Fig. 4.

Modulation of the excitability of neuronal networks. a Shape change of the fixed-point curve (see Fig. 2c) by varying the strength of the recurrent synaptic coupling C_rec, i.e. the self-excitation degree. At fixed self-inhibition feedback g and without any additional current ΔI, the network has stable stationary states at low firing rate (open coloured circles). Intersections marked by black dots are unstable fixed points, and Up/Down oscillations are expected. Larger C_rec (red) are those with higher ν. b Fixed-point curves changing the incoming current ΔI. C_rec = 100% and g = 1 θ/s. c Fixed-point curves at different self-inhibition feedback g. C_rec = 100% and ΔI = 0 θ/s. Larger gs are those inducing a larger range of input current change (flatter gray lines). Smaller gs make the network more excitable such that states at high ν are preferred. d Spontaneous activity in simulated network of 1,000 excitatory IF neurons for C_rec = 100%, ΔI = 0 θ/s changing g. From larger self-inhibition feedback (darker, bottom) to smaller gs (lighter, top) the network shifts from an asynchronous low firing state to the random occurrence of short Up states, to a periodic Up/Down oscillation, finally showing a persistent asynchronous high firing state only occasionally interleaved by short Down states