Hugs and kisses - The role of motor preferences and emotional lateralization for hemispheric asymmetries in human social touch.

Social touch is an important aspect of human social interaction - across all cultures, humans engage in kissing, cradling and embracing. These behaviors are necessarily asymmetric, but the factors that determine their lateralization are not well-understood. Because the hands are often involved in social touch, motor preferences may give rise to asymmetric behavior. However, social touch often occurs in emotional contexts, suggesting that biases might be modulated by asymmetries in emotional processing. Social touch may therefore provide unique insights into lateralized brain networks that link emotion and action. Here, we review the literature on lateralization of cradling, kissing and embracing with respect to motor and emotive bias theories. Lateral biases in all three forms of social touch are influenced, but not fully determined by handedness. Thus, motor bias theory partly explains side biases in social touch. However, emotional context also affects side biases, most strongly for embracing. Taken together, literature analysis reveals that side biases in social touch are most likely determined by a combination of motor and emotive biases.