Striatal Activity and Reward Relativity: Neural Signals Encoding Dynamic Outcome Valuation.

The striatum is a key brain region involved in reward processing. Striatal activity has been linked to encoding reward magnitude and integrating diverse reward outcome information. Recent work has supported the involvement of striatum in the valuation of outcomes. The present work extends this idea by examining striatal activity during dynamic shifts in value that include different levels and directions of magnitude disparity. A novel task was used to produce diverse relative reward effects on a chain of instrumental action. Rats (Rattus norvegicus) were trained to respond to cues associated with specific outcomes varying by food pellet magnitude. Animals were exposed to single-outcome sessions followed by mixed-outcome sessions, and neural activity was compared among identical outcome trials from the different behavioral contexts. Results recording striatal activity show that neural responses to different task elements reflect incentive contrast as well as other relative effects that involve generalization between outcomes or possible influences of outcome variety. The activity that was most prevalent was linked to food consumption and post-food consumption periods. Relative encoding was sensitive to magnitude disparity. A within-session analysis showed strong contrast effects that were dependent upon the outcome received in the immediately preceding trial. Significantly higher numbers of responses were found in ventral striatum linked to relative outcome effects. Our results support the idea that relative value can incorporate diverse relationships, including comparisons from specific individual outcomes to general behavioral contexts. The striatum contains these diverse relative processes, possibly enabling both a higher information yield concerning value shifts and a greater behavioral flexibility.

The elegance of energy balance: Insight from circuit-level manipulations.

Mechanisms of energy balance were first examined using very powerful neuroscience techniques such as lesions and electrical stimulation. This early work identified the hypothalamus as a key structure involved in hunger and feeding; however, neural resolution of cell-defined populations contributing to appetite regulation remained elusive. Recent innovations in neuroscience have produced constructs that allow for a high degree of specificity in loss- and gain-of-function manipulations in molecularly circumscribed neural subsets as well as monosynaptic circuit mapping and in vivo neurophysiology. These complimentary techniques have provided researchers an unprecedented amount of empirical agility. As a result, cell populations in two subregions of the hypothalamus have emerged as key players in the physiological control of feeding behavior. The arcuate nucleus of the hypothalamus and the paraventricular nucleus of the hypothalamus contain neural populations that have a direct role in the promotion of hunger and satiety. These include neurons that express agouti-related peptide, pro-opiomelanocortin, single-minded homolog 1 protein, and the melanocortin-4 receptor. This review focuses on how these neural subsets communicate with one another, link up to build elaborate networks, and ultimately contribute to alterations in food intake. The continuing advancement of neuroscience tools, as well as a multimodal integration of findings, will be critical in illuminating an exhaustive and clinically relevant hunger circuit.

Ultrasonic vocalizations, predictability and sensorimotor gating in the rat.

Prepulse inhibition (PPI) is a measure of sensorimotor gating in diverse groups of animals including humans. Emotional states can influence PPI in humans both in typical subjects and in individuals with mental illness. Little is known about emotional regulation during PPI in rodents. We used ultrasonic vocalization recording to monitor emotional states in rats during PPI testing. We altered the predictability of the PPI trials to examine any alterations in gating and emotional regulation. We also examined PPI in animals selectively bred for high or low levels of 50kHz USV emission. Rats emitted high levels of 22kHz calls consistently throughout the PPI session. USVs were sensitive to prepulses during the PPI session similar to startle. USV rate was sensitive to predictability among the different levels tested and across repeated experiences. Startle and inhibition of startle were not affected by predictability in a similar manner. No significant differences for PPI or startle were found related to the different levels of predictability; however, there was a reduction in USV signals and an enhancement of PPI after repeated exposure. Animals selectively bred to emit high levels of USVs emitted significantly higher levels of USVs during the PPI session and a reduced ASR compared to the low and random selective lines. Overall, the results support the idea that PPI tests in rodents induce high levels of negative affect and that manipulating emotional styles of the animals alters the negative impact of the gating session as well as the intensity of the startle response.