Learning of probabilistic punishment as a model of anxiety produces changes in action but not punisher encoding in the dmPFC and VTA

Delay of punishment highlights differential vulnerability to developing addiction-like behavior toward sweet food

Resistance to punishment is commonly used to measure the difficulty in refraining from rewarding activities when negative consequences ensue, which is a hallmark of addictive behavior. We recently developed a progressive shock strength (PSS) procedure in which individual rats can titrate the amount of punishment that they are willing to tolerate to obtain food rewards. Here, we investigated the effects of a range of delays (0-12 s) on resistance to punishment measured by PSS break points. As expected from delay discounting principles, we found that delayed shock was less effective as a punisher, as revealed by higher PSS breakpoints. However, this discounting effect was not equally distributed in the population of rats, and the introduction of a delay highlighted the existence of two populations: rats that were sensitive to immediate punishment were also sensitive to delayed shock, whereas rats that were resistant to immediate punishment showed strong temporal discounting of delayed punishment. Importantly, shock-sensitive rats suppressed responding even in subsequent non-punishment sessions, and they differed from shock-resistant rats in anxiety-like behavior, but not in sensitivity to pain. These results show that manipulation of temporal contingencies of punishment in the PSS procedure provides a valuable tool to identify individuals with a double vulnerability to addiction: low sensitivity to aversion and excessive discounting of negative future consequences. Conversely, the shock-sensitive population may provide a model of humans who are vulnerable to opportunity loss due to excessive anxiety.

Orbitofrontal and Prelimbic Cortices Serve Complementary Roles in Adapting Reward Seeking to Learned Anxiety

BACKGROUND

Anxiety is a common symptom of several mental health disorders and adversely affects motivated behaviors. Anxiety can emerge from associating risk of future harm while engaged in goal-guided actions. Using a recently developed behavioral paradigm to model this aspect of anxiety, we investigated the role of 2 cortical subregions, the prelimbic medial frontal cortex (PL) and lateral orbitofrontal cortex (lOFC), which have been implicated in anxiety and outcome expectation, in flexible representation of actions associated with harm risk.

METHODS

A seek-take reward-guided instrumental task design was used to train animals (N = 8) to associate the seek action with a variable risk of punishment. After learning, animals underwent extinction training for this association. Fiber photometry was used to measure and compare neuronal activity in the PL and lOFC during learning and extinction.

RESULTS

Animals increased action suppression in response to punishment contingencies. This increase dissipated after extinction training. These behavioral changes were associated with region-specific changes in neuronal activity. PL neuronal activity preferentially adapted to the threat of punishment, whereas lOFC activity adapted to safe aspects of the task. Moreover, correlated activity between these regions was suppressed during actions associated with harm risk, suggesting that these regions may guide behavior independently under anxiety.

CONCLUSIONS

These findings suggest that the PL and lOFC serve distinct but complementary roles in the representation of learned anxiety. This dissociation may provide a mechanism to explain how overlapping cortical systems are implicated in reward-guided action execution during anxiety.