The longitudinal relations between mental state talk and theory of mind.

BACKGROUND: Previous investigations of associations between children's Theory of Mind (ToM) and parents' use of words relating to mental states (or mental state talk; MST) have predominantly been performed using cross-sectional designs and false belief tasks as indicators of ToM. METHODS: We here report a longitudinal study of 3-5 year-olds (n = 80) investigating ToM development using the ToM scale and three different parental MST types: the absolute frequency of words, the proportions of words, and the vocabulary size. RESULTS: Our results revealed significant relations between all parental MST types and later child ToM. Proportions of parental MST were most often related to the children's ToM at 4 years of age. However, the rate at which the children developed ToM from 3 to 5 years of age was associated with the other two parental MST type measures, namely, absolute frequency and vocabulary size. Additionally, our analyses revealed that parents' use of cognitive MST words (e.g., think, or know) were most frequently associated with children's ToM at 4 years of age compared to emotion and desire-related MST words. CONCLUSIONS: We conclude that the parental ability to capture the thoughts, beliefs, and knowledge present in different scenarios is associated with children's ability to understand other minds. Moreover, parents' way of talking about the mental states of others is associated with their children's ability to understand and further develop ToM.

Nav1.7 is required for normal C-low threshold mechanoreceptor function in humans and mice.

Patients with bi-allelic loss of function mutations in the voltage-gated sodium channel Nav1.7 present with congenital insensitivity to pain (CIP), whilst low threshold mechanosensation is reportedly normal. Using psychophysics (n = 6 CIP participants and n = 86 healthy controls) and facial electromyography (n = 3 CIP participants and n = 8 healthy controls), we found that these patients also have abnormalities in the encoding of affective touch, which is mediated by the specialized afferents C-low threshold mechanoreceptors (C-LTMRs). In the mouse, we found that C-LTMRs express high levels of Nav1.7. Genetic loss or selective pharmacological inhibition of Nav1.7 in C-LTMRs resulted in a significant reduction in the total sodium current density, an increased mechanical threshold and reduced sensitivity to non-noxious cooling. The behavioural consequence of loss of Nav1.7 in C-LTMRs in mice was an elevation in the von Frey mechanical threshold and less sensitivity to cooling on a thermal gradient. Nav1.7 is therefore not only essential for normal pain perception but also for normal C-LTMR function, cool sensitivity and affective touch.

Neural correlates of gentle skin stroking in early infancy.

Physical expressions of affection play a foundational role in early brain development, but the neural correlates of affective touch processing in infancy remain unclear. We examined brain responses to gentle skin stroking, a type of tactile stimulus associated with affectionate touch, in young infants. Thirteen term-born infants aged 11-36days, recruited through the FinnBrain Birth Cohort Study, were included in the study. Soft brush strokes, which activate brain regions linked to somatosensory as well as socio-affective processing in children and adults, were applied to the skin of the right leg during functional magnetic resonance imaging. We examined infant brain responses in two regions-of-interest (ROIs) known to process gentle skin stroking - the postcentral gyrus and posterior insular cortex - and found significant responses in both ROIs. These results suggest that the neonate brain is responsive to gentle skin stroking within the first weeks of age, and that regions linked to primary somatosensory as well as socio-affective processing are activated. Our findings support the notion that social touch may play an important role in early life sensory processing. Future research will elucidate the significance of these findings for human brain development.

Gentle touch perception: From early childhood to adolescence.

Affective touch plays an important role in children's social interaction and is involved in shaping the development of the social brain. The positive affective component of touch is thought to be conveyed via a group of unmyelinated, low-threshold mechanoreceptive afferents, known as C-tactile fibers that are optimally activated by gentle, slow, stroking touch. Touch targeting these C-tactile fibers has been shown to decrease the heart rate in infants. The current study investigated the relationship between age and psychophysical ratings in response to affective touch. A total of n=43 participants (early childhood: aged 5-8 years, 9 girls, 12 boys; late childhood: aged 9-12 years, 12 girls, 10 boys) were presented with C-tactile optimal and sub-optimal stroking velocities and rated touch pleasantness on an affective pictorial scale. For both age groups, we found that children preferred C-tactile-targeted stimulation. A comparison with previously published data showed that the children's preference for C-tactile-targeted stimulation was similar to those obtained in adolescents and adults. We speculate that the effect of C-tactile-targeted touch, which is linked with pleasantness, shapes the children's preference for C-tactile over non-C-tactile-targeted stimulation, and that C-tactile afferent stimulation is important for social development.

Visual and physical affective touch delivered by a rotary tactile stimulation device: A human psychophysical study.

The discovery that pleasant touch is coded by C-tactile fibers has generated considerable research interest and increased understanding of the skin as a channel for social information via cutaneous senses. However, no study has differentiated between the pleasant response to visual and tactile non-human stimulations. Our study investigated pleasant touch in which the visual and haptic touch information was obtained from an affective, but non-social experience, by a custom-built non-human device. Participants (n=19) received soft brush strokes on their lower left arm delivered by a rotary tactile stimulator (physical session) or watched a video of an arm being stroked by a rotary tactile stimulator (visual session). The brush strokes were delivered at the same velocities (0.3, 1, 3, 10, 30cm/s) and force (0.4N) in both sessions. After each trial, participants rated the pleasantness of the touch. Analysis of variance was used to assess the effects of velocity and modality (visual touch vs. physical touch) on the pleasantness rating. Participants rated strokes between 1 and 10cm/s as most pleasant under both conditions. The pleasantness rating patterns differed significantly among velocities; however, no significant differences were found between modalities. Visual and physical (without human-to-human interaction) touch elicited similar behavioral responses, including an inverted U-shaped perception of pleasantness. These findings suggest that the pleasantness of touch is influenced by the velocity of the strokes in both visual and physical touch with a non-human stimulation.

Gentle touch perception across the lifespan.

Pleasant, affective touch provides various health benefits, including stress and depression relief. There is a dichotomy between mechanoreceptive afferents that predominantly signal discriminative (myelinated A-beta) and affective (unmyelinated C-tactile) aspects of touch. It is well documented that discriminative abilities of touch decline with age. However, a thorough investigation of how the pleasant aspects of touch develop with age has not been previously attempted. Here, we investigated the relationship between age and psychophysical ratings in response to gentle stroking touch. One hundred twenty participants (60 males, 60 females) ages 13-82 years were presented with C-tactile optimal and suboptimal stroking velocities, and rated pleasantness and intensity. Moreover, to examine the specificity of age effects on touch perception, we used olfactory stimuli as a cross-sensory comparison. For all ages, we found that C-tactile optimal stimuli were rated significantly more pleasant than C-tactile suboptimal stimuli. Although, both touch and olfactory intensity ratings were negatively correlated with age, a positive correlation between pleasantness ratings of touch (but not olfactory stimuli) and age was found. We conclude that the affective, but not the discriminative, aspects of touch are enhanced with increasing age. The increase of pleasantness of all touch stimuli in late adulthood is discussed in relation to cognitive modulations.