Noninvasive Brain Stimulation Rescues Cocaine-Induced Prefrontal Hypoactivity and Restores Flexible Behavior

BACKGROUND: To obtain desirable goals, individuals must predict the outcome of specific choices, use that information to direct appropriate actions, and adjust behavior accordingly in changing environments (behavioral flexibility). Substance use disorders are marked by impairments in behavioral flexibility along with decreased prefrontal cortical function that limits the efficacy of treatment strategies. Restoring prefrontal hypoactivity, ideally in a noninvasive manner, is an intriguing target for improving flexible behavior and treatment outcomes. METHODS: A behavioral flexibility task was used in Long-Evans male rats (n = 97) in conjunction with electrophysiology, optogenetics, and a novel rat model of transcranial alternating current stimulation (tACS) to examine the prelimbic cortex (PrL) to nucleus accumbens (NAc) core circuit in behavioral flexibility and determine whether tACS can restore cocaine-induced neural and cognitive dysfunction. RESULTS: Optogenetic inactivation revealed that the PrL-NAc core circuit is necessary for the ability to learn strategies to flexibly shift behavior. Cocaine self-administration history caused aberrant PrL-NAc core neural encoding and deficits in flexibility. Optogenetics that selectively activated the PrL-NAc core pathway prior to learning rescued cocaine-induced cognitive flexibility deficits. Remarkably, tACS prior to learning the task reestablished adaptive signaling in the PrL-NAc circuit and restored flexible behavior in a relatively noninvasive and frequency-specific manner. CONCLUSIONS: We establish a role of NAc core?projecting PrL neurons in behavioral flexibility and provide a novel noninvasive brain stimulation method in rats to rescue cocaine-induced frontal hypofunction and restore flexible behavior, supporting a role of tACS as a therapeutic to treat cognitive deficits in substance use disorders. https://doi.org/10.1016/j.biopsych.2020.12.027 comes associated with specific stimuli, use that information to guide behavior, and adjust behavior to navigate ever-changing environments, i.e., behavioral flexibility. Substance use disorders (SUDs) are marked by impairments in behavioral flexibility, which may lead to poor decision making and limit the efficacy of current treatment strategies (1). Because individuals with SUDs show decreased function in cortical regions (2,3) linked to cognitive flexibility (4), reversing frontal hypoactivity is an intriguing therapeutic strategy for improving decision-making deficits and enhancing treatment outcomes. Behavioral flexibility can be measured in rats using reinforcer devaluation tasks in which the expected value of an upcoming reward is decreased. Here, several processes are necessary to perform this task: 1) forming an association between a cue and an outcome, 2) registering the decreased value of the outcome after its devaluation, and 3) integrating

Automated summary

The study establishes the importance of the PrL-NAc core circuit in behavioral flexibility and introduces a novel noninvasive brain stimulation method to rescue cocaine-induced frontal hypofunction and restore flexible behavior in rats.