Stroking !EXCLUSIVE!
In the light of this evidence, we predicted that human equivalents of rat LG should modify associations between an index of prenatal stress, prenatal depression, and subsequent physiological and behavioral outcomes in offspring. Thus far no studies in humans have identified candidates for maternal behaviours that may be the equivalent of rat LG. However, in rats the effects of LG can be mimicked by stroking the pups with a brush [6], consequently we asked mothers on two occasions over the first 9 weeks of their infants' lives how often they stroked the face, limbs and body of their babies. We predicted that, in humans, the effect of maternal prenatal depression on infant reactivity would be modified by tactile stimulation over the first weeks of life assessed by how often mothers reported stroking their babies. Modification would be evidenced in a statistical interaction between depression and frequency of stroking on both biological and behavioral indices of stress reactivity.
stroking
A joint analysis of baseline vagal tone, vagal withdrawal and Infant Behavior Questionnaire (IBQ) distress to limitations and fear, each normally distributed, was undertaken using multivariate regression. As shown in Table 2 estimates of the primary effects of interest - prenatal depression, maternal stroking, and their interaction - were obtained both before and after inclusion of potential confounders (maternal depression at 5, 9, and 29 weeks and breast-feeding). Breast feeding was included as a predictor of each outcome both as a main effect and in interaction with the index of prenatal stress, maternal depression. The stratification variable was also included as a covariate to verify that the estimated effects did not arise from sample selection bias. We report analyses for all infants with RSA following multiple imputation for occasional missing covariates (100 replicates). Multiple imputation was carried using the ice procedure in Stata [35], [36] allowing for all the main effects and interactions that formed part of the analysis. All tests reported were two-tailed Wald tests.
Summary of multivariate regression analyses showing coefficients (standard errors) and significance for the effect of maternal report of stroking and prenatal depression with adjustment for sample stratification and 5, 9 and 29 week postnatal depression and breast feeding confounders.
As a further check on the robustness of findings we fitted by maximum-likelihood a latent variable model using gllamm shown in Figure 2 for vagal tone and in Figure 3 for negative emotionality, using data from the general population extensive and stratified intensive samples. The 5 weeks and 9 weeks stroking data were analysed separately for computational simplicity and to test for replication with this novel measure. The left of the diagram shows the one-factor item-response measurement model fitted to the four 5-category ordinal stroking items (each item has 4 threshold parameters and a factor loading (discrimination parameter)). The stroking factor may be correlated with the baseline vagal tone factor but may also have a direct impact on vagal withdrawal (through λ). In addition, as illustrated for a single risk factor, risks and confounders may be associated with stroking (through δ1) and baseline vagal tone (through δ2) and may influence vagal withdrawal (through β) directly. Finally, the impact of the prenatal risk may be moderated by the stroking score, giving an interaction effect (through γ). Algebraically, the total direct effect on vagal withdrawal for infant j is given by ληj+βxj+γxjηj, where x is the prenatal risk and η is the stroking factor and the γ parameters estimate the interaction effect of measured prenatal risk and latent stroking.
The figure shows the factor loadings for mothers' reports of stroking at 5 and 9 weeks, and RSA at 29 weeks. The values of λ (direct effect of stroking on vagal withdrawal), δ1, δ2, and β (associations of risks and confounders with stroking, vagal tone and vagal withdrawal respectively), and γ (interaction between maternal stroking and prenatal maternal depression), are shown in Table 3.
The figure shows the factor loadings for mothers' reports of stroking at 5 and 9 weeks, and IBQ negative emotionality (Distress to Limitations and Fear) at 29 weeks. The values of λ (direct effect of stroking on IBQ), δ and β (associations of risks and confounders with stroking and IBQ respectively), and γ (interaction between maternal stroking and prenatal maternal depression), are shown in Table 4.
Parameter Estimates and Standard Errors for the Vagal Tone (RSA) Model of Figure S2 (which shows the stroking and vagal tone factor loadings) for the effects of stroking with adjustment for stratification and confounders.
Parameter Estimates and Standard Errors for the IBQ Distress to Limitations and IBQ Fear model of Figure S3 (which shows the stroking factor loadings) for the effects of stroking with adjustment for stratification and confounders.
Frequency of infant stroking, assessed via maternal self-report at two time points in the early postnatal period, modified associations between prenatal maternal depression and both infant physiology and emotional reactivity. The effect of prenatal depression on the infant outcomes differed depending on post-natal exposure to maternal stroking, as evidenced in a statistical interaction between prenatal depression and maternal stroking. In each case the direction of effects was the same. Increasing maternal depression was associated with decreasing vagal withdrawal, a measure of physiological adaptability, and with increasing negative emotionality, only in the presence of low maternal stroking. These findings represent initial evidence in humans of maternal behaviors that modify developmental outcomes of prenatal stress in a manner analogous to the effects of early maternal behaviors on gene expression and stress reactivity seen in rodents.
In common with many other studies of the developmental consequences of prenatal affective symptoms we used a self-report measure of symptoms of depression. It remains to be seen whether maternal stroking also modifies outcomes following diagnosed depressive disorder assessed by interview. These findings need replication in other longitudinal studies and naturalistic observational methods of assessing parental stroking need to be established. Frequency of parental stroking may vary under different environmental conditions, and so future experimental observational studies might contrast stroking frequencies under standardized stressful and non-stressful conditions. Many other questions remain to be addressed. For example, although we could find no evidence that maternal stroking was a function of a mother's level of depression either before or after the birth of her child, nor that the effect could be explained by the extent of another maternal behavior that includes skin to skin contact, namely breast feeding, it remains a distinct possibility that stroking is only a proxy for another causal aspect of parenting. To further substantiate this as the counterpart of the maternal tactile stimulation mechanism seen in rats, effects of experimentally generated, as well as naturally occurring, variations in stroking could be explored. Examination of gene expression in humans is currently limited to peripheral tissue, however against the background of extensive animal work, demonstrating differences in GR expression within experimental designs would be highly informative.
Significant decreases were found for the pleasantness and wanting of stroking at 3 cm/s over stroking repetitions; this decrease over time was not found for stroking at 0.3 and 30 cm/s. Furthermore, the pleasantness and wanting of touch was significantly higher for stroking at 3 cm/s, as compared to 0.3 or 30 cm/s.
Stroking at 3 cm/s was rated as significantly more pleasant and wanted than stroking at 0.3 or 30 cm/s. However, there was no significant difference between the value of pleasantness or wanting of touch at 3 cm/s stroking, whereas pleasantness was significantly higher for stroking at 0.3 and 30 cm/s.
Significant decreases were found over time in pleasantness and wanting ratings for stroking at 3 cm/s and at 30 cm/s in the separate groups of participants. Pleasantness and wanting decreased at a faster rate for stroking at 3 cm/s, as compared to at 30 cm/s.
The mean pleasantness and wanting ratings varied in level with the stroking velocity. This indicated that pleasantness and wanting could be distinguished as different concepts; however, pleasantness could be significantly predicted from wanting, showing that the two measures were highly related. This may be due to the fact that the order of VAS ratings was not varied and that they directly followed each other. Thus, the relationship between pleasantness and wanting needs to be interpreted carefully, in particular since further validation of the two measures is required to establish their contribution in touch satiety.
Introduction: Touch has been found to entail positive effects in the person receiving it, whereas effects on the person giving touch have previously been unexplored. We investigated whether stroking the partner also is a pleasant experience for the person performing it, and whether it has similar effects on well-being and autonomic nervous function as being stroked or stroking oneself. Furthermore, we compared the hedonic and autonomic nervous effects of stroking the partner and self-stroking.
Methods: In the first experiment, 40 subjects stroked the forearm of their respective partner, while ratings of pleasantness were obtained from both Stroker and Receiver. Heart rate was monitored throughout the session and stroking velocity was tracked. The participants could not see each other faces during the experiment to avoid feedback. In experiment 2, the design was replicated with 20 subjects, and self-stroking and rest conditions were added. 041b061a72