Figure 6.

GABA_A,slow synapses are necessary for theta-gamma responses to weak periodic drive. Model parameters as in Figs. 4 and 5 for control simulations (filled symbols). Vector strengths measure the degree to which the GABA_A,slow cells synchronize at the stimulus frequency. (a) Vector strengths (means ± σ; n = 5) in response to normally distributed phases of sinusoidal input (σ_ϕ = standard deviation). Solid squares and diamonds indicate delivery of the 8-Hz input to the GABA_A,slow and GABA_A,fast cells of the control network, respectively. Open symbols indicate responses of a network in which the postsynaptic responses driven by GABA_A,slow cells have been transformed into GABA_A,fast responses. Vector strengths are measured in the population of formerly GABA_A,slow cells. For open circles (error bars too small to resolve), the new network had maximal conductances as in the control case. Open triangles indicate a network with uniform GABA_A,fast kinetics in which values of synaptic conductance have been scaled up to preserve the area of the postsynaptic response, and thus leave the average amount of inhibition at a given firing rate unchanged from the control case. (b) Vector strengths in GABA_A,slow cells, measured in response to uniformly distributed phases of 8-Hz input to GABA_A,slow (squares) or GABA_A,fast cells (diamonds).