![]() ![]() Given the brainstem's phylogenetic evolutionary tenure and its role in generating behaviors that mediate social signaling in early organisms ( Bass et al., 2008), evidence for brainstem involvement in social engagement may deepen the understanding of the evolutionary pathway of humans as social beings. Along with these essential cortical systems, the underpinning distributed network that subserves social engagement has been thought to involve ancestral brainstem streams, as well as the later emerging central thalamus–dorsal striatum and medial–dorsal thalamus ( Bolhuis et al., 2010).ĭespite this compelling framework, no direct evidence has yet been presented for the involvement of brainstem projections in the social engagement of humans, particularly of human infants. The majority of the research concerning the development of social and affective behavior has concentrated on cortical-related activity, mostly the amygdala–limbic system and the medial prefrontal and fronto-parietal systems ( Amodio and Frith, 2006). ![]() The integrity of brainstem transmission of sensory information during the final weeks of gestation may scaffold the development of social disengagement, thereby attesting to the brainstem's preserved evolutionary role in developing humans as social organisms prior to engaging in social encounters.įrom the very beginning, human infants are acutely sensitive to social stimuli, especially faces ( Maurer and Salapatek, 1976 Morton and Johnson, 1991 Striano and Rochat, 1999), and from 3 to 5 months their gaze and affective behavior reflect increased sensitivity to their partner's slight deviations in gaze and facial expressions ( Symons et al., 1998 Striano and Stahl, 2005). Analysis of variance of infants’ social engagement with ABR, neonatal risk, maternal stress and cardiac vagal tone showed a main effect for ABR and an ABR by gestational age interaction. Data show that neonates with a disrupted I–V waveform, evident mostly by delayed wave V, exhibit shorter latencies to gaze averts in episodes involving direct face-to-face interactions but engage gaze as controls when interacting with masked agents or with agents whose faces are partly veiled by toys. At 4 months, infants were tested in a set of structured vignettes that required varying levels of social engagement and cardiac vagal tone was assessed. In this longitudinal study, neonatal brainstem functioning was measured by auditory brainstem-evoked responses (ABRs) in 125 healthy neonates born prematurely before 35 weeks’ gestational age. Evidence for its involvement in social engagement in human infants may deepen the understanding of the evolutionary pathway of humans as social beings. The role of the brainstem in mediating social signaling in phylogenetic ancestral organisms has been demonstrated. ![]()
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