Fig. 3.
Burst stimulation of the MD modulates hippocampal-evoked firing in PFC neurons. A, In 12 of 18 PFC←Hipp neurons that did not fire in response to MD stimulation, burst stimulation of the MD inhibited FF-evoked firing (black bars; mean + SEM), relative to the firing probability observed after single-pulse stimulation of the FF alone at the same stimulation intensity (gray bars; mean + SEM). B, In another 6 of 18 PFC←Hipp neurons, burst stimulation of the MD facilitated FF-evoked firing. C, Representative data from individual neurons.C1, Ten overlaid traces showing the effect of single-pulse stimulation of the MD (100 μA) 25 msec before stimulation of the FF (680 μA). C2, In the same neuron, 10 traces showing the effect of burst stimulation of the MD (last 2 pulses shown) before FF stimulation. Over 10 sweeps, single-pulse stimulation of the MD had no effect over FF-evoked firing, but burst stimulation substantially reduced the probability of firing over the same number of trails. D, Location of PFC←Hipp neurons the evoked firing of which was inhibited (open squares and minus sign) and facilitated (black squares) by burst stimulation of the MD. E, Diagrams of the stimulation protocol used in this experiment. Here, the MD was stimulated with a four-pulse, 20 Hz train (1) 10–50 msec before single-pulse stimulation of the FF (2). MD stimulation did not evoke firing in any of these neurons. Significant difference versus single-pulse stimulation of the FF: **p < 0.01.