Journal of Neuroscience, Vol 11, 3379-3387, Copyright © 1991 by Society for Neuroscience
Patterns of activity coding discrimination of auditory stimuli differ between mid- and posterolateral thalamus of cats
CD Woody, O Melamed and V Chizhevsky
Mental Retardation Research Center, UCLA Medical Center 90024.
The auditory function of units in the mid- (lateralis dorsalis and
centrolateral nuclei) and posterolateral (lateralis posterior-pulvinar
complex) thalamus of cats was assessed during performance of conditioned
eye blink responses (CRs) elicited discriminatively by a forward-paired, 70
dB click conditioned stimulus (CS) as opposed to a backward-paired, 70 dB
hiss discriminative stimulus (DS). Discharges in response to the CS or DS
were found in over 40% of units tested in each area, with onset latencies
as short as 28-32 msec in mid-thalamus and 14 msec in posterolateral
thalamus. The results provide evidence that both mid- and posterolateral
thalamic regions of cats contain sufficient numbers of auditory responsive
neurons to be considered part of the auditory system functionally. Patterns
of activity changed after conditioning discriminative responses to the
click CS. In mid-thalamus, the ratio of CS-evoked activity to baseline
activity increased relative to levels found before conditioning. This
increase was attributable to an increase in the magnitude of response to
the CS. In posterolateral thalamus, an increase in the signal: noise ratio
of activity in response to the CS was also found after conditioning, but
this increase depended in large part on a decrease in the rate of baseline
firing. Posterolateral thalamic units had substantially higher mean rates
of baseline firing than mid-thalamic units before any conditioning sessions
were begun.(ABSTRACT TRUNCATED AT 250 WORDS)