Figure 4.
Sublinear summation of synaptic potentials underlying supralinear spike output. A, Membrane potential responses to bars A and B in an example layer 4 simple cell. Spikes have been removed. B, Average PSPs in response to A and B together at varying intervals (black) compared to the predicted responses calculated as the linear sum of the responses to A and B alone (dashed). At short intervals, the observed responses were smaller in amplitude than the expected responses and were advanced in time. C, Expanded traces of the observed responses to A and B individually and A and B together at an ISI of 0 ms are shown with the linear prediction of A and B (dashed). The response to A and B together was larger than the responses to either A or B alone. D, Expanded traces from the box in B of the observed (black) and expected (dashed) responses to A and B together at an ISI of 0 ms. The membrane potential trajectory (dVm/dt) of the observed response was faster than that of the expected response.