Control of Emotional Expressivity in the First Year of Life.

Evidence suggests that the neurological substrate of emotional behavior is lateralized by brain hemisphere early in life. A study examined the emotional expressions of preterm infants, some of whom had unilateral periventrical echodensities (PVE), as a model for addressing this issue. The study population of 25 preterm infants was videotaped at 3 months and again at 12 months corrected age during 3 situations designed to illicit joy, surprise, or anger. The group included 9 children with right or left hemisphere PVE, most of whom also had bilateral intraventricular hemorrhage (IVH), 5 with IVH only, and 11 with no ultrasonographic abnormalities. The infants' facial expressions were coded, and positions of the brows, eyes, and mouth were noted every second for 10 seconds following stimulus onset. At each age a number of comparisons were made to test whether one cerebral hemisphere dominated the control of all the emotional expressions or whether dominance was a function of the valence of the expression. Comparisons also focused on the impact of IVH, additional medical complications, and mothers' affect. There were few significant differences in any of the comparisons at 3 months, though data suggested support for the hypothesis that the right brain hemisphere predominates in control of anger and the left hemisphere controls joy expressions. At 12 months, there were many more significant differences than at 3 months, but data did not support theories of lateralized control of expressivity. (Author/AC)