Ventral Pallidal Representation of Pavlovian Cues and Reward: Population and Rate Codes

Abstract

We recorded neural activity in the ventral pallidum (VP) while rats learned a pavlovian reward association. Rats learned to distinguish a tone that predicted sucrose pellets (CSϩ) from a different tone that predicted nothing (CSϪ). Many VP units became responsive to CSϩ, but few units responded to CSϪ. When two CSϩ were encountered sequentially, the earliest predictor of reward became most potent. Many VP units were also activated when the sucrose reward was received [unconditioned stimulus (UCS)]. These VP units for UCS remained responsive to sucrose reward after learning, even when sucrose was already predicted by CSϩ. Neural representation of reward learning and reward itself was characterized by population codes. The population of units that responded to CSϩ increased with learning, whereas the population that responded to UCS did not change. A relative firing rate code also represented the identities of conditioned stimuli and UCS. Firing rate differences among stimuli were acquired early and remained stable during subsequent training, whereas population codes and behavioral conditioned responses continued to develop during subsequent training. Thus, the VP makes use of dynamic CS population and rate codes to encode pavlovian reward cues in reward learning and uses stable UCS population and firing codes to encode sucrose reward itself.

Disentangling pleasure from incentive salience and learning signals in brain reward circuitry

“…Problematically, however, it has never been clear how NAc-VP circuitry could distinguish various reward signals from each other. Existence of multiple anatomical loops connecting the NAc and VP provides a way to segregate the mixture of reward components, but some NAc and VP subregions and single neurons may also need to represent more than one signal (6,35,47). Here, we find that disentangling of signals can still be faithfully achieved.…”

Individual Differences in Reward Drive Predict Neural Responses to Images of Food

“…The pallidum has seldom been reported in functional imaging studies of reward (Elliott et al, 2000), but comparative research has shown that this area is an important component of the neural systems underlying food motivation and hedonics (McAlonan et al, 1993;Pecina and Berridge, 2000;Tindell et al, 2004;Smith and Berridge, 2005).…”

Affective neuroscience of pleasure: reward in humans and animals

“…This alternative draws on the distinction between phasic dopamine signals (spike-triggered release limited to within synapses) and tonic dopamine signals (spike-independent release extending outside synapses) and typically assigns a learning role specifically to phasic signals (Grace 1991;Grace et al 2007;Niv et al 2007;Phillips et al 2003;Schultz 1997;. Learning and prediction roles of dopamine have been conceptualized as teaching signals, S-S prediction signals about future rewards, and S-R stamping-in or habit reinforcement ( Schultz et al 1997;Tobler et al 2005) and by target systems in nucleus accumbens and related forebrain structures (Aldridge et al 1993;Barnes et al 2005;Carelli 2004;Cromwell et al 2005;Day and Carelli 2007;Ghitza et al 2004;Roitman et al 2005;Taha and Fields 2006;Tindell et al 2004;Wan and Peoples 2006).…”