Relationship between motor area activity during observation and subsequent imitation performance of sequential actions

In the present study, we investigated whether motor area was activated during observation of sequential actions in relation to the subsequent imitation performance. We found a significant correlation between the imitation score and the motor area activity, indicating that the motor area is involved in imitation learning. Keywords―mirror neuron system, imitation learning, action observation, near-infrared spectroscopy 1.Introduction Mirror neuron system (MNS) is considered to play an important role in understanding and imitation learning of other’s action. A previous study showed that activity in inferior frontal and parietal cortices during action observation is increased when participants intended to subsequently reproduce the observed action [1]. Another study reported that the primary sensorimotor area is also involved in imitation learning [2]. In our previous study [3], we investigated how unnaturalness (jerkiness) of an action affects MNS by inserting short pauses in the middle of the observed action. The result showed that the sensorimotor area was activated when the subjects observed an action being inserted a few pauses in the middle action. However, when the subjects observed an action with more pauses, the sensorimotor area showed to be ‘deactivated’. This suggests that a slightly, not largely, jerky action would enhance MNS activity. The present study investigated whether the sensorimotor area activity show a correlation with performance in imitation learning of sequential actions. The brain activity throughout the experiment was measured by near-infrared spectroscopy (NIRS) as in our previous study [4]. In so doing, slightly jerky actions were utilized in order to modulate MNS activity. We predict that jerky actions would enhance the MNS activity and lead to a higher imitation performance. 2.Method 2.1 Subjects Twelve healthy subjects participated in the experiment (twelve males, age 19-24). Written informed consent was obtained from all participants. The experiments were approved by the local ethics committee. 2.2 Procedure The subjects observed videos in which a human model put a puzzle together in a transparent box. The puzzle consisted of ten pieces (Fig.1). The action sequences lasted for 70s. The same action sequence was repeated three times, intermitted with a rest period of 25s. We prepare two different action sequences of the model to solve the puzzle (pattern-1 and pattern-2). In addition to the original stimuli (no-pause), we prepare another video stimulus by inserting two short pauses (0.07s for each) in the middle of each action. By inserting a pause into an action, the action seems jerky (unnatural). First pause was put between when pinching a piece and when setting the piece off the box. Second pause was put between when setting a piece off the box and when setting back model’s hand at first position. Thus, there were four experimental conditions (2 patterns 2 pause conditions). The subject was instructed to watch the video and later solve the puzzle with the same sequence as the video demonstration. The order of experimental conditions was counterbalanced across subjects. Fig.1 Tridimensional puzzle 2.3 NIRS measurement The brain activity in C3 of the 10/2 system was measured with NIRS through the experiment. The arrangement of NIRS probe is shown in Fig.2 Fig.2 Arrangement plan of the NIRS’s probe [P3-14]