Long-term potentiation in the dentate gyrus is induced preferentially on the positive phase of theta-rhythm.

Long-term potentiation (LTP), a long lasting enhancement of synaptic efficacy is considered a model for learning and memory. In anesthetized rats, theta-rhythm was induced in the dentate gyrus by midbrain stimulation. Short trains of pulses were applied to the perforant pathway either at the peak of theta-rhythm or its trough. Trains applied at the peak of theta-rhythm induced LTP while trains applied at the trough produced a decrease of synaptic efficacy or had no effect. Thus, theta-rhythm may play a modulating role in the induction of LTP, suggesting a possible mnemonic function for the rhythm during the behaviors in which it occurs.