Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus.
This study examines patterns of neural activity in response to single biphasic electrical pulses, presented alone or following a forward masking pulse train, delivered by a cochlear implant. Recordings were made along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) in ketamine/xylazine anesthetized guinea pigs. The partial tripolar electrode configuration was used, which provided a systematic way to vary the tonotopic extent of ICC activation between monopolar (broad) and tripolar (narrow) extremes while maintaining the same peak of activation. The forward masking paradigm consisted of a 200 ms masker pulse train (1017 pulses per second) followed 10 ms later by a single-pulse probe stimulus; the current fraction of the probe was set to 0 (monopolar), 1 (tripolar), or 0.5 (hybrid), and the fraction of the masker was fixed at 0.5. Forward masking tuning profiles were derived from the amount of masking current required to just suppress the activity produced by a fixed-level probe. These profiles were sharper for more focused probe configurations, approximating the pattern of neural activity elicited by single (non-masked) pulses. The result helps to bridge the gap between previous findings in animals and recent psychophysical data.
Bierer
Julie Arenberg
JA
Department of Speech and Hearing Sciences, University of Washington, WA 98105, USA. jbierer@u.washington.edu
Bierer
Steven M
SM
Middlebrooks
John C
JC
D000161:Acoustic Stimulation; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001307:Auditory Perception; D001309:Auditory Threshold; D003054:Cochlear Implants; D004558:Electric Stimulation; D006168:Guinea Pigs; D007245:Inferior Colliculi / Q000502:physiology*; D010470:Perceptual Masking; D013997:Time Factors