a. Schematic of L6 projections.
b. Left, coronal section of V1 from NTSR1-Cre, floxed-tdTomato, GAD67-GFP mouse. Inset, L6 projection to dLGN (V1 of NTSR1-Cre mouse was injected with floxed-tdTomato virus). Right, The two types of L6 neurons labeled by the NTSR1-Cre line. Dendrites: black; axons: gray.
c. Schematic of setup.
d. Cortical visual responses with (blue) and without (black) L6 photo-stimulation. Left, raster plot of multiunit activity grouped by depth. Control and photo-stimulation trials were interleaved but are separated here for clarity. Black bar: visual stimulus (1.5 s); blue bar: LED illumination (0.5 s). Right, normalized PSTH; top: upper layers; bottom: L6.
e. Summary (n = 6 experiments). Control in black and increasing LED intensities in darker blues.
f. Suppression of multiunit activity with increasing L6 activity.
g. Visual response of single L4 unit with (blue) and without (black) L6 photo-stimulation. Scale bar, 20 spikes/s.
h. Response of each regular spiking unit with and without strong photo-stimulation of L6.
i. Average normalized PSTH (n = 47 units tested with 5 LED intensities). Colors as in (e).
j. Suppression of single unit activity.