Tactile Feature Processing and Attentional Modulation in the Human Somatosensory System

Abstract

The somatosensory system offers us diverse functionality. It is responsible for the sensation of touch, which involves perception of external objects. It provides information about the body’s own components and is critically involved in the planning and execution of motor actions. Considerable effort has been directed towards elucidating how somatosensory processing is organized to subserve these various functions. Based on this, Dijkerman and de Haan proposed a model to describe the cortical processing of somatosensory information (Dijkerman and de Haan 2007). The aim of the present thesis was to extend this model of somatosensory processing for perception and action, focussing on feature processing and attentional modulation during tactile perception. To this end, two functional magnetic resonance imaging experiments were performed, in which Braille-like tactile stimulation was presented to human volunteers. The first experiment sought to determine the role of feature-specific higher-order processing for tactile perception and involved moving or patterned stimulation during passive touch. We found that the visual motion-sensitive area hMT+/V5 and the inferior parietal cortex were selectively activated during motion and pattern processing, respectively. The responses covaried with participants’ perceptual performance in identifying the respective stimulus attribute and were functionally coupled to the responses in primary somatosensory cortex. The results of this study provided evidence for the direct engagement of feature-specific cortical areas in tactile perception. The second experiment aimed at investigating the functional significance of top-down attentional gating during tactile task accomplishment. The task involved selective attention to the spatial pattern or to the temporal frequency of the tactile stimulation and the detection of changes in the respective stimulus attribute. We found that a frontoparietal network was selectively activated during the detection of task-relevant change. Analysis of effective connectivity revealed that the functional integration of task-relevant sensory information occured in a network composed of the somatosensory cortices and the inferior frontal gyrus. Modeling context-dependent causal influences within this functional network identified top-down attentional biasing for gating perception of tactile stimulus attributes. Based on the findings presented here, functions for feature processing and attentional modulation were added to the model by Dijkerman and de Haan. The extended model contributes to the understanding of how the somatosensory system processes tactile input and allows formulating testable hypotheses to motivate future research questions. In this way, the present findings might further be useful for the development of treatments for people suffering from somatosensory system deseases.