Short Time-Scale Sensory Coding in S1 during Discrimination of Whisker Vibrotactile Sequences

Abstract

Rodent whisker input consists of dense microvibration sequences that are often temporally integrated for perceptual discrimination. Whether primary somatosensory cortex (S1) participates in temporal integration is unknown. We trained rats to discriminate whisker impulse sequences that varied in single-impulse kinematics (5–20-ms time scale) and mean speed (150-ms time scale). Rats appeared to use the integrated feature, mean speed, to guide discrimination in this task, consistent with similar prior studies. Despite this, 52% of S1 units, including 73% of units in L4 and L2/3, encoded sequences at fast time scales (≤20 ms, mostly 5–10 ms), accurately reflecting single impulse kinematics. 17% of units, mostly in L5, showed weaker impulse responses and a slow firing rate increase during sequences. However, these units did not effectively integrate whisker impulses, but instead combined weak impulse responses with a distinct, slow signal correlated to behavioral choice. A neural decoder could identify sequences from fast unit spike trains and behavioral choice from slow units. Thus, S1 encoded fast time scale whisker input without substantial temporal integration across whisker impulses.

Increased excitation-inhibition ratio stabilizes synapse and circuit excitability in four autism mouse models

“…For each PYR cell, we found the minimum L4 stimulation intensity required to evoke a detectable EPSC, denoted Eθ, and then measured input-output curves for EPSCs and IPSCs at 1.0-1.5x Eθ. For analysis, currents were integrated over 20 ms, matching the time scale of L2/3 sensory integration in vivo (McGuire et al, 2014).…”

Tactile enrichment drives emergence of functional columns and improves sensory coding in L2/3 of mouse S1

“…We constructed two neural decoders – one to detect a whisker deflection compared to spontaneous activity, and one to discriminate stimulus identity among 9 whiskers - from single-trial mean ΔF/F of individual ROIs and ensembles of ROIs. For the discrimination decoder, each ROI was represented by a one-versus-all (OVA) classifier that was trained by logistic regression to report the probability of each stimulus given the mean ΔF/F during the evoked window following a single whisker deflection, selected randomly from each stimulus iteration (structured as in (McGuire et al, 2016)). Each classifier was composed of 9 logistic functions, one for each stimulus.…”

Learning a tactile sequence induces selectivity to action decisions and outcomes in the mouse somatosensory cortex

“…Neurons in the naïve S1bf have limited temporal integration: they report on, or encode, sensory input accumulated over just a few tens of milliseconds [21][22][23][24][25][26]. In earlier studies, this temporal integration remained limited even after learning of tasks in which performance could benefit from greater integration [25].…”

“…Sensory-guided tasks mediated by whisker input can be carried out without cortical participation [18,19], and recent results have highlighted that the flow of sensory information through cortical pathways is task-dependent [20]. Moreover, although neurons in S1bf encode well-defined stimulus features, in naïve animals they do not integrate sensory information over time [21][22][23][24][25][26]. Here, we determined whether S1bf and successive cortical processing stages are needed to solve the elementary sequence recognition task, and whether neuronal responses in S1bf become selective to the target sequence as a result of learning.…”