Single neurons in the dentate gyrus and CA1 of the hippocampus exhibit inverse patterns of encoding during trace fear conditioning

Trace fear conditioning is a hippocampus-dependent learning task that requires the association of an auditory conditioned stimulus (CS) and a shock unconditioned stimulus (US) that are separated by a 20-s trace interval. Single-neuron activity was recorded simultaneously from the dentate gyrus (DG) and CA1 of rats during unpaired pseudoconditioning and subsequent trace fear conditioning. Single neurons in DG showed a progressive increase in learning-related activity to the CS and US across trace fear conditioning. Single neurons in CA1 showed an early increase in responding to the CS, which developed into a decrease in firing later in trace conditioning. Correlation analyses showed that DG and CA1 units exhibit inverse patterns of responding to the CS during trace fear conditioning.