Neural coding during active somatosensation revealed using illusory touch

Abstract

Active sensation requires the convergence of external stimuli with representations of body movements. We used mouse behavior, electrophysiology and optogenetics to dissect the temporal interactions between whisker movement, neural activity, and sensation of touch. We photostimulated layer 4 activity in single barrels in closed-loop with whisking. Mimicking touch-related neural activity caused illusory perception of an object at a particular location, but scrambling the timing of spikes over one whisking cycle (tens of milliseconds) did not abolish the illusion, indicating that knowledge of instantaneous whisker position is unnecessary for discriminating object locations. Illusions were induced only during bouts of directed whisking, when mice expected touch, and in the relevant barrel. Reducing activity biased behavior consistent with a spike count code for object detection at a particular location. Our results show that mice integrate coding of touch with movement over timescales of a whisking bout to produce perception of active touch.

What single-cell stimulation has told us about neural coding

“…Similarly, Histed and Maunsell [104] applied photostimulation in order to investigate the contribution of pulse duration and intensity to the detectability of a direct optical stimulation of excitatory neurons in the mouse V1 and found that psychophysical performance was well predicted by the total number of spikes, induced by increased amounts of light. Similar results were obtained at the somatosensory cortex in a study which examined the effects of optogenetic stimulation of layer 4 (L4) excitatory neurons on report of illusory touch [105]. The researchers trained mice to report the position of a pole using their whiskers and then manipulated the sensation by photostimulating L4 activity.…”

Cortical Correlates of Low-Level Perception: From Neural Circuits to Percepts

“…Thus, the existence and use of temporal codes may be specific only to some relay stations and pathways, possibly used for specific computations. Recent studies in auditory and somatosensory cortex show a good correlation (Bathellier et al, 2012), possibly even a causal link (Musall et al, 2014;O'Connor et al, 2013), between cortical rate codes and perception. But the simplicity of the stimuli and the behavioral model used in these studies do not exclude the possibility that cortical structures with a high information load such as primate V1 use a sparse code based on precise spike timing, as observed during high-dimensional natural-scene stimulation (Baudot et al, 2013;Vinje and Gallant, 2000).…”

For things needing your attention: the role of neocortical gamma in sensory perception

“…As discussed below, under specific conditions of sensory drive, [67 ] also observed that FS activation could suppress performance in a similar detection task. Also, O'Connor and colleagues (2013) [77] found that optogenetic stimulation across interneuron types (using the VGAT-ChR2 promoter) also decreased stimulus-related firing rates and suppressed behavior, in this case for an active sensing vibrissal task. In the Sachidhanandam and O'Connor studies, no attempt was made to explicitly emulate FS-gamma oscillations.…”