ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pPP69. Rate of rise sensitivity of medial geniculate neurons in the squirrel monkey.

John F. Olsen

Lab. Neurophysiol., NIMH, NIH, Bldg. 110, P.O. Box 608, Poolesville, MD 20837

In this study neural sensitivity to rate of rise was measured. The responses of 32 medial geniculate neurons to linear increments of a broadband noise from a defined baseline level were recorded extracellularly. Step rise time (3--96 ms), step amplitude (6--24 dB), and baseline level (0--73 dB SPL) were varied independently. A typical response to the step consisted of a transient burst of 1--8 spikes. Response probability increased as a function of the step's rate of rise (amplitude/rise time), such that increases in rise time could be traded for proportional increases in step amplitude to obtain a criterion response. Increases in baseline level decreased the slope of the probability versus rate of rise function and increased the threshold rate of rise. Response probability was independent of peak level (=baseline level+step amplitude). The results show that the response of a common type of medial geniculate neuron is determined by the rate at which stimulus amplitude increases from a defined background level, indicating a possible role for these neurons in the perceptual segregation of auditory events [A. S. Bregman, P. A. Ahad, and J. Kim, 2694--2703 (1994)].