Active avoidance requires inhibitory signaling in the rodent prelimbic prefrontal cortex

Maria M Diehl, Christian Bravo-Rivera, Jose Rodriguez-Romaguera, Pablo A Pagan-Rivera, Anthony Burgos-Robles, Ciorana Roman-Ortiz, Gregory J Quirk

eLife (2018)

DOI: https://doi.org/10.7554/eLife.34657

The conceptual gap or the scientific question: how prelimbic cortex (PL) contributes to active avoidance behaviors?

How the authors proposed the question: this study is an ongoing work of their previous work (Neural structures mediating expression and extinction of platform-mediated avoidance, 2014; Persistent active avoidance correlates with activity in prelimbic cortex and ventral striatum, 2015). The series of studies from this lab were based on the behavioral studies from Joseph E. LeDoux's lab. The neural mechanisms of active avoidance behavior is an emerging field which just at its dawning time, and their should be burst of research coming out in the following years. Gregory J Quirk is a wave rider in this field.

Brief summary: by training rats to perform an active avoidance, the authors found that lesions of PL with musicmol decreased the avoidance behaviors. More PL neurons were suppressed by active avoidance responses comparing to that of the control task. Optogenetic suppression of the rostral, but not the caudal PL shortened the latence for avoidance response. On the contrary, optogenetic activation of the rostral PL at 4Hz, but not at 2Hz, impaired the avoidance responses. These data indicated that the inhibitory activity in the rostral PL is a key controller for active avoidance behaviors. 

The most impressive experiment in this study is the comparison of the neuronal activity of PL neurons in the cue-avoicance task and the cue-reward control task. The results shown that even though a larger proportion of neurons were activated, it was the neuron group with an inhibition during avoicance response displayed a significant decrease. This is the key observation constructing the scaffold of the entire story.

The ongoing question(s) inspired by the current study: the correlates of the inhibition of rPL with avoidance response indicate that PL should function as a disinhibitor of other avoidance-suppressing neurons, either in PL per se or in some downstream brain areas, such as the striatum. It is the direction in this field to figure out those related pathways in the future.