P 70. The role of parietal cortex in awareness of motor intention – human rTMS study

Abstract

Voluntary movement implies a subjective experience of the intention to move as well as motor execution. Previous patients studies showed that the parietal cortex (PC) plays a key role in awareness of motor intentions. However, the results in lesion studies are conflicting. To clarify the functional relevance of the PC in the awareness of motor intention, we used transient suppression of focal neural processing induced by low-frequency rTMS. Twelve right-handed healthy volunteers participated in the study. The experimental paradigm was based on that of Libet (1983). Subjects were asked to report the position of the clock’s hand at the time they pushed the button (M-judgment) or at the time they first became aware of their intention to move (W-judgment). We applied 0.9 Hz rTMS (1200 total pulses) over individually determined left PC to suppress cortical activity and measured subsequent task performance before, immediately after and 15 min after rTMS. rTMS over the left PC significantly prolonged the timing of W-judgment immediately after rTMS. In M-judgment, rTMS over the left PC had no effect on task performance. The neural processing in the left PC might be important for the awareness of the intention to move, because the duration from the intention to movement was prolonged after the transient suppression of the left PC. One previous study showed the decrease that duration in patients with PC lesion (Sirigu, 2004). However, there are another study reporting the normal W-judgment time in those patients (Lafargue, 2008). This controversy may be due to the functional compensation in the chronic stage. The functional suppression induced by rTMS may be similar to the acute one, so that the present results cannot be directly comparable to the chronic stroke patients. However, at least, our results suggest the essential role of the left PC in the generation of the intention to move, although the exact role of the left PC is not known yet.