Extended Data Fig. 1: Cortical silencing
From: Cortical direction selectivity emerges at convergence of thalamic synapses
a, Experimental configuration. Channelrhodopsin-2 (ChR2) is expressed in cortical inhibitory neurons to suppress neuronal activity upon illumination with a blue LED while performing extracellular recordings. b, Visually evoked activity (full-field drifting gratings) from units isolated throughout the cortical depth is suppressed upon LED illumination. Black lines, ChR2 was expressed in all GABAergic neurons (GABA, γ-aminobutyric acid; VGAT-ChR2 mice; 138 units recorded with silicon probes; 98.9 ± 2.7% silencing in 25 units recorded above 500 μm depth; 99.4 ± 2% silencing in 113 units recorded below 500 μm; 5 mice). Red lines, ChR2 was conditionally expressed in parvalbumin (PV)-expressing neurons through viral injection into the visual cortex of the PV-Cre mouse line (13 loose patch recordings in layer 4; 2 mice; 100% silencing). c, As in b but specifically for units recorded between 450–650 μm depth (black; 99.8 ± 0.6% silencing; n = 26; 3 mice) and 650–950 μm depth (green; putative layer 6; 99.8 ± 2.4% silencing; n = 48; 3 mice). These units are a subset of the units from VGAT-ChR2 mice illustrated in b for which the recording depth could be estimated. d, Percentage of visually evoked spikes remaining during LED illumination across cortical depths deeper than 450 μm. The units are the same as in c. e, Peristimulus time histogram of two units located at 615 μm (left) and 890 μm (right) depth in response to drifting gratings under control conditions (black) and during cortical silencing (blue). The duration of the visual stimulus and of the LED illumination is illustrated by the horizontal bars. f, Experimental configuration. As in a but whole-cell recordings from layer 4 neurons instead of extracellular recordings. g, Whole-cell voltage-clamp recording (Vholding = −70 mV) of a layer 4 neuron (same neuron as in Fig. 2a). Response to drifting gratings (left; two identical cycle averages are shown for clarity) and static gratings (right; average of 10 traces). The grey indicates control conditions; the black trace was recorded during LED illumination to isolate thalamic excitation. h, Distribution of remaining excitatory charge upon LED illumination for drifting gratings (66 recordings as in g, left) and static gratings presented at the preferred spatial phase (53 recordings as in g, right). The visually evoked excitation was reduced by about 65% (drifting grating, 63 ± 16%; static grating, 68 ± 16).
