Figure 1.

Basal-dendritic fEPSPs reveal larger LTP when a high-frequency train was delivered during walking compared with any other behavioral state: REM, SWS, or IMM. Inset (top left) shows location of electrodes. fEPSPs were negative at the alvear surface (electrode R2) and positive at CA1 stratum radiatum (deep electrode R1) after test-pulse stimulation (90 μA, 0.1 msec) of the contralateral CA1 (stimulating electrode L1). For each experiment (A-D, horizontal row of traces), a 200 Hz train stimulation of 60 μA pulses (pulse duration 0.1 msec) and 0.5 sec train duration (indicated by an open arrow, saturated EEG not shown) was delivered to the basal-dendritic afferents during a given behavioral state. The behavioral state remained undisrupted by the tetanus, as seen by the similar EEG patterns before and after the tetanus (left traces). Average basal-dendritic fEPSPs (right traces) are shown during baseline (0 min), 30 min, 120 min, and 1 d after the train stimulation. Tetanus delivered during walking (A) gave the largest LTP compared with during REM (B), SWS (C), and IMM (D). Both surface and deep electrodes show similar results. The experiments were done in the sequence shown (A-D) on the same rat (913), with at least 6 d between experiments; the same test pulse intensity and the same tetanus intensity were used across experiments.