Richards, J.E., Guy, M., Zieber, N., Xie, W., & Roberts, J.E. (2017). Brain changes in response to faces in the first year. Paper presented at the Society for Research in Child Development, Austin, TX. April, 2017.(pdf )
Brain changes in response to faces in the first year
Infant’s behavioral responses to faces changes over the first year. These changes often are hypothesized to result from experience-dependent changes in the brain areas that process faces. The course of development in those brain areas has not been directly studied over the first year. The current study examined the neural response of infants to pictures of faces and objects from 4.5 months through 12 months with event-related potentials (ERP) and cortical source analysis with realistic head models.
Method: Infants were tested at 4.5 (N = 25), 6 (N = 26), 7.5 (N = 19), 9 (N = 10) or 12 (N = 24) months. The infants were presented with brief (500 ms) stimuli on a computer monitor. The stimuli were pictures of women’s faces, or infant-oriented toys. A 128-channel EEG recording system (EGI, Eugene, OR) was used for EEG recording. The ERPs in response to the faces were calculated for the P1, N290, P400, and Nc components. Cortical source analysis used the current density reconstruction (CDR) technique and realistic head models based on structural MRIs of the infant or an infant with a close-sized head.
ERP Components: Figure 1 shows the ERP responses to faces and toys in the occipital, lateral parietal, and frontal central leads. The ERP components in response to faces and toys were examined separately for the ERP components. We found the P1 amplitude at about 100 ms post-stimulus-onset was larger for faces and toys overall, but the difference between faces and toys increased over age, especially from 6 to 12 months (Figure 2a). Similarly, the N290, a negative deflection in the ongoing ERP about 290 ms following stimulus onset, also showed this increasing differentiation in responses to faces and toys, becoming larger over age to the face stimuli (Figure 2b). The P400 and Nc components differed for faces and toys at the earliest ages, but by 12 months were at the same level.
Cortical Sources: The neural sources of the ERP components were identified with cortical source analysis in “regions-of-interest” (ROIs) theoretically involved in face processing. The sources of the P1 component were generally found in the lateral occipital and posterior-lateral temporal areas (e.g., lateral inferior occipital gyrus; posterior portion of the inferior temporal gyrus). The activity of the CDR across the time interval of the P1 paralleled the P1 responses upon which the analysis was based, and showed the same increasing differentiation over age. The sources of the N290 were in the middle fusiform gyrus, anterior fusiform gyrus, parahippocampal gyrus, and temporal pole. The increase from 4.5 to 7.5 months of age in the ERP component showed an increasingly peaked response in the middle fusiform gyrus though the overall CDR amplitude to faces and toys were similar. By 9 and 12 months of age the CDR amplitude in this and adjacent neural areas differed for faces and toys, and also showed the enhanced peak around the time of the N290 peak amplitude.