Distinct hippocampal oscillation dynamics in trace eye-blink conditioning task for retrieval and consolidation of associations.

Trace eyeblink conditioning (TEBC) has been widely used to study associative learning in both animals and humans. In this paradigm, conditioned responses (CRs) to conditioned stimuli (CS) serve as a measure for retrieving learned associations between the CS and the unconditioned stimuli (US) within a trial. Memory consolidation i.e. learning over time, can be quantified as an increase in the proportion of CRs across training sessions. However, how hippocampal oscillations differentiate between successful memory retrieval within a session and consolidation across TEBC training sessions remains unknown. To address this question, we recorded local-field potentials (LFPs) from the rat dorsal hippocampus during TEBC and investigated hippocampal oscillation dynamics associated with these two functions. We show that transient broadband responses to the CS were correlated with memory consolidation, as indexed by an increase in CRs across TEBC sessions. In contrast, induced alpha (8-10 Hz) and beta (16-20 Hz) band responses were correlated with the successful retrieval of the CS-US association within a session, as indexed by the difference in trials with and without CR.Significance statement Trace eyeblink conditioning is widely used to study the neural basis of learning. How brain oscillatory signatures for instantaneous retrieval of associations differ from those reflecting long-term memory consolidation is not well understood. We recorded local-field potentials from the rat hippocampus during conditioning to dissociate oscillation dynamics associated with these functions. We show that a transient, early, broadband response is correlated with memory consolidation (increase in conditioned responses across training sessions) whereas long-latency sustained alpha and gamma oscillations are associated with the performance within a given trial in a session.