About this Research Topic
Recent research has begun to explore an affective dimension of touch integral to the neural processing and conscious experience of tactile sensations. The affective dimension of touch pertains to the hedonic valence of tactile sensation. It may also play a vital role in social interactions in humans and other mammals. A better neuroscientific understanding of touch will provide the basis for identifying critical brain processes underlying this affective dimension. The aim of this Research Topic is to expand the current boundaries of this nascent field, and to provide an interdisciplinary overview of research exploring the neural processing of affective touch. We encourage submissions that apply various methods (eg, fMRI, electrophysiology, TMS, fNIRS, behavior, pharmacology, immunology, genetics) on healthy, child, psychiatric, and neurological populations. We particularly welcome submissions involving work on nonhuman species as well as developmental investigations. This Research Topic will introduce readers to the many facets of neuroscientific research on affective touch, which uses a variety of experimental approaches to chart neural pathways, from the periphery to central nervous system projections and neuromodulation.
The scope of the Topic includes several key areas of potentially high relevance for the study of affective touch, including its role in:
Social interactions, grooming, and bonding.
Positive affect and hedonic feelings hold individuals together in social bonds. In romantic partnerships, relationship satisfaction, previous experience of familial affection, and trust are positively correlated with self-reports of mutual grooming (Nelson and Geher 2007). Grooming, indeed, may reinforce pair-bonding (Dunbar 2008). Healthy individuals with high autistic traits show disturbances in affective touch systems and regions associated with social processing (Voos et al., 2012).
Stress and anxiety.
A role for social touch in stress alleviation has been suggested. For example, the contact pressure of holding hands reduces the anxiety posed by an impending threat (Coan et al., 2006). Effects of touch in social interactions have been found to increase liking of a person or place, to facilitate trust or compliance, and increase prosocial behavior (eg, Fisher et al. 1976, Hornik 1992, Burgoon et al. 1992).
CT afferents and interoception.
A key discovery in the study of affective touch has been the characterization of human CT (tactile C) afferent nerve fibers. These show a preference for stimuli that move gently over the skin, such as a caress (Löken et al, 2009). fMRI studies show increased posterior insula activation for CT-fiber stimulation (Olausson et al. 2002, 2008). CT-mediated affective touch may have more in common anatomically with interoceptive and visceral systems than to afferent systems processing other classes of tactile and nociceptive stimuli (Björnsdotter, 2010).
Touch can convey thoughts and feelings and regulate them in others. Hertenstein et al. (2006) defines tactile communication as ‘‘systematic changes in another’s perceptions, thoughts, feelings, or behavior as a function of another’s touch in relation to the context in which it occurs.’’
Touch is central in early parent-offspring interactions in most mammals. Maternal licking of rat pups can influence the behavior of the adult rat (Menard et al. 2004), and monkey infants deprived of tactile contact with a mother or mother surrogate become stressed and even ill-nourished (e.g., Harlow 1958). Despite this, little research has been done on the ontogeny and development of affective touch pathways.
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