Active and passive touch differentially activate somatosensory cortex in texture perception

Abstract

The neural mechanisms behind active and passive touch are not yet fully understood. Using fMRI we investigated the brain correlates of these exploratory procedures using a roughness categorization task. Participants either actively explored a surface (active touch) or the surface was moved under the participant's stationary finger (passive touch). The stimuli consisted of three different grades of sandpaper which participants were required to categorize as either coarse, medium, or fine. Exploratory procedure did not affect performance although the coarse and fine surfaces were more easily categorized than the medium surface. An initial whole brain analysis revealed activation of sensory and cognitive areas, including post-central gyrus and prefrontal cortical areas, in line with areas reported in previous studies. Our main analysis revealed greater activation during active than passive touch in the contralateral primary somatosensory region but no effect of stimulus roughness. In contrast, activation in the parietal operculum (OP) was significantly affected by stimulus roughness but not by exploration procedure. Active touch also elicited greater and more distributed brain activity compared with passive touch in areas outside the somatosensory region, possibly due to the motor component of the task. Our results reveal that different cortical areas may be involved in the processing of surface exploration and surface texture, with exploration procedures affecting activations in the primary somatosensory cortex and stimulus properties affecting relatively higher cortical areas within the somatosensory system.

Lateralized enhancement of auditory cortex activity and increased sensitivity to self-generated sounds

“…Similarly, using positron-emission tomography it has been shown that increases in speech production rate result in increased cerebral blood flow in auditory cortices even when auditory feedback was blocked by white noise that was kept constant across rates 20 . Other studies report enhancement of the fMRI signal in S1 during perception of self-generated tactile stimuli compared with similar stimuli externally generated 21,22 . Finally, the fMRI signal in the auditory cortex during active speaking (relative to passive listening) has been shown to be attenuated in STG but enhanced in superior temporal sulcus of the same subjects 23 .…”

Multimodal Interactions between Proprioceptive and Cutaneous Signals in Primary Somatosensory Cortex

“…Neural recordings were made while the hand was statically positioned in the desired conformation, allowing us to quantify proprioceptive and multimodal integration effects in the absence of volitional motor commands. Indeed, some studies have examined how cutaneous responses are modulated by active large-scale limb movements (London and Miller, 2013; Shaikhouni et al, 2013; Simoes-Franklin et al, 2011; Weber et al, 2011), or how somatosensory neurons represent active limb position and hand grasping (Debowy et al, 2001; Gardner et al, 2007; Mountcastle and Powell, 1959; Ro et al, 2000). However, it is unclear whether effects are due to endogenous commands enacted by the motor system ( e.g.…”

The Role of Insula-Associated Brain Network in Touch

“…A number of early reports show that tactile stimulation evokes activation in the parietal operculum [25, 41–45]. The parietal operculum and insula (and their subregions) are spatial neighbors [9]; however, these regions have different cytoarchitectonic features [29, 46].…”