Abstract:
An electrode assembly for use in a prosthetic hearing implant is disclosed, the electrode assembly comprising: an elongate carrier member for implantation into the cochlea, said carrier member having a proximal end adapted to be positioned in a basal region of the cochlea, and a distal end adapted to be positioned toward an apical region of the cochlea, wherein a substantial portion of said carrier member has a fabiform cross section; and a plurality of electrodes disposed along said carrier member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from U.S. Provisional Patent Application 60/748,217 entitled “Promoting Curvature and Maintaining Orientation In An Electrode Carrier Member Of A Prosthetic Hearing Implant,” filed Dec. 8, 2005; U.S. Provisional Patent Application 60/748,273 entitled “Electrode Carrier Member Having An Embedded Stiffener For A Prosthetic Hearing Implant,” filed Dec. 8, 2005; U.S. Provisional Patent Application 60/748,274 entitled “Electrode Carrier Member for a Prosthetic Hearing Implant Having Optical Length for Atraumatic Implantation,” filed Dec. 8, 2005; and U.S. Provisional Patent Application 60/748,314 entitled “Electrode Carrier Member For A Prosthetic Hearing Implant Having Variable Pitch Electrodes To Facilitate Atraumatic Implantation,” filed Dec. 8, 2005, all of which are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to stimulating medical devices and, more particularly, to promoting curvature and maintaining orientation of an electrode carrier member of a stimulating medical device. 
     2. Related Art 
     Hearing loss is generally of two types, namely conductive and sensorineural. The treatment of both of types of hearing loss has been quite different, relying on different principles to deliver sound signals to be perceived by the brain as sound. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. In such cases, hearing loss is often improved with the use of conventional hearing aids, which amplify the sound so that acoustic information reaches the cochlear hair cells. Such hearing aids utilize acoustic mechanical stimulation, whereby the sound is amplified according to a number of varying techniques, and delivered to the inner ear as mechanical energy. This may be through a column of air to the eardrum, or through direct delivery to the ossicles of the middle ear. 
     On the other hand, sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which are needed to transduce acoustic signals into auditory nerve impulses. Individuals suffering from this type of hearing loss are unable to derive any benefit from conventional hearing aid systems regardless of the volume of the acoustic stimulus. This is because the natural mechanisms for transducing sound energy into auditory nerve impulses are either absent or damaged. In such cases, cochlear implants (also referred to as cochlear devices, cochlear prostheses, cochlear implant systems, and the like; simply “cochlear implants” herein) have been developed to provide the sensation of hearing to such individuals. In cochlear implants, electrical stimulation is provided via stimulating electrodes positioned as close as possible to the nerve endings of the auditory nerve, essentially bypassing the hair cells in a normally functioning cochlea. The application of a stimulation pattern to the nerve endings causes impulses to be sent to the brain via the auditory nerve, resulting in the brain perceiving the impulses as sound. 
     More recently, there has been an increased interest in Electro-Acoustical Stimulation (EAS) in which electrical stimulation of the cochlea is used in conjunction with acoustical stimulation. It is relatively common in hearing impaired individuals to experience sensorineural hearing loss for sounds in the high frequency range, and yet still be able to discern sounds in the middle to low frequency range, through the use of a conventional hearing aid, or naturally. Traditionally, in the majority of such cases, the recipient would only receive treatment to preserve and improve the hearing for the middle to low frequency sounds, most probably via a conventional hearing aid, and little would be done to attempt to restore the hearing loss for the high frequency sounds. This is due to the potential trauma caused by the implantation of an electrode assembly into the cochlea. Only if the individual lost the ability to perceive middle to low frequency sounds would consideration then be given to restoring the hearing loss for the high frequency sounds, in which case a cochlear implant would be considered a possible solution. 
     SUMMARY 
     In accordance with one aspect of the present invention, an electrode assembly for use in a prosthetic hearing implant is disclosed, the electrode assembly comprising: an elongate carrier member for implantation into the cochlea, said carrier member having a proximal end adapted to be positioned in a basal region of the cochlea, and a distal end adapted to be positioned toward an apical region of the cochlea, wherein a substantial portion of said carrier member has a fabiform cross section; and a plurality of electrodes disposed along said carrier member. 
     In another aspect of the invention, an electrode assembly for use in a prosthetic hearing implant is disclosed, the electrode assembly comprising: an elongate carrier member for implantation into the cochlea, said carrier member having a proximal end adapted to be positioned in a basal region of the cochlea, and a distal end adapted to be positioned toward an apical region of the cochlea; and a plurality of electrodes disposed along said carrier member, wherein said carrier member is configured to encourage said carrier member to medially curve about a vertical axis of the carrier member toward the modiolus of the cochlea, to retain its orientation once inserted into the cochlea, and to resist axial rotation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an example of an implanted cochlear implant suitable for implementing embodiments of the present invention; 
         FIG. 2A  is a side view of an electrode assembly in accordance with one embodiment of the present invention; 
         FIG. 2B  is a top view of the electrode assembly illustrated in  FIG. 2A ; 
         FIG. 2C  is a cross-sectional view of one embodiment of the electrode assembly illustrated in  FIGS. 2A-2B  taken along section line  2 C- 2 C illustrated in  FIG. 2B ; 
         FIG. 3A  is an enlarged view of one embodiment of a tip region of the electrode assembly illustrated in  FIG. 2A ; 
         FIG. 3B  is an alternative embodiment of a tip region of the electrode assembly illustrated in  FIG. 2A ; and 
         FIG. 3C  is an alternative embodiment of a tip region of the electrode assembly illustrated in  FIG. 2A . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are generally directed to an apparatus and method for facilitating implantation of an electrode assembly of a stimulating medical device into a patient (referred to herein as a recipient). Embodiments of the present invention are described below in connection with one type of stimulating medical device, a prosthetic hearing implant and, more specifically, a cochlear implant. Cochlear implants use direct electrical stimulation of auditory nerve cells to bypass absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use multi-contact electrodes inserted into the scala tympani of the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound. Such devices are also used to treat a smaller number of patients with bilateral degeneration of the auditory nerve. For such patients, the cochlear implant provides stimulation of the cochlear nucleus in the brainstem. Such devices, therefore, are commonly referred to as auditory brainstem implants (ABIs). 
     Exemplary embodiments of a cochlear implant include a Contour™, Freedom™, Nucleus™ or Cochlear™ implant sold by Cochlear Limited, Australia. Such devices are described in U.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894, and 6,697,674, the entire contents and disclosures of which are hereby incorporated by reference herein. It should be understood to those of ordinary skill in the art that embodiments of the present invention may be used in other stimulating medical devices such as neurostimulators, cardiac pacemakers/defibrillators, etc. as well as other medical devices which utilize an elongate carrier member to temporarily or permanently implant, deliver or otherwise introduce a therapeutic agent, sensor, device, etc. into a recipient. 
       FIG. 1  is a cut-away view of the relevant components of outer ear  101 , middle ear  102  and inner ear  103 , which are described next below. In a fully functional ear, outer ear  101  comprises an auricle  105  and an ear canal  106 . An acoustic pressure or sound wave  107  is collected by auricle  105  and channeled into and through ear canal  106 . Disposed across the distal end of ear cannel  106  is a tympanic membrane  104  which vibrates in response to acoustic wave  107 . This vibration is coupled to oval window, or fenestra ovalis,  110  through three bones of middle ear  102 , collectively referred to as the ossicles  111 . 
     Ossicles  111  comprises the malleus  112 , the incus  113  and the stapes  114 . Bones  112 ,  113  and  114  of middle ear  102  serve to filter and amplify acoustic wave  107 , causing oval window  110  to articulate, or vibrate. Such vibration sets up waves of fluid motion within cochlea  115 . Such fluid motion, in turn, activates tiny hair cells (not shown) that line the inside of cochlea  115 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells (not shown) to auditory nerve  116  and, ultimately, to the brain where they are perceived as sound. In some persons experiencing sensorineural hearing loss, there is an absence or destruction of the hair cells. Cochlear implant  120  is utilized to directly stimulate the ganglion cells to provide a hearing sensation to such persons. 
       FIG. 1  also shows how cochlear implant  120  is positioned in relation to outer ear  101 , middle ear  102  and inner ear  103 . Cochlear implant  120  comprises external component assembly  122  which is directly or indirectly attached to the body of the recipient, and an internal component assembly  124  which is temporarily or permanently implanted in the recipient. External assembly  122  comprises microphone  125  for detecting sound which is provided to a behind-the-ear (BTE) speech processing unit  126  that generates coded signals. The coded signals are provided to an external transmitter unit  128 , along with power from a power source (not shown) such as a battery. External transmitter unit  128  comprises an external coil  130  and, preferably, a magnet (not shown) secured directly or indirectly in external coil  130 . 
     Internal component assembly  124  comprises an internal receiver unit  132  having an internal coil (not shown) that transcutaneously receives power and coded signals from external assembly  122 , and provides such signals to a stimulator unit  134 . In response to the coded signals, stimulator  134  applies stimulation signals to cochlea  115  via an implanted electrode assembly  140 . Electrode assembly  140  enters cochlea  115  via a cochleostomy  142  or through round window  110 , and has an array  144  of one or more electrodes  150  positioned to be substantially aligned with portions of tonotopically-mapped cochlea  115 . The delivery of stimulation signals at various locations along cochlea  115  causes a hearing percept representative of the received sound  107 . 
     While cochlear implant  120  is described as having external components, in another embodiment, the controller, including the microphone, speech processor and power supply, may also be implantable. In such embodiments, the controller may be contained within a hermetically sealed housing or the housing used for stimulator unit  134 . 
     Electrode assembly  140  preferably assumes an optimal electrode position in cochlea  115  upon or immediately following implantation into the cochlea. It is also desirable that electrode assembly  140  be configured such that the insertion process causes minimal trauma to the sensitive structures of cochlea  115 . Usually electrode assembly  140  is pre-curved, held in a straight configuration at least during the initial stages of the implantation procedure, conforming to the natural shape of the cochlea during and subsequent to implantation. 
       FIG. 2A  is a side view of an embodiment of electrode assembly  140 , referred to herein as electrode assembly  200 .  FIG. 2B  is a top view of electrode assembly  200 .  FIG. 2C  is a cross-sectional view of one embodiment of electrode assembly  200  taken along section line  2 C- 2 C illustrated in  FIG. 2B . 
     Electrode assembly  200  comprises a carrier member  202 , a stop member  204  and lead  206 . Carrier member  202  has a distal end  208  adapted to be implanted furthest into cochlea  115 , and a proximal end  210  connected to a distal end  214  of laterally-extending stop member  204 . The opposing proximal end  216  of stop member  204  is connected to lead  206 . Lead  206  physically and electrically connects electrode assembly  200  with stimulator unit  134 . 
     When implanted in a recipient, the surface of carrier member  202  which faces the interior of cochlea  115  is referred to herein as the medial surface  216  of carrier member  202 . The opposing side of carrier member  202 , referred to herein as lateral surface  218 , faces the external wall and bony capsule (not shown) of cochlea  115 . It should be understood that the terms medial surface, medial direction, and the like, are generally used herein to refer to the surfaces, features and directions toward the center of cochlea  115 , while the terms lateral surface, lateral direction, and the like, are generally used herein to refer to surfaces, features and directions toward the exterior of cochlea  115 . In addition, a longitudinal axis  250  ( FIGS. 2A ,  2 B) and a horizontal axis  220  and vertical axis  222  ( FIG. 2C ) are utilized herein to facilitate understanding of the cross-sectional shape and other features of carrier member  202 . 
     A plurality of spaced-apart electrodes  212  are mounted on or in carrier member  202 . Electrodes  212  may be disposed in a linear or non-linear array on or in carrier member  202 , and may be positioned to align with predetermined regions of tonotopically mapped cochlea  115 . In alternative embodiments, electrodes  212  are implemented as described in U.S. Provisional Patent Application 60/748,217, 60/748,273 and 60/748,314, hereby incorporated by reference herein. 
     As shown in  FIG. 2C , electrodes  212  are, in this embodiment, half-band electrodes disposed on medial surface  216  of carrier member  202 . It should be appreciated, however, that any electrodes now or later developed suitable for a particular application may be used in alternative embodiments of the invention. For example, in one alternative embodiment, electrodes  212  are banded electrodes extending substantially around carrier member  202 . In another alternative embodiment, electrodes  212  do not laterally extend to or around the edges of carrier member  202 . 
     Typically, each electrode  212  is arranged such that its exposed surface is generally parallel with vertical axis  222  of carrier member  202 , as depicted in  FIG. 2C . It should be appreciated, however, that other electrode positions and orientations may be implemented in alternative embodiments. It should further be appreciated that the quantity of electrodes  212  may vary from as few as one or two to as many as twenty-four or more. 
     In certain embodiments, at least one electrode  212  has a surface that is at least adjacent medial surface  216  of carrier member  202 . Preferably, one or more electrodes  212  has a surface that is collocated with medial surface  216  of carrier member  202 , as shown in  FIG. 2C . In other embodiments, the surfaces of electrodes  212  are raised above or recessed into medial surface  216  of carrier member  202 . 
     Electrodes  212  may be manufactured from a biocompatible conductive material such as platinum, although other materials or combinations of materials may be used. Alternatively, electrodes  212  may be coated with a biocompatible covering that does not interfere with transfer of stimulation signals to cochlea  115 . 
     Each electrode  212  is electrically connected to at least one multi- or single-filament wire  252  that is embedded within flexible carrier member  202 , stop member  204  and lead  206 . In one embodiment, wires  252  are embedded in the volumetric core  280  of carrier member  202 . In an alternative embodiment, wires  252  may be located at or near surfaces  216  and/or  218  of carrier member  202 . In other embodiments, wires  252  are embedded in different regions of carrier member  202  to facilitate curvature and/or to maintain orientation of carrier member  202  once it is implanted. It is through wires  252  that stimulator unit  134  ( FIG. 1 ) provides electrical stimuli to selected electrodes  212 . In one embodiment, wires  252  are connected to electrodes  212  by welding, although any suitable techniques now or later developed to electrically connect electrodes  212  to wires  252  may be used. 
     It should be appreciated that the quantity of wires  252  connected to each electrode  212  may vary. For example, in one alternative embodiment, at least two electrically conducting wires  252  are connected to electrode  212 . It should also be appreciated that suitable transmission means other than filament wires may be used to communicably couple receiver/stimulator unit  134  and electrodes  212 . For example, semiconductor or wireless technologies may be used. 
     In one embodiment, lead  206  ( FIGS. 2A ,  2 B) may extend from carrier member  202  to stimulator  134  or at least the housing thereof. In one particular embodiment, lead  206  is continuous with no electrical connectors, at least external the housing of stimulator unit  134 ; that is, there are no external connectors required to electrically connect electrode assembly  200  to stimulator  134 . One advantage of this arrangement is that there is no need for a surgeon implanting electrode assembly  200  to make a requisite electrical connection between wires  252  extending from electrodes  212  and stimulator  134 . Stimulator  134  is preferably encased within an implantable housing that is implantable within the recipient. The housing for stimulator  134  is preferably implantable within a recess in the bone behind the ear posterior to the mastoid. 
     Carrier member  202  has a fabiform, i.e. bean-shape, cross section as shown in  FIG. 2C . Carrier member  202  comprises an elongate central region  226  and unitary or integral side regions  228 . In the embodiment shown in  FIG. 2C , side regions  228  vertically extend along vertical axis  222  from opposing sides of central region  226 . In addition, side regions  228  are substantially uniform in dimensions and orientation. As such, this embodiment of carrier member  202  is substantially symmetrical about horizontal axis  220 . 
     The surface tangent of medial surface  216 , lateral surface  218  and surfaces  230  of side regions  228  change gradually from one surface to an adjacent surface to form a smooth, contiguous carrier member surface with no sharp or locally discrete edges or corners. Each of these surfaces  216 ,  218  and  230  are described in detail next below. 
     The portion of lateral surface  218  at central region  226 , referred to as lateral surface  218 C, has a convex shape with a substantially consistent radius of curvature. Similarly, the shape of lateral surface  218  at side regions  228 , referred to as lateral surfaces  218 S, are similarly convex and also have a consistent radius of curvature. As shown in  FIG. 2C , the radius of curvature of central and side region lateral surfaces  218 C,  218 S is substantially the same, resulting in a carrier member lateral surface  218  that has a substantially consistent radius across the entire lateral surface. 
     The portion of medial surface  216  at central region  226 , referred to as medial surface  216 C, is a concave surface. The portion of medial surface  216  at side regions  228 , referred to herein as medial surfaces  216 S, are convex. The surface slope of carrier member  202  transitions gradually from medial surfaces  216 S of side regions  228  to medial surface  216 C at central region  226 , as shown in  FIG. 2C . 
     It should be appreciated that the radius of curvature of concave surface  216 C and convex surfaces  216 S may be different in alternative embodiments depending, for example, on the relative thickness of central region  226  and side regions  228 , the desired rate of change of the surface slope across medial surface  216 , and the desired proximity of electrodes  212  disposed on medial surface  216 . 
     Side surfaces  230  comprise convex surface  238  between and contiguous with convex surfaces  216 S and  218 S. In other words, side regions  228  each have convex surface  238  that provides a transition between opposing medial and lateral surfaces  216 S,  218 S. As shown in  FIG. 2C , side surfaces  230  have no sharp edges. Rather, side surfaces  230  have a minimum radius of curvature which is greater than zero to provide smooth, curved ends on carrier member  202 . This reduces the likelihood that side surfaces  230  of carrier member  202  may damage cochlea  115  or its surrounding anatomy during or after implantation. 
     In certain embodiments, carrier member  202  has a minimized volume to facilitate implantation. This reduced cross-sectional volume may cause conventional carrier members to bend in unintentional directions during implantation. To prevent this from occurring, embodiments of carrier member  202  have longitudinally-extending structural support as described in International Application PCT/US06/34010 entitled, “Elongate Implantable Carrier Member Having An Embedded Stiffener,” and filed Aug. 31, 2006; U.S. patent application entitled “Prosthetic Hearing Implant Electrode Assembly Having Optimal Length for Atraumatic Implantation,” filed concurrently U.S. application Ser. No. 11/605,952 (US Publication 2007/0162098 A1); and U.S. patent application entitled “Flexible Electrode Assembly Having Variable Pitch Electrodes for a Stimulating Medical Device,” filed concurrently under U.S. application Ser. No. 11/605,960 (US Publication 2007/0135885 A1) all of which are hereby incorporated by reference herein. 
     In other embodiments, such support is additionally or alternatively provided by the distribution of embedded wires  252 . In alternative embodiments, such structural support may be provided by other materials embedded in carrier member  202 , by varying the density or materials used to form carrier member  202 , etc. Such embodiments provide for establishing selective flexibility along carrier member  202  to, for example, increase the “pushability” and “trackability” of carrier member  202  during insertion. It should be appreciated, however, that such selective flexibility should not prevent carrier member  202  from being able to coil or turn  290 ,  292  about vertical axis  222  so that it may follow the contour of cochlea  115  during implantation. In other words, such structural support serves to increase the longitudinal rigidity and, perhaps, limit curving  294  about horizontal axis  220  while permitting curving  290  about vertical axis  222 . In one embodiment, the thickness of carrier member  202  is substantially constant for at least a majority of its length. In other embodiments, the thickness may be longitudinally tapered as described in the above-noted US Provisional Applications. 
     This fabiform cross-section of carrier member  202  is continuous along axial direction  250  of electrode assembly  200  and may be achieved by any manufacturing process now or later developed. In one embodiment, carrier member  202  is formed by excluding material (either or both silicone carrier and platinum contacts) from carrier member  202 . 
     The fabiform cross-section encourages carrier member  202  to curve or coil about a vertical axis  222 ; that is, curving medially toward the modiolus of cochlea  115 . This arrangement provides an electrode carrier member  202  that retains its natural stiffness, however, when encouraged (such as when a straight electrode assembly  200  makes contact with a lateral wall of cochlea  115 ) the electrode assembly  200  will more easily and naturally curve in the desired direction (medially) thus reducing impact and friction forces. This is because there is less mass of material created by the concave cross-section, the resistance to coiling toward a convex surface, and/or other features. 
     An advantage of the noted fabiform cross-sectional shape of carrier member  202  over conventional carrier members is a reduction of the risk of causing residual hearing loss upon insertion of electrode assembly  200 . Hence, this is particularly suited for straight electrode assemblies that are intended to preserve residual hearing. Straight electrode assemblies rely on the fragile cochlea structures to guide and curve the carrier member as it progresses along the lateral wall of cochlea  115 . Being able to reduce the forces on these structures provides significant benefits. However, the fabiform profile can be used for non-EAS applications as well. 
     Additionally, electrode assembly  200  will tend to retain its orientation once inserted into cochlea  115 . Having a non-symmetrical cross-section also ensures that some stiffness is maintained perpendicular to the curvature, therefore ensuring that electrode assembly  200  does not twist or rotate axially, ensuring electrodes  212  are always directed toward the nerve. This is similar to say a tape measure whose curvature helps maintain orientation whilst still allowing it to be retracted and curled into the housing. 
     Maintaining orientation allows the placement of electrodes  212  on medial side  216  only, so that lateral side  218  of carrier member  202  can be a continuous smooth silicone surface, further reducing friction. 
     A further alternative arrangement is for concave surface  216 C to be parabolic, thereby providing additional benefits as far as focusing the charge from each electrode  212 . This may improve stimulation specificity. 
     Another advantage of certain aspects and embodiments of the present invention is that elongate carrier member  202  facilitates atraumatic implantation through the round window membrane  110 . Creating cochleostomy  142  has the potential of inducing trauma as a result of drilling the cochlea bone. For example, the drilling may cause bone dust to enter cochlea  115 , mechanical trauma, suction of perilymph, etc. In addition, there is a likelihood that the location of cochleostomy  142  is less than optimal for atraumatic insertion of an electrode assembly carrier member. In contrast, implantation through round window  111  guarantees a proper positioning of the electrode assembly in the scala tympani, and requires no drilling. However the anatomy of round window  111  requires utilizing either a very thin carrier member (&lt;0.5 mm) or a carrier member of the present invention having a kidney bean cross-sectional shape to allow insertion through a slit in round window membrane  111  (parallel to lateral vertical axis  222 ), whilst still leaving the round window intact and mobile. 
       FIG. 3A  is an enlarged view of one embodiment of a tip region of the electrode assembly illustrated in  FIG. 2A , referred to herein as tip region  302 . In certain embodiments, a longitudinally-tapered tip region is formed at distal end  208  of carrier member  202 . In one embodiment, the thickness of carrier member  202  gradually tapers toward distal end  208  in tip region  302 . Tip region  302  facilitates the insertion of carrier member  202  into a recipient&#39;s cochlea. In one embodiment, tip region  302  comprises a taper  308  which slopes from lateral surface  218  rearward and inward toward medial surface  216 . Such a tapered tip region  208  aids the coiling of carrier member  202  during implantation and further helps prevent damage to the delicate structures of the cochlea. In alternative embodiments, tip region  302  is a rounded surface  306  extending from medial surface  216  to front edge  304 , and a rounded surface  308  extending from lateral surface  218  to front edge  304 . Thus, in this embodiment, both sides of carrier member  202  are tapered, with each having a different radius of curvature. 
     An alternative embodiment of a tip region of electrode assembly  200  is illustrated in  FIG. 3B , referred to herein as tip region  320 . Here, tip region  320  has a bottle-nose configuration. That is, at tip region  320  medial surface  216  is curved  322  toward lateral surface  218 . An extension  324  extends beyond curvature  322  to form a plateau  326 . The surface of extension  324  opposing plateau  326  is, in this embodiment, planar and contiguous with lateral surface  218 . The leading edge of extension  324  is curved or rounded to provide a blunt leading surface on a carrier member  202  implanting tip region  320 . The radius of curvature of curved surface  350  preferably transitions gradual from medial surface  216  and plateau  326  to avoid abrasions. 
       FIG. 3C  is a side view of another embodiment of a tip region of carrier member  202 , referred to herein as tip region  350 . Tip region  350  is configured to facilitate coiling of carrier member  202  around vertical axis  222  toward medial surface  216 , as well as to minimize trauma, when carrier member  202  is inserted through round window  110  of cochlea  115 . 
     Tip region  350  tapers  354  toward a narrower distal end  352  on lateral surface  218  taper  354  begins at a curvature  358  that has a radius of curvature that substantially matches the curvature of the lateral wall of cochlea  115 . In this exemplary embodiment, the opposing side  356  is substantially planar and is continuous with medial surface  216 . 
     Surfaces  354  and  356  merge at distal end  352 , as shown in  FIG. 3C . Distal end  352  has a radius of curvature that is substantially small such that the diameter defined by such radius of curvature is substantially less than the thickness or diameter  360  of the body of carrier member  202 . 
     Profiled tip region  350  reduces the contact area with the spiral ligament and also increase the safe/atraumatic insertion angle range. Additionally tip region  350  has been shown to more easily be inserted through the round window  111  as it acts as a wedge, opening up the slit membrane as carrier member  202  is inserted. That is, after the membrane forming round window  111  has been slit the surgeon must open the slit to some extent to pass carrier member  202  through. If a conventional blunt electrode is used, the force required to pass it through the slit may be greater than the force required to buckle electrode assembly  200 . In contrast, a carrier member  202  having a profiled tip  350  reduces the force required to introduce electrode assembly  200  through round window  110 , allowing the use of a more flexible electrode assembly  200 . 
     In alternative embodiments, the tip region of carrier member  202  may be as described in U.S. patent application Ser. No. 10/825,358 (Now Abandoned), which is hereby incorporated by reference herein. 
     Although the present invention has been fully described in conjunction with several embodiments thereof with reference to the accompanying drawings, it is to be understood that various changes and modifications may be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom. 
     All documents, patents, journal articles and other materials cited in the present application are hereby incorporated by reference, herein.