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Affective touch: a meta-analysis on sex differences
Full text linkThe unmyelinated C-tactile afferents system holds a hedonic function in touch experiences, shaping social functioning in the so-called affective touch hypothesis. Despite the fact that females are recognized as more sensitive to discriminative aspects of touch and respond more positively to touch than men, sex differences in the perception of affective touch have not been extensively investigated. We aimed to fill this gap by meta-analyzing existing studies on this topic. Thirteen studies were eligible and pooled effect sizes (Hedges⿿ g) were compared. Random effect models were used. Results, which are not influenced by publication bias, show that there is a sex asymmetry in the pleasantness perceived during an affective tactile stimulation, with females showing higher pleasantness ratings than males. The size of the association does not vary as a function of sex distribution, age and methodological quality. Hormonal as well as evolutionary differences related to the caregiving and nurturing function of females may explain sex differences in affective touch. Results are limited by the small number of studies included in the meta-analysis.The unmyelinated C-tactile afferents system holds a hedonic function in touch experiences, shaping social functioning in the so-called affective touch hypothesis. Despite the fact that females are recognized as more sensitive to discriminative aspects of touch and respond more positively to touch than men, sex differences in the perception of affective touch have not been extensively investigated. We aimed to fill this gap by meta-analyzing existing studies on this topic. Thirteen studies were eligible and pooled effect sizes (Hedges’ g) were compared. Random effect models were used. Results, which are not influenced by publication bias, show that there is a sex asymmetry in the pleasantness perceived during an affective tactile stimulation, with females showing higher pleasantness ratings than males. The size of the association does not vary as a function of sex distribution, age and methodological quality. Hormonal as well as evolutionary differences related to the caregiving and nurturing function of females may explain sex differences in affective touch. Results are limited by the small number of studies included in the meta-analysis
Impaired visual processing of contralesional stimuli in neglect patients: a visual-evoked potential study
No full textTransient visual-evoked potentials (VEPs) were recorded in II patients with right brain damage and spatial neglect. High-resolution EEG was recorded using focal stimuli located in the four visual quadrants. VEPs to left stimuli, i.e. located in the neglected side, were compared to VEPs to right stimuli. Results showed that bottom-up processing of a visual stimulus located in the neglected hemifield was intact up to 130 ms from stimulus onset. Hemispheric differences were not significant for either CI or PI components representing the activity of striate and extrastriate areas, respectively. In contrast, visual processing in more dorsal areas adjacent to the superior parietal lobe was changed from normal. We failed to record the NIa component for left visual field stimuli expected in the 130-160 ms time range. Furthermore, the NIp (140-180 ms) and P2 (180-220) components were delayed and/or reduced in amplitude for stimuli located on the neglected side. The source of the NIa was previously localized in the intraparietal sulcus in the dorsal occipital cortex; NIp may represent a reactivation of area V3A and P2 reactivation of occipital visual areas including VI due to top-down feedbacks. Six patients with left brain damage (LBD) and no neglect and 2I healthy subjects were also tested in the same experimental conditions used for patients with neglect. In LBD patients, all components evoked by contralesional stimuli were comparable to ipsilesional components. Overall, data allow localizing in time and space the processing deficit specific for patients with neglect. The first takes place around 130 ms in the bottom-up processing at the level of the anatomically intact dorsal parietal areas; the second is located at the level of the reactivation of the striate and extrastriate areas via feedback connections from higher visual areas. The two functional impairments were limited to left-field stimuli
Tactile sensitivity, tactile acuity, and affective touch. From childhood to early adolescence
No full textThe development of somatosensation and affective touch acquires a central role throughout our lives, for several reasons. In adults, these functions are driven by different, neuroanatomically and functionally segregated fibres. To date, very little is known about the basic features of these fibres in childhood and this lack of knowledge is mirrored in the affective touch domain, where there are no studies on the main physiological features of the tactile processes linked to the stimulation of the hairy skin, namely the preferential site of affective touch. Thus, our study aims to analyze (1) tactile sensitivity and tactile acuity of children's hairy forearms; (2) a possible dissociation between somatosensation and the affective touch; and (3) the presence/absence of the perception of affective touch already in childhood. To these aims, participants (160 children, aged 6 to 14years), were administered with the Von Frey (tactile sensitivity) and the 2 Point Discrimination (tactile acuity) tests. Affective touch was measured following the classic protocol and pleasantness ratings were recorded. Our findings showed a correlation between age and somatosensation, suggesting a progressive reduction of sensitivity and acuity as age grows. Further, there was no overlap between affective touch and somatosensation, suggesting a behavioural segregation. Lastly, we found higher pleasantness ratings for Affective versus Neutral stimulations at all ages and an enhanced preference for Affective as age grows. We concluded that both somatosensation and affective touch are already present as two separate components of touch in childhood and change as a function of ag
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