Reward-associated inhibition and pain-associated excitation lasting seconds in single intralaminar thalamic units.

Abstract

Reward sites in the medial forebrain bundle (MFB) and aversive reticular sites (RET) send projections to the medial thalamus and elicit opposite changes in intralaminar unit activity with durations (seconds) similar to those of subjective sensations produced by reinforcing stimuli. To describe the anatomical distribution and to estimate the number of cells showing prolonged rate changes (10-sec poststimulus periods) to MFB and RET stimuli (0.2 sec, 100 Hz, 0.5-msec cathodal pulses), 427 units were recorded in 15 unanesthetized post-collicular cerveau isole´rats. Longlasting MFB-elicited inhibition and RET-elicited excitation converged on single cells located in the intralaminar thalamus. Convergence of MFB- and RET-evoked excitation was found in the habenula, reticular formation, superior colliculus and thalamus; converging inhibition occurred in the cerebral cortex, reticular formation and thalamus. In the intralaminar thalamus, there was more variation and habituation of unit responses to multimodal sensory stimuli than to MFB or RET stimuli. These anatomical distributions and functional properties of single cells may be useful in the unit analysis of the interrelated reinforcing, arousal and sensory properties of stimuli. The data support the proposition that intralaminar unit activity may play a role in integrating reward and pain mechanisms, with prolonged decreased and increased unit firing related to rewarding and aversive inputs respectively.