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Brain Res. 1996 May 20;721(1-2):22-38.

Stimulus-related and movement-related single-unit activity in rabbit cingulate cortex and limbic thalamus during performance of discriminative avoidance behavior.

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Department of Psychology, University of Illinois, Urbana-Champaign 61801, USA.


Neuronal discharges related to acoustic conditional stimuli and locomotive behavioral responses of 152 anterior and medial dorsal (MD) thalamic and cingulate cortical single-units sorted from multi-unit activity were recorded as rabbits performed in a discriminative avoidance task. The goals were: (1) to document the single-unit constituents of multi-site, multi-unit activity recorded previously in response to the conditional stimuli used for avoidance training; and (2) to document neuronal activity related to the onset of the behavioral avoidance response. Ninety-five units showed discriminative discharges: significantly different firing rates 90-700 ms after a foot shock-predictive conditional stimulus (CS+) than to a safety-predictive conditional stimulus (CS-). In accord with the multi-unit data, a majority of these units discharged at higher rates after the CS+ than after the CS-. The discharge rates of 87 units were greater during the 2-s period preceding the onset of avoidance responses than during comparable trial periods after CS-presentations followed by no response. Fifty-six of the 87 avoidance-related units exhibited a progressive ramp-like firing increase 2 s before the avoidance response, with the maximal discharge rate occurring 200 ms before the response. These dynamic pre-avoidance discharges occurred first in limbic thalamus then in cingulate cortex, suggesting that cortical pre-motor processing may confer temporal specificity upon a more generalized command volley relayed from thalamus. Unlike the multi-unit data, 24 neurons exhibited inverse discrimination, i.e., significantly greater discharges in response to the CS-than to the CS+. Also 27 neurons showed significantly more firing in the 2-s period before the end of CS-trials in which no behavioral response occurred, than in the 2-s pre-avoidance period on CS+ trials with responses. This "inverse' CS-related and pre-avoidance activity occurred at low incidence (< 15%) in all areas except the MD nucleus, wherein it was exhibited by 45% of the recorded units. The inverse activity may reflect the operation of local inhibitory neurons which suppress the discharges of other neurons in response to the CS-. The prevalence of inverse activity in the MD nucleus suggested an involvement of this area in behavioral inhibition.

[Indexed for MEDLINE]

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