inFIG. 8C can include any given electrode subset that is active at one or more times, with active electrodes located in one or bothelectrode rows851,852. In certain situations, an initial set or subset of electrodes carried by an electrode device can be used to initially apply stimulation signals. Depending upon embodiment details, the initial set of electrodes can include some or all of the electrodes carried by the electrode device. After a first time period during which the patient experiences a favorable therapeutic response, particular electrodes (e.g., one or more most-posterior electrodes) within the initial set of electrodes can be activated at a reduced signal intensity, level, or duration, or deactivated during a second time period, and the patient monitored to determine whether a sufficiently high or adequate level of therapeutic benefit is present. Such a stimulation procedure can successively, over time, determine a minimum number of active electrodes that are useful for achieving or maintaining therapeutic efficacy. In the event that therapeutic efficacy changes or degrades over time following a generally stable period of therapeutic benefit, the foregoing stimulation procedure can be repeated, or additional electrodes can be successively (re)activated, until a sufficient or desired level of therapeutic benefit occurs. For example, the patient's neuropsychological stability may be adversely affected after several months, such as 6 or 12 months, possibly due to an event in the patient's life.
• In several embodiments, a threshold signal intensity or level corresponding to a given electrode subset can be determined by applying stimulation signals to this electrode subset, and measuring or estimating a minimum or near-minimum stimulation signal level that gives rise to a predetermined or minimum degree of change in neurocognitive task performance. A treatment signal intensity or level that is applied to the patient during a therapy period can be based upon a threshold signal level corresponding to one or more electrode subsets. For instance, a treatment signal level can be a given percentage of (e.g., approximately 20-95%, or approximately 50%, 80%, or 90% of) the activation threshold signal level corresponding to the particular electrode subset that gave rise to the lowest threshold signal level relative to each electrode subset considered. The threshold level can correspond to a level (e.g., current level or voltage level) that causes action potentials in a large enough portion of the target neural population to produce the patient function associated with the target neural population. During a therapy period, a treatment signal can be applied to the particular electrode subset that gave rise to this lowest threshold level, and/or one or more other electrode subsets. In addition or as an alternative to the foregoing, a treatment signal intensity can be a mathematical function such as an average or a weighted average of a plurality of threshold signal intensities, where in some embodiments a weighting function can prioritize a threshold signal intensity associated with neurons in particular neural locations (e.g., more anterior neurons) more heavily than a threshold signal intensity associated with neurons within other (e.g., more posterior) neural locations. In yet other embodiments, a treatment signal can be or include a set of pulses that are delivered approximately at or even slightly above a threshold or expected threshold level.
• Many of the foregoing embodiments include techniques for identifying a target neural population, a target stimulation site, stimulation parameters, stimulation modalities, and/or suitable patients using functional techniques, alone or in combination with techniques based on the structure of the patient's brain. An expected advantage of these techniques is that they can more accurately identify characteristics associated with a stimulation therapy than can techniques that rely on brain structure alone. In some cases, these techniques can eventually be correlated with brain structures that are common from one patient to the next and, in such cases, a practitioner can revert back to site identification and/or other parameter selection on the basis of one or more structures that are defined with a new level of precision. In other cases, the foregoing techniques can continue to be used on a patient-by-patient basis to more accurately identify the stimulation characteristics.
• From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made in other embodiments. For example, the practitioner may use structurally based and/or functionally based techniques that differ from those specifically described above. The practitioner may use more than two levels of information to identify target neural populations in at least some cases. In some cases, the practitioner may produce an actual image upon which to base a parameter selection, and in other cases, at least some aspects of the parameter selection may be automated and/or may rely on the underlying data used to produce the image without actually producing the image itself. For example, fractional anisotropy levels may be determined without the need for an actual image, and regions of high tract density may be correlated with a location in space (referenced to a fiducial or anatomic feature) again, without the need for an actual image. The signals applied in any of the foregoing methods can have a direct effect on the target neural population that lasts for as long as the signal is active, or a long-term effect that can enhance, enable, augment and/or otherwise facilitate the patient's natural neuroplastic responses. Such long term effects can last for days, weeks, months or years after the stimulation has ceased.
• Several examples were described above in the context of depression, but the same or generally similar methodologies can be used to address other neuropsychiatric/neuropsychological conditions, including post-traumatic stress disorder (PTSD), eating disorders and others identified previously. In still further embodiments, the foregoing methods can be applied to patients without disorders, e.g. to improve the cognitive functioning of a normal or above-normal patient. Many of the foregoing techniques may be applied on a case-by-case basis that is specific to individual patients. However, as discussed above, after a sufficient database (e.g., group atlas) has been established as a result of collecting individual data, practitioners may in some cases be able to circumvent certain steps over the course of time. For example, practitioners may find that for certain conditions (e.g., certain types of depression), the same area of the DLPFC, (as identified by anatomical landmarks), is always or nearly always a suitable target neural population.
• Several examples were provided above with reference to specific brain areas (e.g., Brodmann areas 10 and 25) and/or specific loops (e.g., thalamocortical loops). In other embodiments, similar techniques can be applied to other areas. For example, when treating depression, the anterior cingulate cortex (ACC) may be identified as a non-superficial component of the thalamocortical loop that also includes the DLPFC. Accordingly, target cortical neural populations may be selected on the basis of tract density descending to the ACC.
• Certain aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, aspects of the technique described in the context ofFIG. 1 may be combined with aspects of the technique described inFIG. 3. Further, while advantages associated with certain embodiments have been described in the context of those embodiments, other embodiments may also exhibit such advantages and not all embodiments need necessarily exhibit such advantages to fall within the scope of the present disclosure.

Claims (5)

1-25. (canceled)

26. A method for treating a patient, comprising:

identifying a patient as having depression;

identifying a baseline level of the patient's motor cortex excitability;

for multiple areas of the patient's DLPFC:

applying stimulation to the patient's DLPFC using rTMS techniques;

after applying stimulation to the patient's DLPFC, identifying a change in the patient's motor cortex excitability using paired-pulse TMS stimulation;

based at least in part on identified changes in the patient's motor cortex excitability for the multiple areas of the patient's DLPFC, selecting a signal delivery site;

implanting at least one electrode proximate to the signal delivery site, within a cranial cavity of the patient's skull and outside a cortical surface of the patient's brain; and

reducing or eliminating patient depression by preferentially directing electrical signals from the at least one electrode to the signal delivery site.

27. The method ofclaim 26 wherein selecting a signal delivery site includes selecting the signal delivery site to be at an area of the DLPFC that has a greater effect on motor cortex excitability than other areas of the DLPFC.

28. The method ofclaim 26, wherein applying stimulation to the patient's DLPFC includes applying stimulation for a period of about 20 minutes.

29. The method ofclaim 26, further comprising repeating the process of identifying a change in the patient's motor cortex excitability and the process of selecting a signal delivery site during the course of the patient's therapy to account for patient adaptation to the electrical signals.

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