Human Brain Activity Related to the Tactile Perception of Stickiness

Abstract

While the perception of stickiness serves as one of the fundamental dimensions for tactile sensation, little has been elucidated about the stickiness sensation and its neural correlates. The present study investigated how the human brain responds to perceived tactile sticky stimuli using functional magnetic resonance imaging (fMRI). To evoke tactile perception of stickiness with multiple intensities, we generated silicone stimuli with varying catalyst ratios. Also, an acrylic sham stimulus was prepared to present a condition with no sticky sensation. From the two psychophysics experiments–the methods of constant stimuli and the magnitude estimation—we could classify the silicone stimuli into two groups according to whether a sticky perception was evoked: the Supra-threshold group that evoked sticky perception and the Infra-threshold group that did not. In the Supra-threshold vs. Sham contrast analysis of the fMRI data using the general linear model (GLM), the contralateral primary somatosensory area (S1) and ipsilateral dorsolateral prefrontal cortex (DLPFC) showed significant activations in subjects, whereas no significant result was found in the Infra-threshold vs. Sham contrast. This result indicates that the perception of stickiness not only activates the somatosensory cortex, but also possibly induces higher cognitive processes. Also, the Supra- vs. Infra-threshold contrast analysis revealed significant activations in several subcortical regions, including the pallidum, putamen, caudate and thalamus, as well as in another region spanning the insula and temporal cortices. These brain regions, previously known to be related to tactile discrimination, may subserve the discrimination of different intensities of tactile stickiness. The present study unveils the human neural correlates of the tactile perception of stickiness and may contribute to broadening the understanding of neural mechanisms associated with tactile perception.

Functional Connectivity Evoked by Orofacial Tactile Perception of Velocity

“…For seed-based FC analyses, a whole-brain approach was used to identify cortical areas that were differentially connected with bilateral SI and SII among four conditions (5, 25, 65 cm/s, and "All ON"). The four seeds (see Table 1) were chosen based on the literature (Lin and Kajola, 2003;Pastor et al, 2004;Reed et al, 2004;Dresel et al, 2008;Ackerley et al, 2012;Popescu et al, 2013;Custead et al, 2017;Oh et al, 2017;Yeon et al, 2017) because bilateral SI and SII were most consistently identified across imaging studies with different parameters. We chose to compute all possible cross-correlation coefficients between the time series of the seeds and all residual voxels in the brain, and 3 http://www.nitrc.org/projects/artifact_detect/ then convert them to Z-scores.…”

“…The human somatosensory system decodes tactile stimuli from peripheral sensory receptors through a complex process involving interactions between bottom-up thalamocortical and topdown corticocortical/cortico-thalamo-cortical pathways (Avivi-Arber et al, 2011;Lundblad et al, 2011;Zembrzycki et al, 2013;Hwang et al, 2017). Studies of cortical representations of tactile stimulation of different body parts have identified the primary (SI) and secondary (SII) somatosensory cortices, as well as the supplementary motor area responsible for sensory processing (Ibáñez et al, 1995;Backes et al, 2000;Grodd et al, 2001;Backlund et al, 2003;Paus et al, 2006;Backlund Wasling et al, 2008;Bjornsdotter et al, 2009;Ackerley et al, 2012;Zembrzycki et al, 2013;Akselrod et al, 2017;Custead et al, 2017;Oh et al, 2017;Yeon et al, 2017). SI, which is located in the postcentral gyrus, processes complex information about the location, velocity, and other characteristics of tactile stimulation from the thalamus through the thalamocortical axons.…”

“…Furthermore, neuroimaging studies also indicated that there are different cortical representations for different tactile stimuli in humans (e.g., location, type of motion, direction, velocity, etc.) (Reed et al, 2004;Miyamoto et al, 2006;Backlund Wasling et al, 2008;Eickhoff et al, 2008;Bjornsdotter et al, 2009;Moulton et al, 2009;Avivi-Arber et al, 2011;Grabski et al, 2012;Huang et al, 2012;Khoshnejad et al, 2014;Yang et al, 2014;Custead et al, 2015Custead et al, , 2017Hwang et al, 2017;Oh et al, 2017;Yeon et al, 2017).…”

Neural Activity Patterns in the Human Brain Reflect Tactile Stickiness Perception

“…In our previous fMRI study, we successfully found brain regions exhibiting correlations of blood oxygen level-dependent (BOLD) signals with perceived tactile stickiness using conventional uni-variate analyses and an in-house sticky stimulus set (Yeon et al, 2017 ). Based on the psychophysical experimental results on our stimulus set, the sticky stimuli were divided into three disjoint groups in terms of perceptual intensity: Supra-threshold (sticky stimuli that can consistently evoke sticky sensation), Infra-threshold (sticky stimuli that barely evoke sticky sensation), and Sham (tactile stimuli that contain no sticky property) groups.…”

“… Our previous human fMRI study found brain activations correlated with tactile stickiness perception using the uni-variate general linear model (GLM) (Yeon et al, 2017 ). Here, we conducted an in-depth investigation on neural correlates of sticky sensations by employing a multivoxel pattern analysis (MVPA) on the same dataset.…”