Two distinct neuronal populations in the rat parafascicular nucleus oppositely encode the engagement in stimulus-driven reward-seeking

Abstract

The thalamus is a phylogenetically well-preserved structure. Known to densely contact cortical regions, its role in the transmission of sensory information to the striatal complex has been widely reconsidered in recent years. The parafascicular of the thalamus (Pf) has been implicated the orientation of attention towards salient sensory stimuli. In a stimulus-driven reward seeking task, we sought to characterize the electrophysiological activity of Pf neurons in rats. We observed a predominance of excitatory responses over inhibitory responses for all events of the task. Neurons responded more strongly to the stimulus compared to lever-pressing and collecting reward, confirming the strong involvement of the Pf in sensory information processing. The use of long sessions allowed us to compare neuronal responses to stimuli when the animal engaged in action or when it did not. We distinguished two populations of neurons responding in an opposite way: MOTIV+ neurons responded more intensively to stimuli followed by a behavioral response than those that did not. Conversely, MOTIV-neurons responded more strongly when the stimulus was ignored by the animal. In addition, MOTIV-neurons excitations appeared at a shorter latency after the stimulus than MOTIV+ neurons. Through this encoding, Pf could perform an early selection of environmental stimuli transmitted to the striatum according to motivational level. HIGHLIGHTSO_LIPf neurons respond to reward-predicting stimuli and reward-related actions C_LIO_LIMOTIV+ Pf neurons were more active to stimuli evoking reward-seeking C_LIO_LIMOTIV- Pf neurons were more active to stimuli ignored by the animal C_LIO_LIStimuli-evoked excitations latencies were shorter in MOTIV- than MOTIV+ neurons C_LI