Brain responses to meaningless postures as measured by near-infrared spectroscopy.

We used 24-channel near-infrared spectroscopy to investigate brain activity during the observation of sequentially presented meaningless postures, without the observers moving their limbs. The participants' task was to observe target postures and recognize whether a test posture was presented in the preceding target postures. The sequence varied in terms of number of joints (1-step and 4-step conditions) functioning during the changes in neighboring postures. The results revealed that the oxy-hemoglobin concentrations in the lower part of the precentral gyrus increased to a greater extent in the 4-step condition than in the 1-step condition. This suggests that the area related to action plans is activated when observers recognize the possibility of body movement even during the observation of static meaningless postures.