Behavioral perception and brain mechanism for processing Affective Touch appear to be altered in Disorganized compared to Organized attachment.

Introduction : The emotional aspect of touch has been called “Affective Touch” (AT), a term capturing tactile processing with a hedonic, motivational and social significance (e.g. affiliative behaviors or mother-infant bonding). AT is driven by C-Tactile (CT) fibers that are present in hairy skin and respond specifically to slow, gentle touch (McGlone et al., 2014). CT fibers project to a neural network including the insular cortex and other areas involved in the social domain (Morrison, 2016). The perception and the neural processing of AT appear to be modulated by psychological factors such as attachment patterns (Krahé et al., 2018); despite this, nothing is known about the Disorganized attachment dimension. Our study aims to compare the perception and brain esponses to AT in a sample of adults classified as having a Organized (OA) or a Disorganized attachment (DA). Methods : 46 OA and 17 DA individuals (as coded via Adult Attachment Interview) underwent a behavioral tactile procedure for basic somatosensation (comprising Von Frey Monofilaments, 2PD, and thermal sensitivity) and a psychological assessment (including SCL-90-R and PID-5). AT perception was measured applying Affective (AS) and Neutral Stimulations (NS) with a watercolor brush on the forearm, respectively at 3 or 30 cm/s; pleasantness ratings for AS and NS and a index of preference (AT index) were collected. A randomly selected subset of 12 OA and 8 DA underwent also a fMRI block design, during affective and neutral tactile stimulations (four run of 5 repetitions of AS and 5 repetitions of NS each), in addition of two resting-state sessions for a functional connectivity analysis (fc-fMRI). Results : No differences emerged for somatosensation and psychological scales. A MANOVA on AS and NS ratings showed that DA vs OA reported lower ratings for AS and no difference for NS. A t-test on AT index showed that DA vs OA preferred NS. A fMRI F omnibus contrast revealed the involvement of posterior insula (PI), somatosensory primary cortex (S1), supramarginal gyrus (SMG) and amygdala during AS and NS. A 2 (OA vs DA) x 2 (AS vs NS) mixed factorial ANOVA on hemodynamic responses showed an effect of stimulation, with higher activation for NS in PI, S1 and amygdala, and an effect of group, with DA showing higher activation in amygdala. An interaction in amygdala showed higher activation for NS vs AS in DA, but not in OA. fc-fMRI showed connectivity between PI and SMG and PI and S1. Discussion : Results showed that DA perceived AT as less pleasant and preferred NS compared to OA, suggesting that adults who experience difficulties in the ways to relate to others in the affectivity domain, and, in particular, referring to attachment history, are specifically impaired in AT perception, but not in other basic functions of somatosensation. Altered AT perception appeared to be also mirrored by differences in brain mechanism for processing AT. In fact, we found a higher activation in amygdala for AS and NS in DA compared to OA, suggesting different mechanisms for coding motivational and hedonic aspect of AT. Further studies are needed to understand whether this atypical response to AT refers to attribution of a negative or positive value to these stimuli.