The present invention in directed generally toward methods and systems for establishing parameters for neural stimulation, including techniques for applying neural stimulation parameters from a first neural population having a first neural function to a second neural population having a second neural function different than the first.
A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. In some areas of the brain, such as in the sensory or motor cortices, the organization of the brain resembles a map of the human body; this is referred to as the “somatotopic organization of the brain.” There are several other areas of the brain that appear to have distinct functions that are located in specific regions of the brain in most individuals. For example, areas of the occipital lobes relate to vision, regions of the left inferior frontal lobes relate to language in the majority of people, and regions of the cerebral cortex appear to be consistently involved with conscious awareness, memory, and intellect. This type of location-specific functional organization of the brain, in which discrete locations of the brain are statistically likely to control particular mental or physical functions in normal individuals, is herein referred to as the “functional organization of the brain.”
Many problems or abnormalities with body functions can be caused by damage, disease and/or disorders of the brain. A stroke, for example, is one very common condition that damages the brain. Strokes are generally caused by emboli (e.g., obstruction of a vessel), hemorrhages (e.g., rupture of a vessel), or thrombi (e.g., clotting) in the vascular system of a specific region of the cortex, which in turn generally causes a loss or impairment of a neural function (e.g., neural functions related to face muscles, limbs, speech, etc.). Stroke patients are typically treated using physical therapy to rehabilitate the loss of function of a limb or another affected body part. For most patients, little can be done to improve the function of the affected limb beyond the recovery that occurs naturally without intervention.
One existing physical therapy technique for treating stroke patients constrains or restrains the use of a working body part of the patient to force the patient to use the affected body part. For example, the loss of use of a limb is treated by restraining the other limb. Although this type of physical therapy has shown some experimental efficacy, it is expensive, time-consuming and little-used. Stroke patients can also be treated using physical therapy plus adjunctive therapies. For example, some types of drugs, including amphetamines, increase the activation of neurons in general. These drugs also appear to enhance neural networks. However, these drugs may have limited efficacy because mechanisms by which they operate are very non-selective and they cannot be delivered in high concentrations directly at the site where they are needed. Still another approach is to apply electrical stimulation to the brain to promote the recovery of functionality lost as a result of a stroke. While this approach has been generally effective, it has not adequately addressed all stroke symptoms.
In addition to the motor-related symptoms described above, stroke patients may also suffer from cognitive defects. For example, patients may suffer from neglect, a defect that causes patients to lose cognizance of portions of their surroundings and/or themselves. In other cases, patients may suffer from other cognitive defects, such as memory loss or loss of reasoning ability, in connection with a stroke or other event that causes neural damage. While electromagnetic stimulation has been proposed generally to address cognitive defects, the application of such techniques may in some cases be difficult because, unlike motor neurons which can immediately indicate activation by a corresponding muscle action, cognitive and other non-motor neurons typically do not provide such a readily discernable indication of activation. Accordingly, there is a need to improve the manner in which stimulation is applied to cognitive and other non-motor neurons.
A. Introduction
The present invention is directed generally toward methods and systems for establishing stimulation parameters for neural stimulation processes. In particular embodiments, the methods and systems are directed to establishing stimulation parameters for non-motor and/or non-sensory neurons. In still further embodiments, the stimulation parameters selected for non-motor and/or non-sensory neurons can be based at least in part on stimulation parameters established for motor and/or sensory neurons.
In many instances, it may be desirable to electrically stimulate neurons at subthreshold levels. For example, it may be desirable to provide stimulation to motor neurons at subthreshold levels, and then rely on the (perhaps limited) ability of the neuron to supplement the stimulation signal. The combination of the external electrical stimulation and the neuron's internal or intrinsic ability to generate at least some increase in potential can be enough to exceed the threshold level and generate an action potential. In such instances, it can be important to determine, approximately determine, or estimate what the threshold potential for a given neural population is. Otherwise, the target neurons may be overstimulated, or the neurons may not receive a therapeutically useful dose of stimulation (e.g., if the stimulation is provided outside of a particular stimulation parameter range). In particular instances, however, it may be desirable to briefly stimulate neurons with near threshold, threshold, and/or suprathreshold pulses or bursts, possibly in association with subthreshold stimulation.
In the case of motor neurons, a threshold level can generally be readily determined by varying a stimulation parameter (e.g., increasing a voltage, current, and/or frequency of the stimulation signal) until a motor response is detected. The motor response can often be detected by simply observing or measuring (e.g., using electromyography (EMG)) a muscle action exhibited by the patient. In a generally similar manner, particular sensory neurons can be stimulated and a threshold for such neurons can be detected when the patient receives, reports, or becomes aware of a corresponding sensation. However, for at least some neurons, it may be difficult to detect when the threshold level is exceeded because the patient neither displays an outward action nor reports a sensation. This difficulty can arise, for example, when stimulating neurons associated with cognitive function; or more generally, when stimulating neurons that may be associated with patient functions or responses that are difficult and/or time consuming to readily observe or measure. Such neurons are referred to herein as “silent” neurons.
A method in accordance with one aspect of the invention includes applying a first stimulus to a first neural population associated with a first neural function (e.g., a motor function), using a first set of stimulation parameters. The method can further include detecting a response to the first stimulus at least proximate to the patient's central nervous system. The method can still further include applying a second stimulus to a second neural population associated with a second neural function (e.g., a cognitive function) different than the first neural function using a second set of stimulation parameters, based at least in part on the response to the first stimulus and on the first set of stimulation parameters. In a particular instance, detecting a response to the first stimulus can include detecting a response that is also exhibited by the second neural population. The response can be detected by detecting electrical signals transmitted by the central nervous system, by detecting a change in cerebral blood flow, and/or by detecting a change in a quantity that depends upon cerebral blood flow or upon cerebral blood oxygen levels.
A method for treating a patient in accordance with another aspect of the invention can include directing an electrical signal having a first set of stimulation parameters to a target neural population via an electrode. The method can further include detecting a response to the electrical signal at least proximate to the patient's central nervous system, and changing a value of at least one stimulation parameter of the electrical signal, at least until the response reaches a preselected level. A second set of stimulation parameters can then be selected based at least in part on the value of the stimulation parameter associated with the preselected level. The method can further include directing additional electrical signals to the patient in accordance with the second set of stimulation parameters. Accordingly, the foregoing method need not include stimulation of two different types of neural populations, but can instead rely (at least in part) on responses detected at least proximate to the patient's central nervous system.
A method in accordance with still a further aspect of the invention can include detecting evidence of a neural activity (with the evidence being detected at least proximate to the patient's central nervous system), and then automatically triggering electromagnetic stimulation of a target neural population at the patient's central nervous system, based at least in part on the detected evidence. In particular embodiments, the method can include detecting evidence of a patient's attempt(s) to engage in a neural activity. Accordingly, the foregoing method (and systems that perform the method) can autonomously trigger electromagnetic stimulation at one or more times when the stimulation may be most therapeutic for and/or helpful to the patient carrying out a particular task (e.g., a motor task or cognitive task) that may facilitate the restoration and/or development of a neural function.
B. Methods for Establishing Stimulation Parameters. Including Stimulation Parameters for Diverse Neural Populations
Process portion 106 can include applying a second stimulus to a second neural population associated with a second neural function different than the first neural function. For example, process portion 106 can include applying a second stimulus to a cognitive, neuropsychological, neuropsychiatric, or other “silent” neuron. The second stimulus can be applied using a second set of stimulation parameters, the selection of which is based at least in part on the response to the first stimulus and on the first set of stimulation parameters. For example, if the first set of stimulation parameters have a desired relationship relative to the threshold level of the first neural population, then the second set of stimulation parameters can be selected based at least in part on the first stimulation parameters, so as to produce a similar (or calculatedly different) relationship relative to an expected threshold level for the second neural population. In a particular embodiment, a practitioner can determine one or more parameters corresponding to the threshold level of stimulation for a motor neuron, and can interpolate or extrapolate this data to provide a corresponding threshold or non-threshold level of stimulation for a non-motor neuron. In a further particular embodiment, the practitioner can select values for one or more parameters in a manner expected to provide stimulation at between 10% and 90% (e.g., between approximately 25% and 75%, or at approximately 50%) of the threshold value for the non-motor neuron, based on data obtained from stimulation of a motor neuron. If the threshold level is expected to change (e.g., drift) during the course of treatment, the practitioner can update the stimulation parameters accordingly. This function can also be performed automatically in some embodiments.
In another embodiment, if it is determined that stimulating the first neural population with the first set of stimulation parameters produces a desired or beneficial result, some or all aspects of the second set of stimulation parameters (applied to the second neural population) can be selected to be at least approximately identical to the first set of stimulation parameters. A beneficial result in the case of a motor neural population may be the patient's increased ability to perform a motor task. When the same or a similar stimulation parameter is used to stimulate a cognitive neural population, the beneficial result may be the patient's increased ability to perform a cognitive task.
In some instances, it may be desirable to stimulate the prefrontal cortex 129, for example, to provide a cognitive or neuropsychological, neuropsychiatric, and/or other benefit to the patient. However, as described above, it may not be immediately apparent what stimulation parameters should be used to produce the desired beneficial effect because (a) the patient may not exhibit a readily ascertainable external response indicating when the threshold level is closely approached, reached, or exceeded, and/or (b) it may require a significant period of time to determine whether the stimulation produces long-lasting cognitive benefits to the patient. Accordingly, a practitioner can first provide stimulation to a first neural population 130 located at the primary motor cortex 127 to identify stimulation parameters that can then be applied to a second neural population 131 located at the prefrontal cortex 129.
C. Applying Electrical Stimulation
The electrode device 301 can be coupled to a pulse system 310 with a communication link 303. The communication link 303 can include one or more leads, depending (for example) upon the number of electrodes 350 carried by the electrode device 301. The pulse system 310 can direct electrical signals to the electrode device 301 to stimulate target neural tissues.
The pulse system 310 can be implanted at a subclavicular location, as shown in
In one embodiment, the integrated controller 313 can include a processor, a memory, and a programmable computer medium. The integrated controller 313, 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 in
The integrated controller 313 is operatively coupled to, and provides control signals to, the pulse generator 316, which may include a plurality of channels that send appropriate electrical pulses to the pulse transmitter 317. The pulse generator 316 may have multiple channels, with at least one channel associated with a particular one of the electrodes 350 described above. The pulse generator 316 sends appropriate electrical pulses to the pulse transmitter 317, which is coupled to the electrodes 350 (
The pulse system 310 can be programmed and operated to adjust a wide variety of stimulation parameters, for example, which electrodes are active and inactive, whether electrical stimulation is provided in a unipolar or bipolar manner, and/or how the stimulation signals are varied. In particular embodiments, the pulse system 310 can be used to control the polarity, frequency, duty cycle, amplitude, and/or spatial and/or temporal qualities of the stimulation. The stimulation can be varied to match naturally occurring burst patterns (e.g., theta burst stimulation), and/or the stimulation can be varied in a predetermined, pseudorandom, and/or aperiodic manner at one or more times and/or locations.
Stimulation can be provided to the patient using devices in addition to or in lieu of those described above. For example,
In a particular embodiment, a device generally similar to the device shown in
Further details of electrode devices that may be suitable for electromagnetic stimulation in accordance with other embodiments of the invention are described in the following pending U.S. Patent Applications, all of which are incorporated herein by reference: 10/891,834, filed Jul. 15, 2004; Ser. No. 10/418,796, filed Apr. 18, 2003; and Ser. No. 09/802,898, filed Mar. 8, 2001. Further devices and related methods are described in a copending U.S. Application No. ______, titled “Systems and Methods for Patient Interactive Neural Stimulation and/or Chemical Substance Delivery,” (Attorney Docket No. 33734.8082US) and U.S. Application No. ______, titled “Methods and Systems for Establishing Parameters for Neural Stimulation,” (Attorney Docket No. 33734.8079US), both filed concurrently herewith and incorporated herein by reference.
In still further embodiments, other techniques may be used to provide stimulation to the patient's brain. Such techniques can include electromagnetic techniques in addition to purely electrical techniques. In particular, such techniques can include transcranial magnetic stimulation techniques, which do not require that an electrode be implanted beneath the patient's skull. In still further embodiments, other techniques, which also may not require an implant, can be used. Such additional techniques can include transcranial direct current stimulation.
D. Techniques For Detecting a Response to Neural Stimulation
Once the appropriate stimulation device has been selected and positioned, the practitioner can apply stimulation and, particularly if the practitioner is stimulating the first neural population, detect a response. The practitioner may also wish to detect a response when stimulation is applied to the second neural population, e.g., to verify that the stimulation provided in accordance with the second set of stimulation parameters is or appears to be producing a desired response, condition, state, or change. In a particular aspect of either process, the response is detected at least proximate to the patient's central nervous system, and in a further particular aspect, at the patient's brain. One or more of several techniques may be employed to determine the neural response to the stimulation. Many suitable techniques rely on hemodynamic properties, e.g., they measure or are based on concentrations of oxy-hemoglobin and/or deoxy-hemoglobin. Such techniques can include functional magnetic resonance imaging (fMRl), measurements or estimates of cerebral blood flow, cerebral blood volume, cerebral metabolic rate of oxygen (CMRO), Doppler flowmetry, and/or optical spectroscopy using near infrared radiation. Magnetic resonance techniques (e.g., fMRI techniques) can be performed inside a magnetic resonance chamber, as described below with reference to
Certain other techniques, e.g., thermal measurements and/or flowmetry techniques, can be performed subdermally on the patient. Still further techniques, in particular, optical techniques such as near infrared spectroscopy techniques, are generally noninvasive and do not require penetration of the patience's scalp or skull. These techniques can include placing a near infrared emitter and detector (or an array of emitter/detector pairs) on the patient's scalp to determine species concentrations of both oxy-hemoglobin and deoxy-hemoglobin. Representative devices for measuring hemodynamic quantities (that correspond to neural activity) are disclosed in U.S. Pat. No. 5,024,226, U.S. Pat. No. 6,615,065, both incorporated herein by reference, and are available from ISS, Inc. of Champaign, Ill., and Somanetics of Troy, Mich. Further devices and associated methods are disclosed in pending U.S. Application No. ______, titled “Neural Stimulation and Optical Monitoring Systems and Methods,” (Attorney Docket No. 33734-8084US), filed concurrently herewith and incorporated herein by reference. Any of the foregoing techniques can be used to identify and/or quantify parameters and/or states associated with the patient's level of neural functioning. Such states may determine, influence, and/or alter signal properties such as intensity, power, spectral, phase, coherence, and/or other signal characteristics.
Some embodiments of the invention may involve magnetic resonance spectroscopy (MRS) techniques, which may facilitate the identification or determination of various chemical species and/or relative concentration relationships between such species in particular brain regions. Stimulation sites may be selected based upon, for example, a detected imbalance between particular neurotransmitters. Additionally or alternatively, the effect(s) of neural stimulation may be evaluated or monitored on a generally immediate, short term, and/or long term basis using MRS and/or other imaging techniques.
In other embodiments, a net (or other network) generally similar to that shown in
The method described above with reference to
In a particular application of the process 1000, stimulating the motor neural population can include applying electrical stimulation to a neural population located at the primary motor cortex. Detecting a first patient response resulting from stimulating the motor neural population can include detecting evidence that the stimulation has met or exceeded the level required for activation of the neural population. For example, detecting the first patient response can include observing or measuring a muscle action by the patient. Detecting the second patient response can include detecting a physiological characteristic that is shared by the first and second neural populations, for example, detecting a change in cerebral blood flow or other hemodynamic quantity, or detecting an electrical signal emitted by the motor neural population. The second patient response can be generally simultaneous with the first patient response (or at least clearly linked with the first patient response). For example, if it is determined that the cerebral blood flow changes by a certain amount (or has a certain value) when the motor neuron is stimulated at a current and/or voltage sufficient to produce an action potential, this information can be used to provide similar stimulation to the non-motor neural population. Accordingly, the non-motor neural population may not exhibit a response similar to the first patient response, but may exhibit the second patient response. By correlating the second patient response with the first patient response using the motor neural population, the non-motor neural population can be stimulated in a manner at least correlated with (and in some cases, generally similar to) that of the motor neural population, without requiring the non-motor neural population to exhibit the first patient response (e.g., the muscle action). In other embodiments, a generally similar approach can be followed, using different neurons to generate the first patient response. For example, sensory neurons can be stimulated to generate a first patient response that includes a sensation by the patient. The second patient response can be generally the same as any of those described above (e.g., a hemodynamic response).
The technique described above with reference to
In further particular embodiments, the process 1200 can include storing information corresponding to the detected evidence and/or the stimulation levels (process portion 1206). This information can be used by the practitioner to track parameters associated with the stimulation (e.g., how often the stimulation is triggered, and what characteristics the stimulation signals have). The process can also include checking for a change in neural function and/or activity (process portion 1208). In process portion 1210, it can be determined whether the change is occurring, or if it is occurring, whether it is occurring appropriately (e.g., at the appropriate pace and/or in the appropriate direction). If not, the stimulation parameters can be updated (process portion 1212) and the method can return to process portion 1202. In a particular embodiment, this feedback process can be used to identify changes or drifts in the patient's threshold stimulation levels over the course of a treatment regimen, and can automatically update the stimulation parameters accordingly. If the change is occurring appropriately, the process can further include checking to see if additional stimulation (with the existing stimulation parameters) is appropriate (process portion 1214). If so, the process returns to process portion 1202. If not, the process can end.
In at least some embodiments, process portion 1202 can include detecting hemodynamic properties that tend to change in response to changes in the patient's neural activity level(s). In many cases, an increase in perfusion levels can indicate a (desirable) increase in brain activity levels. However, this is not always the case. For example, some neuropsychiatric disorders (e.g., attention deficit disorder) can be accompanied by hyperperfusion in particular brain areas. Conversely, other neuropsychiatric disorders (e.g. depression) and some types of neuropsychiatric or cognitive dysfunctions may be indicated by hypoperfusion of a target neural area, and in still other disorders, a patient's brain may exhibit hypoperfusion in certain neural regions and hyperperfusion in other neural regions. Accordingly, effective therapy may be detected by noting or detecting a desirable or undesirable perfusion condition in one or more target neural populations. Effective treatment (e.g., provided by electrical stimulation, possibly in association with an adjunctive therapy such as behavioral therapy and/or drug therapy) may shift perfusion levels in particular target neural populations toward more normal or desirable levels. In some cases, the foregoing effects may be hidden or partially hidden by medications the patient takes, because such medications may directly or indirectly affect a neural population under consideration. Accordingly, one technique for detecting evidence of neural activity can include performing a check on a neural activity level after the patient has ceased taking a drug, as the effects of the drug wear off, and/or after the drug has worn off and the patient has returned to a “drug-off” state.
In some cases detecting evidence of neural activity can include detecting a particular value of a parameter (e.g., blood flow volume or oxygen content) that corresponds to an activity level. In other embodiments, detection includes detecting a change, rather than a particular value, of the parameter. The nature of these changes may be specific to individual patients, and/or may vary with the patient's condition. For example, changes may be quantitatively and/or qualitatively different for patients of different ages.
A lead or link 1394 may couple the monitoring element 1393 to a sensing unit 1395. The sensing unit 1395 may in turn be coupled to a controller 1313, pulse generator 1316, and pulse transmitter 1317, which are coupled back to the stimulating element 1393. Accordingly, the monitoring element 1393 can detect signals indicative of neural activity associated with particular neural populations and, via the controller 1313, can direct the stimulating element 1392 to deliver or apply stimulation signals to the same or a different target neural population. Information corresponding to the sensed data and/or the stimulation data can be stored at a memory device 1396 or other computer-readable medium (e.g., an implanted memory and/or external memory or disk drive). Aspects of some or all of the foregoing functionalities can reside on programmable computer-readable media.
In a particular embodiment, the monitoring element 1393 may include an array of cortical sensing electrodes, a deep brain electrode, and/or one or more other electrode types. In other embodiments, the monitoring element can include devices generally similar to those described above for monitoring hemodynamic quantities (e.g., optical spectroscopy monitors, cerebral blood flow monitors, cerebral blood volume monitors, Doppler flowmetry monitors, and/or others).
In some embodiments (e.g., when the monitoring element monitors electrical signals), the delivery of stimulation signals to a target neural population may interfere with the detection of signals corresponding to neural activity. As a result, the controller 1313 and/or the pulse system 1316 may periodically interrupt a neural stimulation procedure, such that during stimulation procedure interruptions, the sensing unit 1395 may analyze signals received from the monitoring element 1393. Outside of such interruptions, the sensing unit 1395 may be prevented from receiving or processing signals received from the monitoring element 1393. In particular embodiments, stimulation pulses may be interleaved with sensing “windows” so that the stimulation and monitoring tasks may be performed in alternating succession. In other embodiments, the sensing unit 1395 may compensate for the presence of stimulation signals, for example, through signal subtraction, signal filtering, and/or other compensation operations, to facilitate detection of neural activity or evidence of neural activity simultaneous with the delivery of stimulation signals to a target neural population.
In embodiments in which a neural stimulation procedure is periodically interrupted to facilitate detection of neural activity or evidence of such activity, the interface 1390 may include a single electrode arrangement or configuration in which any given electrode element used to deliver stimulation signals during the neural stimulation procedure may also be used to detect neural activity during a neural stimulation procedure interruption.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example, in some embodiments, data obtained from a first neural population can be used to identify stimulation parameters for a second neural population of the same patient. In other embodiments, data obtained from stimulating one type of neural population in one patient can be used to at least influence the choice of stimulation parameters selected for a different type of neural population in a different patient. Once stimulating parameters for a particular target neural population have been identified, a corresponding treatment regimen can include adjunctive therapies in addition to electromagnetic stimulation. Adjunctive therapies can include cognitive-based activities when the target neural population includes neurons associated with such activities, and/or other types of activities (e.g., physical therapy, auditory activities, visual tasks, speech production or language comprehension) for neurons associated therewith. Adjunctive therapies can also include drug-based therapies. Aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, aspects of the automated feedback system described in the context of