CORTICOFUGAL AMPLIFICATION OF SUBCORTICAL RESPONSES TO SINGLE TONE STIMULI
IN THE MUSTACHED BAT.
Yunfeng Zhang and Nobuo Suga.
Department of Biology, Washington University, One Brookings Drive, St.
Louis, MO 63130, U.S.A..
APStracts 4:183N, 1997.
ABSTRACT
Since 1962, physiological data of corticofugal effects on subcortical auditory
neurons have been controversial: inhibitory, excitatory or both. An inhibitory
effect has been much more frequently observed than an excitatory effect.
Recent studies performed with an improved experimental design indicate that
corticofugal system mediates a highly focused positive feedback to
physiologically "matched" subcortical neurons, and widespread lateral
inhibition to "unmatched" subcortical neurons, in order to adjust and improve
information processing. These results lead to a question: what happens to
subcortical auditory responses when the corticofugal system, including matched
and unmatched cortical neurons, is functionally eliminated? We temporarily
inactivated both matched and unmatched neurons in the primary auditory cortex
of the mustached bat with muscimol (an agonist of inhibitory synaptic
transmitter) and measured the effect of cortical inactivation on subcortical
auditory responses. Cortical inactivation reduced auditory responses in the
medial geniculate body and the inferior colliculus. This reduction was larger
(60% vs. 34%) and faster (11 min. vs. 31 min.) for thalamic neurons than for
collicular neurons. Our data indicate that the corticofugal system amplifies
collicular auditory responses by 1.5 times and thalamic responses by 2.5 times
on the average. The data are consistant with a scheme in which positive
feedback from the auditory cortex is modulated by inhibition which may mostly
take place in the cortex.
Received 12 May 1997; accepted in final form 5 August 1997.
APS Manuscript Number J386-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997