Figure 6.

Activation of Infragranular Layers Mediates SHs in L2/3Ps of V1

(A) Photostimulation (PS) of L5Ps hyperpolarized overlying L2/3Ps in V1 (grand-average ± SEM; n = 5).

(B) Diagram showing the mean onset latencies ± SEM of (1) hyperpolarizations of V1 L2/3Ps driven by A1 photostimulation, (2) SHs of L2/3Ps in V1, (3) sound-driven activation of L5Ps in V1 (left) and hyperpolarizations of L2/3Ps in V1 driven by the phostimulation of L5Ps in V1 (right).

(C) Top: whole-cell recordings from L2/3Ps after the injection of muscimol in infragranular layers of V1. Bottom: Nissl-counterstained, coronal section through V1 showing that the injected fluorescent muscimol did not leak into supragranular layers. Bar, 400 μm.

(D) Muscimol abolished spiking in L5 (gray) without modifying the resting V_m of L2/3Ps (black) and its variance over time (“L5/6” in bottom plots). On the contrary, muscimol diffusion to the entire cortex dramatically affected the resting V_m and its variance (“Cortex” in bottom plots, ^∗∗∗p < 0.001 for post hoc test).

(E) Acute inactivation of L5/6 activity by a local puff of muscimol counteracted SHs in overlying L2/3Ps of V1 (red, n = 16) with respect to controls (black, n = 19; ^∗∗∗p < 0.01). Squares in the box plot (right) indicate the experiments with fluorescent muscimol.

See also Figure S6.