Dissociating the Neural Correlates of Experiencing and Imagining Affective Touch

Abstract

This functional magnetic resonance imaging (fMRI) study examined experiencing and imagining gentle arm and palm touch to determine whether these processes activate overlapping or distinct brain regions. Although past research shows brain responses to experiencing and viewing touch, this study investigates neural processing of touch absent of visual stimulation. C-tactile (CT) nerves, present in hairy skin, respond specifically to caress-like touch. CT-targeted touch activates "social brain" regions including insula, right posterior superior temporal sulcus, amygdala, temporal poles, and orbitofrontal cortex ( McGlone et al. 2012). We addressed whether activations reflect sensory input-driven mechanisms, cognitive-based mechanisms, or both. We identified a functional dissociation between insula regions. Posterior insula responded during experienced touch. Anterior insula responded during both experienced and imagined touch. To isolate stimulus-independent mechanisms recruited during physical experience of CT-targeted touch, we identified regions active to experiencing and imagining such touch. These included amygdala and temporal pole. We posit that the dissociation of insula function suggests posterior and anterior insula involvement in distinct yet interacting processes: coding physical stimulation and affective interpretation of touch. Regions active during experiencing and imagining CT-targeted touch are associated with social processes indicating that imagining touch conjures affective aspects of experiencing such touch.

Keywords: C-tactile; fMRI; insula; social brain; touch.

Figure 1.

fMRI experimental design.

Figure 2.

Experience > Imagine results at P = 0.05 at a whole-brain level (k = 153) (A), and using a bilateral insula mask (k = 20) (B).

Figure 3.

Imagine Arm > Palm contrast within Experience Arm > Palm mask (P = 0.05, k = 10).

Figure 4.

Event-related averaging of 4 functionally defined insula regions (as shown in Fig. 2), showing percent signal change over time in volumes. Significant time points show activation greater than zero. Left anterior insula: volume 2 is significant in the experience condition, and volumes 2 and 3 are significant in the imagine condition (A). Right anterior insula: volumes 2 and 3 are significant in the experience condition, and volumes 2 and 3 are significant in the imagine condition (B). Left posterior insula: volumes 2 and 3 are significant in the experience condition, and no volumes are significant in the imagine condition (C). Right posterior insula: volumes 2 and 3 are significant in the experience condition, and no volumes are significant in the imagine condition (D).