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Human studies consistently report a 60%-80% maternal left cradling preference. The dominant explanation points to an engagement of the emotionally more-attuned right brain. In contrast, we found equal incidences of left (31.3%), right (34.3%) and no-preference (34.3%) cradling in an impoverished South African population living under adverse conditions characterized by extreme dangers. We found striking differences on the Parenting Stress Index (PSI) between mothers with no cradling laterality preference and mothers with either a left or right preference. In several mammals a homologous left preference becomes stronger when acute threats prevail, rendering the rightwards shift we observed under dangerous conditions seemingly paradoxical. We propose this paradox can be resolved in terms of life-history strategy theory which predicts reduced parental investment in chronically dangerous environments. We interpret our high PSI score findings in no-preference cradlers as indicative of poorer, or at least ambivalent, maternal coping which many studies show is typically associated with reduced emotional sensitivity and responsiveness. We suggest that the latter may be a psychological mechanism mediating a partial withdrawal of parental investment in response to an enduringly adverse environment. To the best of our knowledge, this is the first study investigating cradling laterality preferences in an adverse socioeconomic environment.

A recent article in the Journal of Deaf Studies and Deaf Education (Leigh, Brice, & Meadow-Orlans, 2004) explored attachment between deaf mothers and their 18-month-old children and reported relationship patterns similar to those for hearing dyads. The study reported here explores a marker of early mother-child relationships: cradling laterality. Results indicated that, overall, the cradling bias of deaf mothers is similar to that of hearing mothers, but that there are significant differences among deaf mothers related to the hearing status of their own parents and, in a complex way, to the hearing status of their children. Deaf mothers of deaf parents showed a strong leftward cradling bias with both hearing and deaf children, whereas deaf mothers of hearing parents showed a leftward cradling bias with hearing children and a rightward cradling bias with deaf children. Possible explanations for these patterns of behavior are discussed.

Objective: To assess competing explanations for the universal preference of mothers to cradle infants on their left side and to propose a relation to hemispheric asymmetry for social attachment and communication behaviour., Methods: A review of observational, experimental, physiological, psychological, neuro-physiological, and neuro-psychological studies, including new findings on the cradling behaviour of mothers with auditory or visual impairments., Results: A significant left-cradling bias is observed in both right- and left-handed mothers which cannot adequately be explained by arguments based on handedness or closer contact to the soothing sound of the maternal heartbeat. Observations of primate behaviour have led to the suggestion that the left-cradling bias may be related to a left visual field (right hemisphere) advantage for monitoring an infant's facial expressions of distress. However, more than just monitoring, cradling subserves the mother's connection with the infant. For that reason, we have suggested that left cradling might be related to a right hemisphere specialisation for emotional communication, i.e. the speech melody, smiles, signals, and stroking which mothers use to interact with their infants. Studies of mother-infant interaction show that the sound of the mother's voice is more soothing when cradling on the left, more stimulating when cradling on the right. Cradling laterality may thus be related to emotional state and behavioural intent. There is also evidence to suggest that left cradling is linked to a special role of the right hemisphere in social attachment behaviour. This function may be disturbed in mothers with post-natal depression who show abnormal right hemisphere activity., Conclusion: Cradling embodies the symbiotic relationship between mother and infant; various lines of evidence support the suggestion that the universal preference of mothers to cradle infants on their left side is related to a right hemisphere dominance for social attachment and communication behaviour.