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Revisiting touch observation in anterior parietal cortex: vicarious activation in somatosensory cortex?

26.512, Saturday, 17-May, 2:45 pm - 6:45 pm, Pavilion
Session: Perception and action: Neural mechanisms

Annie Chan1, Chris Baker1; 1National Institute of Mental Health

Recent studies have reported that seeing a hand being touched elicits strong of activation in somatosensory cortex (SI, SII), suggesting that these regions may play an important role in understanding other’s experiences. However, prior research has not systematically mapped out the location of these activations or examined their functional specificity. To understand the topography of visual hand representations in parietal cortex and the nature of these representations, we used fMRI to investigate visual responses to the observed touch of a hand. First, we carefully identified SI and SII using anatomical and independent functional localizers. We then compared responses to the sight of a static hand being brushed compared to brush alone. We found that observing a hand being brushed elicited activation in superior and inferior parietal cortex, but not the hand representation in SI and SII. We then characterized the functional properties of these parietal regions in three separate experiments. Experiment 1 revealed that while the presence of both a hand and a brush was necessary, observation of actual touch was not needed, brushing near hand was sufficient. Further, there was no difference between observing a left or a right hand being touched. Experiment 2 showed no effect of perspective, with equivalent responses to egocentric and allocentric views of hands. Finally, Experiment 3 revealed some selectivity for the form of the object and the nature of the movement with reduced responses to a hand being “brushed” by a laser beam, a foot being brushed, and finger movement. Overall our results question the role of somatosensory cortex in understanding other’s experiences. Instead, we find that observing touch activates regions in parietal cortex, but not somatosensory cortex of hand, with properties that reflect the interaction between a hand and an object, consistent with an involvement in visually guided action.

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