Content representation of tactile mental imagery in primary somatosensory cortex.

Abstract

The imagination of tactile stimulation has been shown to activate primary somatosensory cortex (SI) with a somatotopic specificity akin to that seen during the perception of tactile stimuli. Using fMRI and MVPA, we investigate if this recruitment of sensory regions also reflects content-specific activation, i.e. whether the activation in SI is specific to the mental content participants imagined. To this end, healthy volunteers (n=21) either perceived or imagined three types of vibrotactile stimuli (mental content) while fMRI data was acquired. Independent of the content, during tactile mental imagery we found activation of fronto-parietal regions, supplemented with activation in the contralateral BA2 subregion of SI, replicating previous reports. While the imagery of the three different stimuli did not reveal univariate activation differences, using multivariate pattern classification we were able to decode the imagined stimulus type from BA2. Moreover, cross-classification revealed that tactile imagery elicits activation patterns similar to those evoked by the perception of the respective stimuli. These findings promote that mental tactile imagery involves the recruitment of content-specific activation patterns in sensory cortices, namely in SI.Significance StatementIt has been shown previously that mental imagery of sensations in different modalities can activate respective primary sensory cortices (visual/auditory/tactile). However, a relation of such activation to the imagined mental content was mainly shown for the visual system. Here, we generalize this concept to the somatosensory domain by showing that content-specific activation during tactile mental imagery can be found in primary somatosensory cortex subarea BA2. Most importantly, we show that tactile imagery elicits activation patterns similar to those evoked by sensory stimulation. Our results provide further evidence that sensory recruitment is among the brain processes that allow conscious information representation.