Fig. 4. Layer 6 corticothalamic (L6-CT) activation suppresses spiking in layer 5 but enhances spiking in superficial layers.
a Upper: Experimental configuration for layer-resolved silicon-probe recordings in S1 hindlimb cortex (S1HL) of anesthetized mice (n = 3). Lower: stimulation protocol for three interleaved stimulation conditions: L6-CT activation (L), mechanical paw stimulation (M), and combined L6-CT + mechanical simulation (ML). Time windows for unit spike analysis are indicated in orange. b Example responses for L, M, and ML conditions in L2/3 (light gray), L4 (gray), L5 (red), and L6 (blue). Top: raster examples; middle: mechanical pressure (gray shading) and first temporal derivative of pressure (dP/dt, black); bottom: corresponding PSTHs (bin size = 20 ms, smoothed with BARS method76). c Breakdown of layer-specific population responses to L/M/ML conditions showing proportion and counts of enhanced and suppressed units for each L/M/ML condition. A minority of units had only changes in spike timing, not spike counts (counts at zero). See Supplementary Fig. 8e for the population overlap of L/M/ML—sensitive units in each layer. d L6-CT stimulation enhances superficial layers’ paw responses, but suppresses those of L5. Modulation indices pooled per condition and cortical layer. See Supplementary Fig. 8e for stimulus-evoked changes in spiking rates. Unit counts were n = 25, 62, 323, and 341 for L2/3, L4, L5, and L6 units, respectively, pooled from three independent experiments. Data were shown as median and interquartile range. e Depth-resolved modulation indices (MI) for L2/3, L4, L5, and L6 units in S1HL for L, M, and ML conditions (left, middle, right rows, respectively; n values as in d). Each unit is represented by one data point; the size and color of markers are proportional to the spontaneous spiking rate (black to yellow: low to high). Depth values are slightly jittered for visibility. Non-significantly modulated units are not shown. f MIL, MIM, and MIML distributions with overlaid medians and first and third quartiles for significantly modulated units by layer (data replotted from d to facilitate comparison across layers). g Summary of functional effects of L6-CT activation on VPL and S1HL cortical layers; arrow widths proportional to experimental MIL. * represents p < 0.05; 4c: Two-sided X2 test followed by Marascuillo procedure; 4d, f: Friedman test with post hoc two-sided Wilcoxon signed-rank test; Exact p values in Supplementary Table 1. Source data for b–f are provided as a Source Data file.