Fig. 4.

A, Simulation of interval selectivity. The top and bottom tracesrepresent the output of the Ex and Inh unit, respectively, in response to three intervals of 50, 100, and 200 msec. The responses to each interval are overlaid. Depending on the strength of the connections onto the Ex and Inh units, the Ex unit can respond selectively to 50 (red), 100 (green), or 200 (blue) msec intervals. B, Parametric analysis of synapse space and interval selectivity displayed as an RGB plot. As color-coded in A, red represents regions of synapse space in which the Ex unit fires exclusively to the second pulse of a 50 msec IPI, but not to the 100 or 200 msec IPI, i.e., a 50 msec interval detector. Similarly, green anddark blue areas represent regions of synapse space in which the Ex units respond only to the 100 or 200 msec interval, respectively. In the same manner that a computer screen makes yellow by mixing red and green, yellow in this RGB represents conditions in which the Ex unit responded to both 50 and 100 msec intervals, but not the 200 msec interval. White areas represent regions that respond to all the intervals, but not to the first pulse. The general scheme is represented in the color cube to theright. Black areas represent regions in which the cell was not interval-selective: not firing at all or in response to the first pulse. The three unfilled white squares show the areas of synapse space of the traces inA. The other synaptic weights were GABA_A → Ex = 150 nS; GABA_B → Ex = 4 nS; GABA_B → Inh = 6 nS. The color changes in thebottom left corner reflect a more nonlinear region of synapse space corresponding to an area in which the strength of the Input → Inh synapse is still subthreshold to the first pulse but not to the second pulses.