I know this face: neural activity during mother's face perception in 7- to 8-month-old infants as investigated by near-infrared spectroscopy.

Previously, we used near-infrared spectroscopy (NIRS) to measure infant's brain activity during face processing by detecting changes in hemodynamic responses, oxy-Hb, deoxy-Hb, and total-Hb concentrations [1,2]. We found that the right temporal cortex of the brain was activated when infants looked at upright frontal faces rather than inverted faces, and at the frontal view as well as the profile view on 8-month-olds. In the present study, we investigated 7- and 8-month-olds' brain activity related to the perception of mother's and stranger's faces by NIRS. The finding was that oxy-Hb and total-Hb concentrations in the right temporal cortex increased against the baseline during presentation of the mother's face. For strangers' faces, the total-Hb concentration in the right temporal cortex was greater than the baseline. By contrast, oxy- and total-Hb concentrations in the left temporal cortex increased only in the presentation of mother's face. The great activity in the right temporal region for faces irrespective of familiarity was consistent with a predominance of the right temporal cortex found previously in infants [1,2] as well as functional magnetic resonance imaging (fMRI) studies in adults [3,4]. In contrast to the activity in the right temporal cortex, the greater hemodynamic response in the left temporal cortex was observed only in the mother's face condition. These findings suggest that the processing of the mother's face enhances activity in bilateral temporal cortex. This is the first study to clarify the location of brain activity in infants related to the perception of their mother's face.