Novel physiological paradigm for assessing reward anticipation and extinction using cortical direct current potential responses in rats

Abstract

Abstract Anhedonia is characterized by reduced motivation, decreased sensitivity to rewards, and diminished pleasure. However, no direct neurophysiological method is available to assess motivational anhedonia with disrupted reward anticipation. We established a novel physiological paradigm using cortical direct current (DC) potential responses in rats to assess reward anticipation. This paradigm consisted of five daily 1-h sessions with two tones, where the rewarded tone was followed by electrical stimulation of the medial forebrain bundle every second, while the unrewarded tone was not. On day 1, both tones led to a negative DC shift immediately after auditory responses. This negative shift progressively increased and peaked on day 4, with the rewarded tone exhibiting a significantly larger magnitude. The DC shift from 600 to 1000 ms significantly increased following the rewarded tone compared with that following the unrewarded tone on day 3. This DC shift was prominent in the frontal cortex and played a crucial role in discriminative anticipation. During the extinction sessions, the shift diminished significantly on day 1. These findings suggest that cortical DC potential is related to reward anticipation and could be a valuable tool for evaluating animal models of depression, providing a testing system for anhedonia.