Fig. 2. Position of electrodes. A,B, Traces (indicated by arrows) of the recording electrode in the dentate gyrus (A) and three bipolar stimulation electrodes (medial, central, lateral) in the angular bundle (B) (coronal sections, cresyl violet). C, Stimulation protocols. Left, Single test pulses were delivered through the central electrode in the angular bundle (circle), with anode and cathode at different depths (ab). Right, Induction of LTP by tetanic stimulation across the angular bundle, with anode and cathode varied between six stimulation sites (c–f). Sequence of stimulation:ce, df, cf,de, cd, ef (first and third stimulation session) and ec, fd,da, fc, dc,fe (second and fourth stimulation session). For each combination, eight trains (high-frequency group) or eight single pulses (low-frequency group) were delivered, with combinations separated by 30 sec intervals.