Where are motivation and value encoded in the brain?

Cues that have been paired with rewards like food and drugs can become incentive cues, which have the ability to induce motivational states like craving, and to invigorate reward-seeking behaviors. One area of the brain where neurons encode motivational vigor is in the ventral pallidum. Around 70% of ventral pallidum neurons increase their activity following a sound cue predicting the availability of sugar. Importantly, we can predict based on these increases in activity whether animals will make a reward seeking response, and how fast they will be to make this response. And when we inhibit these neurons during the cue animals are slower and less likely to seek out sugar. These results make the ventral pallidum a promising area of the brain to study encoding of incentive value. Going forward, I hope to address the following questions in the ventral pallidum, and in other parts of the brain that encode motivated behavior: 

  1. Do neurons that encode cue-elicited reward seeking actions ("operant responses") similar encode other types of reward-seeking behaviors?
  2. Do cue responses that encode motivational vigor also encode the value of expected reward, or are these dissociable?
  3. How do changes in physiological state (e.g. hunger or specific physiological need) impact encoding of reward-predictive cues?
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