Differential brain response to one- or two-hand handling action: an fMRI study

Keiko Tagai,¹ Hitomi Shimakura,¹ Sadaki Takata,¹ Masayoshi Nagai,² Katsumi Watanabe,³ Kazuhisa Niki,² Sunao Iwaki,² Takatsune Kumada<sup>2

1</sup>Shiseido Research Center, Kanagawa, Japan; ²National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki, Japan; ³The University of Tokyo, Tokyo, Japan

Abstract: In interpersonal communication, body posture and actions serve as important channels for transmitting social signals, which often vary among cultures and possess functional and affective elements. In Asian cultures, it tends to be commonly considered that handing an object with two hands is more polite than using only one hand. Using functional magnetic resonance imaging (fMRI), we examined whether an individual handing an object with one versus two hands would produce differential brain activity in the receiver. Thirteen participants observed 10 second movie clips in which a model moved an object using either two hands or one hand and the perceived politeness of each action was evaluated. In the control condition, two static images of the first and last frames of a movie were presented. Results showed that ratings of politeness were significantly higher for actions involving two hands compared to one hand. Significant fMRI signal changes were found in the bilateral occipital lobe in both the two-handed and one-handed conditions relative to the control condition. Compared to the use of one hand, observing an action involving two hands was associated with a higher politeness rating and increased activation in the inferior frontal gyrus. These results suggest that activation in the bilateral occipital lobe is involved in the processing of hand actions and the inferior frontal gyrus is associated with interpersonal cognition.

Keywords: fMRI, social cognition, nonverbal behavior, handing action, politeness