Figure 3. Behavior-induced alterations to DG circuit function assessed by response to perforant path stimulation. A, The CSD (black traces) was computed from the recorded voltage traces (gray) to remove volume conducted signals. The sites determined to be located in slm, molecular layer and granule cell compartments (orange arrows) were used for further evaluation. The average ± SEM (shading) sl-CSD are shown. B, Average CSD heatmaps were generated for each group. Cooler colors are sinks (inward current) and warmer colors are sources (outward current). The sink in the molecular layer appears to increase with experience and cognitive demand. C, The AUC of the pre-spike response (1.5 ms after the stimulation was delivered until the spike occurred) and the post-spike response (from the spiking activity until 20 ms after stimulation) were quantified at the maximum stimulation given to all animals (800 μA) for each layer of the somatodendritic axis of the dorsal hippocampus. The pre-spike sink at the molecular layer is not changed by experience whereas the post-spike sink in the molecular layer is significantly altered by experience. CA1: so = stratum oriens, pyr = pyramidal cell layer, strat. rad. = stratum radiatum, DG: mol = molecular layer, grc = granule cell layer. D, top, The I-O curve that characterizes the pre-spike sink, synaptic population response to the full range of stimulus intensities, is significantly increased in conditioned rats compared to both no-shock and home-cage groups. Bottom, The post-spike response to increasing stimulation intensity is significantly increased in conditioned rats compared to the no-shock response, which is also significantly increased compared to home-cage rats. E, The sl-fEPSP characterizing the population synaptic response at the molecular layer is significantly increased by conditioning, confirming the findings based on the sl-AUC. F, The sl-fEPSP at the granule cell layer is significantly different between conditioned and home-cage groups. G, The PS response at the granule cell layer is significantly increased by experience. Example CSD waveforms are plotted in E–G in black for illustration with schematization of the measurement corresponding to the figure. The voltage trace is underlaid in gray. Home-cage, n = 6; no-shock, n = 6; conditioned, n = 7. Data are mean ± SEM. *p < 0.05. Colored asterisks indicate which group is different from the other two.