Figure 1

Temporal changes in firing rates. The horizontal axis is time [s] and the vertical axis is the firing rate [Hz]. When τ = 10, the firing rate oscillates with high frequency with an almost constant amplitude. When the values of τ become smaller, as in (b) and (c), the amplitudes of the firing rate become larger. When τ ≤ 1.7, as in (d), (e), and (f), the amplitudes change irregularly, exhibiting sudden increases in the firing rates. When τ takes a value close to unity, as shown in (g) and (h), the firing rate periodically repeats sudden increases and decreases with very slow frequency (<0.002 Hz).