fNIRS detects temporal lobe response to affective touch

Abstract

Touch plays a crucial role in social-emotional development. Slow, gentle touch applied to hairy skin is processed by C-tactile (CT) nerve fibers. Furthermore, 'social brain' regions, such as the posterior superior temporal sulcus (pSTS) have been shown to process CT-targeted touch. Research on the development of these neural mechanisms is scant, yet such knowledge may inform our understanding of the critical role of touch in development and its dysfunction in disorders involving sensory issues, such as autism. The aim of this study was to validate the ability of functional near-infrared spectroscopy (fNIRS), an imaging technique well-suited for use with infants, to measure temporal lobe responses to CT-targeted touch. Healthy adults received brushing to the right forearm (CT) and palm (non-CT) separately, in a block design procedure. We found significant activation in right pSTS and dorsolateral prefrontal cortex to arm > palm touch. In addition, individual differences in autistic traits were related to the magnitude of peak activation within pSTS. These findings demonstrate that fNIRS can detect brain responses to CT-targeted touch and lay the foundation for future work with infant populations that will characterize the development of brain mechanisms for processing CT-targeted touch in typical and atypical populations.

Keywords: CT afferents; affective touch; autistic traits; fNIRS; superior temporal sulcus.

Fig. 1

Activation to arm > palm touch. The lighter region encompasses the pixels analyzed in the group-level GLM analyses. Activations indicate regions with a greater response to arm touch relative to palm touch (P < 0.05). Activation is presented on the right cortical surface, in Montreal Neurological Institute space.

Fig. 2

Activation to arm vs palm touch within the pSTS ROI. (a) Visualization of the peak voxel used for ROI analysis, with the extent of the sphere depicting the average distance from the peak voxel of interest that included the four recording channels used for the individualized ROI analysis (average radius = 2.3 cm). (b) Waveforms for the four-channel pSTS group ROI analysis (arm touch > palm touch), with stimulus from 2 to 8 s. (c) Peak amplitude of pSTS response to arm touch in the high (N = 5) and low (N = 5) AQ groups, restricted within the time window of 5–12 s post-stimulus onset. Range of AQ scores for each group are shown in parentheses (low-medium and high-medium groups not shown here).