Methods and apparatus for effectuating a lasting change in a neural-function of a patient
Methods and apparatus for treating an impaired neural function in a brain of a patient. In one embodiment, a method for treating a neural function in a brain of a patient includes determining a therapy period during which a plurality of therapy sessions are to be performed to recover functional ability corresponding to the neural function. The method continues by identifying a stimulation site in or on the brain of the patient associated with the neural function, and positioning an electrode at least proximate to the identified stimulation site. The patient is then treated by providing electrical stimulation treatments to the stimulation site. The treatment can comprise delivering electrical stimulation signals to the electrode during the therapy sessions. After expiration of the therapy period, the method includes preventing electrical stimulation signals from being delivered to the stimulation site.
This application is a Continuation-in-Part of U.S. application Ser. No. 09/802,808, filed Mar. 8, 2001.
TECHNICAL FIELDSeveral embodiments of methods and apparatus in accordance with the invention are related to electrically stimulating a region in the cortex or other area of the brain for a limited treatment period to bring about a lasting change in a physiological function and/or a mental process of a patient.
BACKGROUNDA 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 or motor cortices) are organized according to physical or cognitive functions. There are also several other areas of the brain that 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 interior frontal lobes relate to language, and the 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. Effectively treating such abnormalities may be very difficult. For example, a stroke is a 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 brain. Such events generally result in a loss or impairment of a neural function (e.g., neural functions related to facial muscles, limbs, speech, etc.). Stroke patients are typically treated using various forms of physical therapy to rehabilitate the loss of function of a limb or another affected body part. Stroke patients may also be treated using physical therapy plus an adjunctive therapy such as amphetamine treatment. For most patients, however, such treatments are minimally effective and little can be done to improve the function of an affected body part beyond the recovery that occurs naturally without intervention. As a result, many types of physical and/or cognitive deficits that remain after treating neurological damage or disorders are typically considered permanent conditions that patients must manage for the remainder of their lives.
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 synoptically 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 a series of action potentials when the integration exceeds a threshold potential. A neural firing threshold, for example, may be approximately −55 mV.
It follows 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 electrodes.
The neural stimulation signals used by these approaches may comprise a series of electrical or magnetic pulses that can affect neurons within a target neural population. Stimulation signals may be defined or described in accordance with stimulation signal parameters including pulse amplitude, pulse frequency, duty cycle, stimulation signal duration, and/or other parameters. Electrical or magnetic stimulation signals applied to a population of neurons can depolarize neurons within the population toward their threshold potentials. Depending upon stimulation signal parameters, this depolarization can cause neurons to generate or fire action potentials. Neural stimulation that elicits or induces action potentials in a functionally significant proportion of the neural population to which the stimulation is applied is referred to as supra-threshold stimulation; neural stimulation that fails to elicit action potentials in a functionally significant proportion of the neural population is defined as sub-threshold stimulation. In general, supra-threshold stimulation of a neural population triggers or activates one or more functions associated with the neural population, but sub-threshold stimulation by itself does not trigger or activate such functions. Supra-threshold neural stimulation can induce various types of measurable or monitorable responses in a patient. For example, supra-threshold stimulation applied to a patient's motor cortex can induce muscle fiber contractions in an associated part of the body.
Although electrical or magnetic stimulation of neural tissue may be directed toward producing an intended type of therapeutic, rehabilitative, or restorative neural activity, such stimulation may result in collateral neural activity. In particular, neural stimulation delivered beyond a certain intensity, period of time, level, or amplitude can give rise to seizure activity and/or other types of collateral activity. It will be appreciated that collateral neural activity may be undesirable and/or inconvenient in a neural stimulation situation.
Conventional neural stimulation systems and techniques are generally directed toward treating or managing chronic patient symptoms on a perpetual or essentially perpetual basis, i.e., throughout a patient's lifespan. Therefore, conventional neural stimulation systems and methods may not be ideally suited for applications directed toward restoring rather than perpetually treating impaired functions.
BRIEF DESCRIPTION OF THE DRAWINGS
The following disclosure describes several methods and apparatus for intracranial electrical stimulation to treat or otherwise effectuate a change in neural-functions of a patient. Several embodiments of methods described herein are directed toward enhancing or otherwise inducing neuroplasticity to effectuate a particular neural-function. Neuroplasticity refers to the ability of the brain to change or adapt over time. It was once thought adult brains became relatively “hard wired” such that functionally significant neural networks could not change significantly over time or in response to injury. It has become increasingly more apparent that these neural networks can change and adapt over time so that meaningful function can be restored in response to brain injury. An aspect of several embodiments of methods in accordance with the invention is to provide the appropriate triggers for adaptive neuroplasticity. These appropriate triggers appear to cause or enable increased synchrony of functionally significant populations of neurons in a network.
Neural stimulation applied or delivered in various manners described herein may excite a portion of a neural network involved in or associated with a functionally significant task such that a selected population of neurons can become more strongly associated with that network. Because such a network will subserve a functionally meaningful task, such as motor relearning, the changes are more likely to be lasting because they are continually being reinforced by natural use mechanisms. The nature of stimulation in accordance with several embodiments of the invention ensures that the stimulated population of neurons links to other neurons in the functional network. It is expected that this occurs because action potentials are not actually caused by the stimulation, but rather the action potentials are caused by interactions with other neurons in the network. Several aspects of the electrical stimulation in accordance with selected embodiments of the invention increase the probability of restoring neural functionality when the network is activated by a combination of electrical stimulation and favorable activities, such as rehabilitation or limb use.
Various methods in accordance with the invention can be used to treat brain damage (e.g., stroke, trauma, etc.), brain disease (e.g., Alzheimer's, Pick's, Parkinson's, etc.), brain disorders (e.g., epilepsy, depression, etc.), neurological malfunction (e.g., dyslexia, autism, etc...), and/or other neurological conditions. Various methods in accordance with the invention can also be used to enhance functions of normal, healthy brains (e.g., learning, memory, etc.), or to control sensory functions (e.g., pain).
Certain embodiments of methods in accordance with the invention electrically stimulate the brain at a stimulation site where neuroplasticity is occurring. The stimulation site may be different than the region in the brain where neural activity is typically present to perform the particular function according to the functional organization of the brain. In one embodiment in which neuroplasticity related to the neural-function occurs in the brain, the method can include identifying the location where such neuroplasticity is present. This particular procedure may accordingly enhance a change in the neural activity to assist the brain in performing the particular neural function. In an alternative embodiment in which neuroplasticity is not occurring in the brain, an aspect is to induce neuroplasticity at a stimulation site where it is expected to occur. This particular procedure may thus induce a change in the neural activity to instigate performance of the neural function. Several embodiments of these methods are expected to produce a lasting effect on the intended neural activity at the stimulation site.
The specific details of certain embodiments of the invention are set forth in the following description and in
A. Methods for Electrically Stimulating Regions of the Brain
1. Embodiments of Electrically Enhancing Neural Activity
The method 100 includes a diagnostic procedure 102 involving identifying a stimulation site at a location of the brain. In one approach, the stimulation site may be a location of the brain where an intended neural activity related to a given type of neural-function is present or is expected to be present. For example, the stimulation site may be particular neurological regions and/or cortical structures that are expected to direct, effectuate, and/or facilitate specific neural functions in most individuals. In another approach, the stimulation site may be a location of the brain that supports or is expected to support the intended neural-function.
The diagnostic procedure 102 may include identifying one or more exterior anatomical landmarks on the patient that correspond to such neurological regions and/or structures within the brain. The external anatomical landmarks serve as reference points for locating a structure of the brain where an intended neural activity may occur. Thus, one aspect of the diagnostic procedure 102 may include referencing the stimulation site on the brain relative to external anatomical landmarks.
More specifically, identifying an anatomical landmark may include visually determining the location of one or more reference structures (e.g., visible. cranial landmarks), and locating underlying brain regions or structures (e.g., the motor strip and/or the Sylvian fissure) relative to the external location of the reference structures. Such reference structures may include, for example, the bregma, the midsagittal suture, and/or other well-known cranial landmarks in a manner understood by those skilled in the art. The methods for locating the underlying brain structure typically involve measuring distances and angles relative to the cerebral topography as known in the art of neurosurgery.
In another embodiment, the diagnostic procedure 102 includes generating an intended neural activity in the brain from a “peripheral” location that is remote from the normal location, and then determining where the intended neural activity is actually present in the brain. In an alternative embodiment, the diagnostic procedure 102 can be performed by identifying a stimulation site where neural activity has changed in response to a change in the neural-function.
The method 100 continues with an implanting procedure 104 involving positioning at least a first electrode relative to the identified stimulation site; and a stimulating procedure 106 involving applying an electrical current to the first electrode. Many embodiments of the implanting procedure 104 position two or more electrodes at the stimulation site, but other embodiments of the implanting procedure involve positioning only one electrode at the stimulation site and another electrode remotely from the stimulation site. As such, the implanting procedure 104 of the method 100 can include implanting at least one electrode at the stimulation site. Additional embodiments of the diagnostic procedure 102 and the procedures 104 and 106 are described in greater detail below.
The neural activity in the first region 210, however, can be impaired. In a typical application, the diagnostic procedure 102 begins by taking an image of the brain 200 that is capable of detecting neural activity to determine whether the intended neural activity associated with the particular neural function of interest is occurring at the region of the brain 200 where it normally occurs according to the functional organization of the brain.
One embodiment of the diagnostic procedure 102 involves generating the intended neural activity remotely from the first region 210 of the brain, and then detecting or sensing the location in the brain where the intended neural activity has been generated. The intended neural activity can be generated by applying an input that causes a signal to be sent to the brain. For example, in the case of a patient that has lost the use of limb, the affected limb is moved and/or stimulated while the brain is scanned using a known imaging technique that can detect neural activity (e.g., functional MRI, positron emission tomography, etc.). In one specific embodiment, the affected limb can be moved by a practitioner or the patient, stimulated by sensory tests (e.g., pricking), or subject to peripheral electrical stimulation. The movement/stimulation of the affected limb produces a peripheral neural signal from the limb that is expected to generate a response neural activity in the brain. The location in the brain where this response neural activity is present can be identified using the imaging technique.
An alternative embodiment of the diagnostic procedure 102 involves identifying a stimulation site at a second location of the brain where the neural activity has changed in response to a change in the neural-function of the patient. This embodiment of the method does not necessarily require that the intended neural activity be generated by peripherally actuating or stimulating a body part. For example, the brain can be scanned for neural activity associated with the impaired neural-function as a patient regains use of an affected limb or learns a task over a period of time. This embodiment, however, can also include peripherally generating the intended neural activity remotely from the brain explained above.
In still another embodiment, the diagnostic procedure 102 involves identifying a stimulation site at a location of the brain where the intended neural activity is developing to perform the neural-function. This embodiment is similar to the other embodiments of the diagnostic procedure 102, but it can be used to identify a stimulation site at (a) the normal region of the brain where the intended neural activity is expected to occur according to the functional organization of the brain and/or (b) a different region where the neural activity occurs because the brain is recruiting additional matter to perform the neural-function. This particular embodiment of the method involves monitoring neural activity at one or more locations where the neural activity occurs in response to the particular neural-function of interest. For example, to enhance the ability to learn a particular task (e.g., playing a musical instrument, memorizing, etc.), the neural activity can be monitored while a person performs the task or thinks about performing the task. The stimulation sites can be defined by the areas of the brain where the neural activity has the highest intensity, the greatest increases, and/or other parameters that indicate areas of the brain that are being used to perform the particular task.
Several embodiments of methods for enhancing neural activity in accordance with the invention are expected to provide lasting results that promote a desired neural-function. Before the present invention, electrical and magnetic stimulation techniques typically stimulated the normal locations of the brain where neural activity related to the neural-functions occurred according to the functional organization of the brain. Such conventional techniques, however, may not by themselves be effective because one or more subpopulations of neurons in the “normal locations” of the brain may not be capable of carrying out the neural activity because of brain damage, disease, disorder, and/or because of variations of the location specific to individual patients. Several embodiments of methods for enhancing neural activity in accordance with the invention overcome this drawback by identifying a stimulation site based on neuroplastic activity that appears to be related to the neural-function. By first identifying a location in the brain that is being recruited to perform the neural activity, it is expected that therapies (e.g., electrical, magnetic, genetic, biologic, and/or pharmaceutical) applied to this location will be more effective than conventional techniques. This is because the location that the brain is recruiting for the neural activity may not be the “normal location” where the neural activity would normally occur according to the functional organization of the brain. Therefore, several embodiments of methods for enhancing neural activity in accordance with the invention are expected to provide lasting results because the therapies are applied to the portion of the brain where neural activity for carrying out the neural-function actually occurs in the particular patient.
Various embodiments of methods for enhancing neural activity in accordance with the invention may also provide lasting results because electrical stimulation therapies described herein may be applied or delivered to a patient in conjunction or simultaneous with one or more synergistic or adjunctive therapies. Such synertistic or adjunctive therapies may include or involve the patient's performance of one or more behavioral therapies, activities, and/or tasks.
2. Electrically Inducing Desired Neural activity
The method 100 for effectuating a neural-function can also be used to induce neural activity in a region of the brain where such neural activity is not present. As opposed to the embodiments of the method 100 described above for enhancing existing neural activity, the embodiments of the method 100 for inducing neural activity initiate the neural activity at a stimulation site where it is estimated that neuroplasticity will occur. In this particular situation, an image of the brain seeking to locate where neuroplasticity is occurring may be similar to
A stimulation site may be identified by estimating where the brain will likely recruit neurons for performing the neural-function. In one embodiment, the location of the stimulation site is estimated by defining a region of the brain that is proximate to the normal location where neural activity related to the neural-function is generally present according to the functional organization of the brain. An alternative embodiment for locating the stimulation site includes determining where neuroplasticity has typically occurred in patients with similar symptoms. For example, if the brain typically recruits a second region of the cortex to compensate for a loss of neural activity in the normal region of the cortex, then the second region of the cortex can be selected as the stimulation site either with or without imaging the neural activity in the brain.
Several embodiments of methods for inducing neural activity in accordance with the invention are also expected to provide lasting results that initiate and promote a desired neural-function. By first estimating the location of a stimulation site where desired neuroplasticity is expected to occur, therapies applied to this location may be more effective than conventional therapies for reasons that are similar to those explained above regarding enhancing neural activity. Additionally, methods for inducing neural activity may be easier and less expensive to implement because they do not require generating neural activity and/or imaging the brain to determine where the intended neural activity is occurring before applying the therapy.
3. Applications of Methods for Electrically Stimulating Regions of the Brain
The foregoing methods for enhancing existing neural activity or inducing new neural activity are expected to be useful for many applications. As explained above, several embodiments of the method 100 involve determining an efficacious location of the brain to enhance or induce an intended neural activity that causes the desired neural-functions to occur. Additional therapies can also be implemented in combination with the electrical stimulation methods described above. Several specific applications using embodiments of electrical stimulation methods in accordance with the invention either alone or with synergistic or adjunctive therapies will now be described, but it will be appreciated that the methods in accordance with the invention can be used in many additional applications.
a. General Applications
The embodiments of the electrical stimulation methods described above are expected to be particularly useful for rehabilitating or restoring a loss of mental functions, motor functions and/or sensory functions caused by damage to the brain. In a typical application, the brain has been damaged by a stroke or trauma (e.g., automobile accident). The extent of the particular brain damage can be assessed using functional MRI or another appropriate imaging technique as explained above with respect to
Several specific applications are expected to have a stimulation site in the cortex because neural activity in this part of the brain effectuates motor functions and/or sensory functions that are typically affected by a stroke or trauma. In these applications, the electrical stimulation can be applied directly to the pial surface of the brain or at least proximate to the pial surface (e.g., the dura mater, the fluid surrounding the cortex, or neurons within the cortex). Suitable devices for applying the electrical stimulation to the cortex are described in detail with reference to
In accordance with the present invention, a limited duration treatment program 110 may effectuate or facilitate at least some degree of permanent, essentially permanent, or long term rehabilitation or restoration of a patient's ability to perform one or more types of physical and/or cognitive functions that had been lost or degraded due to neurological damage or a neurological disorder. A limited duration treatment program 110 may alternatively or additionally effectuate or facilitate at least some degree of permanent, essentially permanent, or long term development, acquisition, and/or establishment of a patient's ability to perform one or more types of physical and/or cognitive functions that had been at least partially absent or impaired as a result of a neurological malfunction. Therefore, the treatment program 110 need not be directed toward managing a chronic condition that exists over a very long period of time or throughout a patient's life. Rather, the treatment program 110 may be applied over a limited time that corresponds to the extent of the patient's recovery or functional gain(s). For example, the treatment program 110 may occur over a period of six weeks, three months, six months, one year, three years, or another limited timeframe. Alternatively or additionally, the treatment program 110 may be applied over a predetermined number of treatment sessions, for example, twenty, thirty, fifty, or some other number of treatment sessions in total. Another aspect may limit the duration of the treatment program to an accumulated or aggregate time that stimulation has been applied over some number of treatment sessions. An exemplary treatment program 110 may include one to four or more hours of electrical stimulation per stimulation session, three to seven stimulation sessions per week, throughout a therapy period of one to six or more weeks. Alternatively, a treatment program 110 may apply continuous or essentially continuous neural stimulation during one or more portions of a therapy period. The overall length or duration of the treatment program 110 (i.e., the therapy period), and possibly the type(s) and/or location(s) of applied neural stimulation, may depend upon the nature, number, and/or severity of the patient's functional deficits, as well as a degree of patient recovery or functional development.
The stimulating procedure 106 may further include an assessing procedure 112 for determining the extent of the patient's functional rehabilitation, recovery, and/or development at particular intervals or over time. Such intervals may be, for example, every n weeks, or every kth treatment session. The assessing procedure 112 may involve rating or measuring the patient's physical and/or cognitive abilities in accordance with one or more standard functional measures or tests. Such functional measures may include or be based upon, for example, a Fugl-Meyer Assessment of Sensorimotor Impairment; a National Institute of Health (NIH) Stroke Scale; a Stroke Impact Scale (SIS); an ADL scale; a Quality of Life (QoL) scale; physical measures such as grip strength or finger tapping speed; a neuropsychological testing battery; a walking, movement, and/or dexterity test; a behavioral test; a language test; a comprehension test; and/or other measures of patient functional ability. The assessing procedure 112 may additionally or alternatively include one or more neural imaging procedures. The assessing procedure 112 can also be used to determine the severity of the patient's functional deficits or other neurological conditions at the beginning and throughout the therapy period.
In one embodiment, the stimulating procedure 106 may include an analyzing procedure 114 for examining results obtained from one or more assessing procedures 112. The analyzing procedure 114 may involve data analysis and/or trend analysis techniques. In the event that the patient's functional development and/or recovery has significantly slowed or plateaued, but further recovery may be likely or possible, the stimulating procedure 106 may include a modification procedure 116 for changing, adjusting, or adapting the limited duration treatment program 110. The treatment program 110 may be changed, adjusted, or adapted by varying stimulation type(s), stimulation location(s), stimulation parameters, and/or particular synergistic or adjunctive therapies (e.g., behavioral therapies, activities, and/or tasks).
The stimulating procedure 106 may further include a determining procedure 118 for deciding whether to continue a treatment program 110. In the event that a treatment program 110 is not yet complete or has been modified or adjusted, the treatment program 110 may resume or restart. In the event that the patient has functionally developed and/or recovered to an intended, acceptable, or maximum extent, the stimulating procedure 106 may include a termination procedure 120 for discontinuing the treatment program 110. After the treatment program 110 is completed or discontinued, the patient's functional recovery or gains in functional ability may persist or be retained on a permanent, essentially permanent, or long term basis without further electrical stimulation therapy.
Various embodiments of the electrical stimulation methods described above may be useful for treating brain diseases, such as Alzheimer's, Parkinson's, and other brain diseases. In this application, a stimulation site can be identified by monitoring the neural activity using functional MRI or other suitable imaging techniques over a period of time to determine where the brain is recruiting material to perform the neural activity that is being affected by the disease. It may also be possible to identify a stimulation site by having the patient try to perform an act that the particular disease has affected, and monitoring the brain to determine whether any response neural activity is present in the brain. After identifying where the brain is recruiting additional matter, the electrical stimulation can be applied to this portion of the brain. It is expected that electrically stimulating the regions of the brain that have been recruited to perform the neural activity which was affected by the disease will assist the brain in offsetting the damage caused by the disease.
Various embodiments of the electrical stimulation methods described above are also expected to be useful for treating neurological disorders, such as depression, passive-aggressive behavior, weight control, and other disorders. In these applications, the electrical stimulation can be applied to a stimulation site in the cortex or another suitable part of the brain where neural activity related to the particular disorder is present. The embodiments of electrical stimulation methods for carrying out the particular therapy can be adapted to either increase or decrease the particular neural activity in a manner that produces the desired results. For example, an amputee may feel phantom sensations associated with the amputated limb. This phenomenon can be treated by applying an electrical pulse that reduces the phantom sensations. The electrical therapy can be applied so that it will modulate the ability of the neurons in that portion of the brain to execute sensory functions.
b. Pulse Forms and Potentials
The electrical stimulation methods in accordance with the invention can use several different pulse forms to effectuate the desired neuroplasticity. The pulses can be a bi-phasic or monophasic stimulus that is applied to achieve a desired potential in a sufficient percentage of a population of neurons at the stimulation site. In one embodiment, the pulse form has a frequency of approximately 2-1000 Hz, but the frequency may be particularly useful in the range of approximately 40-200 Hz. For example, initial clinical trials are expected to use a frequency of approximately 50-100 Hz. The pulses can also have pulse widths of approximately 10 μs-100 ms, or more specifically the pulse width can be approximately 20-200 μs. For example, a pulse width of 50-100 μs may produce beneficial results.
It is expected that one particularly useful application of the invention involves enhancing or inducing neuroplasticity by raising the resting membrane potential of neurons to bring the neurons closer to the threshold level for firing an action potential. Because the stimulation raises the resting membrane potential of the neurons, it is expected that these neurons are more likely to “fire” an action potential in response to excitatory input at a lower level.
The actual electrical potential applied to electrodes implanted in the brain to achieve a subthreshold potential stimulation will vary according to the individual patient, the type of therapy, the type of electrodes, and other factors. In general, the pulse form of the electrical stimulation (e.g., the frequency, pulse width, wave form, and voltage potential) is selected to raise the resting potential in a sufficient number neurons at the stimulation site to a level that is less than a threshold potential for a statistical portion of the neurons in the population. The pulse form, for example, can be selected so that the applied voltage of the stimulus achieves a change in the resting potential of approximately 10%-95%, and more specifically of 60%-80%, of the difference between the unstimulated resting potential and the threshold potential.
In one specific example of a subthreshold application for treating a patient's hand, electrical stimulation is not initially applied to the stimulation site. Although physical therapy related to the patient's hand may cause some activation of a particular population of neurons that is known to be involved in “hand function,” only a low level of activation might occur because physical therapy only produces a low level of action potential generation in that population of neurons. However, when the subthreshold electrical stimulation is applied, the resting membrane potentials of the neurons in the stimulated population are elevated. These neurons now are much closer to the threshold for action potential formation such that when the same type of physical therapy is given, this population of cells will have a higher level of activation because these cells are more likely to fire action potentials.
Subthreshold stimulation may produce better results than simply stimulating the neurons with sufficient energy levels to exceed the threshold for action potential formation. One aspect of subthreshold stimulation is to increase the probability that action potentials will occur in response to the ordinary causes of activation —such as physical therapy. This will allow the neurons in this functional network to become entrained together, or “learn” to become associated with these types of activities. If neurons are given so much electricity that they continually fire action potentials without additional excitatory inputs (suprathreshold stimulation), this will create “noise” and disorganization that will not likely cause improvement in function. In fact, neurons that are “overdriven” soon deplete their neurotransmitters and effectively become silent.
The application of a subthreshold stimulation is very different than suprathreshold stimulation. Subthreshold stimulation in accordance with several embodiments of the invention, for example, does not intend to directly make neurons fire action potentials with the electrical stimulation in a significant population of neurons at the stimulation site. Instead, subthreshold stimulation attempts to decrease the “activation energy” required to activate a large portion of the neurons at the stimulation site. As such, subthreshold stimulation in accordance with certain embodiments of the invention is expected to increase the probability that the neurons will fire in response to the usual intrinsic triggers, such as trying to move a limb, physical therapy, or simply thinking about movement of a limb, etc. Moreover, coincident stimulation associated with physical therapy is expected to increase the probability that the action potentials that are occurring with an increased probability due to the subthreshold stimulation will be related to meaningful triggers, and not just “noise.”
The stimulus parameters set forth above, such as a frequency selection of approximately 50-100 Hz and an amplitude sufficient to achieve an increase of 60% to 80% of the difference between the resting potential and the threshold potential are specifically selected so that they will increase the resting membrane potential of the neurons, thereby increasing the likelihood that they will fire action potentials, without directly causing action potentials in most of the neuron population. In addition, and as explained in more detail below with respect to
B. Devices for Electrically Stimulating Regions of the Brain
1. Implantable Stimulation Apparatus with Integrated Pulse Systems
The embodiment of the stimulation apparatus 600 shown in
Several embodiments of the stimulation apparatus 600 are expected to be more effective than existing transcranial electrical stimulation devices and transcranial magnetic stimulation devices. It will be appreciated that much of the power required for transcranial therapies is dissipated in the scalp and skull before it reaches the brain. In contrast to conventional transcranial stimulation devices, the stimulation apparatus 600 is implanted so that the electrodes are at least proximate to the pial surface of the brain 708. Several embodiments of methods in accordance with the invention can use the stimulation apparatus 600 to apply an electrical therapy directly to the pia mater 708, the dura mater 706, and/or another portion of the cortex 709 at significantly lower power levels than existing transcranial therapies. For example, a potential of approximately 1 mV to 10 V can be applied to the electrodes 660; in many instances a potential of 100 mV to 5 V can be applied to the electrodes 660 for selected applications. It will also be appreciated that other potentials can be applied to the electrodes 660 of the stimulation apparatus 600 in accordance with other embodiments of the invention.
Selected embodiments of the stimulation apparatus 600 are also capable of applying stimulation to a precise stimulation site. Again, because the stimulation apparatus 600 positions the electrodes 660 at least proximate to the pial surface 708, precise levels of stimulation with good pulse shape fidelity will be accurately transmitted to the stimulation site in the brain. It will be appreciated that transcranial therapies may not be able to apply stimulation to a precise stimulation site because the magnetic and electrical properties of the scalp and skull may vary from one patient to another such that an identical stimulation by the transcranial device may produce a different level of stimulation at the neurons in each patient. Moreover, the ability to focus the stimulation to a precise area is hindered by delivering the stimulation transcranially because the scalp, skull and dura all diffuse the energy from a transcranial device. Several embodiments of the stimulation apparatus 600 overcome this drawback because the electrodes 660 are positioned under the skull 700 such that the pulses generated by the stimulation apparatus 600 are not diffused by the scalp 702 and skull 700.
2. Integrated Pulse Systems for Implantable Stimulation Apparatus
The pulse system 630 shown in
Referring to
The pulse system 1200 can be housed within the stimulation apparatus 600 (not shown). In one embodiment, the pulse system 1200 includes an antenna 1260 and a pulse delivery system 1270. The antenna 1260 incorporates a diode (not shown) that rectifies the broadcast RF energy from the antenna 1242. The pulse delivery system 1270 can include a filter 1272 and a pulse former 1274 that forms electrical pulses which correspond to the RF energy broadcast from the antenna 1242. The pulse system 1200 is accordingly powered by the RF energy in the pulse signal from the external controller 1210 such that the pulse system 1200 does not need a separate power supply carried by the stimulation apparatus 600.
The pulse system 1300 can include a ferrite core 1360 and a coil 1362 wrapped around a portion of the ferrite core 1360. The pulse system 1310 can also include a pulse delivery system 1370 including a rectifier and a pulse former. In operation, the ferrite core 1360 and the coil 1362 convert the changes in the magnetic field generated by the magnetic coupler 1350 into electrical pulses that are sent to the pulse delivery system 1370. The electrodes 660 are coupled to the pulse delivery system 1370 so that electrical pulses corresponding to the electrical pulses generated by the pulse generator 1330 in the external controller 1310 are delivered to the stimulation site on the patient.
3. Electrode Configurations
Several embodiments of the stimulation apparatus described above with reference to
4. Implantable Stimulation Apparatus with Biasing Elements
Although several embodiments of the stimulation apparatus shown in
5. Implantable Stimulation Apparatus with External Pulse Systems
The stimulation apparatus 3100, however, does not have an internal pulse system carried by the portion of the device that is implanted in the skull 700 of the patient 500. The stimulation apparatus 3100 receives electrical pulses from an external pulse system 3130. The external pulse system 3130 can have an electrical connector 3132 with a plurality of contacts 3134 configured to engage the contacts within the receptacle 3120. The external pulse system 3130 can also have a power supply, controller, pulse generator, and pulse transmitter to generate the electrical pulses. In operation, the external pulse system 3130 sends electrical pulses to the stimulation apparatus 3100 via the connector 3132, the receptacle 3120, and the lead line 3124.
Referring to
6. Alternate Embodiments of Implantable Stimulation Apparatus
In one embodiment, the stimulation apparatus 3600 can receive electrical pulses from an external controller 3630. For example, the external controller 3630 can be electrically coupled to the stimulation apparatus 3600 by a lead line 3632 that passes through a hole 711 in the skull 700. In an alternative embodiment, the stimulation apparatus 3600 can include an integrated pulse system similar to the pulse systems described above with reference to
The stimulation apparatus 4100 illustrated in
The limiting module 4112 provides a limited duration treatment that terminates operation of the signal general 4130 or otherwise disconnects the signal generator 4130 from either the power supply 4120 or the electrode array. The limiting module 4112 can be a hardware or software switch. In one embodiment, the limiting module causes the controller 4110 to deactivate the signal generator 4130 so that the signal generator 4130 does not produce signals after expiration of the therapy period. The limiting module 4112 can also be a hardware or software switch in the controller 4110 that disconnects the power supply 4120 from the signal generator 4130. In another embodiment, the limiting module 4112 can be a hardware or software switch that disconnects the signal generator 4130 from the electrode array.
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.
Claims
1-28. (Cancelled)
29. A method for effectuating a neural-function affected by a stroke, comprising:
- determining a therapy period during which at least one therapy session is to be performed to recover and/or develop the neural-function affected by the stroke;
- identifying a stimulation site at the cortex associated with the neural-function affected by the stroke;
- applying electrical stimulation to the stimulation site at the cortex; and
- preventing the electrical stimulation from being delivered to the stimulation site at the cortex.
30. The method of claim 29 wherein determining the therapy period comprises setting a limiting module to terminate stimulation after a period from approximately one day to not more than one year.
31. The method of claim 29 wherein determining the therapy period comprises setting a limiting module to terminate stimulation after a period from approximately one day to not more than one month.
32. The method of claim 29 wherein determining the therapy period comprises setting a limiting module to terminate stimulation after a period from approximately one day to not more than one week.
33. The method of claim 29 wherein preventing the electrical stimulation from being delivered to the stimulation site comprises setting a limiting module to terminate stimulation after a predetermined number of therapy sessions.
34. The method of claim 29 wherein the electrical stimulation is applied by a stimulation apparatus having a housing implanted in the patient, a power supply in the housing, and a pulse generator in the housing, and wherein preventing the electrical stimulation from being delivered to the stimulation site comprises activating a switch that prevents electrical pulses from being sent to an electrode array.
35. The method of claim 34 wherein activating the switch comprises activating a hardware switch in the stimulation apparatus.
36. The method of claim 34 wherein activating the switch comprises activating a software switch.
37. A method for recovering a neural-function affected by a stroke, comprising:
- applying electrical stimulation to a cortical stimulation site selected to promote recovery of the affected neural-function in accordance with a predetermined therapy plan having a defined therapy period, the cortical stimulation site being at least proximate to the cortex; and
- precluding the electrical stimulation from being applied to the cortical stimulation site after expiration of the therapy period.
38. The method of claim 37, further comprising determining the therapy period by setting a limiting module to terminate stimulation after a period from approximately one day to not more than one year.
39. The method of claim 37, further comprising determining the therapy period by setting a limiting module to terminate stimulation after a period from approximately one day to not more than one month.
40. The method of claim 37, further comprising determining the therapy period by setting a limiting module to terminate stimulation after a period from approximately one day to not more than one week.
41. The method of claim 37 wherein precluding the electrical stimulation from being delivered to the stimulation site comprises setting a limiting module to terminate stimulation after a predetermined number of therapy sessions.
42. The method of claim 37 wherein the electrical stimulation is applied by a stimulation apparatus having a housing implanted in the patient, a power supply in the housing, and a pulse generator in the housing, and wherein precluding the electrical stimulation from being delivered to the stimulation site comprises activating a switch that prevents electrical pulses from being sent to an electrode array.
43. The method of claim 42 wherein activating the switch comprises activating a hardware switch in the stimulation apparatus.
44. The method of claim 42 wherein activating the switch comprises activating a software switch.
45. A method for recovering a neural-function impaired by a stroke, comprising:
- implanting an electrode at a cortical stimulation site selected to promote recovery of the impaired neural-function, the cortical stimulation site being at least proximate to the cortex;
- applying electrical stimulation to the cortical stimulation site in accordance with a predetermined therapy plan having a defined therapy period;
- performing an adjuctive therapy related to a body part affected by the stroke; and
- precluding the electrical stimulation from being applied to the cortical stimulation site after expiration of the therapy period.
46. The method of claim 45 wherein the adjunctive therapy comprises electrically stimulating the body part.
47. The method of claim 45 wherein the adjunctive therapy comprises electrically stimulation the body part while electrically stimulating the cortical stimulation site.
48. The method of claim 45 wherein the adjuctive therapy comprises moving the body part.
49. The method of claim 45 wherein the adjuctive therapy comprises moving the body part while electrically stimulating the cortical stimulation site.
50. The method of claim 45 wherein implanting the electrode comprises placing the electrode proximate to the dura mater at the cortex.
51. The method of claim 45 wherein implanting the electrode comprises placing the electrode in contact with the dura mater at the cortex.
52. The method of claim 45 wherein implanting the electrode comprises placing the electrode proximate to the pia mater at the cortex.
53. The method of claim 45 wherein implanting the electrode comprises placing the electrode in contact with the pia mater at the cortex.
54. The method of claim 45 wherein implanting the electrode comprises positioning the electrode at the supplementary motor cortex anterior to a location of the stroke.
55. The method of claim 45 wherein electrically stimulating the cortical stimulation site comprises passing an anodic current through the electrode.
56. The method of claim 45 wherein electrically stimulating the cortical stimulation site comprises passing a cathodic current through the electrode.
57. The method of claim 45 wherein applying electrical stimulation comprises applying a signal having a voltage of approximately 50 mV to 5V directly to the cortex at the cortical stimulation site.
58. The method of claim 45 wherein applying electrical stimulation comprises applying a signal having a voltage effective to raise an expected resting potential of a population of neurons at the stimulation site by at least approximately 10% of a difference between the expected resting potential and an action potential for the population of neurons.
59. The method of claim 45 wherein applying electrical stimulation comprises applying a signal having a voltage effective to raise an expected resting potential of a population of neurons at the stimulation site by at least approximately 60% of a difference between the expected resting potential and an action potential for the population of neurons.
60. The method of claim 45 wherein applying electrical stimulation comprises applying a signal having a voltage effective to raise an expected resting potential of a population of neurons at the stimulation site by at least approximately 10-80% of a difference between the expected resting potential and an action potential for the population of neurons.
61. The method of claim 45 wherein applying electrical stimulation comprises applying a signal having a frequency of approximately 40-200 HZ.
62. The method of claim 45 wherein applying electrical stimulation comprises applying a signal having a frequency of approximately 50 HZ.
Type: Application
Filed: Aug 6, 2004
Publication Date: Jan 27, 2005
Inventors: Andrew Firlik (New Cannan, CT), Jeffrey Balzer (Allison Park, PA), Bradford Gliner (Sammamish, WA), Alan Levy (Bellevue, WA)
Application Number: 10/913,183