Cortical signatures of wakeful somatosensory processing

Sensory inputs carry critical information for the survival of an organism. In mice, tactile information conveyed by the whiskers is of high behavioural relevance, and is broadcasted across cortical areas beyond the primary somatosensory cortex. Mesoscopic voltage sensitive dye imaging (VSDI) of cortical population response to whisker stimulations has shown that seemingly ‘simple’ sensory stimuli can have extended impact on cortical circuit dynamics. Here we took advantage of genetically encoded voltage indicators (GEVIs) that allow for cell type-specific monitoring of population voltage dynamics in a chronic dual-hemisphere transcranial windowed mouse preparation to directly compare the cortex-wide broadcasting of sensory information in wakening (lightly anesthetized to sedated) and awake mice. Somatosensory-evoked cortex-wide dynamics is altered across brain states, with anatomically sequential hyperpolarising activity observed in the awake cortex. GEVI imaging revealed cortical activity maps with increased specificity, high spatial coverage, and at the timescale of cortical information processing.

. Altered response decay of sensory-evoked S1 pyramidal population across brain states due to hyperpolarising component.
(A) Depolarising amplitude of the initial peak response in contra SSp-bfd is constant both through the transition from wakening towards wakefulness (upper, black traces, Spearman's rank correlation (rs) = -0.218, p = 0.128) and in the fully awake condition (upper, red traces, rs = 0.060, p = 0.680). Faint traces: trace for individual 50-trial imaging datasets, solid traces: grand average. For the wakening condition (N = 13 datasets, 5 mice), a main contributor to altered response decay component across brain states is the level of hyperpolarising activity at ~50 ms after the initial response (lower, black traces, rs = 0.815, p < 0.001; Note positive rs value indicates reduction in hyperpolarising amplitude) that decreases through waking up. For the awake condition (N = 16 datasets, 5 mice), while depolarising amplitude remains comparable, the repolarising component increases (i.e. decrease in the measured amplitude; lower, red traces, rs =-0.516, p < 0.001) indicating a potential decrease in alertness through the course of the awake imaging session. (B) Similar comparisons for ipsi SSp-bfd. For the wakening condition (N = 13 datasets, 5 mice), initial depolarising amplitude decreases modestly through the transition from wakening towards wakefulness (upper, black traces; rs = -0.633, p < 0.001), with modest changes in hyperpolarising component (lower, black traces; rs = 0.368, p = 0.009). For the awake condition (N = 16 datasets, 5 mice), changes in initial depolarising amplitude is modest (upper, red traces; rs = -0.338, p = 0.016), and an increase in repolarising/hyperpolarising activity is observed (lower, red traces; rs = -0.697, p < 0.001).

Supplementary Fig. S3. Whisker stimulation-evoked responses in left and right SSp-bfd.
Superimposed voltage imaging traces from left and right SSp-bfd in response to contralateral multiwhisker stimulation displays no lateralisation. (Wakening condition: N = 13 datasets, 5 mice; Awake condition: N = 16 datasets, 5 mice; mean ± SEM). Datasets for right-side stimulation (i.e. left SSp-bfd being the contralateral side) are left-right flipped after functional registration, and pooled for producing grand average. Note selected datasets in the awake condition that is reminiscent of the wakening condition (marked with asterisks, mouse may have fallen asleep); not excluded from analysis. (C) Same as B for awake condition (N = 16 datasets, 5 mice). Green shading highlights the largely constant depolarising amplitude from contralateral SSp-bfd, SSs and VISrl, whilst depolarising response amplitude in other ROIs decreases through the imaging session, correlating with decreasing alertness. (For clarity, only average traces are shown). Lower -Same as Upper, for the repolarising/hyperpolarising response component. (D) Spearman's rank correlation of grand average trend changes in components of sensory-evoked response depicted in (B) and (C) for the selected ROIs in (A) through the dataset, for both wakening and awake conditions. Orange shading: positive rs; blue shading: negative rs; green shading: rs between ±0.1; bold box outline: p < 0.05. Note for hyperpolarising/repolarising amplitudes, positive rs depicts a decreasing trend in this response component through the datasets.
Movie S2. Grand average registered ROI regional average movie of sensory-evoked pyramidal response under wakening condition (N = 13 datasets, 5 mice).
Movie S4. Grand average registered ROI regional average movie of sensory-evoked pyramidal response under awake condition (N = 16 datasets, 5 mice).