Systems and methods for enhancing or optimizing neural stimulation therapy for treating symptoms of parkinson's disease and/or other movement disorders

Description of equivalent WO 2004052183 A2

SYSTEMS AND METHODS FOR ENHANCING OR OPTIMIZING NEURAL

STIMULATION THERAPY FOR TREATING SYMPTOMS OF PARKINSON'S

DISEASE AND/OR OTHER MOVEMENT DISORDERS

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] The present disclosure incorporates by reference U.S. Application No.

09/978,134 entitled "Systems and Methods for Automatically Optimizing Stimulus Parameters and Electrode Configurations for Neuro-Stimulators," filed on October 15, 2002; and U.S. Application No. 10/xxx,xxx entitled "System and Method for Treating Parkinson's Disease and Other Movement Disorders," filed on December 9, 2003 (Perkins Coie Docket No. 33734.8040US01 - Express Mail No. EV335522310US), which claims the benefit of U.S. Provisional Application No. 60/432,073.

TECHNICAL FIELD

[0002] The present disclosure relates generally to systems and methods for treating symptoms of Parkinson's Disease and/or other movement disorders. More particularly, the present disclosure describes a system and method for enhancing or optimizing the effectiveness of neural stimulation in treating the symptoms of movement disorders such as Parkinson's Disease.

BACKGROUND

[0003] A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. For example, various physical or cognitive functions are directed or affected by neural activity within the sensory or motor cortices. Across most individuals, particular areas of the brain appear to have distinct functions. In the majority of people, for example, the areas of the occipital lobes relate to vision; the regions of the left interior frontal lobes relate to language; portions of the cerebral cortex appear to be consistently involved with conscious awareness, memory, and intellect; and particular regions of the cerebral cortex as well as the basal ganglia, the thalamus, and the motor cortex cooperatively interact to facilitate motor function control. [0004] Many problems or abnormalities with body functions can be caused by damage, disease, and/or disorders in the brain. For example, Parkinson's Disease (PD) is related to the degeneration or death of dopamine producing neurons in the substantia nigra region of the basal ganglia in the brain. Dopamine is neurotransmitter that transmits signals between areas of the brain. As the neurons in the substantia nigra deteriorate, the reduction in dopamine causes abnormal neural activity that results in a chronic, progressive deterioration of motor function control. Conservative estimates indicate that PD may affect more than one million individuals in the United States alone.

[0005] PD patients typically exhibit one or more of four primary symptoms. One primary symptom is a tremor in an extremity (e.g., a hand) that occurs while the extremity is at rest. Other primary symptoms include a generalized slowness of movement (bradykinesia); increased muscle rigidity or stiffness (rigidity); and gait or balance problems (postural dysfunction). In addition to or in lieu of these primary symptoms, PD patients may exhibit secondary symptoms including: difficulty initiating or resuming movements; loss of fine motor skills; lack of arm swing on the affected side of the body while walking; foot drag on the affected side of the body; decreased facial expression; voice and/or speech changes; cognitive disorders; feelings of depression or anxiety; and/or other symptoms.

[0006] Effectively treating PD or other movement disorders related to neurological conditions can be very difficult. Current treatments for PD symptoms include drugs, ablative surgical intervention, and/or neural stimulation. Drug treatments or therapies may involve, for example, the administration of a dopamine precursor that is converted to dopamine within the central nervous system (i.e., Levodopa (L-dopa)). Other types of drug therapies are also available. Unfortunately, drug therapies frequently become less effective or ineffective over time for an undesirably large patient population. A PD patient may require multiple drugs in combination to extend the time period of efficacy of drug therapies. Drug treatments additionally have a significant likelihood of inducing undesirable physical side effects; motor function complications such as uncontrollable involuntary movements (dyskinesias) are a particularly common side effect. Furthermore, drug treatments may induce undesirable cognitive side effects such as confusion and/or hallucinations. [0007] Ablative surgical intervention for PD typically involves the destruction of one or more neural structures within the basal ganglia or thalamus that have become overactive because of the lack of dopamine. Unfortunately, such neural structures reside deep within the brain, and hence ablative surgical intervention is a very time consuming and highly invasive procedure. Potential complications associated with the procedure include risk of hemorrhage, stroke, and/or paralysis. Moreover, because PD is a progressive disease, multiple deep brain surgeries may be required as symptoms progressively worsen over time. Although ablative surgical intervention may improve a PD patient's motor function, it is not likely to completely restore normal motor function. Furthermore, since ablative surgical intervention permanently destroys neural tissue, the effects of such intervention cannot be readily adjusted or "fine tuned" overtime.

[0008] Neural stimulation treatments have shown promising results for reducing some of the symptoms associated with PD. Neural activity is governed by electrical impulses or "action potentials" generated in and propagated by neurons. While in a quiescent state, a neuron is negatively polarized and exhibits a resting membrane potential that is 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 a series of action potentials in the event that the integration exceeds a threshold potential. A neural firing threshold, for example, may be approximately -55 mV. Action potentials propagate to the neuron's synapses and are then conveyed to other synaptically connected neurons.

[0009] Neural activity in the brain can be influenced by neural stimulation, which involves the application of electrical and/or magnetic stimuli to one or more target neural populations within a patient using a waveform generator or other type of device. Various neural functions can thus be promoted or disrupted by applying an electrical current to one or more regions of the brain. As a result, researchers have attempted to treat certain neurological conditions, including PD, using electrical or magnetic stimulation signals to control or affect brain functions.

[0010] Deep Brain Stimulation (DBS) is a stimulation therapy that has been used as an alternative to drug treatments and ablative surgical therapies. In DBS, one or more electrodes are surgically implanted into the brain proximate to deep brain or subcortical neural structures. For treating PD or other movement disorders, the electrodes are positioned in or proximate to the ventrointermediate nucleus of the thalamus; basal ganglia structures such as the globus pallidus internalis (GPi); or the Subthalamic Nucleus (STN). The location of the stimulation site for the electrodes depends upon the symptoms that a patient exhibits and the severity of the symptoms.

[0011] In a typical DBS system, a pulse generator delivers a continuous or essentially continuous electrical stimulation signal having a pulse repetition frequency of approximately 100 Hz to each of two deep brain electrodes. The electrodes are bilaterally positioned on the left and right sides of the brain relative to particular neural structures such as those indicated above. U.S. Patent No. 5,883,709 discloses one conventional DBS system for treating movement disorders.

[0012] Although DBS therapies may significantly reduce one or more PD symptoms, particularly when combined with drug treatments, they are highly invasive procedures. In general, configuring a DBS system to properly function within a patient requires two time consuming, highly invasive surgical procedures for implanting the DBS electrodes. Each such surgical procedure has essentially the same risks as those described above for ablative surgical intervention. Moreover, DBS may not provide relief from some movement disorders.

[0013] Motor Cortex Stimulation (MCS) is another type of brain stimulation treatment that has been proposed for treating Parkinson's Disease. MCS involves the application of stimulation signals to the motor cortex of a patient. One MCS system includes a pulse generator connected to a strip electrode that is surgically implanted over a portion of only the motor cortex (precentral gyms). The use of MCS to treat PD symptoms is described in Canavero, Sergro, Extradural Motor Cortex Stimulation for Advanced Parkinson's Disease: Case Report, Movement Disorders (Vol. 15, No. 1 , 2000).

[0014] Because MCS involves the application of stimulation signals to surface regions of the brain rather than deep neural structures, electrode implantation procedures for MCS are significantly less invasive and time consuming than those for DBS. As a result, MCS may be a safer and simpler alternative to DBS for treating PD symptoms. Present MCS techniques, however, fail to address or adequately consider a variety of factors that may enhance or optimize the extent to which a patient experiences short term and/or long term relief from PD symptoms. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic illustration of a neural stimulation system for treating symptoms of Parkinson's Disease and/or other neurological disorders according to an embodiment of the invention.

[0016] Figure 2 is a graph illustrating several stimulation parameters that may define, describe, or characterize stimulation signals.

[0017] Figure 3 is a flowchart illustrating various methods for refining, enhancing, or optimizing neural stimulation therapy for treating symptoms of Parkinson's Disease and/or other movement disorders according to an embodiment of the invention.

[0018] Figure 4 is a flowchart illustrating various methods for establishing, adjusting, or adapting a test protocol according to an embodiment of the invention.

[0019] Figure 5 is a flowchart illustrating various methods for determining neural stimulation parameters according to an embodiment of the invention.

[0020] Figure 6 is a flowchart illustrating various methods for modifying, adjusting, or adapting neural stimulation therapy in view of a likelihood or possibility of a lasting or long term neuroplastic change occurring within a patient over time.

DETAILED DESCRIPTION

[0021] The following disclosure describes neural stimulation systems and methods for enhancing or optimizing the extent to which a patient may experience relief from symptoms associated with Parkinson's Disease (PD), other movement or motor disorders, and/or various neurological disorders that may have multiple types of symptoms. Such symptoms may include, for example, tremor, rigidity, bradykinesia, postural dysfunction, spasticity, speech deficits, visual disturbances, olfactory deficits, cognitive deficits, memory deficits, emotional or psychiatric disturbances, paresis, pain and/or other symptoms.

[0022] Different symptoms may respond to neural stimulation in different manners, and/or across different time scales. For example, neural stimulation optimized to beneficially affect tremor and/or rigidity to a significant degree may provide less significant or minimal benefit relative to other symptoms such as postural dysfunction. Additionally, neural stimulation that has a nearly immediate or reasonably rapid effect upon tremor and/or rigidity may have a significantly or greatly delayed effect upon other symptoms such as bradykinesia. Systems and/or methods described herein may facilitate enhancement or optimization of neural stimulation therapy for treating multiple patient symptoms that may exhibit different treatment response characteristics and/or different response timeframes.

[0023] Neural stimulation may facilitate or effectuate neuroplastic changes within a patient's brain, for example, in a manner described in U.S. Application No. 09/802,808, which is incorporated herein by reference. Neuroplastic changes can include adaptive structural changes or reorganizations in particular brain regions, which may result in enhancement or restoration of one or more functional abilities (i.e., physical, sensory, and/or cognitive functions) associated with such brain regions, possibly on a long term or lasting basis. Application of neural stimulation to a patient in accordance with the principles described herein may increase the likelihood that neuroplastic changes can occur to facilitate at least partial recovery of diminished or lost functionality associated with or giving rise to one or more patient symptoms. Such functional recovery may itself reduce the extent to which the patient requires neural stimulation and/or other therapy on an ongoing basis.

[0024] Figure 1 is a schematic illustration of a neural stimulation system 100 for treating symptoms of PD and/or other disorders according to an embodiment of the invention. In one embodiment, the neural stimulation system 100 comprises a pulse generator 110a configured to deliver stimulation signals to a patient 190 using a set of electrodes 140. The pulse generator 110a may be coupled to the set of electrodes 140 by one or more leads 112. The pulse generator 110a may further be configured for wireless and/or wire-based communication with a programming unit 160. Depending upon embodiment details, the system 100 may further include one or more patient monitoring units 180 configured to detect, monitor, indicate, measure, and/or assess the severity of particular types of patient symptoms.

[0025] The set of electrodes 140 may include one or more cortical electrodes 142 configured to provide, deliver, and/or apply stimulation signals to particular cortical regions of the patient's brain 192 and/or neural populations synaptically connected and/or proximate thereto. A cortical electrode 142 may include one or more electrically conductive contacts 144 carried by a substrate 146 in a manner understood by those skilled in the art. The set of electrodes 140 may alternatively or additionally include one or more penetrating, depth, and/or deep brain electrodes. The set of electrodes 140 may further include or provide one or more stimulation signal return electrodes (i.e., electrodes that provide a current return path) that may be positioned relative to a variety of locations within and/or upon the patient's body.

[0026] The characteristics and/or placement of the set of electrodes 140 may depend upon the nature of patient's underlying disorders) and/or the type and/or severity of symptoms that the patient 190 experiences or exhibits. In one embodiment, one or more portions of the set of electrodes 140 may be surgically implanted to deliver stimulation signals to target neural populations within the patient's brain in a manner described in U.S. Application No. 10/xxx,xxx, entitled "System and Method for Treating Parkinson's Disease and Other Movement Disorders," filed on December 9, 2002 (Perkins Coie Docket No. 33734.8040US00).

[0027] The pulse generator 110a may comprise hardware and/or software for generating and outputting stimulation signals to the set of electrodes 140 in accordance with internal instruction sequences and/or in response to control signals, commands, instructions, and/or other information received from the programming unit 160. The pulse generator 110a may include a power supply, a pulse unit, a control unit, a programmable computer medium, and a communication unit. The power supply may comprise a battery or other type of power storage device. The pulse unit may comprise circuitry for generating pulse sequences that may be defined or characterized in accordance with various stimulation signal parameters, which are further described below with reference to Figure 2. The control unit may comprise hardware and/or software configured to direct or manage the local operation of the pulse generator 110a. The communication unit may comprise a user interface that facilitates communication with devices external to the pulse generator 110a, for example, through telemetric signal transfer. The programmable computer medium may comprise hardware and/or memory resident software. The programmable computer medium may store operational mode information and/or program instruction sequences that may be selected and/or specified in accordance with information received from the programming unit 160. The pulse generator 110a may be configured to deliver stimulation signals to particular electrodes 142 and/or specific electrical contacts 144 within the set of electrodes 140 on a selective basis at any given time, in a manner identical, essentially identical, or analogous to that described in U.S. Application No. 09/978,134. [0028] Each element of the pulse generator 110a may be incorporated or embedded into a surgically implantable case or housing. Depending upon embodiment details, the pulse generator 110a may be surgically implanted into the patient 190 in a subclavicular location. Alternatively, a pulse generator 110b may be surgically implanted above the patient's neck, for example, in a skull location posterior to the patient's ear and/or proximate to an electrode implantation site. A surgically formed tunnel or path may route the set of leads 112 that couple the pulse generator 110a, 110b to the set of electrodes 140, in a manner understood by those skilled in the art. Additionally, one or more electrically conductive portions of the pulse generator's case or housing may serve as a return electrode for electrical current.

[0029] The programming unit 160 may comprise a device configured to communicate control signals, commands, instructions, and/or other information to the pulse generator 110a. The programming unit 160 may additionally be configured to receive information from the pulse generator 110a. Communication between the programming unit 160 and the pulse generator 110a may facilitate or effectuate specification, selection, and/or identification of operational modes, instruction sequences, and/or procedures for treating symptoms of PD and/or other neurological disorders in accordance with the present invention, as described in detail below with reference to Figures 3 through 6.

[0030] In one embodiment, the programming unit 160 includes a processing unit 162, a programmable computer medium 164, and a communication unit 166. The programmable computer medium 164 may store an operating system, program instructions, and/or data, and may comprise various types of hardware and memory resident software, including volatile and/or nonvolatile memory as well as one or more data storage devices. The communication unit 166 may include a wire-based and/or wireless telemetry interface 170 that employs magnetic, radio frequency (RF), and/or optical signaling techniques to communicate with the pulse generator 110a. The communication unit 166 may additionally or alternatively include one or more wire- based and/or wireless interfaces that facilitate communication with other devices such as a computer.

[0031] A patient monitoring unit 180 may comprise essentially any type of device, subsystem, and/or system configured to detect, monitor, indicate, measure, and/or assess the severity of one or more types of patient symptoms associated with PD and/or other neurological disorders. For example, a patient monitoring unit 180 may comprise a motion detection system configured to detect patient movement associated with tremor. A motion detection system may include light emitting and/or detecting devices and/or accelerometers coupled to particular patient extremities. As another example, a patient monitoring unit 180 may comprise an Electromyography (EMG) system that includes a set of surface or depth electrodes positioned relative to particular muscle groups for detecting electrical signals corresponding to muscle fiber innervation. As another example, a patient monitoring unit 180 may comprise an Electroencephalograpy (EEG) system. As yet another example, a patient monitoring unit 180 may comprise a neural imaging system. As a final example, a patient monitoring unit 180 may comprise one or more electrodes and/or probes (e.g., cerebral bloodflow monitors) positioned upon, proximate, and/or within given target neural populations, and associated hardware and/or software for detecting, presenting, and/or analyzing signals received therefrom.

[0032] As previously indicated, the pulse generator 110a generates and outputs stimulation signals. In the context of the present invention, stimulation signals may comprise electromagnetic pulse sequences. Any given pulse sequence may comprise at least one, and possibly multiple, pulse trains, which may be separated by quiescent intervals. Figure 2 is a graph illustrating several stimulation parameters that may define, describe, or characterize a pulse train. A stimulus start time t₀ defines an initial point at which a pulse train is applied to one or more elements within the set of electrodes 140. In one embodiment, the pulse train may be a biphasic waveform comprising a series of biphasic pulses, and which may be defined, characterized, or described by parameters including a pulse width t, for a first pulse phase; a pulse width t₂ for a second pulse phase; and a pulse width t₃ for one or more biphasic pulses. The parameters can also include a pulse repetition rate 1/t₄ corresponding to a pulse repetition frequency; a pulse duty cycle equal to t₃ divided by t₄; a pulse burst time t₅ that defines a number of pulses in a pulse train; and/or a pulse train repetition rate t₆. Other parameters include a peak current intensity or amplitude I., for a first pulse phase and a peak current intensity l₂ for a second pulse phase.

[0033] In various embodiments, the pulse width of successive pulses and/or successive pulse phases may vary, such that the pulse repetition frequency within a pulse train and/or a pulse sequence is a function of time. A pulse train having a frequency that varies in time may give rise to a "chirped" frequency profile. Additionally or alternatively, the pulse intensity or amplitude may decay during the first and/or second pulse phases, and the extent of such decay may differ across successive or subsequent pulse phases. Those skilled in the art will understand that a pulse may be a charge-balanced waveform, and that in an alternate embodiment, pulses can be monophasic or polyphasic. Additional stimulation parameters may specify manners in which pulse trains are applied to selected configurations of elements within the set of electrodes 140, such as particular electrodes 142 and/or contacts 144, at any given time.

[0034] As defined herein, a test protocol may define or specify neural stimulation parameters associated with one or more pulse sequences to be applied to a patient 190 across or within a given test period duration that may include one or more neural stimulation delivery periods and possibly one or more quiescent periods during which the patient 190 receives no neural stimulation. A test protocol may further define or specify a spatial and/or temporal distribution of elements within the set of electrodes 140 to which neural stimulation may be applied during one or more portions of the test period; and corresponding signal polarities corresponding to particular elements within the set of electrodes 140 relative to one or more portions of the test period. Neural stimulation delivered in accordance with a^'test protocol comprises a test therapy.

[0035] Figure 3 is a flowchart illustrating various methods for refining, enhancing, or optimizing neural stimulation therapy for treating symptoms of PD and/or other neurological disorders according to an embodiment of the invention. In one embodiment, a method 200 includes an identification procedure 202 that involves identification of one or more patient symptoms to which neural stimulation therapy, possibly in conjunction with one or more adjunctive therapies, may be directed. The method 200 may also include a symptom selection procedure 204 that involves selection or consideration of a first, a next, or an additional subset of patient symptoms to which neural stimulation therapy may be directed. The symptom selection procedure 204 may facilitate initial selection of symptoms expected to rapidly respond to neural stimulation, such as tremor and/or rigidity, followed by selection of other symptoms such as bradykinesia that may respond more slowly.

[0036] The method 200 may further include a test protocol management procedure 206 that involves establishing, adjusting, and/or adapting a test protocol that specifies or defines a test therapy intended to be applied to the patient 190 for a given test period. The test protocol may specify or define neural stimulation parameters corresponding to the test therapy, and may also specify parameters corresponding to one or more adjunctive therapies such as drug therapies. The method 200 may additionally include a test delivery procedure 208 that involves application or delivery of the test therapy to the patient 190 in accordance with the test protocol; and an observation procedure 210 that involves observation, monitoring, and/or measuring of patient symptoms at one or more times in association with and/or following the delivery procedure 208. The observation procedure 210 may involve one or more patient monitoring units 180, and/or direct human observation of the patient 190.

[0037] The method 200 may further include an evaluation procedure 212 involving determination of an extent to which one or more patient symptoms currently under consideration have improved or changed as a result of the most recently applied test therapy. In a manner analogous to that for the observation procedure 210, the evaluation procedure 212 may involve one or more patient monitoring units 180 and/or direct human evaluation of the patient 190. In the event that further improvement of symptoms currently under consideration is necessary, likely, or possible, the method 200 may return to the test protocol management procedure 206. Alternatively, in the event that additional patient symptoms require consideration, the method 200 may return to the symptom selection procedure 204.

[0038] In addition to procedures directed toward refining, enhancing, or optimizing an extent to which one or more symptoms can be successfully or adequately treated by neural stimulation (possibly in conjunction with one or more adjunctive therapies), the method 200 may include an ongoing treatment delivery procedure 218 that involves application of an arrived-at ongoing therapy to the patient in accordance with an ongoing, essentially ongoing, or generally ongoing treatment protocol. The ongoing treatment protocol may correspond to or be based upon a previously considered test protocol, and may involve one or more adjunctive therapies. In particular, the ongoing treatment protocol may be identical or essentially identical to a recently considered test protocol, with the exception that an ongoing treatment duration corresponding to the ongoing treatment protocol may be significantly longer than that of the test period corresponding to such a test therapy.

[0039] The method 200 may also include a reevaluation procedure 220 that involves a one-time, occasional, or periodic reevaluation, adjustment, and/or adaptation of a most recent ongoing treatment protocol in view of potential or likely neuroplastic changes, variations in ongoing treatment effectiveness, and/or overall patient health or condition over time. Such reevaluation, adjustment, or adaptation may occur after a predetermined time interval, such as 1 month, several months, or 1 or more years following initiation of an ongoing treatment delivery procedure 218. The reevaluation procedure 220 may be performed on a one-time or repeated basis based upon the judgment of a medical professional.

[0040] The reevaluation procedure 220 may itself involve one or more steps of the method 200. Through a reevaluation procedure 220, it may be determined that one or more patient symptoms may be better, successfully, or adequately treated or managed in accordance with a different pulse repetition frequency function; a lower peak intensity or amplitude; less frequent neural stimulation; a modified configuration of elements within the set of electrodes 140 and/or modified signal polarities applied thereto; lower dosage and/or less frequent drug therapy; and/or other variations in or modifications to the ongoing treatment protocol. As further described below with reference to Figure 6, a reevaluation procedure 220 that indicates that better, successful, or adequate treatment or management of one or more patient symptoms may be achieved with less intense and/or less frequent neural stimulation may be indicative of compensatory, restorative, and/or rehabilitative neuroplastic change within the patient 190.

[0041] Figure 4 is a flowchart illustrating various methods for establishing, adjusting, or adapting a test protocol according to an embodiment of the invention. Such methods may be used in the test protocol management procedure 206 of Figure 3. In one embodiment, a method 300 includes an adjustment procedure 302 that involves adjustment, cessation, or interruption of patient therapies currently in progress as required. Such therapies may comprise neural stimulation and/or one or more adjunctive therapies such as a drug therapy. The method 300 may also include a waiting procedure 304 during which effects of recently adjusted, discontinued, or interrupted therapies are allowed to subside, stabilize, or "wash out." The waiting procedure 304 may maximize or increase a likelihood that a previously applied therapy has a minimal or negligible effect upon an upcoming test therapy (i.e., no carry-over effects). The method 300 may further include an assessment procedure 306 that involves assessment, qualification, and/or quantification of the severity of one or more patient symptoms, possibly to establish a baseline or reference patient condition.

[0042] The method 300 may additionally include a duration establishment procedure

308 that involves determination or definition of a test period duration during which a test therapy may be applied to the patient 190. A test period duration may be short or relatively short, for example, approximately 1 or more minutes or hours, to facilitate efficient determination of the effectiveness of a test protocol upon acute or readily responsive patient symptoms. Alternatively, a test period duration may be relatively long, for example, approximately 1 or more days, weeks, or even months, to facilitate determination of the effectiveness of a test protocol upon patient symptoms having slower or prolonged treatment response characteristics. The method 300 may further include a first test protocol definition procedure 310 that involves determination, selection, and/or specification of neural stimulation parameters that comprise one or more portions of the test protocol. The method 300 may additionally include a second test protocol definition procedure 312 that involves determination or definition of a set of parameters corresponding to one or more adjunctive therapies that may form a portion of the test protocol. Such parameters may include, for example, a drug dosage and delivery schedule.

[0043] Figure 5 is a flowchart illustrating various methods for determining neural stimulation parameters according to an embodiment of the invention. Such methods may be used in the first test protocol definition procedure 310 of Figure 4. In one embodiment, a method 400 includes a delivery period selection procedure 402 that involves determination or selection of a first or next time interval within the current test period that neural stimulation may be delivered to the patient 190. The method 400 may further include a pulse sequence duration procedure 404 that involves selection and/or specification of one or more pulse sequence durations and/or quiescent intervals within and/or between pulse sequences for the neural stimulation delivery period currently under consideration. The method 400 may accommodate multiple pulse sequences, variable types of pulse train sequences, and/or quiescent intervals between pulse sequences to provide enhanced flexibility with respect to establishing test protocols that may be useful for efficiently treating symptoms of various disorders.

[0044] Relative to treating PD symptoms, stimulation that reduces the output activity of the globus pallidus internalis (GPi) can be highly beneficial. Deep Brain Stimulation (DBS) research has shown that stimulation delivered to the globus pallidus internalis (GPi) may significantly reduce GPi activity over a period that can last several seconds beyond the termination of such stimulation. For example, a continuous or essentially continuous pulse train lasting 3 seconds may result in reduced or significantly reduced GPi output activity that lasts approximately 1.5 seconds beyond termination of the 3 second pulse train. Delivering or applying neural stimulation to one or more target neural populations having synaptic projections into the GPi or associated neural circuitry such that pulse sequences or pulse trains are separated by one or more appropriate quiescent intervals may therefore maintain or sustain reduced GPi activity while eliminating the need to deliver continuous stimulation. Delivery of neural stimulation in such a manner advantageously reduces power consumption. Thus, a pulse sequence comprising periodic pulse trains lasting approximately 3 seconds separated by quiescent intervals lasting approximately 1.5 seconds may provide significant therapeutic benefit in a power efficient manner. The method 400 may additionally include a waveform definition procedure 406 that involves selection and/or specification of a set of waveform parameters that define or describe each pulse sequence currently under consideration. Such waveform characteristics may include a pulse repetition frequency or frequency function, a pulse amplitude decay function, and/or other pulse sequence parameters. Depending upon embodiment details and/or current symptoms under consideration, the pulse repetition frequency may vary within any given pulse sequence, and/or from one pulse sequence to another. By accommodating such variation, the method may facilitate the definition of a test protocol or an arrived-at ongoing treatment protocol that includes multiple pulse repetition frequencies, where particular individual pulse frequencies or pulse frequency subsets may be directed toward maximizing or enhancing the effectiveness of neural stimulation in treating particular PD and/or movement disorder symptoms. As an illustrative example, if (a) a pulse repetition frequency of approximately 25 Hz appears optimal or nearly optimal for treating tremor, (b) a pulse repetition frequency of approximately 30 Hz appears optimal for treating rigidity, and (c) a pulse repetition frequency of approximately 15 Hz appears optimal for treating bradykinesia, then a test protocol or an ongoing treatment protocol may call for neural stimulation that periodically alternates between these pulse repetition frequencies in accordance with given neural stimulation delivery periods and possibly including one or more quiescent periods therebetween. Alternatively, the test protocol or the ongoing treatment protocol may call for neural stimulation that sweeps between 15 and 30 Hz in a continuous or nearly continuous manner.

[0046] In general, a test protocol may call for neural stimulation having one or more pulse repetition frequencies specified in accordance with a temporal and/or mathematical function that is based upon individual pulse repetition frequencies determined to be optimal or near-optimal for treating particular subsets of patient symptoms. Such a temporal and/or mathematical function may be based upon the nature and/or severity of such symptoms. For example, if the patient's baseline or reference state indicates that the patient experiences tremor in a significantly more severe manner than bradykinesia, a test protocol may call for neural stimulation in which an amount of time spent delivering stimulation optimized or nearly optimized for treating tremor exceeds an amount of time spent delivering stimulation optimized or nearly optimized for treating bradykinesia. Additionally or alternatively, the test protocol may call for neural stimulation having a frequency function that is weighted or biased relative to individually determined frequencies corresponding to particular symptom subsets. Such a test protocol may call for neural stimulation that delivers, for example, a combined frequency of 27 Hz for treating both tremor and rigidity, as well as a pulse repetition frequency of 15 Hz for treating bradykinesia. Furthermore, a test protocol may call for neural stimulation having a pulse repetition frequency function that depends upon one or more treatment response times associated with particular symptoms, and/or one or more time intervals that relief from particular symptoms persists in the absence of neural stimulation.

[0047] The method 400 may further include an electrode element selection procedure

408 that involves identifying or defining a spatial and/or temporal distribution of electrodes 142 and/or contacts 144 to which neural stimulation may be directed during the delivery period under consideration. The electrode element selection procedure 408 may alternatively or additionally select or define signal polarities corresponding to particular electrodes 142 and/or contacts 144 relative to one or more portions of the test period. In the event that a current test period includes more than one delivery period, the method 400 may return to the delivery period selection procedure 402.

[0048] The method 400 may also include a threshold determination procedure 412 that involves determination of a minimum or near minimum neural stimulation amplitude or intensity that evokes or induces a given type of patient response, reaction, behavior, and/or sensation. A neural stimulation threshold may be determined by successively applying higher amplitude neural stimulation signals to the patient 190 until an observable or detectable response occurs. Each threshold determination attempt may apply a limited duration neural stimulation signal to the patient 190, for example, a pulse sequence lasting 0.5 seconds, 1 second, 3 seconds, or some other length of time. A waiting, quiescent, or washout period between successive threshold determination attempts, during which the patient 190 receives no neural stimulation, may ensure that each threshold determination attempt is independent or essentially independent of residual effects associated with previously applied signals. A quiescent period may span several seconds to one or more minutes, for example, approximately one minute. In one embodiment, the threshold determination procedure 412 involves determination of a motor, movement, or motion threshold through motion detection techniques and/or visual observation. In another embodiment, the threshold determination procedure 412 may involve determination of an EMG threshold and/or another type of neural stimulation threshold.

[0049] The method 400 may further include an amplitude determination procedure 414 that involves determination or selection of peak or average amplitudes or intensities corresponding to the set of pulse sequences defined or specified within the current test period based upon the results or outcome of the threshold determination procedure 412. Depending upon embodiment details, a peak pulse sequence amplitude may be defined as a given percentage of a neural stimulation threshold, for example, 50% of a movement threshold or 70% of an EMG threshold. In some embodiments, different pulse sequences within a delivery period or test period may have different peak amplitudes.

[0050] Figure 6 is a flowchart illustrating various methods for modifying, adjusting, or adapting neural stimulation therapy in view of a likelihood or possibility of a lasting or long term neuroplastic change occurring within a patient 190 over time. Such methods may involve the reevaluation procedure 220 and/or other procedures described above with in association with Figure 3. The propensity of a given neural population to undergo neuroplastic change may depend upon the application of an initial neural stimulation regimen to the neural population in a particular manner, such as a continuous, generally continuous, or frequent manner over a given or minimum amount of time. This may in turn facilitate or effectuate initiation and reinforcement of chemical and/or structural adaptations or changes in the neural population and/or neural circuitry associated therewith, thereby "priming" the neural population to accept and/or maintain long term or lasting neuroplastic change.

[0051] As an illustrative example, depending upon symptom type and severity, effective or generally effective treatment of PD or other movement disorder symptoms may initially require continuous, essentially continuous, or nearly continuous neural stimulation for a neuroplastic priming period of approximately one month. After such a neuroplastic priming period, however, effective treatment of one or more symptoms may require stimulation for a limited number of hours per day, such as during the patient's normal waking hours. Alternatively, effective treatment may require continuous stimulation for approximately 30 minutes, after which treatment may be interrupted for approximately 30 minutes, and so on. In another embodiment, the stimulation can be applied on a twenty four hour basis for an initial period and then on a reduced basis for a subsequent period. The stimulation, for example, can be applied all throughout each day for an initial period of approximately one month, and then it can be applied only during waking hours after the initial period. This is expected to provide sufficient results in many situations and conserve battery life.

[0052] One method 500 for modifying, adjusting, or adapting neural stimulation therapy in view of a likelihood or possibility of a lasting or long term neuroplastic change may include a first stimulation optimization or refinement procedure 502 that involves determination of a continuous neural stimulation protocol for treating one or more patient symptoms. The method 500 may further include a continuous stimulation procedure 504 that involves delivery or application of neural stimulation to the patient 190 in accordance with the continuous neural stimulation protocol for a predetermined time period, for example, one or more weeks or one or more months. The predetermined time period may correspond to an expected or likely neuroplastic priming period. The method 500 may additionally include a second stimulation optimization or refinement procedure 506 that involves determination of a noncontinuous and/or periodically interrupted neural stimulation protocol for treating patient symptoms under consideration. The method 500 may also include a noncontinuous or interrupted stimulation procedure that involves delivery of noncontinuous and/or interrupted neural stimulation to the patient 190 in accordance with the noncontinuous and/or interrupted neural stimulation protocol. The first and/or second stimulation optimization or refinement procedures 502, 506 may include or encompass one or more procedures described above in association with Figure 3. Additionally, the second stimulation optimization or refinement procedure 506 may be repeated following application of noncontinuous or interrupted stimulation to the patient 190 for a given amount of time.

[0053] Additional embodiments of the invention are directed to establishing or adjusting the stimulation parameters with applying stimulation to the patient. One embodiment, for example, is a method for establishing stimulation parameters for a patient having symptoms corresponding to a neurological disorder. This embodiment comprises determining a first set of stimulation parameters capable of treating a first subset of symptoms, and determining a second set of stimulation parameters capable of treating a second set of symptoms. The method further includes establishing the stimulation parameters that are to be applied to the patient based upon the first set of neural stimulation parameters and the second set of neural stimulation parameters.

[0054] Another embodiment of a method for establishing stimulation parameters for a patient having symptoms corresponding to a neurological disorder includes evaluating the efficacy of a first set of neural stimulation parameters and a second set of neural stimulation parameters. The first and second sets of stimulation parameters can be applied to the patient before evaluating the efficacy of the parameters, or they can be determined from stimulation parameters applied to a population of patients with similar symptoms. This method continues by adjusting the stimulation parameters based upon the efficacy of the first and second sets of stimulation parameters.

[0055] 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 spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.