Fig. 6.

White matter stimulation produces larger paired-pulse depression than layer IV stimulation. A, Example of responses evoked by a complete ISI series (20–2560 msec) applied at medium stimulation intensity first to the white matter (top traces) and subsequently to layer IV (bottom traces). In each case only the second response is shown.B, Average results of 37 experiments performed as inA (the results of 30 of these experiments are also included in Fig. 3). Plotted in the top panel are the paired-pulse response ratios obtained with varying ISIs for both white matter stimulation (○) and layer IV stimulation (●). ISIs at which the effect of stimulation site was significant (0.01 level; see Results) are labeled with an asterisk. The difference in paired-pulse ratio between the two stimulation sites was computed for each ISI in each experiment. The average results are shown in the bottom panel.