Functional MRI responses to passive, active and observed touch in somatosensory and insular cortices of the macaque monkey.

J Neurosci. 2018 Mar 14;:

Authors: Sharma S, Fiave PA, Nelissen K

Abstract
Neurophysiological data obtained in primates suggests that merely observing others' actions can modulate activity in the observer's motor cortices. In humans, it has been suggested that these multimodal vicarious responses extend well beyond the motor cortices, including somatosensory and insular brain regions, that seem to yield vicarious responses when witnessing others' actions, sensations or emotions (Gazzola and Keysers, 2009). Despite the wealth of data with respect to shared action responses in the monkey motor system, whether the somatosensory and insular cortices also yield vicarious responses during observation of touch remains largely unknown. Using independent tactile and motor fMRI localizers, we first mapped the hand representations of two male monkeys' primary (SI) and secondary (SII) somatosensory cortices. In two subsequent visual experiments, we examined fMRI brain responses to 1) observing a conspecific's hand being touched or 2) observing a human hand grasping or mere touching an object or another human hand. While functionally defined 'tactile SI' and 'tactile SII' showed little involvement in representing observed touch, vicarious responses for touch were found in parietal area PFG, consistent with recent observations in humans (Chan and Baker, 2015). Interestingly, a more anterior portion of SII, and posterior insular cortex, both of which responded when monkeys performed active grasping movements, also yielded visual responses during different instances of touch observation.SIGNIFICANCE STATEMENTCommon coding of one's own and others' actions, sensations and emotions seems to be widespread in the brain. While it is currently unclear to what extent human somatosensory cortices yield vicarious responses when observing touch, even less is known about the presence of similar vicarious responses in monkey somatosensory cortex. We therefore localized monkey somatosensory hand representations using fMRI and investigated whether these regions yield vicarious responses while observing various instances of touch. While 'tactile SI and SII' did not elicit responses during touch observation, a more anterior portion of SII, in addition to area PFG and posterior insular cortex, all of which responded during monkeys' own grasping movements, yielded vicarious responses during observed touch.

PMID: 29540550 [PubMed - as supplied by publisher]