title: Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus.
abstract: 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.
authors: Department of Speech and Hearing Sciences, University of Washington, WA 98105, USA. jbierer@u.washington.edu
authors: Julie Arenberg
authors: JA
authors: Bierer
authors: Steven M
authors: SM
authors: Bierer
authors: John C
authors: JC
authors: Middlebrooks
mesh_terms: 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