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Emi Nakato, Yumiko Otsuka, So Kanazawa, Masami K Yamaguchi, Ryusuke Kakigi; Infants' neural responses to facial expressions using Near-Infrared Spectroscopy. Journal of Vision 2010;10(7):575. doi: 10.1167/10.7.575.
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Facial expressions play an important role in social communication during infancy. 3-month-olds can discriminate between happy and anger faces (Barrera & Maurer, 1981), and 7-month-olds have the ability to categorize happy facial expressions, but not fearful ones (Ludemann & Nelson, 1988). Neuroimaging studies in adults revealed that the superior temporal sulcus (STS) was implicated in the processing of facial expressions (Haxby et al, 2000). Our previous near-infrared spectroscopy (NIRS) study demonstrated that the right STS was mainly activated in the perception of faces in infants (Nakato et al, 2009). However, infants' brain regions involved in perceiving facial expressions has not been investigated. To examine whether STS was responsible for the perception of facial expressions in infants, we used NIRS to measure the neural activation in STS when infants looked at happy and angry faces. Twelve 6- and 7-month-old infants viewed five happy and five angry female faces passively. The measurement area was located in the bilateral temporal area which was centered at T5 and T6 according to the International 10-20 system of EEG. Our findings indicated that the time-course of the average changes in oxy-Hb concentrations showed a distinct pattern of the hemodynamic response between happy and angry faces. The hemodynamic response increased gradually when infants looked at happy faces. In contrast, the hemodynamic response peaked quickly when infants looked at angry faces. Following this peak, the hemodynamic response decreased until the stimuli disappeared. Moreover, we found that the right temporal area of infants' brain was significantly activated against the baseline when infants looked at angry faces, while the left temporal area was activated for happy faces. These findings suggest hemispheric differences in STS when processing positive and negative facial expressions in infants.
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