DG and the STDP protocols. A, Illustration of a typical granule cell within the granule cell layer (GCL) and the electrode placements are indicated (S, stimulation electrode; R, recording electrode). B, The STDP protocols with paired presynaptic stimulation and two postsynaptic action potentials at 100 Hz. Δt < 0 means postsynaptic before presynaptic stimulation, and Δt > 0 means presynaptic before postsynaptic stimulation.