Neural effects of viewing children's faces on mental fatigue: a magnetoencephalography study.

We examined whether the recovery from fatigue could be facilitated by viewing the children's faces. Seventeen healthy mothers with child or children over 6 years old participated in our experiment. After performing a 2-back task for 40 min, they viewed the pictures of children's and adult's faces in the target and control conditions, respectively. The target and control conditions were performed on the separate days in a two-crossover design. Neural activity caused by viewing the children's faces was recorded using magnetoencephalography and electrocardiography was performed to assess the index of heart rate variability (low-frequency component power/high-frequency component power ratio, LF/HF) reflecting fatigue. The subjective level of mental fatigue sensation and LF/HF ratio was decreased after viewing the children's faces and the overactivation of the visual cortex caused by performing the 2-back task, assessed by the alteration of alpha band power in the visual cortex, was attenuated by viewing the children's faces, suggesting that viewing the children's faces affected the time course of mental fatigue after performing the 2-back task.