Figure 2: Simulated effects of neurostimulation on mean firing rates of excitatory and inhibitory neuronal populations.

(A) Mean pyramidal firing rates during trials with small expected value difference. Yellow box indicates period of stimulus-based inputs. Depolarization (red) increases firing rates of pyramidal populations (p1, p2), whereas hyperpolarization (green) decreases their firing rates, relative to no stimulation control (blue). Inset shows differences during the pre-stimulus interval (500 to 50 ms before stimulus onset) between the pyramidal populations that reflect the chosen and unchosen option. (B) Mean interneuron firing rates during trials with small expected value difference. Depolarization of the network also increases firing rates of inhibitory populations, due to stronger excitatory inputs from pyramidal neurons (cf. Model in Fig. 1), whereas hyperpolarization decreases firing rates. Inset indicates stimulation effects during the pre-stimulus interval, thus paralleling the stimulation effects during stimulus presentation. (C) Mean pyramidal firing rates during trials with large differences in expected value. Stimulation (depolarization: red, hyperpolarization: green) has no effect on the steady-state firing rate during visual stimulation relative to control (blue). Inset shows differences during the pre-stimulus interval as in (A). Differences in pre-stimulus firing rates between pyramidal populations of chosen and unchosen options are reduced compared to trials with small expected value difference (A). Depolarization increases these differences relative to control. (D) Mean interneuron firing rates during trials with large differences in expected value. Effects are the same as those during trials with small expected value difference (B). Error bars in insets indicate 1 SEM, asterisks indicate reliable condition differences at p < 0.05 (Bonferroni corrected).