Patent Publication Number: US-2022226653-A1

Title: Devices and methods for treating tinnitus using electrical stimulation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. application Ser. No. 62/856,535, filed on Jun. 3, 2019. The disclosure of the prior application is considered part of the disclosure of this application, and is incorporated in its entirety into this application 
    
    
     STATEMENT AS TO FEDERALLY SPONSORED RESEARCH 
     This invention was made with government support under W81XWH-19-1-0021 awarded by the U.S. Army. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     1. Technical Field 
     This document relates to devices for treating tinnitus and methods of treating tinnitus using the devices. For example, this document relates to implantable electrodes and stimulation devices for delivering electrical stimulation to the cochlear promontory, region of the cochlear promontory (including promontory surface, intraosseous, or subendosteal positions), round window niche and/or round window membrane to treat tinnitus. 
     2. Background Information 
     Subjective tonal tinnitus (i.e., ringing in the ear) is the phantom perception of sound when no external generating stimulus is present. Tinnitus may be unilateral, bilateral or non-localizing, and may present intermittently or continuously. 
     Subjective tonal tinnitus affects approximately a fourth of the US population and is a major source of disability affecting many domains of life. For some, tinnitus is merely a fleeting annoyance; however for many individuals, tinnitus may cause audiological, neurological or cognitive impairment resulting in poor attention, increased distractibility, anxiety, depression, and even suicide. Tinnitus remains the number one disability experienced by U.S. veterans. In 2011 alone, more than 10 percent of all veteran disability claims were due to tinnitus, making it a top research priority of the U.S. Department of Defense and the Veterans Health Administration. 
     Despite substantial clinical research in humans and study of animal models, the exact mechanism(s) behind tinnitus remain largely unknown. It is currently held that tinnitus likely reflects inadequate or maladaptive reorganization within the central nervous system following a peripheral auditory system injury. The theory of cochlear deafferentation as a cause for tinnitus parallels phantom limb pain, where cortical maladaptation develops in response to loss of sensory input. 
     Currently, there are no FDA approved pharmacological therapies or surgical devices available for the treatment of tinnitus. Current treatment methods largely focus on counseling, cognitive behavioral therapy, masking, and sound therapy. Such strategies may help render tinnitus more tolerable, but such strategies do not abolish the symptom or reverse the underlying pathophysiological process. 
     SUMMARY 
     This document describes devices for treating tinnitus and methods of treating tinnitus using the devices. For example, this document describes implantable electrodes and stimulation devices for delivering electrical stimulation to the cochlear promontory to treat tinnitus. In some embodiments, the implantable electrodes and stimulation devices can be used to deliver electrical stimulation to one or more other regions including, but not limited to, the otic capsule, cochlea bone, cochlear region, vestibular region (e.g., vestibule or semicircular canals), the vestibulocochlear nerve, or the brainstem. 
     In one aspect, this disclosure is related to an implantable system for delivering electrical pulse stimuli to a patient&#39;s cochlear region. Such an implantable system includes: (i) a stimulator device configured to generate the electrical pulse stimuli; (ii) a lead comprising an elongate insulated electrical conductor and defining a longitudinal axis, the electrical conductor in electrical communication with the stimulator device to conduct the electrical pulse stimuli; and (iii) a single electrode disposed at a distal end of the lead and in electrical communication with the electrical conductor to deliver the electrical pulse stimuli to the patient&#39;s cochlear region. The single electrode is spaced apart from the longitudinal axis. 
     Such an implantable system can optionally include one or more of the following features. The single electrode may be spherical and define a center. The center of the single electrode may be spaced apart from the longitudinal axis by at least 0.4 mm. The center of the single electrode may be spaced apart from the longitudinal axis by at least 1.0 mm. The electrical conductor may include one or more bends that cause the single electrode to be spaced apart from the longitudinal axis. The lead may be a malleable member that retains a shape after being bent into the shape. In some embodiments, at least a portion of the electrical conductor extends along a helical path. The lead may include a textured portion configured to enhance cohesion of the lead with an adhesive. The system may also include a receiver coupled to the stimulator device and comprising an electrical coil configured for inductively communicating with an external device through a scalp of the patient. 
     In another aspect, this disclosure is directed to another implantable system for delivering electrical pulse stimuli to a patient&#39;s cochlear region. The system includes: (a) a stimulator device configured to generate the electrical pulse stimuli; (b) a lead comprising an elongate insulated electrical conductor and defining a longitudinal axis, the electrical conductor in electrical communication with the stimulator device to conduct the electrical pulse stimuli, the lead including a textured portion configured to enhance cohesion of the lead with an adhesive; and (c) a single electrode disposed at a distal end of the lead and in electrical communication with the electrical conductor to deliver the electrical pulse stimuli to the patient&#39;s cochlear region. 
     Such an implantable system for delivering electrical pulse stimuli to a patient&#39;s cochlear region may optionally include one or more of the following features. The system may also include a receiver coupled to the stimulator device and comprising an electrical coil configured for inductively communicating with an external device through a scalp of the patient. The textured portion may be part of an outer insulative layer over the elongate insulated electrical conductor. A portion of the electrode may be insulated by an outer insulative layer. The single electrode may be spherical and define a center. The center of the single electrode may be spaced apart from the longitudinal axis by at least 0.4 mm. The center of the single electrode may be spaced apart from the longitudinal axis by at least 1.0 mm. The electrical conductor may include one or more bends that cause the single electrode to be spaced apart from the longitudinal axis. The lead may be a malleable member that retains a shape after being bent into the shape. At least a portion of the electrical conductor may extend along a helical path. 
     In another aspect, this disclosure is directed to a method of treating a tinnitus condition of a patient. The method includes: (1) drilling a recess in a cochlear promontory bone of the patient, wherein said drilling comprises creating the recess in the cochlear promontory bone without completely breaking through the cochlear promontory bone; (2) implanting an implantable system for delivering electrical pulse stimuli within the patient, wherein said implanting comprises intraosseously placing an electrode within the recess; and (3) delivering, via the electrode, electrical pulse stimuli, generated by the implantable system, to the cochlear promontory bone of the patient. 
     Such a method of treating a tinnitus condition of a patient may optionally include one or more of the following features. The implanting may include applying an adhesive to anchor, to the patient&#39;s anatomy, a lead comprising an elongate insulated electrical conductor of the implantable system. The lead may include a textured portion configured to enhance cohesion of the lead with the adhesive. The anatomy to which the lead is anchored may include a posterior bony ear canal of the patient. The textured portion may be part of an outer insulative layer over the elongate insulated electrical conductor. The electrode may be at the distal end of the lead. A portion of the electrode may be insulated. 
     Particular embodiments of the subject matter described in this document can be implemented to realize one or more of the following advantages. First, electrical stimulation delivered to the region of the cochlear promontory by an intraosseous electrode attached to an implanted receiver/stimulator electronics package, can provide an effectual long-term treatment of tinnitus in many patients. Second, in some cases the efficacy of the treatment is enhanced by locating the electrode in an intraosseous recess that is drilled in the surface of the cochlear promontory during the implant procedure. Third, in some embodiments the electrode lead has an offset tip portion that facilitates visibility and placement accuracy of the electrode during the implant procedure. Fourth, in particular embodiments the electrode lead includes a portion that is structured to enhance its affinity for cohering with an adhesive. Fifth, the electrode and stimulator systems described herein are either partially implantable or totally implantable and essentially imperceptible after implantation. Sixth, the stimulator systems described herein are configured to communicate wirelessly through the scalp of the patient with an external programmer device. Seventh, the systems described herein can treat tinnitus while only being activated for a portion of the time. For example, in some patients tinnitus will be substantially relieved with a treatment period of only about 30 minutes per day. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description herein. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of an example implantable receiver/stimulator device in accordance with some embodiments. 
         FIG. 2  depicts a distal end portion of an example electrode device in accordance with some embodiments provided herein. 
         FIG. 3  depicts an example implant site for the electrode devices described herein. 
         FIG. 4  depicts a distal end portion of an example drill device that can be used to create a recess in bony tissue for receiving electrodes described herein. 
         FIG. 5  depicts the example implant site of  FIG. 3  with a recess now created in the cochlear promontory. 
         FIG. 6  depicts a cross-sectional view of the cochlear promontory of  FIG. 5 . 
         FIG. 7  depicts the cross-sectional view of the cochlear promontory as in  FIG. 6 , with the addition of an electrode positioned in the recess. 
         FIG. 8  depicts the example implant site of  FIG. 3  with an electrode positioned in the recess in the cochlear promontory. 
         FIG. 9  depicts the example implant site of  FIG. 3  with the electrode positioned in the recess in the cochlear promontory and the electrode lead secured to the posterior bony ear canal. 
     
    
    
     Like reference numbers represent corresponding parts throughout. 
     DETAILED DESCRIPTION 
     This document describes devices for treating tinnitus and methods of treating tinnitus using the devices. For example, this document describes implantable intraosseous electrodes and stimulation devices for delivering electrical stimulation to the cochlear promontory to treat tinnitus. In some embodiments, the implantable electrodes and stimulation devices can also be used to deliver electrical stimulation to one or more other regions including, but not limited to, the otic capsule, cochlea bone, cochlear region, vestibular region (e.g., vestibule or semicircular canals), the vestibulocochlear nerve, or the brainstem. 
     In some cases, patients can treat tinnitus by self-activating the implantable intraosseous electrodes and stimulation devices described herein, for a relatively short period of time each day. For example, in some patients tinnitus will be substantially relieved with a treatment period of only about 30 minutes per day. In some cases, patients can simply turn on the tinnitus implant when experiencing troublesome tinnitus and gain relief. With increasing use, it is likely many patients will enjoy lasting tinnitus suppression, hours and even days after the device is turned off (i.e., residual inhibition). 
     Using intraosseous, surface, endosteal, subendosteal, or short intracochlear electrodes (or a combination thereof), customized monopolar or bipolar stimulation can be performed to target specific patterns and frequencies of tinnitus. Endosteal and/or intraosseous electrodes in the cochlear promontory can place the electrical stimulation in closer proximity to the modiolus (the conical central axis of the cochlea) without risking sensorineural hearing loss. In some cases, using a surface grid of electrodes may have the advantage of improved cochlear coverage. A short intracochlear electrode offers a direct method of cochlear stimulation. Devices and methods for each of the aforementioned treatment modalities are within the scope of this disclosure. 
     Referring to  FIG. 1 , an implantable receiver/stimulator device  100  can be used in conjunction with the various types of electrode devices described herein. In the depicted embodiment, an example electrode lead  140  is coupled with the implantable receiver/stimulator device  100 . 
     In some embodiments, receiver/stimulator device  100  can be functionally akin to an implantable receiver/stimulator device used for cochlear implant electrical stimulation. Accordingly, receiver/stimulator device  100  is implanted under the post-auricular scalp and the lead wire(s) (e.g., electrode lead  140 ) can travel through the mastoid and facial recess to the target electrode location(s). With this system, electrical stimulation can be delivered continuously or intermittently. Further, treatment parameters can be tailored to individual patient needs according to an optimally programmed schedule, or can be administered on-demand by the patient. 
     In some cases, for treating tinnitus, the target electrode location may be the cochlear promontory (e.g., endosteally and/or intraosseously), bony cochlea, or otic capsule. In some cases, for treating balance disorders, the target electrode location may be the bony labyrinth (e.g., surface, intraosseous, or intra-labyrinthine) including the semicircular canals and vestibule. For example, surface, intraosseous, and intra-labyrinthine electrodes can be placed in the region of the semicircular canals and vestibule to stimulate labyrinthine function. Electrical stimulation of this organ may be used to rehabilitate vestibular hypofunction or treat ongoing or recurrent vestibular diseases, such as Meniere&#39;s disease. 
     In the depicted embodiment, the implantable receiver/stimulator device  100  includes a magnet  110 , a receiver coil  120 , and a stimulator  130 . Stimulator  130  controls the operations of receiver/stimulator device  100  and is the source of the electrical stimuli (with the energy from an on-board battery). In some embodiments, the on-board battery can be inductively recharged by an external battery charger device via the receiver coil  120 . 
     An external device (not shown) can be used to wirelessly communicate (through the patient&#39;s scalp) with the implanted receiver/stimulator device  100 . Such an external device can function to activate, program, power, control, and/or otherwise interact with receiver/stimulator device  100  (e.g., to get impedance readings from the implanted receiver/stimulator device  100  to determine whether the electrode(s) is/are properly positioned). 
     In some cases, receiver/stimulator device  100  can be programmed to generate a particular pulse width, current amplitude, stimulus rate, stimulation mode, and the like. Magnet  110  can be used to magnetically couple and align receiver/stimulator device  100  with such an external device. Receiver coil  120  is used to communicate wirelessly with such an external device. It should be understood that the depicted embodiment of receiver/stimulator device  100  provides just one non-limiting example of the types of implantable receiver/stimulator devices that can be used in conjunction with the various types of electrode devices provided herein. 
     The electrode lead  140  includes an insulated lead wire  142  and an electrode  150  disposed at a distal end of the lead wire  142 . The insulated lead wire  142  conducts the electrical stimuli to electrode  150 . In some embodiments, the electrode lead  140  is monopolar and the casing of the implanted receiver/stimulator device  100  can act as the ground for the electrical stimuli delivered by the electrode  150 . In some embodiments, one or more separate ground leads extending from the implantable receiver/stimulator device  100  is/are included. 
     Electrode  150  is configured to deliver the electrical stimuli to tissue of the patient. It should be understood that while a single electrode  150  is depicted, in some embodiments two or more electrodes are included. That is, various types of electrode configurations can be used for electrode  150 . 
     In some cases, prior to permanent placement of the electrode  150 , one or more test electrodes can be temporarily placed on the patient&#39;s cochlear promontory (or cochlea region) via transtympanic placement using local anesthetic with the patient awake. An instrument set can be used to apply varying patterns and/or intensities of electrical stimulation, and the patient can convey parameters resulted in greatest tinnitus reduction. Individual instruments will vary based on the number of electrodes and the distance between electrodes. Additionally, “pitch-masking” (also referred to as frequency matching) and CT imaging may assist in determining optimal positioning of the electrode  150 . 
     Referring to  FIG. 2 , here a distal end portion of the lead wire  140  is shown in an enlarged view. The lead wire includes the insulated lead wire  142  and the electrode  150  disposed at a distal end of the lead wire  142 . The lead wire  140 , in conjunction with the receiver/stimulator device  100  described above, can be used to deliver electrical pulses, e.g., to a patient&#39;s cochlear promontory, or other areas in a patient&#39;s cochlear region, to treat tinnitus. 
     The example lead wire  142  includes an electrical conductor  141  that is encased within a primary electrically insulative layer  143  (e.g., made of silicone or any other suitable biocompatible insulative material). The electrode  150  is attached to a distal end of the electrical conductor  141 . The lead wire  142  also includes a textured region  144 . As described further below, the textured region  144  can provide physical structural features to enhance the affinity of the lead wire  142  for cohering with an adhesive to anchor the lead wire  140  to the patient&#39;s tissue. Such physical structural features can include, but are not limited to, surfacing texturing, irregular surfaces with one or more peaks and/or valleys, knurling, indentations, and the like, and combinations thereof. 
     In some cases, the electrical conductor  141  has a diameter of 50 μm, 75 μm, 100 μm, or 125 μm, without limitation. The electrical conductor  141  can be made of any suitable material. In one example, the electrical conductor  141  is made of 90% platinum and 10% iridium. In some embodiments, the electrical conductor  141  can be configured in a helical configuration within the primary electrically insulative layer  143 . Such a helical configuration can facilitate desired lateral flexibility and bending compliance properties of the lead wire  140 . 
     The electrical conductor  141  emerges from a distal end of the primary insulative layer  143  and extends toward the electrode  150 . In some embodiments, the portion of the electrical conductor  141  extending between the distal end of the primary insulative layer  143  and the electrode  150  is electrically insulated with an outer layer of electrically insulative material (e.g., silicone or another suitable insulative material). In some cases, the insulative layer  143  extends to cover and insulate the electrical conductor  141  entirely. In some cases, the insulative material can extend to cover a portion of the electrode  150 , such as a proximal portion (e.g., proximal hemispherical portion) of the electrode  150 . In some embodiments, that portion of the electrical conductor  141  is uninsulated. 
     As shown, in some embodiments the portion of the electrical conductor  141  extending between the distal end of the primary insulative layer  143  and the electrode  150  is configured so that the center of the electrode  150  is offset from the longitudinal axis of the lead wire  142  by a distance “D.” The offset distance D provides for enhanced visibility of the electrode  150  during the implant procedure. In some embodiments, the offset distance D can be in a range between 0.0 to 0.5 mm, between 0.2 mm to 0.7 mm, between 0.4 mm to 0.9 mm, between 0.6 mm to 1.2 mm, or between 1.0 mm to 2.0 mm, or more than 2.0 mm, without limitation. In some embodiments, the offset distance D can be at least 0.2 mm, at least 0.4 mm, at least 0.6 mm, at least 0.8 mm, at least 1.0 mm, at least 1.2 mm, or at least 1.4 mm. 
     In the depicted embodiment, the portion of the electrical conductor  141  extending between the distal end of the primary insulative layer  143  and the electrode  150  is configured with two 90° bends to create the offset distance D. In some embodiments, other suitable bend configuration (e.g., two 45° bends, curves, etc.) can be used. 
     The offset of the portion of the electrical conductor  141  extending between the distal end of the primary insulative layer  143  and the electrode  150  also provides some springiness by which, if desired, a small preload force can be applied to bias the electrode  150  into contact with its mating surface. Alternatively, or additionally, in some embodiments the portion of the electrical conductor  141  extending between the distal end of the primary insulative layer  143  and the electrode  150  can comprise or consist of a shape-memory material (e.g., Nitinol, etc.). When heated, such a shape-memory material can deform to a shape that provides a small preload force to bias the electrode  150  into contact with its mating surface. For example, in some embodiments the pre-heated shape of the portion of the electrical conductor  141  extending between the distal end of the primary insulative layer  143  and the electrode  150  can be bent as depicted in  FIG. 2 , and when heated one or more of the bends can tend to straighten and thereby provide a small preload force to bias the electrode  150  into contact with its mating surface. 
     In some embodiments, the textured region  144  can be a molded portion of the primary insulative layer  143  that creates multiple ridges and recesses in the outer diameter of the otherwise cylindrical primary insulative layer  143 . In some embodiments, the texture region  144  is about 9 mm long and ends about 6 mm from the distal end of the primary insulative layer  143 . The textured region  144 , along with an adhesive (e.g., otologic bone cement and the like), can be used to anchor the lead wire  142  to the patient&#39;s tissue at the target site, and to provide migration resistance so that the electrode  150  stays positioned relative to the patient&#39;s anatomy as desired. One example of a suitable bone cement is “FUSE Glass Ionomer Cement” or “ProCem Otologic Cement” from Grace Medical, Memphis, Tenn., USA. In some cases, one or more mechanical anchors such as a screw, clip, helix, suture, or barbed member can be used (additionally or alternatively) to anchor the lead wire  142  to tissue. In some embodiments, the lead wire  142  can include one or more fenestrations that can receive adhesive and/or a mechanical anchor. 
     The electrode  150  is spherical in the depicted example. In some embodiments, the electrode  150  can be cylindrical, conical, frustoconical, a polyhedron, and combinations thereof. The diameter of the spherical electrode  150  can be in a range between 0.0 to 0.4 mm, between 0.1 mm to 0.5 mm, between 0.2 mm to 0.6 mm, between 0.3 mm to 0.7 mm, or between 0.4 mm to 0.9 mm, or between 0.6 mm to 1.2 mm, or between 0.8 mm to 1.6 mm, or between 1.4 mm to 2.0 mm, or more than 2.0 mm, without limitation. In some embodiments, the electrode  150  is created by flaming the electrical conductor  141 , or by any other suitable method (e.g., laser welding, using an adhesive, etc.). 
     Referring to  FIG. 3 , a surgical site  200  of a patient is depicted. The surgical site  200  is made by a postauricular (behind the ear, such as behind the right ear in the depicted example) surgical incision that extends through the skin and subcutaneous tissue of the patient. The promontory is then exposed through a posterior tympanotomy (facial recess). Portions of the cochlear promontory  10  are thereby exposed for access. To orient the reader/viewer to the location of the surgical site  200 , some other anatomical landmarks are shown, including the cochlear round window  12 , the stapes  14 , and the pharyngotympanic (auditory) tube  16 . 
     Referring also to  FIG. 4 , in some embodiments an example micro-drill instrument  300  can be used with a rotary driver to create a recess in the cochlear promontory  10  that will receive the electrode  150  ( FIG. 2 ). Placement of the electrode  150  intraosseously in the cochlear promontory is, in some cases, preferred to a purely surface contact electrode because an intraosseous design confers a more stable electrode bed to reduce electrode migration or displacement; increases the surface area of electrode-bone contact; reduces the probability of untoward current spread during stimulation that might result in discomfort or facial nerve stimulation; and reduces stimulation threshold requirements thereby enhancing battery life and mitigating aberrant electrical stimulation. 
     The example micro-drill instrument  300  includes a shank  310  and a working portion  320  at a distal end of the shank  310 . Working portion  320  includes cutting edges (course fluted burrs or more smooth diamond burrs) that can remove tissue such as bone tissue to create a recess or hole (e.g., such as a blind hole or through hole) in the target tissue layer (e.g., anywhere on the cochlear promontory  10  including near or at the oval window, near or at the round window  12 , etc.). In the depicted embodiment, the working portion  320  is spherical to correspond to the spherical electrode  150  ( FIG. 2 ). That is, the working portion  320  is sized and shaped to create a recess that will be sized and shaped to receive the spherical electrode  150 . For example, the working portion  320  can have a diameter in a range between 0.0 to 0.4 mm, between 0.1 mm to 0.5 mm, between 0.2 mm to 0.6 mm, between 0.3 mm to 0.7 mm, or between 0.4 mm to 0.9 mm, or between 0.6 mm to 1.2 mm, or between 0.8 mm to 1.6 mm, or between 1.4 mm to 2.0 mm, or more than 2.0 mm, without limitation. 
     The micro-drill instrument  300  can include a depth limiter or indicator. For example, in the depicted embodiment the working portion  320  includes a circumferential marker  330  that can be used a visual indication of the depth to which the working portion  320  has penetrated into a substance such as the cochlear promontory  10 . The depth marker  330  can advantageously prevent the recess created in the cochlear promontory  10  from becoming a through-hole (i.e., from penetrating completely through the opposite side of the cochlear promontory  10 ). In general, the target depth for the recess to be created in the cochlear promontory  10  is between about ½ and ⅔ of the thickness of the wall of the cochlear promontory  10 . 
     Other types of depth limiters or indicators are also envisioned. For example, an annular ring can be included on the working portion  320  instead of, or in addition to, the circumferential marker  330 . In some cases, a side-arm stopper extending along the side the micro-drill instrument  300  can be attached to the rotary driver. Patient populations naturally have differing anatomical features (such as promontory thicknesses and the like). Accordingly, a variety of differently sized drill instruments  300  can be available so as to suit an individual patient&#39;s anatomy and/or electrode size. 
     In most cases, the most suitable micro-drill instruments  300  and/or electrode device for a particular patient can be determined in advance of the implant procedure. For example, in some cases a patient can undergo a pre-operative imaging procedure, such as a computerized tomography (CT) scan, to determine the patient&#39;s anatomical features such as, but not limited to, promontory thickness. Based on the inventor&#39;s investigations, minimal promontory thickness is about 0.4-0.5 mm and maximal promontory thickness is about 2.0-2.2 mm. Thus, a desirable hole depth (and intraosseous electrode length) can be about 0.3 mm to about 0.7 mm, or about 0.5 mm to about 0.9 mm, or about 0.7 mm to about 1.1 mm, or about 0.9 mm to about 1.3 mm, or about 1.1 mm to about 1.5 mm, or about 1.3 mm to about 1.7 mm, or about 1.5 mm to about 1.9 mm, or about 1.7 mm to about 2.1 mm, and/or anywhere within such ranges. In some cases, a set of multiple drill instruments  300  will be made available in 0.2 mm depth increments, or 0.1 mm depth increments. 
     Referring now to  FIGS. 5 and 6 , a recess  220  in the cochlear promontory  10  has been created in preparation for receiving the intraosseous electrode  150  ( FIG. 2 ). The recess  220  can be created using the drill instrument  300 , or any other suitable instrument/technique. In general, the target depth for the recess to be created in the cochlear promontory  10  is between about ½ and ⅔ of the thickness of the wall of the cochlear promontory  10  (i.e., without breaking through the entire thickness of the cochlear promontory  10 ). 
     The recess  220  can be created anywhere on the cochlear promontory  10 . For example, in the depicted embodiment the recess  220  is near to the round window  12 . As an alternative to placing the electrode  150  in the recess  220  as described herein, in some embodiments a plug containing an electrode can be placed into the round window  12 , for example. 
     Referring now to  FIGS. 7 and 8 , the implantable receiver/stimulator device  100  (refer to  FIG. 1 ) and the electrode lead  140  are shown as implanted at/via the surgical site  200 . Accordingly, receiver/stimulator device  100  is implanted under the post-auricular scalp (not visible) and the electrode lead  140  is extending therefrom through the mastoid and facial recess such that the electrode  150  is positioned in the recess  220  in the cochlear promontory  10 . 
     The electrode lead  140  is installed relative to the anatomy so that there is a slight pressure exerted by the electrode  150  to the recess  220 . In some embodiments, the electrode lead  140  is suitably shapeable/malleable to allow for the electrode lead  140  to be shaped and configured as needed for the implantation procedure. In some such embodiments, the electrode lead  140  will tend to retain the shape to which it is configured. 
     Referring to  FIG. 9 , in some embodiments an adhesive  400  (e.g., otologic bone cement, tissue glue, etc.) can be used to anchor the electrode lead  140  to the patient&#39;s anatomy for migration resistance. For example, in the depicted implantation a bone cement  400  is adhering the electrode lead  140  (as facilitated by the textured region  144 , obscured from view here; refer to  FIG. 8 ) to the patient&#39;s posterior bony ear canal. This completes the implantation process of the implantable receiver/stimulator device  100  (refer to  FIG. 1 ) and the electrode lead  140  which can thereafter be used to deliver electrical stimuli intraosseously to the cochlear promontory  10  to treat tinnitus. 
     ADDITIONAL INFORMATION, DESIGN VARIATIONS AND EMBODIMENTS 
     The systems described herein for treating tinnitus by delivering stimuli intraosseously to the cochlear promontory can be adjusted to deliver a range of various stimulation parameters (amplitude, pulse width, etc.). For example, in some cases stimulation pulses can be biphasic or triphasic pulses charge balanced delivered in a monopolar configuration. Parameters can be set up based on subjective patient feedback. Upper stimulation limits can be applied from the existing limits used in Cochlear Implants. In some cases, pulse duration can be limited to a maximum of 200 microseconds, and charge per phase can be limited to 282.8 nC. In some cases, the charge per phase could be chosen higher in the tinnitus implants described herein, as the geometric surface area of the ball contact of the tinnitus implant electrode (e.g., about 0.48 mm{circumflex over ( )}2) is significantly larger than the geometric surface area per cochlear implant channel (e.g., about 0.14 mm{circumflex over ( )}2). 
     The surgical procedure for implanting the systems described herein for treating tinnitus by delivering stimuli intraosseously to the cochlear promontory is further described as follows. Following induction of general endotracheal anesthesia, the subject is placed in a supine position with the head gently turned away. Bipolar orbicularis oculi and orbicularis oris facial nerve monitoring electrodes are placed for continuous intraoperative facial nerve electromyographic monitoring. The subject is then prepped and draped in the usual fashion for otologic surgery. A postauricular incision is marked and infiltrated with lidocaine with epinephrine 1:1000. The planned position of the device is then marked to facilitate accurate placement later in the case. 
     A postauricular incision is then made through skin and subcutaneous tissue and elevated forward in a loose areolar plane. A separate staggered musculoperiosteal incision is then made to the mastoid cortex and elevated forward in a subperiosteal plane. A self-retaining retractor is then placed. 
     Next, using an operative microscope, a cortical mastoidectomy with antrotomy is performed using a combination of cutting and diamond drill bits and continuous irrigation. Care is taken to avoid uncovering the temporal dura or sigmoid sinus. A standard facial recess (posterior tympanotomy) is made, preserving the chorda tympani and facial nerve. The position on the promontory for electrode placement is marked. Using an otologic mini-drill (e.g., with a 0.5 mm drill bit), a small well is created on the cochlear promontory surface to accommodate the intraosseous promontory electrode. Care is taken to not breach the endosteum of the cochlea or enter the cochlear lumen. 
     Next, a tight subperiosteal pocket is created under the temporal scalp and temporalis muscle to fixate the internal device. An electrode channel is then drilled to accommodate the electrode lead. The surgical field is then copiously irrigated with antibiotic solution, meticulous hemostasis is obtained, and the surgeon&#39;s gloves are changed to maximize field sterility. 
     The device is then brought into the field and monopolar cautery is removed from the field. The device is placed in a tight subperiosteal pocked and the electrode contact is positioned within the cochlear promontory well. After ensuring good bone contact via direct microscopic visualization and device impedance testing, the electrode is secured to the posterior bony ear canal (e.g., using otologic bone cement). The bone cement is left undisturbed for 5 minutes to cure and harden. The redundant portion of the electrode is then coiled in the mastoid. Adequate electrode contact between the electrode and promontory well is once again confirmed visually and via impedance testing. 
     The incision is then closed in anatomical layers using single interrupted suture and a standard otologic headwrap is applied. The subject is then awakened, extubated, and transferred to the post-anesthesia care unit for recovery. Following surgery, the subject is examined by the surgeon to ensure they have not experienced any adverse events related to surgery. Once standard outpatient discharge criteria have been met, the subject is discharged from the hospital. 
     Experiments have been performed to confirm the feasibility of the systems described herein for treating tinnitus. Twenty-five subjects enrolled in the study, although three withdrew before undergoing promontory stimulation. The mean age at enrollment for the remaining 22 subjects was 59.3 years (SD 7.7) and included 14 (64%) men and 8 (36%) women. 
     Each patient received three sessions of in-office promontory stimulation using biphasic charge balanced pulses. Following successful transtympanic placement of an insulated monopolar stimulation probe, a calibration session to assess optimal stimulation parameters for the therapeutic session was carried out using an output of 0 to 1000 μA for pulse frequencies 100 Hz, 800 Hz and 1600 Hz. For each stimulus frequency, current levels were gradually up-titrated to determine the following perceptual parameters: 1) detection threshold defined as the first detection of the electrical stimulus (tactile or auditory) as reported by the subject; 2) maximum comfort threshold defined as the level first causing discomfort as reported by the subject. 
     The subject then received 10 minutes of stimulation at 80% of the maximum comfort threshold for each of the predetermined pulse frequencies. Each subject underwent this stimulation cycle in three separate sessions, each spaced one week apart. 
     Efficacy of stimulation was assessed by comparing baseline scores to post-stimulation scores from three validated tinnitus questionnaires: TFI, THI, and Tinnitus VAS. Safety of stimulation was primarily assessed by comparing baseline hearing thresholds via standard behavioral audiometry to post-stimulation thresholds for the conventional frequencies 0.25 to 8 kHz, including interoctaves. 
     All 22 subjects had clinically significant improvement in THI score defined as a change of at least 7 points; 20 had clinically significant improvement in TFI score defined as a change of at least 13 points; and 17 had clinically significant improvement in Tinnitus VAS score defined as a change of at least 20 points. In total, 17 (77%) subjects had clinically significant improvement in all three scores, 20 (91%) had improvement in two of the three scores, and 22 (100%) had improvement in one of the three scores. 
     In some cases, patients experience tinnitus in just one ear. In other cases, patients experience tinnitus in both ears. A single system described herein for treating tinnitus by delivering stimuli intraosseously to the cochlear promontory can be implanted to treat either condition (i.e., tinnitus in one ear or in both ears). Alternatively, in some cases two systems described herein for treating tinnitus by delivering stimuli intraosseously to the cochlear promontory can be implanted in a single patient to treat tinnitus in both ears. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described herein as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the embodiments described herein should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single product or packaged into multiple products. 
     Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.