Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-03-31
2001-01-16
Layno, Carl H. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06175767
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system and method for electrical stimulation of the inner ear. More particularly, the present invention relates to an implantable device for electrical stimulation of the 8
th
nerve. Even more particularly, the present invention relates to an implantable device for electrical stimulation of the 8
th
nerve to produce the sensation of hearing.
It is well known that brain and nerve impulses are electrical in nature. It is also known that electrical stimuli applied to receptor centers such as the nerves cause a reaction dependent on the electrical characteristics of the stimuli. Many devices utilize these characteristics to compensate for defective performance of sensory organs of the body.
In normal hearing, the hair cells are a critical link in the hearing chain. They serve two functions in association with the brain: (1) they establish a background nerve activity that is perceived as silence (“active silence” as described below); and (2) when sound enters the ear, they generate a potential that varies and modulates this background nerve activity in response to the sound. The resulting nerve activity is a constant plus the derivative of the atmospheric pressure. This derivative or rate of change of pressure carries the sound information. Important to the present invention is the recognition that the rate or frequency or density of the resultant nerve activity may be viewed as a carrier modulated by sound.
In the profoundly deaf patient, the principal cause of deafness is the loss of function of the hair cells. In 30% of the deaf, the loss of nerve fibers from the spiral ganglion to the non-functioning hair cells is a contributory cause of deafness. This may be caused due to inactivity of the nerve fibers from the hair cells to the spiral ganglion. Therefore, to restore hearing to a person with a partial or total (profound) loss of hearing, a replacement of these functions is required past the point of loss of function, that is at a higher link to the brain.
In the case of the ear and associated hearing functions, many devices have been designed to electrically stimulate the auditory nerve of the human body, which is known as the 8th cranial nerve. However, these devices operate on principles derived from an inappropriate extrapolation of certain observations made by Beckesy in the 1930's. Beckesy's observations concerned the Basilar membrane, which extends the entire length of the Cochlea. These observations revealed that the Basilar membrane vibrates in response to sound vibrations that enter the ear. It was observed by Beckesy, and confirmed by others, that the sound vibrations caused the membrane to vibrate with a standing wave wherein the maximum amplitude of the standing wave occurred at a location on the membrane dependent on the frequency of the entering sound vibrations. Individual hair cell activity at these locations was also particularly pronounced at the locations of the maximum amplitude of the standing wave. High frequencies result in a maximum amplitude at the entrance to the Cochlea. As the frequency decreases, the location of this maximum amplitude moves toward the extreme end of the Cochlea.
While this mechanical action is true and individual hair cell activity is emphasized at these maximum amplitude locations, others have inappropriately extrapolated these observations to conclude that hearing was effected by the response of the individual nerve fibers along the length of the Cochlea that were frequency dependent. Thus, the theory developed, known as the Place Theory of hearing, that the nerve fibers in the Cochlea conduct different frequencies to the brain dependent on their location in the Cochlea. It is curious that the absolute length of the cochlear duct, which varies from 5 mm in the chicken to over 100 mm in the whale, does not seem to play a very important role in the frequency range of the Cochlea, i.e., the whale has a slightly greater frequency range than a chicken even though the Place Theory of hearing would suggests that, with a Cochlea that is 20 times longer, the whale's frequency range should be 20 times greater than the chicken's.
The Place Theory of hearing requires that the nerves in the Cochlea operate in a manner different from the manner in which all other nerves in the body operate. The present invention is based on a model of hearing that is entirely different than the Place Theory. This invention, in contrast to the Place Theory, is based upon the application of signal processing principles to the function of the nerve fibers of the 8
th
nerve terminating in the vestibule and Cochlea, much like the operation of modern communication receivers that use Digital Signal Processing to reduce noise and process information.
The nerves terminating in the Vestibule and/or Cochlea that transfer sound sensation are non-specific and may be fired in sequence or as a sustained background nerve activity by a single pulse which, when modulated, produces the sensation of the sound of the modulation for a given period of time. Accordingly, given the principles guiding the present invention, the nerve fibers in the 8
th
nerve operate in a manner identical to those throughout the body. In particular, the signal sent by the nerves is non-specific but the number of nerves firing and the rate of firing conveys information to the brain that the brain translates into sound. The number of nerve fibers firing simultaneously or at such a high repetition rate that it appears simultaneous is a function of the instantaneous sound intensity, variations of this nerve activity is perceived as sound.
The model of hearing upon which the present invention is based recognizes that many nerve fibers of the Cochlea have functions other than the conduction of sound. It is recognized that the very regular and orderly spatial arrangement of the sensory elements in the Cochlea predispose it to work on the basis of spatial principles, however, not in accordance with the Place Theory of hearing. It has been observed that stimulation of many of these fibers does not produce the sensation of sound. The brain utilizes the Cochlea as a mechanism to control the sound pressure variations as a result of the sound vibrations and thereby serve as a means of volume control.
In this mode, some of the outer hair cells of the Cochlea sense the motion of the Basilar membrane, transmit this information to the brain which in turn sends back signals to many of the hair cells in the Cochlea to control the stiffness of the Basilar membrane and thereby control the mechanical impedance at the entrance from the Vestibule to the Cochlea. This then allows for an automatic volume control (in the mechanical domain) and possibly a means of controlling the frequency response to improve intelligibility. Changing the mechanical characteristics of the Basilar membrane changes the mechanical transfer of energy to the hair cells thus effecting sensitivity and frequency response. The Cochlea may also contribute to the process of sound localization.
Audio signals of speech and music are found to have most of their energy concentrated in the lower-frequency ranges. To achieve an improvement in the signal-to-noise ratio, preemphasis (boosting the gain of a signal) of the high frequencies should be observed and a corresponding deemphasis at the detection in the brain. Consistent with this notion, Becksey published in 1960 that patterns of vibration of the Cochlear partition of cadavers for various frequencies showed a preemphasis of the high frequencies in the first 10-mm distance from the stapes. In 1974, Rhode published a graph of the input-output ratio, in decibels, for the Malleus and Basilar membrane (FIG.
21
A). The graph shows an increase of 6 dB per octave (or 20 dB per decade) of the frequencies between 200 Hz and 8 kHz. Also
FIG. 21B
shows that a broad range of frequencies stimulates the hair cells in this area. These observations tend to support the concept of preemphasis. Observations also suggest that the outer hai
Layno Carl H.
Scully Scott Murphy & Presser
LandOfFree
Multichannel implantable inner ear stimulator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multichannel implantable inner ear stimulator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multichannel implantable inner ear stimulator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2508975