Principles and outcome in perimodiolar positioning.
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Biomedical subjects
C N Jolly
Publications and source records attributed to C N Jolly.
Guinea pig auditory nerve response triggered by a high density electrode array.
The electrically evoked potential in the auditory nerve is measured when the cochlear is stimulated with a high density electrode array whose microcontacts (20 x 160 microns) are placed close to the nerve cells. Threshold range from 8 to 35 microA with the stimulating electrodes near the spiral ganglion cells. A multi-pole technique for restricting the spread of current with electrical stimulation of the cochlea is tested using neural recording in deafened guinea pigs. The ground based quadrupolar electrode driving configuration has thresholds for neural activation only slightly greater than monopolar stimulation when the electrode contacts are placed less than 50 microns from the neurons. During simultaneous stimulation the monopole and the ground based quadrupolar modes tend to generate similar growth functions (magnitude and latency). The electrode interactions are generally factorial, which means that the algebraic sum of the responses (magnitude growth functions) produced by 2 distinct electrodes is less than when the same 2 electrodes are stimulated simultaneously.
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Quadrupolar stimulation for Cochlear prostheses: modeling and experimental data.
Cochlear implants are electrically driven in monopolar, bipolar, or common ground mode. Ideally, a quadrupolar mode is created with three colinear electrodes, where the outer poles are half the inverse polarity value of the center electrode. The resulting field is highly focused. Models of point sources show that the quadrupolar paradigm offers a greater choice of parameters to shape the field. Simulation with a lumped-parameter model of the cochlea confirms the focusing action of the quadrupole in the layers of the inner ear. Field measurements in saline solution and in the scala tympani of guinea pigs show that focusing occurs with the quadrupolar mode. It is conceivable that quadrupolar stimulation will affect the pitch place coding, reduce channel interaction and limit facial or tactile stimulation induced by current spread.
Animals↗
Effects of electrical current configuration on potential fields in the electrically stimulated cochlea: field models and measurements.
Potential distributions measured within the scala tympani of the anesthetized guinea pig support the assertion that focusing is possible when currents are appropriately delivered to the electrodes in the scala tympani. Results obtained with a lumped-element model agree with measurements made in the inner ears of monkeys during monopolar and bipolar stimulation. The predictions are closer for potential distributions apical to the stimulating electrode than they are for basal distributions. In one monkey, in which electrodes were implanted in the middle ear as well as in the inner ear, we obtained measurements of the impedance from inside the scala tympani to points within the middle ear. These impedances are smaller that those initially used in the model, in which the round window membrane was assumed to have a relatively high impedance. A model of the common ground configuration was developed using finite electrode impedances. Finite impedances broaden the potential distributions in this model. Potential distributions from the lumped element model are compared with those obtained with an analytical model, to suggest ways in which focused and unfocused stimuli can affect the excitation of neurons in the implanted ear.
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