2012 Fiscal Year Final Research Report
Physiological study to revealbrain mechanism of willfor voluntary action
| Project/Area Number |
21700288
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Cognitive science
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| Research Institution | Kyoto University |
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Principal Investigator |
MATSUHASHI Masao 京都大学, 健康長寿社会の総合医療開発ユニット, 特定准教授 (40456885)
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| Project Period (FY) |
2009 – 2012
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| Keywords | 行動意思決定論 / 随意運動 / 脳磁図 / 脳波 / 自由意志 |
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| Research Abstract |
What is will has long been one of the essential questions of mankind. Based on the most influential work in the field of neuroscience reported by Benjamin Libet in 1983, we introduced a new paradigm in 2008 toexplore the perception of human will. In the task, the subjects performed self-paced right index finger extension with interval of 5-10 seconds, while repetitivetones were administered randomly at intervals of 3 to 20 seconds. Subjectswere asked to perform the movement immediately upon the thought to move, but tohalt it if they heard a tone after the thought. Tones they heard before the thought were ignored. The time of the thought to move (T) was calculated from the tone latency distribution relative to the movement onset. While Libet’s clock paradigm tries to measure the time of meta-consciousness when the subject spontaneously recognize one’s own mind and will, this new method is made to explore the time when the subject’s will comes to the bare consciousness state, where one c
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an recognize one’s own will if, but only if, probed externally by the tones. The T time was estimated to be 1.42 seconds on average before the movement onset. This was earlier than the Libet’s W time by more than a second, but still later than the onset of readiness potential that was, on average, -2.17 seconds before the movement onset. The result supports the idea that the neural preparation in the brain starts before we are aware of it, not even encouraged do so, and what we recognize as our will for motion is the perception that such neural procedure reaches a certain threshold level of activity. However, while involvement ofsupplementary area is assumed from the results of neuroimaging studies, the search for the responsible area by means of readiness potential has indicated the importance of primary sensorimotor area and parietal lobe. The role of the early rising readiness potential for will generation and perception is still unclear. In order to find the neurophysiological cortical correlate of the perception of will, we used EEG and MEG to record cortical activity during Libet’s clock paradigm and the new paradigm as described in the previous sentense. The result showed no significant relationship between premovement EEG activity (readiness potential) and the time of will perception by Libet paradigm, concordant to the previous results. On the other hand, premovement MEG activity (readiness field: RF) was larger in the trials in which the subject reported earlier W time when compared to the trials with later W time report. The estimated sources of the activity were distributed mainly in the medial wall ofthe posterior frontal to anterior parietal lobe. The correlation study between T time and RF showed significant correlation around the left supplementary motor area, while correlation between RF and P time, the point of no return when the subject couldn’t stop action even if they heard the tone, showed significant correlation in the left parietal area. These result, put together with the previous neurophysiological and neuroimaging result, supports the idea of fronto-parietal network in the generation and perception of our intention and action. Less
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