Extended Data Fig. 2: Depth Calibration and Validation for S1 Recordings.

a, Current source density (CSD) plots of an exemplar hindpaw wild-type S1 recording. Sources (red) and sinks (blue) are apparent soon after the onset of the step indentation. The depth of an early, prolonged sink (marked by an asterisk) was used to rigidly adjust the depth of the probe so that this sink was at the center of layer IV.

b, Optotagging protocol (top) and corresponding action potential timing of an example optotagged unit (bottom) from an Scnn1a-tg3-Cre;R26^LSL-ChR2 mouse. NBQX (5 mM) was applied to the surface of the brain to block excitatory synaptic transmission starting on trial 16.

c, Probability distributions of the latency to the first spike after LED pulses for two optotagged units. Shaded region represents 95% confidence interval of shuffled distribution.

d, Probability distributions of the latency to the first spike after LED pulses for two non-optotagged units. Shaded region represents 95% confidence interval of shuffled distribution.

e, Mechanical responses to 75-mN step indentations for each unit in a recording from a Scnn1a-tg3-Cre;R26^LSL-ChR2 mouse before (left) and after (right) application of NBQX. Optotagged units (blue) had similar mechanical response profiles to non-optotagged units (gray).

f, Depth distribution (after CSD calibration) of all units (gray, n = 866) recorded from wild-type hindpaw S1 compared with the depth of all optotagged units (blue, n = 24 from 5 recordings from 3 mice). The majority of optotagged units were within layer IV (416.5 – 535.5 μm deep).

g, Typical location of an electrode array in hindpaw S1 superimposed upon post hoc histology of a mouse expressing ChR2-EYFP in layer IV neurons (Scnn1a-tg3-Cre;R26^{LSL-ChR2-EYFP}). The probe was coated in DiI prior to recording. Scale bar, 500 μm.