Gentle Touch Opens the Gate to the Primary Somatosensory Cortex

Abstract

Touch is a primary reinforcer strongly associated with motivational and affective processes that drive social behavior, and it also plays a critical role in massage therapy. Touch in massage is characterized by gentle touches of the skin involving light pressure effleurage and calm stroking movements intended to increase recipients' pleasure and relaxation. The relationships between basic physical parameters, such as patterns of the hand movements, and their neural bases are important for understanding the effects of gentle touch. However, such studies have not yet been performed. Here, we investigated these relationships and underlying neural mechanisms under two basic movement conditions. Methods Using functional Magnetic Resonance Imaging (fMRI), we investigated brain activity induced by Circular (C) and Back-and-forth (BF) massage of participants' left hands with the experimenter's right hand, ensuring that movements were not unpleasant. We assessed subjective feelings, and analyzed fMRI data with Principal Component Analysis (PCA) and correlation analyses to identify associated brain networks. Results In C compared with BF, participants felt more positive emotions. There was greater activation of the right primary Somatosensory Cortex (SI) and left cerebellum (CB), but lower activation of the Anterior Cingulate Cortex (ACC) and Periaqueductal Gray (PAG) in C compared with BF. There was no significant difference in unpleasant feelings between the conditions. Moreover, co-activation of the left mid-lateral Orbitofrontal Cortex (OFC), CB, and Rostral Ventromedial Medulla (RVM), and the right SI and posterior insula showed high loadings on Factor 1, which was negatively correlated with unnatural feelings. Meanwhile, co-activation of the ACC and PAG showed high loadings on Factor 2, which was positively correlated with unpleasant feelings. Conclusion Our findings suggest somatosensory afferents to the SI are regulated by the descending pain modulatory system under the control of the mid-lateral OFC and ACC, even with mild somatosensory stimulation.

Gentle stroking elicits somatosensory ERP that differentiates between hairy and glabrous skin

“…, 2016 ). On the other hand, work contrasting more with less pleasant touch reported activity in primary somatosensory cortex ( Shirato et al. , 2018 ).…”

“…In Experiment 1, the brush stroked the participant’s dorsal forearm, whereas in Experiment 2, the brush stroked her/his palm. Although most studies in the field have probed linear trajectories, recent evidence suggests oval trajectories are more pleasant ( Shirato et al. , 2018 ) and more representative of actual touch interactions ( Lo et al.…”

Discriminative and affective touch converge: Somatosensory cortex represents Aß input in a CT-like manner

“…The present study tackled these issues using a novel tactile stimulation device with the same degrees of freedom as a hand touching skin. Thus, we could implement oval strokes, which are more natural (Lo et al, 2021) and deemed more pleasant than linear strokes (Shirato et al, 2018). We could also equate stimulus duration across conditions, which is critical when dealing with temporally sensitive measures such as the EEG.…”

The Neural Correlates of Product Attachment to Cosmetics: Is It Similar to That of Attachment in Human Relationships?

“…Moreover, we conducted a multiple regression analysis with the score of a subjectively evaluated item that was signi cantly correlated with a feeling of "attachment" as the dependent variable, and the eigenvariate values of the ROIs that were signi cant by the SVC test as the independent variables, in each of the visual with tactile and visual sessions, with a signi cance level of p=0.05 based on the step-wise method. In addition, we added the somatosensory-related ROIs {the right SI (40 -31 59), secondary somatosensory area (SII) (52 -24 20), and posterior insula (PI) (42 -31 21), and the left SII (-58 -20 14)} identi ed in our previous studies [27,28] to the above ROIs in order to con rm the tactile effect on the somatosensory-related regions. Next, we conducted 2×2 (conditions × sessions) repeated measures analysis of variance for the ROI activity versus baseline in each condition (p < 0.05), and compared their activities between the visual with tactile and the visual sessions using a paired t-test based on a Bonferroni correction (p < 0.025 = 0.05/2) when there was a signi cant interaction between conditions and sessions.…”

“…In addition, we explored the relationship between these brain regions and the subjective feeling associated with the feeling of attachment. Moreover, we set the additional somatosensory-related ROIs identi ed in our previous studies [27,28], and investigated the effects of tactile information processing and preference by comparing these brain activities in the visual with tactile session to those in the visual session. Thereafter, we assessed the correlation between the activity in each brainstem region and activities in each of the memory-related ROIs and the somatosensory-related ones.…”