Abstract
According to the hierarchical view of human somatosensory network, somatic sensory information is relayed from the thalamus to primary somatosensory cortex (S1), and then distributed to adjacent cortical regions to perform further perceptual and cognitive functions. Although a number of neuroimaging studies have examined neuronal activity correlated with tactile stimuli, comparatively less attention has been devoted toward understanding how vibrotactile stimulus information is processed in the hierarchical somatosensory cortical network. To explore the hierarchical perspective of tactile information processing, we studied two cases: (a) discrimination between the locations of finger stimulation; and (b) detection of stimulation against no stimulation on individual fingers, using both standard general linear model (GLM) and searchlight multi-voxel pattern analysis (MVPA) techniques. These two cases were studied on the same data set resulting from a passive vibrotactile stimulation experiment. Our results showed that vibrotactile stimulus locations on fingers could be discriminated from measurements of human functional magnetic resonance imaging (fMRI). In particular, it was in case (a) we observed activity in contralateral posterior parietal cortex (PPC) and supramarginal gyrus (SMG) but not in S1, while in case; (b) we found significant cortical activations in S1 but not in PPC and SMG. These discrepant observations suggest the functional specialization with regard to vibrotactile stimulus locations, especially, the hierarchical information processing in the human somatosensory cortical areas. Our findings moreover support the general understanding that S1 is the main sensory receptive area for the sense of touch, and adjacent cortical regions (i.e., PPC and SMG) are in charge of a higher level of processing and may thus contribute most for the successful classification between stimulated finger locations.
Highlights
The somatosensory system conveys mechano-sensory information via sensory afferents through the spinal cord, brainstem, and thalamus to the somatosensory cortex (Kaas, 1993; McGlone and Reilly, 2010; Kalberlah et al, 2013)
Our results showed that vibrotactile stimulus locations on fingers could be discriminated from measurements of human functional magnetic resonance imaging
Exact mechanisms of hierarchical tactile information processing are controversial in the dynamic causal modeling (DCM) studies based on functional magnetic resonance imaging data (Liang et al, 2011; Kalberlah et al, 2013), recent studies (Chung et al, 2013; Kalberlah et al, 2013) provided substantial evidence for hierarchical tactile information processing in human somatosensory cortex
Summary
The somatosensory system conveys mechano-sensory information via sensory afferents through the spinal cord, brainstem, and thalamus to the somatosensory cortex (Kaas, 1993; McGlone and Reilly, 2010; Kalberlah et al, 2013). Exact mechanisms of hierarchical tactile information processing are controversial in the dynamic causal modeling (DCM) studies based on functional magnetic resonance imaging (fMRI) data (Liang et al, 2011; Kalberlah et al, 2013), recent studies (Chung et al, 2013; Kalberlah et al, 2013) provided substantial evidence for hierarchical tactile information processing in human somatosensory cortex These previous observations guide us to form a hypothesis that somatosensory cortical processes are organized hierarchically; S1 contributes to low-level processing while adjacent cortical regions (e.g., PPC and SMG) more likely contribute to high-level processing. It leads us to form a more specific hypothesis on hierarchical somatosensory cortical processes that S1 contributes to the detection of a vibrotactile stimulus in a particular location while PPC and SMG contribute to the discrimination of vibrotactile stimulus locations
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