Latency as a function of intensity in auditory neurons: influences of central processing

The response latencies of sensory neurons typically shorten with increases in stimulus intensity. In the central auditory system this phenomenon shoul d have a significant impact on a number of auditory functions that depend c ritically on an integration of precisely timed neural inputs. Evidence from previous studies suggests that the auditory system not only copes with the potential problems associated with intensity-dependent latency change, but that it also modifies latency change to shape the response properties of m any cells for specific functions. This observation suggests that intensity- dependent latency change may undergo functional transformations along the a uditory neuraxis. The goal of our study was to explore these transformation s by making a direct, quantitative comparison of intensity-dependent latenc y change among a number of auditory centers from the lower brainstem to the thalamus. We found two main ways in which intensity-dependent latency chan ge transformed along the neuraxis: (1) the range of latency change increase d substantially and (2) one particular type of latency change, which has be en suggested to be associated with sensitivity to temporally segregated sti mulus components, occurred only at the highest centers tested, the midbrain and thalamus. Additional testing in the midbrain (inferior colliculus) ind icated that inhibitory inputs are involved in shaping latency change. Our f indings demonstrate that the central auditory system modifies intensity-dep endent latency changes. We suggest that these changes may be functionally i ncorporated, actively enhanced, or modified to suit specific functions of t he auditory system. (C) 2000 Elsevier Science B.V. All rights reserved.