Abstract
Interpersonal touch possesses a strong affective component, which immediately evokes attention. The neural processing of such touch is moderated by specialized C-tactile nerve fibers in the periphery and results in central activation of somatosensory areas as well as regions involved in social processing, such as the superior temporal gyrus (STG). In the present functional neuroimaging investigation, we tested the hypothesis that the attention grasping effect of interpersonal touch as compared to impersonal touch is reflected in a more-pronounced deactivation of the default mode network (DMN). Using functional magnetic resonance imaging, we investigated the neural processing of interpersonal relative to impersonal touch conditions that were furthermore modulated by stroking velocity in order to target c-tactile nerve fibers to a different extent. A sample of 30 healthy participants (19 women, mean age 40.5 years) was investigated. In the impersonal touch, participants were stroked with a brush on the forearm. In the interpersonal touch condition, the experimenter performed the stroking with the palm of his hand. Interpersonal touch was rated as more pleasant and intense than impersonal touch and led to a stronger blood oxygen level dependent (BOLD) signal increase in the somatosensory cortex SII extending to the superior temporal cortex. Over all touch conditions, this activation was coupled in time to the deactivation of prominent nodes of the DMN. Although deactivation of the DMN was most pronounced for interpersonal touch conditions, the direct comparison did not show significant differences in DMN deactivation between interpersonal and impersonal touch or between different stroking velocities. We therefore conclude that all applied touch conditions deactivate the DMN and the strong connection to areas which code the contextual and social characteristics of affective touch may explain the attention grasping effect of touch.
Highlights
As a central aspect of human interaction, affective touch makes critical contributions to important social experiences such as the hug from a friend, the endearment of a lover, or the comforting caress of a mother
Given that touch signals the presence of others, it may initiate a shift in brain processing associated with an attention to the outer world. We propose that this shift is reflected in altered default mode network (DMN) responding
As depression affects DMN activity[23], all participants were screened for symptoms of this disorder with the well-validated Beck Depression Inventory (BDI)[24]; no participant scored in the range of moderate-to-severe depression
Summary
As a central aspect of human interaction, affective touch makes critical contributions to important social experiences such as the hug from a friend, the endearment of a lover, or the comforting caress of a mother. C-tactile fibers are sensitive to temperature, with the highest firing frequency occurring when slow stroking stimulation is presented at about 32 °C – a temperature which resembles skin-to-skin contact[9] Given these characteristics, it has been proposed that c-tactile fibers are tuned to social, interpersonal, touch[10,2]. The activation of primary[3] and secondary[4] somatosensory cortex by c-tactile optimal stimulation is moderated by contextual information during touch presentation; individual perception of touch pleasantness correlates with evoked activity in the superior temporal sulcus[13] and the anterior cingulate cortex[17]. The posterior cingulate cortex (PCC), a third node, is involved in the recollection of prior experiences, as are the inferior parietal lobule (IPL), the lateral temporal cortex (LTC) and the hippocampal and parahippocampal formation (HF)[22]
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