Figure 3. MD input amplifies local PFC connectivity.

(a) MD and cortical FS but not RS show increased firing rates upon task engagement and further increase during the delay (normalized to values outside of task; PFC, 6 mice, RS: 516 cells, FS: 213 cells, MD, 3 mice, 196 cells, grey shading indicates 95% CI of null distribution. (b) RS network connectivity, assessed by granger causality of spike trains.(normalized to values outside of task, n = 6 mice, 43 sessions; median 13 neurons/session). (c) Suppressing MD reduces cortical FS and RS firing rates during task delay (RS: 245, FS: 114, n = 2 mice), as well as RS connectivity (n = 2 mice, 19 sessions; median 13 neurons/session). Enhancing MD excitability increases cortical FS firing rates, connectivity among cortical RS neurons but not RS firing rates (RS: 303, FS: 131, n = 2 mice; RS connectivity [n = 17 sessions; median 18 neurons/session]). (d) Spike transfer function (methods) of PFC→MD is significantly higher compared to MD→PFC (n = 17 sessions, median 11 PFC and 10 MD neurons/session for PFC→MD, median 18 PFC and 15 MD neurons/sessions for MD→PFC, 2 mice per condition, error bars are 95% CI estimated per session). (e) Experimental setup for testing the impact of MD activation on local intra-PFC connectivity. (f) Example RS neuron responses (normalized PSTH, mean ± SEM) to MD activation alone, intra-PFC activation alone or the combination. (g) Comparison of the observed combined response with the arithmetic sum of its individual components shows supra-linearity (P < 10⁻¹⁵, sign-rank test). (h–i) As in e–g but for SSFO-mediated activation of LGN and recordings from V1. (j) Combined stimulation results in a sub-linearity (P < 10⁻⁴, sign-rank test).