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. 2014 Aug 28;8:98. doi: 10.3389/fncom.2014.00098

Figure 4.

Figure 4

Graded amplification of EPSPs. Events consisting of 1, 2, or 4 unitary EPSGs separated by 5 ms intervals were evoked at −65 mV and after delays of 50–800 ms after injection of an artificial conductance (3–10 nS for 1.0 s) that hyperpolarized the membrane to near −80 mV. (A) Top, two separate sweeps in which 2 rEPSGs occurred either at 50 (magenta) or 800 ms (black). Numbers indicate EPSG input count and spike output for each EPSG event. Bottom, overlaid rEPSPs in response to 1 (blue), 2 (black), and 4 (red) rEPSGs at −65 mV (left), and after 50 (middle) and 800 ms (right) at −80 mV. Scale bars also apply to (B). (B) Same as in (A), but for aEPSGs from another cell. (C) Population mean TTDs at 100, 200, 400, and 800 ms in response to 1 (left) and 2 (right) EPSGs. rEPSGs at top, aEPSGs at bottom. Population mean EPSPs at 50 ms (red) are overlaid for comparison. Scale bars apply to all traces in (C) and (D). (D) Temporal summation illustrated by TTDs in response to 1 (left) and 2 (right) aEPSGs at 200 (top) and 800 ms (bottom). Each trace is an average of 4 repetitions in one cell. The traces from each cell were assigned a color based on the response of that cell to 1 aEPSG at 800 ms (lower left), according to whether there was virtually no TTD (blue; n = 13), a large TTD that caused no spike (red; n = 6), or a TTD that caused one or more spikes (black; n = 7). Each cell is represented by the same color in the other three conditions, but to aid clarity, cells with spikes in response to 1 aEPSG at 800 ms are not shown in the case of 2 aEPSGs. If little TTD was present in response to 1 aEPSG, the second aEPSG caused a large TTD. In other cells with a large TTD but no spikes, the second aEPSG caused at least one spike. Similar results were obtained with rEPSGs.