Abstract:
A method of performing a medical procedure on a patient comprises forming a burr hole through the cranium of the patient, mounting a permanently integrated plug electrode within the burr hole, and electrically coupling the plug electrode to an electronics device. Another method of performing a medical procedure on a patient comprises forming a burr hole through the cranium of the patient, mounting an electrode within the burr hole, such that the electrode does not extend within the brain of the patient, and electrically coupling the electrode to an electronics device. A hybrid plug/electrode comprises a plug body configured for being anchored within a burr hole formed within a cranium of a patient, at least one electrode disposed on a distal-facing surface of the plug body, and at least one electrode lead affixed within the plug body in electrical communication with the at least one electrode.

Description:
FIELD OF THE INVENTION 
       [0001]    The present inventions relate to burr hole plugs used to seal and secure electrical stimulation leads and electrodes within a cranial burr hole. 
       BACKGROUND OF THE INVENTION 
       [0002]    Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. For example, it is known to use such systems to treat neurological disorders, such as neurodegenerative diseases (e.g., Alzheimer&#39;s Disease, Parkinson&#39;s Disease, tremor, and epilepsy), brain ischemia, such as stroke, and limbic disorders, as well as non-neurological disorders, such as migraine headaches, obesity, and pain syndromes (such as trigeminal neuralgia) by electrically stimulating selected portions of the brain. While deep brain stimulation (DBS) procedures have been the focus of attention in treating many of these neurological disorders, there have been some considerable developments in cortical brain stimulation procedures, wherein the cortical brain tissue is stimulated to rehabilitate stroke victims, provide pain relief, as well as to provide benefits in the treatment of the other aforementioned disorders. 
         [0003]    A typical implantable neurostimulation system used to electrically stimulate brain tissue includes electrodes, which are implanted at the desired stimulation site in the brain of the patient (in the case of cortical brain stimulation, along the cortex of the brain), and a neurostimulator implanted remotely from the stimulation site (e.g., in the chest region of the patient), but coupled either directly to the electrodes via one or more leads. The neurostimulation system may further comprise a handheld remote control (RC) to remotely instruct the neurostimulator to generate electrical stimulation pulses in accordance with selected stimulation parameters. The RC may, itself, be programmed by a technician attending the patient, for example, by using a Clinician&#39;s Programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon. 
         [0004]    In cortical stimulation procedures, it is typically necessary to place a variety of stimulation electrodes, as well as recording electrodes, along the surface of the cortex. Thus, to provide broad access to the cortex, a craniotomy, which is a relatively invasive procedure that involves removing a large portion of the cranium (referred to as a “turning a bone flap”) and then putting the bone flap back into place after the electrodes have been affixed along the cortex, must be performed on the patient. Alternatively, multiple burr holes can be meticulously cut through the cranium, so that the stimulation/recording electrodes can be placed through the burr holes into contact with the various target sites of the cortex. Titanium or stainless steel bands or a cranial burr hole plug can then be installed over or within each burr hole used during the implantation procedure to hold the electrode in place, as well as to seal the burr hole. A typical burr hole plug includes a multitude of components, including a ring-shaped base that is anchored to the cranium typically using screws, retainer that is integrated with the plug base to secure the electrode in place, and a cap that fits over the plug base to seal the burr hole and/or further secure the electrode in place. 
         [0005]    While providing access to the various target sites of the brain cortex using multiple burr holes is less invasive than performing a craniotomy, the size of the burr holes are still relatively large (typically, 14-15 mm in diameter). In addition to meticulously drilling each burr hole in the cranium, the different components of each burr hole plug must be assembled within the respective burr hole, while maintaining the stimulation lead in place, thereby further increasing the procedure time. 
         [0006]    There, thus, remains a need for a less invasive and efficient means for providing access to, and implanting electrodes adjacent the brain of a patient. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with a first aspect of the present inventions, a method of performing a medical procedure on a patient is provided. The method comprises forming a burr hole through the cranium of the patient. To minimize the invasiveness of the medical procedure, the diameter of the burr hole may be less than 10 mm, and even less than 5 mm. The method further comprises mounting an integrated plug electrode within the burr hole (e.g., by screwing the plug electrode into the burr hole). 
         [0008]    In one method, the plug electrode has at least one electrode formed on an external surface of the plug electrode. In another method, the plug electrode has at least one electrode that is disposed within the burr hole when the plug electrode is mounted within the burr hole. In still another method, a proximal portion of the plug electrode is electrically insulated from the patient, and a distal portion of the plug electrode is exposed to form at least one electrode. In yet another method, the burr hole is formed within the cranium of the patient and the plug electrode is mounted within the burr hole by screwing the plug electrode directly into the cranium of the patent. 
         [0009]    The method further comprises electrically coupling the plug electrode to an electronics device (e.g., a neurostimulator and/or electrical signal recorder). In one method, electrically coupling the plug electrode to the electronics device comprises connecting an electrical lead between the plug electrode and the electronics device. In an optional method, the electronics device is a neurostimulator, and the method further forming another burr hole through the cranium of the patient, mounting another electrode within the other burr hole, such that the other electrode does not extend within the brain the patient, and electrically coupling the other electrode to an electrical signal recorder. 
         [0010]    In accordance with a second aspect of the present inventions, another method of performing a medical procedure on a patient is provided. The method comprises forming a burr hole through the cranium of the patient. To minimize the invasiveness of the medical procedure, the diameter of the burr hole may be less than 10 mm, and even less than 5 mm. The method further comprises mounting an electrode within the burr hole, such that the electrode does not extend into the brain of the patient. In one method, a plug is mounted within the burr hole to secure the electrode within the burr hole. In one example, the plug and electrode form an integrated plug electrode that is mounted within the burr hole to secure the electrode within the burr hole. In another example, the electrode is carried by a lead, and the lead is affixed within the plug to secure the electrode within the burr hole. 
         [0011]    The method further comprises electrically coupling the electrode to an electronics device. In an optional method, the electronics device is a neurostimulator, and the method further forming another burr hole through the cranium of the patient, mounting another electrode within the other burr hole, such that the other electrode does not extend within a cranial cavity of the patient, and electrically coupling the other electrode to an electrical signal recorder. 
         [0012]    In accordance with a third aspect of the present invention, a hybrid plug/electrode comprises a plug body configured for being anchored within a burr hole formed within a cranium of a patient. In one embodiment, the plug body comprises a cylindrical outer wall configured for engaging an inner surface of the burr hole. In another embodiment, the plug body comprises at least one fastening mechanism (e.g., a thread) disposed on the cylindrical outer wall for anchoring the plug body to the inner surface of the burr hole. The hybrid plug/electrode further comprises at least one electrode disposed on a distal-facing surface of the plug electrode, and at least one electrode lead affixed within the plug body in electrical communication with the electrode(s). In the case where a plurality of electrodes is provided, a plurality of electrical leads can be respectively coupled to the electrodes. The hybrid plug/electrode further comprises a connector affixed to the plug body in electrical communication with the electrode lead(s). The connector is configured for being externally accessible when the plug body is anchored within the burr hole. The connector may be configured for receiving a lead extension. 
         [0013]    The hybrid plug/electrode can be used in various systems and methods. For example, a medical system may have the hybrid plug/electrode and an electronics device coupled to the one or more electrode leads. A method of performing a medical procedure on a patient may comprise forming the burr hole through the cranium of the patient, anchoring the hybrid plug/electrode within the burr hole, and electrically coupling the hybrid plug/electrode to an electronics device. Another method of performing a medical procedure on a patient may comprise conveying electrical energy from the electrode(s) of the hybrid plug/electrode to stimulate cortical brain tissue of the patient. Still another method of performing a medical procedure on a patient may comprise recording electrical signals from the cortical brain tissue using the electrode of the hybrid plug/electrode. 
         [0014]    Other and further aspects and features of the invention will be evident from reading the following detailed description of the embodiments, which are intended to illustrate, not limit, the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The drawings illustrate the design and utility of preferred embodiments of the present invention, in which similar elements are referred to by common reference numerals. In order to better appreciate how the above-recited and other advantages and objects of the present inventions are obtained, a more particular description of the present inventions briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0016]      FIG. 1  is a plan view of a cortical brain stimulation system implanted within a patient; 
           [0017]      FIG. 2  is a plan view of exemplary stimulation and recording sites of a patient where electrodes of the cortical brain stimulation system of  FIG. 1  may be implanted 
           [0018]      FIG. 3  is a cross-sectional view of one embodiment of a hybrid plug/electrode array that can be used in the cortical brain stimulation system of  FIG. 1 ; 
           [0019]      FIG. 4  is a cross-sectional view of one embodiment of a minimally invasive plug electrode that can be used in the cortical brain stimulation system of  FIG. 1 ; 
           [0020]      FIG. 5  is a cross-sectional view of another embodiment of a minimally invasive plug electrode that can be used in the cortical brain stimulation system of  FIG. 1 ; 
           [0021]      FIG. 6  is a cross-sectional view of still another embodiment of a minimally invasive plug electrode that can be used in the cortical brain stimulation system of  FIG. 1 ; 
           [0022]      FIG. 7  is a cross-sectional view of yet another embodiment of a minimally invasive plug electrode that can be used in the cortical brain stimulation system of  FIG. 1 ; 
           [0023]      FIG. 8  is a cross-sectional view of yet another embodiment of a minimally invasive plug electrode that can be used in the cortical brain stimulation system of  FIG. 1 ; and 
           [0024]      FIG. 9  is a top view of the minimally invasive plug electrode of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    Turning first to  FIG. 1 , an exemplary cortical brain stimulation system  10  constructed and arranged in accordance with one embodiment of the present inventions is shown implanted within a patient for the treatment of a debilitating disease such as, Parkinson&#39;s disease, dystonia, essential tremor, seizure disorders, obesity, depression, etc. The system  10  comprises a hybrid plug/electrode array  12  and a plurality of minimally invasive plug electrodes  14  implanted within the head  2  of a patient  1  for both stimulating and recording electrical signals from the cortical brain tissue (not shown in  FIG. 1 ). Both of the hybrid plug/electrode array  12  and plug electrodes  14  can be considered plug electrodes, with the main difference being that the hybrid plug/electrode array  12  comprises a plurality of electrodes, whereas the plug electrodes  14  comprise a single electrode. As will be described in further detail below, the hybrid plug/electrode array  12  and plug electrodes  14  are mounted within the cranium of the patient in order to stimulate or record signals of the cortical brain tissue. 
         [0026]    As illustrated in  FIG. 2 , the hybrid plug/electrode array  12 , in one embodiment, is used to stimulate a portion of the cortical brain tissue at a stimulation site, and the plug electrodes  14  are used to record electrical signals at first and second recording sites of the cortical brain tissue. Thus, electrical stimulation energy can be conveyed from the hybrid plug/electrode array  12  into the cortical brain tissue to treat the disease, and electrical signals can be sensed at the plug electrodes  14  to monitor the disease. 
         [0027]    Alternatively, the hybrid plug/electrode array  12  can be used to record electrical signals from one of the two recording sites of the cortical brain tissue, and the plug electrodes  14  may be used to convey stimulation energy to the stimulation site of the cortical brain tissue. In another alternative embodiment, some of the plug electrodes  14  may be used to convey stimulation energy to the stimulation site of the cortical brain tissue, and others of the plug electrodes  14  may be used to record electrical signals from one or both of the recording sites of the cortical brain tissue. In an optional embodiment, the electrical signals sensed at the first and second recording sites can be used to modify or adjust stimulation parameters in accordance with which the stimulation energy is delivered from the plug/electrode array  12  to the stimulation site. Further details discussing this closed-loop manner of delivery stimulation energy to a patient are described in U.S. patent application Ser. No. ______ (Attorney Docket No. 06-00363-01), which is expressly incorporated herein by reference. 
         [0028]    The cortical brain stimulation system  10  further comprises an implantable electronics device  16 . In the illustrated embodiment, the electronics device  16  takes the form of a electronics device  16 , such as an implantable pulse generator (IPG), radio frequency (RF) receiver-stimulator, or any other device coupled to and capable of delivering electrical stimulation energy to the hybrid plug/electrode array  12  in a controlled and therapeutic manner. In the illustrated embodiment, the electronics device  16  may also include recording circuitry capable of processing electrical signals sensed at the plug electrodes  14 . In this manner, the electronics device  16  can be considered both a neurostimulator and a recorder. Alternatively, separate neurostimulator and recording devices can be utilized. In any event, the cortical brain stimulation system  10  further comprises a plurality of individual electrical leads  18  respectively coupled to the hybrid plug/electrode array  12  and plug electrodes  14 , a connector hub  20  that receives the ends of the electrical leads  18 , and a lead extension  22  coupled between the connector hub  20  and the electronics device  16 . As will be described, the electrical leads  18 , in certain cases, may carry electrodes that form portions of the plug electrodes  14 . 
         [0029]    The connector hub  20  may be implanted underneath the scalp of the patient, and the individual electrical leads  18  may be subcutaneously routed from the hybrid plug/electrode array  12  and plug electrodes  14  underneath the scalp, along external surface of the cranium of the patient, to the connector hub  20 . In this manner, the individual electrical leads  18  can be wired through the single lead extension  22 . The lead extension  22  may be subcutaneously advanced underneath the scalp of the patient  1  to the electronics device implantation site, thereby facilitating the location of the electronics device  16  away from the cranium of the patient. The electronics device  16  may be generally implanted in a surgically-made pocket in the torso of the patient (e.g., the chest or shoulder region). The electronics device  16  may, of course, also be implanted in other locations of the patient&#39;s body. In alternative embodiments, the electronics device  16  may be directly implanted on or within the cranium of the patient  1 , as described in U.S. Pat. No. 6,920,359, which is expressly incorporated herein by reference. In this case, the lead extension  22  may not be needed. The system  10  may include external components, such as a patient handheld programmer, a clinician programming station, and an external charger (all not shown), the details of which will not be described herein for purposes of brevity. 
         [0030]    Turning now to  FIG. 3 , the hybrid plug/electrode array  12  will now be described. As there shown, the hybrid plug/electrode array  12  is mounted within a burr hole  4  conventionally formed through the cranium  3  of the patient  1 . The hybrid plug/electrode array  12  comprises a plug body  24  that is sized to firmly fit within the burr hole  4 , thereby firmly anchoring the hybrid plug/electrode array  12  to the cranium  3  and preventing leakage of cerebral spinal fluid between the outer surface of the plug body  24  and the burr hole  4 . To this end, the plug body  24  has a cylindrical outer wall  26  having an outer diameter substantially the same as the diameter of the burr hole  4 . The burr hole  4  may have a conventional size; for example, over 10 mm in diameter, and typically between 14-15 mm in diameter. The plug body  24  comprises a fastener, and in particular, a thread  28  disposed on the outer surface of the cylindrical wall  26 , for engaging the inner surface of the burr hole  4 , and thereby, anchoring the hybrid plug/electrode array  12  within the burr hole  4 . In this manner, the hybrid plug/electrode array  12  may be conveniently screwed into the burr hole  4 . Alternatively, other types of fastening means, such as sutures or bone screws, can be used to anchor the hybrid plug/electrode array  12  to the cranium  3 . 
         [0031]    The plug body  24  further comprises a distal surface  30  that faces the cortical brain tissue  5  of the patient  1  when the hybrid plug/electrode array  12  is anchored within the burr hole  4 . In the illustrated embodiment, the distal surface  30  of the plug body  24  is flat, although in alternative embodiments, may be concave or convex. The height of the plug body  24  has a relatively small profile, such that the distal surface  30  does not protrude into the cranial cavity of the patient (i.e., does not extend past the inner surface of the cranium  3 ) when the hybrid plug/electrode array  12  is anchored within the burr hole  4 . For example, as shown in  FIG. 3 , the distal surface  30  is recessed relative to the inner surface of the cranium  3 . In some cases, it may be desirable for the hybrid plug/electrode array  12  to extend into the cranial cavity and sit or push gently on the dura mater, thus placing the active portion of the hybrid plug/electrode array  12  closer to the target neural tissue. 
         [0032]    The plug body  24  may be composed of a suitable hard biocompatible material, such as titanium, stainless steel (e.g., MP35N), alloys, or hard polymers (e.g., a high durometer silicone, polyurethane, or polyethertheterketone (PEEK)). If the plug body  24  is composed of an electrically conductive material, the hybrid plug/electrode array  12  may comprise an electrically insulative coating (not shown) disposed on the outer surface of the plug body  24  to ensure that the cranium  3  is electrically insulated from the hybrid plug/electrode array  12  and to minimize noise from electromyograms (EMGs) during recording. 
         [0033]    The hybrid plug/electrode array  12  further comprises a plurality of electrodes  32  suitably mounted to the distal surface  30  of the plug body  24 , such that the electrodes  32  face the cortical brain tissue  5 . As shown, because the distal surface  30  of the plug body  24  is recessed within the burr hole  4 , the electrodes  32  are likewise recessed within the burr hole  4 . Although the electrodes  32  are not in direct contact with the cortical brain tissue  5 , they are still electrically coupled to the cortical brain tissue  5  via the dura mater  6  and cerebrospinal fluid  7 . Thus, the electrodes  32  may potentially convey electrical stimulation energy (originating from the electronics device  16 ) to the cortical brain tissue  5  or receive electrical signals from the cortical brain tissue  5  for subsequent processing in the electronics device  16 . The electrodes  32  may be disposed on the distal surface  30  of the plug body  24  in any conventional manner (e.g., electroplating, sputtering, or bonding), and may be composed of any suitable biocompatible, electrically conductive material, such as stainless steel or a platinum alloy. 
         [0034]    The hybrid plug/electrode array  12  further comprises an electrical connector  34  and a plurality of electrode leads  36  (shown in phantom) extending between the electrical connector  34  and the respective electrodes  32 . In the illustrated embodiment, the electrical connector  34  takes the form of a connector header that is affixed to the top of the plug body  24  using suitable means, such as welding. Alternatively, the electrical connector  34  may be formed as a portion of the plug body  24 . The electrical connector  34  includes electrical terminals (not shown) that are external accessible when the hybrid plug/electrode array  12  is anchored within the burr hole  4 . In this manner, the respective electrical lead  18  may be mated with the electrical connector  34 , such that electrical contacts (not shown) located on the proximal end of the electrical lead contact the electrical terminals of the electrical connector  34 . The electrical lead  18  that is coupled to the hybrid plug/electrode array  12  comprises a plurality of insulated wires (not shown)—one for each electrical contact. 
         [0035]    The electrode leads  36  extend through the plug body  24  between the respective electrodes  32  to the electrical connector  34  in contact with the electrical terminals. The electrode leads  36  may be suitably coupled to the electrodes  32  and connector  34 , e.g., using soldering. If the plug body  24  is composed of an electrically conductive material, each of the electrode leads  36  may have an electrically insulative coating (not shown) to prevent electrical shorting between the electrode leads  36  and the plug body  24 . In the illustrated embodiment, the number of electrode leads  36  equals the number of electrodes  32 , such that each electrode lead  36  is connected to a respective one of the electrodes  32 . In an alternative embodiment, the number of electrode leads  36  may be less or more than the number of electrodes  32 . For example, there may be many electrode leads  36  and a single electrode  32 , or there may be many electrodes  32  and a single electrode lead  36 . 
         [0036]    Referring now to  FIGS. 4-9 , various embodiments of the minimally invasive plug electrodes  14  will now be described. Each of the plug electrodes  14  may be configured for being anchored within a very small burr hole  8  formed within the cranium  3 , thereby minimizing the trauma caused to the patient  1 . The diameter of the burr hole  8  is preferably less than 10 mm, and more preferably less than 5 mm. Like the hybrid plug/electrode array  12 , each plug electrode  14  is sized to be firmly secured within the respective burr hole  8 , without extending into the brain of the patient, and in these illustrated cases, without extending within the cranial cavity of the patient. 
         [0037]    Referring specifically to  FIG. 4 , one embodiment of a minimally invasive plug electrode  14 ( 1 ) will now be described. The plug electrode  14 ( 1 ) comprises a plug body  40  that includes comprises a shaft  42  configured for being mounted within the burr hole  8  and a head  44  that is externally accessible when the plug body  40  is anchored within the burr hole  8 . The plug body  24  comprises a fastener, and in particular, a thread  46  disposed on the outer surface of the shaft  42  for engaging the inner surface of the burr hole  8 , and thereby, anchoring the plug electrode  14 ( 1 ) within the burr hole  8 . 
         [0038]    The distal end of the shaft  42  is preferably blunt to ensure that the cortical brain tissue  5  is not pierced or otherwise damaged. The plug body  40  includes a tool engagement element  48  for engaging a tool (not shown) that can provide a mechanical advantage for rotation of the plug electrode  14 ( 1 ). In the illustrated embodiment, the tool engagement element  48  is a slotted recess for receiving a flathead screwdriver. Other types of tool engagement elements, such as a hex recess for receiving a hex wrench, a crossed recess for receiving a Phillips screwdriver, or a bolt head for receiving an open-ended wrench, box-end wrench, or socket wrench can also be used. Thus, it can be appreciated from the foregoing that the plug body  24  takes the form of a screw, which allows the plug electrode  14 ( 1 ) to be conveniently screwed into the burr hole  4 , which may be formed prior to screwing the plug electrode  14 ( 1 ) therein, or may be formed by screwing the plug electrode  14 ( 1 ) directed into the cranium  3 . 
         [0039]    The plug body  40  is composed of a suitable hard and electrically conductive biocompatible material, such as titanium, stainless steel (e.g., MP35N), or alloy. To ensure that the cranium  3  is electrically insulated from the electrically conductive plug body  40  and to minimize noise from electromyograms (EMGs) during recording, the plug electrode  14 ( 1 ) comprises a durable electrically insulative coating  50  (such as, e.g., epoxy or parylene) disposed on the outer surface of the plug body  24  (including the shaft  42  and head  44 ). Significantly, the distal end of the shaft  42  is left exposed to form an electrode  52  that faces the cortical brain tissue  5 . The plug electrode  14 ( 1 ) can be considered permanently integrated in that the plug body  40  and electrode  52  are either formed as a unibody design or are otherwise integrated in a manner (e.g., bonding) that would prevent them from being separated from each other without destroying or otherwise damaging the plug electrode  14 ( 1 ). 
         [0040]    As shown, the exposed electrode  52  is recessed within the burr hole  8 , and therefore, does not extend into the cranial cavity. Although the exposed electrode  52  is not in direct contact with the cortical brain tissue  5 , like the aforementioned electrode array  32  (shown in  FIG. 3 ), it is indirectly electrically coupled to the cortical brain tissue  5  via the dura mater  6  and cerebrospinal fluid  7 . Thus, the electrode  52  may potentially convey electrical stimulation energy (originating from the electronics device  16 ) to the cortical brain tissue  5  or receive electrical signals from the cortical brain tissue  5  for subsequent processing in the electronics device  16 . The electrical lead  18  may be connected to the head  42  of the plug body  40  using suitable means, such as soldering, tightening screws, or sutures. Thus, it can be appreciated that the electrical lead  18  is electrically coupled to the exposed electrode  52  via the shaft  42  of the plug body  40 . 
         [0041]    Referring to  FIG. 5 , another embodiment of a minimally invasive plug electrode  14 ( 2 ) will now be described. The plug electrode  14 ( 2 ) is similar to the plug electrode  14 ( 1 ) illustrated in  FIG. 4  in that it is permanently integrated. In particular, the plug electrode  14 ( 2 ) comprises a plug body  60  that includes a shaft  62  configured for being mounted within the burr hole  8  and a head  64  that is externally accessible when the plug body  40  is anchored within the burr hole  8 . The plug body  24  comprises a fastener, and in particular, a thread  66  disposed on the outer surface of the shaft  62  for engaging the inner surface of the burr hole  8 , and thereby, anchoring the plug electrode  14 ( 2 ) within the burr hole  8 . In this manner, the plug electrode  14 ( 2 ) may be conveniently screwed into the burr hole  4  much like the plug electrode  14 ( 1 ) described above. The distal end of the shaft  62  is preferably blunt to ensure that the cortical brain tissue  5  is not pierced or otherwise damaged. The plug body  40  includes a tool engagement element  68  for engaging a tool (not shown) that can provide a mechanical advantage for rotation of the plug electrode  14 ( 2 ). In the illustrated embodiment, the tool engagement element  68  a pair of slotted recesses for a special tool. Other types of tool engagement elements, such as those described above, can also be used. 
         [0042]    The plug electrode  14 ( 2 ) mainly differs from the plug electrode  14 ( 1 ) in that a portion of the plug body  60  is composed of an electrically insulative material. In particular, the plug electrode  14 ( 2 ) has a top portion  74  (including the head  64  and the proximal end of the shaft  62 ) that is composed of an electrically insulative material, such as PEEK, and a bottom portion  76  (the distal portion of the shaft  62 ) that is composed of a suitable hard and electrically conductive biocompatible material, such as titanium, stainless steel (e.g., MP35N), or alloy. The top portion  74  of the plug body  40  comprises a blind lumen  78  that houses an inner electrical conductor  80 . The distal end of the blind lumen  78  is open, such that the bottom portion  76  of the plug body  40  (i.e., the electrode) is in electrical communication with the inner conductor  80 , and the proximal end of the blind lumen  78  is closed. In the illustrated embodiment, the blind lumen  78 , and thus, the inner conductor  80 , are T-shaped. 
         [0043]    To ensure that the cranium  3  is electrically insulated from the electrically conductive top portion  74  of the plug body  40  and to minimize noise from electromyograms (EMGs) during recording, the plug electrode  14 ( 2 ) comprises a durable electrically insulative coating  70  (such as, e.g., epoxy or parylene) disposed on outer surface of the shaft  62 . Significantly, the distal end of the shaft  62  is left exposed to form an electrode  72  that faces the cortical brain tissue  5 . As shown, the exposed electrode  72  is recessed within the burr hole  8 , and therefore, does not extend into the cranial cavity. Although the exposed electrode  72  is not in direct contact with the cortical brain tissue  5 , like the aforementioned electrode array  32 , it is indirectly electrically coupled to the cortical brain tissue  5  via the dura mater  6  and cerebrospinal fluid  7 . Thus, the electrode  72  may potentially convey electrical stimulation energy (originating from the electronics device  16 ) to the cortical brain tissue  5  or receive electrical signals from the cortical brain tissue  5  for subsequent processing in the electronics device  16 . The electrical lead  18  may be connected to the inner conductor  80  within the plug body  60 , and in particular, the horizontal portion of the inner conductor  80 , via a solder or other suitable connection. Thus, it can be appreciated that the electrical lead  18  is electrically coupled to the exposed electrode  72  via the inner conductor  80  and the bottom portion  76  of the plug body  40 . 
         [0044]    Referring to  FIG. 6 , yet another embodiment of a minimally invasive plug electrode  14 ( 3 ) will now be described. The plug electrode  14 ( 3 ) is similar to the plug electrode  14 ( 1 ) illustrated in  FIG. 4  in that it comprises a plug body  90  that includes a shaft  92  configured for being mounted within the burr hole  8  and a head  94  that is externally accessible when the plug body  90  is anchored within the burr hole  8 . The plug body  90  comprises a fastener, and in particular, a thread  96  disposed on the outer surface of the shaft  92  for engaging the inner surface of the burr hole  8 , and thereby, anchoring the plug electrode  14 ( 3 ) within the burr hole  8 . In this manner, the plug electrode  14 ( 3 ) may be conveniently screwed into the burr hole  4 . The plug body  90  includes a tool engagement element  98  for engaging a tool (not shown) that can provide a mechanical advantage for rotation of the plug electrode  14 ( 3 ). In the illustrated embodiment, the tool engagement element is a slotted recess for receiving a flathead screwdriver, although other types of tool engagement elements, such as those described above, can also be used. 
         [0045]    The plug electrode  14 ( 3 ) mainly differs from the plug electrode  14 ( 1 ) in that it is not permanently integrated. In particular, the plug electrode  14 ( 3 ) includes an inner electrical conductor  104  concentrically and removably disposed within the plug body  90 . In particular, the plug body  90  comprises a lumen  106  extending vertically up the shaft  92  and then out the top of the head  94 . The inner conductor  104  takes the form of a screw that includes a shaft  108 , which is received within the lumen  106  of the plug body  90 , and a head  110  received within the tool engagement element  98  of the plug body  90 . The exterior surface of the shaft  104  of the inner conductor  104  and the inner surface of the lumen  106  include threads  112 , such that the inner conductor  104  can be screwed into the plug body  40  until the distal end of the shaft  108  of the inner conductor  104 , which forms an electrode  102 , distally protrudes from the distal end of the plug body  40 . The distal ends of the shaft  92  of the plug body  90  and shaft  108  of the inner conductor  104  are preferably blunt to ensure that the cortical brain tissue  5  is not pierced or otherwise damaged. The inner conductor  104  includes a tool engagement element  114  for engaging a tool (not shown) that can provide a mechanical advantage for rotation of the inner conductor  104  within plug body  90 . In the illustrated embodiment, the tool engagement element  114  is a slotted recess for receiving a flathead screwdriver, although other types of tool engagement elements, such as those described above, can also be used. 
         [0046]    The plug body  90  is composed of a suitable hard and electrically conductive biocompatible material, such as titanium, stainless steel (e.g., MP35N), or alloy. To ensure that the cranium  3  is electrically insulated from the electrically conductive plug body  90  and to minimize noise from electromyograms (EMGs) during recording, the plug electrode  14 ( 3 ) comprises a durable electrically insulative coating  100  (such as, e.g., epoxy or parylene) disposed on the outer surface of the plug body  90 . While only the head  94  of the plug body  90  is shown with the insulative coating  100 , the shaft  92  of the plug body  90  may have the insulative coating  100  as well. Alternatively, the plug body  90  may be composed of an electrically insulative material, in which case, the electrically insulative coating  100  may not be needed. 
         [0047]    As shown, the electrode  102  is recessed within the burr hole  8 , and therefore, does not extend into the cranial cavity. Although the electrode  102  is not in direct contact with the cortical brain tissue  5 , like the aforementioned electrode array  32 , it is indirectly electrically coupled to the cortical brain tissue  5  via the dura mater  6  and cerebrospinal fluid  7 . Thus, the electrode  102  may potentially convey electrical stimulation energy (originating from the electronics device  16 ) to the cortical brain tissue  5  or receive electrical signals from the cortical brain tissue  5  for subsequent processing in the electronics device  16 . 
         [0048]    In the case where the plug body  90  is composed of an electrically conductive material, the electrical lead  18  may be connected to the head  94  of the plug body  90  using suitable means, such as soldering, tightening screws, or suturing. In the case where the plug body  90  is composed of an electrically insulative material, the distal end of the electrical lead  18  may be inserted through a lumen (not shown) within the head  94  of the plug body  90  and connected to the inner conductor  104  using suitable means, such as soldering. Thus, it can be appreciated that the electrical lead  18 , when connected to the inner conductor  104  (either directly or indirectly through the plug body  90 ), will be electrically coupled to the exposed electrode  102 . 
         [0049]    It can be appreciated that the plug electrode  14 ( 3 ) is particularly advantageous in that the position of the electrode  102  within the burr hole  8  may be adjusted simply by rotating the inner conductor  104  (using the tool). Thus, the electrode  102  can be properly positioned regardless of the thickness of the cranium  3 . 
         [0050]    Referring to  FIG. 7 , yet another embodiment of a minimally invasive plug electrode  14 ( 4 ) will now be described. The plug electrode  14 ( 4 ) is similar to the plug electrode  14 ( 3 ) illustrated in  FIG. 6  in that it comprises a plug body  120  that includes a shaft  122  configured for being mounted within the burr hole  8  and a head  124  that is externally accessible when the plug body  120  is anchored within the burr hole  8 . The plug body  120  comprises a fastener, and in particular, a thread  126  disposed on the outer surface of the shaft  122  for engaging the inner surface of the burr hole  8 , and thereby, anchoring the plug electrode  14 ( 4 ) within the burr hole  8 . In this manner, the plug electrode  14 ( 4 ) may be conveniently screwed into the burr hole  4 . The plug body  120  includes a tool engagement element  128  for engaging a tool (not shown) that can provide a mechanical advantage for rotation of the plug electrode  14 ( 4 ). In the illustrated embodiment, the tool engagement element is a slotted recess for receiving a flathead screwdriver, although other types of tool engagement elements, such as those described above, can also be used. 
         [0051]    The plug electrode  14 ( 4 ) mainly differs from the plug electrode  14 ( 3 ) in that, instead of having a screw-like inner electrical conductor, the electrical lead  18 , itself, is removably disposed within the plug body  120 . In particular, the plug body  120  comprises a lumen  136  extending vertically up the shaft  62  and then horizontally out of the head  124 . The electrical lead  18 , which carries an electrode  132  at its distal end, is configured to firmly slide within the lumen  136 , such that the electrical lead  18  can be threaded into an opening  134  at the head  124  until the electrode  132  distally protrudes from the distal end of the plug body  120 . To this end, the diameter of the lumen  136  is substantially equal to the outer diameter of the electrical lead  18 . The distal end of the shaft  122  of the plug body  120  and the distal end of the electrical lead  18  are preferably blunt to ensure that the cortical brain tissue  5  is not pierced or otherwise damaged. The plug electrode  14 ( 4 ) further comprises a tightening screw  138  that can be screwed into the top of the head  124  to firmly secure the electrical lead  18  once it is confirmed that the electrode  132  is in its proper place. 
         [0052]    To ensure that the cranium  3  is electrically insulated from the plug electrode  14 ( 4 ) and to minimize noise from electromyograms (EMGs) during recording, the plug body  120  may be composed of an electrically insulative material, and the electrical lead  18 , with the exception of its distal end, can be coated within an electrically insulative material. As shown, the exposed electrode  132  is recessed within the burr hole  8 , and therefore, does not extend into the cranial cavity. Although the exposed electrode  132  is not in direct contact with the cortical brain tissue  5 , like the aforementioned electrode array  32 , it is indirectly electrically coupled to the cortical brain tissue  5  via the dura mater  6  and cerebrospinal fluid  7 . Thus, the electrode  132  may potentially convey electrical stimulation energy (originating from the electronics device  16 ) to the cortical brain tissue  5  or receive electrical signals from the cortical brain tissue  5  for subsequent processing in the electronics device  16 . It should be appreciated that the plug electrode  14 ( 4 ) is particularly advantageous in that the position of the electrode  132  within the burr hole  8  may be adjusted simply by sliding the electrical lead  18  within the lumen  136  of the plug body  120  when the tightening screw  138  is loosened. Thus, the electrode  132  can be properly positioned regardless of the thickness of the cranium  3 . 
         [0053]    Referring to  FIG. 8 , yet another embodiment of a minimally invasive plug electrode  14 ( 5 ) will now be described. The plug electrode  14 ( 5 ) is similar to the plug electrode  14 ( 4 ) illustrated in  FIG. 7  in that it comprises a plug body  140  capable of sliding receiving the electrical lead  18 . Thus, the plug body  140  comprises a shaft  142  configured for being mounted within the burr hole  8  and a head  144  that is externally accessible when the plug body  140  is anchored within the burr hole  8 . The plug body  140  comprises a lumen  156  extending vertically up the shaft  142 . The electrical lead  18 , which carries an electrode  152  at its distal end, is configured to firmly slide within the lumen  156 , such that the electrical lead  18  can be threaded into an opening  154  at the head  144  until the electrode  152  distally protrudes from the distal end of the plug body  140 . To this end, the diameter of the lumen  156  is substantially equal to the outer diameter of the electrical lead  18 . The distal ends of the plug base shaft  62  and electrical lead  18  are preferably blunt to ensure that the cortical brain tissue  5  is not pierced or otherwise damaged. The plug electrode  14 ( 5 ) also comprises a tightening screw  158  that can be screwed into the top of the head  144  to firmly secure the electrical lead  18  once it is confirmed that the electrode  152  is in its proper place. 
         [0054]    To ensure that the cranium  3  is electrically insulated from the electrically conductive plug body  140  and to minimize noise from electromyograms (EMGs) during recording, the plug body  140  may be composed of an electrically insulative material, and the electrical lead  18 , with the exception of its distal end, can be coated within an electrically insulative material. As shown, the exposed electrode  152  is recessed within the burr hole  8 , and therefore, does not extend into the cranial cavity. Although the exposed electrode  152  is not in direct contact with the cortical brain tissue  5 , like the aforementioned electrode array  32 , it is indirectly electrically coupled to the cortical brain tissue  5  via the dura mater  6  and cerebrospinal fluid  7 . Thus, the electrode  152  may potentially convey electrical stimulation energy (originating from the electronics device  16 ) to the cortical brain tissue  5  or receive electrical signals from the cortical brain tissue  5  for subsequent processing in the electronics device  16 . It should be appreciated that the plug electrode  14 ( 5 ) is particularly advantageous in that the position of the electrode  52  within the burr hole  8  may be adjusted simply be sliding the electrical lead  18  within the lumen  156  of the plug body  140  when the tightening screw  158  is loosened. Thus, the electrode  152  can be properly positioned regardless of the thickness of the cranium  5 . 
         [0055]    The plug electrode  14 ( 5 ) mainly differs from the plug electrode  14 ( 4 ) in that it uses a different fastening means for anchoring the plug body  140  within the burr hole  8 . In particular, the plug electrode  14 ( 5 ) comprises a series of annular ribs  146  formed on the external surface of the plug body  140 , such that when the plug electrode  14 ( 5 ) is inserted within the burr hole  8 , the annular ribs  146  grasp the burr hole  8 , thereby firmly securing the plug electrode  14 ( 5 ) within the burr hole  8 . Unlike the plug electrode  14 ( 4 ), no tool is needed to anchor the plug electrode  14 ( 5 ) into the burr hole  8 . The electrical lead  18  also comprises a plurality of vertical ribs  158  (as best illustrated in  FIG. 9 ) that facilitate engagement within the lumen  156  of the plug body  140 . 
         [0056]    Although particular embodiments of the present inventions have been shown and described, it will be understood that it is not intended to limit the present inventions to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present inventions. Thus, the present inventions are intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the present inventions as defined by the claims.