Abstract
Tactile interactions with our environment stimulate afferent fibers within the skin, which deliver information about sensations of pain, texture, itch and other feelings to the brain as a comprehensive sense of self. These tactile interactions can stimulate brain regions involved in interoception and reward processing. This study examined subjective, behavioral, and neural processing as a function of age during stimulation of A-beta (Aβ) and C tactile (CT) afferents using a soft brush stroke task. 16 adolescents (ages 15–17), 22 young adults (ages 20–28), and 20 mature adults (ages 29–55) underwent a simple continuous performance task while periodically anticipating and experiencing a soft touch to the palm or forearm, during functional magnetic resonance imaging (fMRI). fMRI results showed that adolescents displayed greater bilateral posterior insula activation than young and mature adults across all conditions and stimulus types. Adolescents also demonstrated greater bilateral posterior insula activation than young and mature adults specifically in response to the soft touch condition. Adolescents also exhibited greater activation than mature adults in bilateral inferior frontal gyrus and striatum during the soft touch condition. However, mature adults showed greater striatum activation than adolescents and young adults during anticipation. In the left anterior cingulate cortex, mature adults exhibited greater activation than adolescents and young adults when anticipating the upcoming touch. These results support the hypothesis that adolescents show an exaggerated neural response to pleasant stimulation of afferents, which may have profound effects on how they approach or avoid social and risky situations. In particular, heightened interoceptive reactivity to pleasant stimuli might cause adolescents to seek experiences that are associated with pleasant stimulation.
Highlights
Our sense of touch is important for how we interpret the world around us
SUBJECT CHARACTERISTICS By definition, AD, Young adults (YA), and Mature adults (MA) significantly differed in age as well as education, but groups did not differ in verbal IQ, ethnicity, gender or Barratt Impulsiveness Scale (BIS) ratings
BEHAVIORAL DATA visual analog scale (VAS) ratings AD, YA, and MA did not differ in their subjective ratings of the pleasantness of the soft touch (See Table 1)
Summary
Our sense of touch is important for how we interpret the world around us. Tactile interactions with our environment stimulate afferent fibers within the skin, which deliver information about sensations of pain, texture, itch, and other feelings from the body to the brain as a comprehensive sense of self (Craig, 2002; Olausson et al, 2002, 2010; Ackerley et al, 2012). Within human skin there are two types of mechanoreceptors known to respond to tactile stimulation: myelinated A-beta (Aβ) fibers and unmyelinated C tactile (CT) fibers These two types of fibers are located in various regions throughout the body and respond to specific stimulation. Aβ fibers provide discriminate information about touch while CT afferents signal affective aspects of touch (Olausson et al, 2002; Bjornsdotter et al, 2010; Morrison et al, 2011b). Together, these afferents provide a comprehensive picture of tactile stimulation to regions of the brain. The present study aims to investigate the functional development of brain regions involved in processing tactile stimulation via soft touch
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