Recruitment and disruption of ventral pallidal cue encoding during alcohol seeking.

A critical area of inquiry in the neurobiology of alcohol abuse is the mechanism by which cues gain the ability to elicit alcohol use. Previously, we found that cue-evoked activity in rat ventral pallidum robustly encodes the value of sucrose cues trained under both Pavlovian and instrumental contingencies, despite a stronger relationship between cue-evoked activity and behavioral latency after instrumental training (Richard et al., 2018, Elife, 7, e33107). Here, we assessed: (a) ventral pallidal representations of Pavlovian versus instrumental cues trained with alcohol reward, and (b) the impact of non-associative alcohol exposure on ventral pallidal representations of sucrose cues. Decoding of cue identity based on ventral pallidum firing was blunted for the Pavlovian alcohol cue in comparison to both the instrumental cue trained with alcohol and either cue type trained with sucrose. Further, non-associative alcohol exposure had opposing effects on ventral pallidal encoding of sucrose cues trained on instrumental versus Pavlovian associations, enhancing decoding accuracy for an instrumental discriminative stimulus and reducing decoding accuracy for a Pavlovian conditioned stimulus. These findings suggest that alcohol exposure can drive biased engagement of specific reward-related signals in the ventral pallidum.

Basolateral amygdala population coding of a cued reward seeking state depends on orbitofrontal cortex.

Basolateral amygdala (BLA) neuronal responses to conditioned stimuli are closely linked to the expression of conditioned behavior. An area of increasing interest is how the dynamics of BLA neurons relate to evolving behavior. Here, we recorded the activity of individual BLA neurons across the acquisition and extinction of conditioned reward seeking and employed population-level analyses to assess ongoing neural dynamics. We found that, with training, sustained cue-evoked activity emerged that discriminated between the CS+ and CS- and correlated with conditioned responding. This sustained population activity continued until reward receipt and rapidly extinguished along with conditioned behavior during extinction. To assess the contribution of orbitofrontal cortex (OFC), a major reciprocal partner to BLA, to this component of BLA neural activity, we inactivated OFC while recording in BLA and found blunted sustained cue-evoked activity in BLA that accompanied reduced reward seeking. Optogenetic disruption of BLA activity and OFC terminals in BLA also reduced reward seeking. Our data suggest that sustained cue-driven activity in BLA, which in part depends on OFC input, underlies conditioned reward-seeking states.

Encoding and context-dependent control of reward consumption within the central nucleus of the amygdala.

Dysregulation of the central amygdala is thought to underlie aberrant choice in alcohol use disorder, but the role of central amygdala neural activity during reward choice and consumption is unclear. We recorded central amygdala neurons in male rats as they consumed alcohol or sucrose. We observed activity changes at the time of reward approach, as well as lick-entrained activity during ongoing consumption of both rewards. In choice scenarios where rats could drink sucrose, alcohol, or quinine-adulterated alcohol with or without central amygdala optogenetic stimulation, rats drank more of stimulation-paired options when the two bottles contained identical options. Given a choice among different options, central amygdala stimulation usually enhanced consumption of stimulation-paired rewards. However, optogenetic stimulation during consumption of the less-preferred option, alcohol, was unable to enhance alcohol intake while sucrose was available. These findings indicate that the central amygdala contributes to refining motivated pursuit toward the preferred available option.

A stable, distributed code for cue value in mouse cortex during reward learning.

The ability to associate reward-predicting stimuli with adaptive behavior is frequently attributed to the prefrontal cortex, but the stimulus-specificity, spatial distribution, and stability of prefrontal cue-reward associations are unresolved. We trained head-fixed mice on an olfactory Pavlovian conditioning task and measured the coding properties of individual neurons across space (prefrontal, olfactory, and motor cortices) and time (multiple days). Neurons encoding cues or licks were most common in the olfactory and motor cortex, respectively. By quantifying the responses of cue-encoding neurons to six cues with varying probabilities of reward, we unexpectedly found value coding in all regions we sampled, with some enrichment in the prefrontal cortex. We further found that prefrontal cue and lick codes were preserved across days. Our results demonstrate that individual prefrontal neurons stably encode components of cue-reward learning within a larger spatial gradient of coding properties.

Encoding and context-dependent control of reward consumption within the central nucleus of the amygdala.

The ability to evaluate and select a preferred option among a variety of available offers is an essential aspect of goal-directed behavior. Dysregulation of this valuation process is characteristic of alcohol use disorder, with the central amygdala being implicated in persistent alcohol pursuit. However, the mechanism by which the central amygdala encodes and promotes the motivation to seek and consume alcohol remains unclear. We recorded single-unit activity in male Long-Evans rats as they consumed 10% ethanol or 14.2% sucrose. We observed significant activity at the time of approach to alcohol or sucrose, as well as lick-entrained activity during the ongoing consumption of both alcohol and sucrose. We then evaluated the ability of central amygdala optogenetic manipulation time-locked to consumption to alter ongoing intake of alcohol or sucrose, a preferred non-drug reward. In closed two-choice scenarios where rats could drink only sucrose, alcohol, or quinine-adulterated alcohol with or without central amygdala stimulation, rats drank more of stimulation-paired options. Microstructural analysis of licking patterns suggests these effects were mediated by changes in motivation, not palatability. Given a choice among different options, central amygdala stimulation enhanced consumption if the stimulation was associated with the preferred reward while closed-loop inhibition only decreased consumption if the options were equally valued. However, optogenetic stimulation during consumption of the less-preferred option, alcohol, was unable to enhance overall alcohol intake while sucrose was available. Collectively, these findings indicate that the central amygdala processes the motivational value of available offers to promote pursuit of the most preferred available option.

Contexts facilitate dynamic value encoding in the mesolimbic dopamine system.

Adaptive behavior in a dynamic environment often requires rapid revaluation of stimuli that deviates from well-learned associations. The divergence between stable value-encoding and appropriate behavioral output remains a critical test to theories of dopamine's function in learning, motivation, and motor control. Yet how dopamine neurons are involved in the revaluation of cues when the world changes to alter our behavior remains unclear. Here we make use of pharmacology, in vivo electrophysiology, fiber photometry, and optogenetics to resolve the contributions of the mesolimbic dopamine system to the dynamic reorganization of reward-seeking. Male and female rats were trained to discriminate when a conditioned stimulus would be followed by sucrose reward by exploiting the prior, non-overlapping presentation of a separate discrete cue - an occasion setter. Only when the occasion setter's presentation preceded the conditioned stimulus did the conditioned stimulus predict sucrose delivery. As a result, in this task we were able to dissociate the average value of the conditioned stimulus from its immediate expected value on a trial-to-trial basis. Both the activity of ventral tegmental area dopamine neurons and dopamine signaling in the nucleus accumbens were essential for rats to successfully update behavioral responding in response to the occasion setter. Moreover, dopamine release in the nucleus accumbens following the conditioned stimulus only occurred when the occasion setter indicated it would predict reward. Downstream of dopamine release, we found that single neurons in the nucleus accumbens dynamically tracked the value of the conditioned stimulus. Together these results reveal a novel mechanism within the mesolimbic dopamine system for the rapid revaluation of motivation.

Dorsomedial Striatal Activity Tracks Completion of Behavioral Sequences in Rats.

For proper execution of goal-directed behaviors, individuals require both a general representation of the goal and an ability to monitor their own progress toward that goal. Here, we examine how dorsomedial striatum (DMS), a region pivotal for forming associations among stimuli, actions, and outcomes, encodes the execution of goal-directed action sequences that require self-monitoring of behavior. We trained rats to complete a sequence of at least five consecutive lever presses (without visiting the reward port) to obtain a reward and recorded the activity of individual cells in DMS while rats performed the task. We found that the pattern of DMS activity gradually changed during the execution of the sequence, permitting accurate decoding of sequence progress from neural activity at a population level. Moreover, this sequence-related activity was blunted on trials where rats did not complete a sufficient number of presses. Overall, these data suggest a link between DMS activity and the execution of behavioral sequences that require monitoring of ongoing behavior.

Reward activity in ventral pallidum tracks satiety-sensitive preference and drives choice behavior.

A key function of the nervous system is producing adaptive behavior across changing conditions, like physiological state. Although states like thirst and hunger are known to impact decision-making, the neurobiology of this phenomenon has been studied minimally. Here, we tracked evolving preference for sucrose and water as rats proceeded from a thirsty to sated state. As rats shifted from water choices to sucrose choices across the session, the activity of a majority of neurons in the ventral pallidum, a region crucial for reward-related behaviors, closely matched the evolving behavioral preference. The timing of this signal followed the pattern of a reward prediction error, occurring at the cue or the reward depending on when reward identity was revealed. Additionally, optogenetic stimulation of ventral pallidum neurons at the time of reward was able to reverse behavioral preference. Our results suggest that ventral pallidum neurons guide reward-related decisions across changing physiological states.

A quantitative reward prediction error signal in the ventral pallidum.

The nervous system is hypothesized to compute reward prediction errors (RPEs) to promote adaptive behavior. Correlates of RPEs have been observed in the midbrain dopamine system, but the extent to which RPE signals exist in other reward-processing regions is less well understood. In the present study, we quantified outcome history-based RPE signals in the ventral pallidum (VP), a basal ganglia region functionally linked to reward-seeking behavior. We trained rats to respond to reward-predicting cues, and we fit computational models to predict the firing rates of individual neurons at the time of reward delivery. We found that a subset of VP neurons encoded RPEs and did so more robustly than the nucleus accumbens, an input to the VP. VP RPEs predicted changes in task engagement, and optogenetic manipulation of the VP during reward delivery bidirectionally altered rats' subsequent reward-seeking behavior. Our data suggest a pivotal role for the VP in computing teaching signals that influence adaptive reward seeking.

Distinct recruitment of dorsomedial and dorsolateral striatum erodes with extended training.

Hypotheses of striatal orchestration of behavior ascribe distinct functions to striatal subregions, with the dorsolateral striatum (DLS) especially implicated in habitual and skilled performance. Thus neural activity patterns recorded from the DLS, but not the dorsomedial striatum (DMS), should be correlated with habitual and automatized performance. Here, we recorded DMS and DLS neural activity in rats during training in a task promoting habitual lever pressing. Despite improving performance across sessions, clear changes in corresponding neural activity patterns were not evident in DMS or DLS during early training. Although DMS and DLS activity patterns were distinct during early training, their activity was similar following extended training. Finally, performance after extended training was not associated with DMS disengagement, as would be predicted from prior work. These results suggest that behavioral sequences may continue to engage both striatal regions long after initial acquisition, when skilled performance is consolidated.