Journal of Neuroscience, Vol 6, 3611-3617, Copyright © 1986 by Society for Neuroscience
Corticofugal influences of S1 cortex on ventrobasal thalamic neurons in the awake rat
B Yuan, TJ Morrow and KL Casey
Corticofugal influences on the responses of 39 ventrobasal (VB) thalamic
neurons to repetitive stimuli were studied in awake rats by focally
suppressing the evoked and spontaneous electrocortical activity of the
primary (S1) somatosensory cortex with magnesium or lidocaine plus
magnesium. Suppression of the S1 cortex reduced the number of spikes
discharged by 19 (66%) of 29 VB units in response to each of 25 electrical
stimuli delivered to the medial lemniscus; 9 units were unaffected and 1
showed an increased response to 1-10 Hz stimuli. The responses of 6 (38%)
of 16 VB units to electrical somatic stimuli were also reduced following S1
cortical suppression; 9 units were unaffected and 1 showed an increased
response to 20-40 Hz stimuli. A comparison of the reduced responsiveness of
5 units studied during medial lemniscal and somatic stimulation did not
reveal any additional response attenuation attributable to subthalamic
corticofugal influences. We conclude that, in the awake rat, somatosensory
transmission to VB thalamic neurons is primarily facilitated by S1
corticothalamic neurons.