Baseline theta activities in medial prefrontal cortex and deep cerebellar nuclei are associated with the extinction of trace conditioned eyeblink responses in guinea pigs.

It has been shown that both the medial prefrontal cortex (mPFC) and the cerebellum are involved in the extinction of trace conditioned eyeblink responses (CR). However, the neural mechanisms underlying the extinction are still relatively unclear. Theta oscillation in either the mPFC or the cerebellum has been revealed to correlate with the performance of trace CRs during the asymptotic acquisition. Therefore, we sought to further evaluate the impacts of pre-conditioned stimulus (CS) spontaneous theta (5.0-10.0Hz) oscillations in the mPFC and the deep cerebellar nuclei (DCN) on the extinction of trace CRs. Albino guinea pigs were given acquisition training for ten daily sessions followed by seven daily sessions of extinction. Local field potential (LFP) signals in the mPFC and the DCN were recorded when the animals received the CS-alone extinction training. It was found that higher mPFC relative theta ratios [theta/(delta+beta)] during the baseline period (850-ms prior to the CS onset) were predictive of fewer CR incidences rather than more adaptive CR performance (i.e., higher CR magnitude and later CR peak/onset latencies). Likewise, the pre-CS DCN theta activity was associated with the faster CR extinction. Furthermore, it was revealed that the power of pre-CS theta activities in the mPFC and the DCN were correlated until the extinction training day 2. Collectively, these results suggest that the mPFC and the DCN may interact with each other, and the brain oscillation state in which baseline theta activities in both areas are present contributes to the subsequent extinction of trace CRs.