Rate representation of tones in noise in the inferior colliculus of decerebrate cats

Citation
R. Ramachandran et al., Rate representation of tones in noise in the inferior colliculus of decerebrate cats, JARO, 1(2), 2000, pp. 144-160
Citations number
56
Categorie Soggetti
Otolaryngology
Journal title
JARO
ISSN journal
15253961 → ACNP
Volume
1
Issue
2
Year of publication
2000
Pages
144 - 160
Database
ISI
SICI code
1525-3961(200009)1:2<144:RROTIN>2.0.ZU;2-1
Abstract
Neurons in the central nucleus of the inferior colliculus (ICC) of decerebr ate cats show three major response patterns when tones of different frequen cies and sound-pressure levels (SPLs) are presented to the contralateral ea r. The frequency response maps of type I units are uniquely defined by a na rrow excitatory area at best frequency (BF: a unit's most sensitive frequen cy) and surrounding inhibition at higher and lower frequencies. its a resul t of this receptive field organization, type I units exhibit strong excitat ory responses to BF tones but respond only weakly to broadband noise (BBN). These response characteristics predict that type I units are well suited t o encode narrowband signals in the presence of background noise. To test th is hypothesis, the dynamic range properties of ICC unit types were measured under quiet conditions and in multiple levels of continuous noise. As obse rved in previous studies of the auditory nerve and cochlear nucleus, type I units showed upward threshold shifts and discharge rate compression in bac kground noise that partially degraded the dynamic range properties of neura l representations at high noise levers. Although the other two unit types i n the ICC showed similar trends in threshold shift and noise compression, t heir ability to encode auditory signals was compromised more severely in in creasing noise levels. When binaural masking effects were simulated, only t ype 1 units showed an enhanced representation of spatially separated signal s and maskers that was consistent with human perceptual performance in inde pendent psychoacoustic observations. These results support the interpretati on that type 1 units play an important role in the auditory processing of n arrowband signals in background noise and suggest a physiological basis for spatial factors that govern signal detection under free-field listening co nditions.