Patterns of brain electrical activity during facial signs of emotion in 10-month-old infants.

Abstract

This study examined electroencephalogram (EEG) asymmetries during the presence of discrete facial signs of emotion. Thirty-five 10-month-old infants were tested in a standard stranger- and mother-approach paradigm that included a brief separation from their mother. Infant facial expression was videotaped, and brain electrical activity from left and right frontal and parietal regions was recorded. The videotapes were coded with two different discrete facial coding systems. Artifact-free periods of EEG were extracted that were coincident with the expression ofthe emotions of joy, anger, and sadness. The data revealed different patterns of EEG asymmetry depending on the type of facial expression and vocal expression of affect that was observed. Expressions of joy that involved facial actions of both zygomatic and orbicularis oculi were seen more often in response to mother approach, whereas smiles that did not involve the action of orbiculaxis oculi were seen more often in response to approach of the stranger. The former type of smile was associated with relative left frontal activation, whereas the latter type was associated with right frontal activation. Facial expressions of anger and sadness exhibited in the absence of crying were associated with left frontal activation, whereas these same facial expressions during crying were associated with right frontal activation. These data underscore the usefulness of EEG measures of hemispheric activation in differentiating among emotional states associated with differences in facial and vocalic expressivity. Recent evidence from the adult neuropsychological literature indicates that the cerebral hemispheres are differentially lateralized for the expression of certain positive and negative emotions (Bear & Fedio, 1977; Davidson, Schwartz, Saron, Bennett, & Goleman, 1979; Gainotti, 1969, 1972; Sackeim, Weiman, Gur, Greenberg, Hungerbuhler, & Geshwind, 1982; reviews by Davidson, 1984; Leventhal & Tomarken, 1986; Silberman & Weingartner, 1986). Evidence both from normal (e.g., Davidson et al., 1979; Tucker, Stenslie, Roth, & Shearer, 1981) and from brain-damaged subjects (Bear & Fedio, 1977; Kolb & Milnet, 1981; Robinson & Benson, 1981) indicates that it is specifically the frontal region that shows this differential lateralization, with lett-sided activation observed during certain positive emotions and right-sided activation associated with certain negative emotions. In a series of studies, we have demonstrated the presence of this differential hemispheric asymmetry in newborn and 10month-old infants (Davidson & Fox, 1982; Fox & Davidson, 1986; Fox & Davidson, 1987). These studies examined electro