Abstract
Social touch is closely related to the establishment and maintenance of
social bonds in humans and the sensory brain circuit for gentle brushing
is already active soon after birth. Brain development is known to be
sexually dimorphic, but the potential effect of sex on brain activation
to gentle touch remains unknown. Here, we examined brain activation to
gentle skin stroking, a tactile stimulation that resembles
affective/social touch, in term-born neonates. Eighteen infants aged
11-36 days, recruited from the FinnBrain Birth Cohort Study, were
included in the study. During natural sleep, soft brush strokes were
applied to the skin of the right leg during functional magnetic
resonance imaging (fMRI) at 3cm/s velocity. We examined potential
differences in brain activation between males (n = 10) and females (n =
8) and found that females had larger blood oxygenation level dependent
(BOLD) responses (brushing vs. rest) in bilateral orbitofrontal cortex
(OFC), right ventral striatum and bilateral inferior striatum, pons and
cerebellum compared to males. Moreover, the psychophysiological
interactions (PPI) analysis, setting left and right OFC as seed regions,
revealed significant differences between males and females. Females
exhibited stronger PPI connectivity between the left OFC and posterior
cingulate/cuneus. Our work suggests that social touch neural responses
are different in male and female neonates, which may have major
ramifications for later brain, cognitive and social development.
Finally, many of the sexually dimorphic brain responses were
subcortical, not captured by surface-based neuroimaging, indicating that
fMRI will be a relevant technique for future studies.