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BIOLOGICAL SCIENCES / NEUROSCIENCE
Actor's and observer's primary motor cortices stabilize similarly after seen or heard motor actions
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*Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, P.O. Box 2200, FIN-02015 HUT, Espoo, Finland; and Department of Clinical Neurophysiology, Helsinki University Central Hospital, FIN-00290, Helsinki, Finland
Contributed by Riitta Hari, March 15, 2007 (received for review July 3, 2006)
We quantified rhythmic brain activity, recorded with whole-scalp magnetoencephalography (MEG), of 13 healthy subjects who were performing, seeing, or hearing the tapping of a drum membrane with the right index finger. In the actor's primary motor (M1) cortex, the level of the 
20-Hz brain rhythms started to decrease, as a sign of M1 activation, 2 s before the action and then increased, with a clear rebound 0.6 s after the tapping, as a sign of M1 stabilization. A very similar time course occurred in the M1 cortex of the observer: the activation, although less vigorous than in the actor, started 0.8 s before the action and was followed by a rebound. When the subject just heard the tapping sound, no preaction activation was visible, but a rebound followed the sound. The 10-Hz somatosensory rhythm, which also started to decrease before own and viewed actions, returned to the baseline level 0.6 s later after own actions than observed actions. This delay likely reflects proprioceptive input to the cortex, available only during own actions, and therefore could be related to the brain signature of the sense of agency. The strikingly similar motor cortex reactivity during the first and third person actions expands previous data on brain mechanisms of intersubjective understanding. Besides motor cortex activation before own and observed (predicted) actions, the M1 cortex of both the viewer and the listener stabilized in a very similar manner after brisk motor actions.
brain rhythms | intersubjectivity | magnetoencephalography | mirror neurons | motor cortex
Author contributions: G.C., V.J., and R.H. designed research; G.C. performed research; V.J. contributed new nonmagnetic drum tools; G.C. and R.H. analyzed data; and G.C., V.J., and R.H. wrote the paper.
The authors declare no conflict of interest.
See Commentary on page 8683.
This article contains supporting information online at www.pnas.org/cgi/content/full/0702453104/DC1.
To whom correspondence should be addressed. E-mail: hari{at}neuro.hut.fi
© 2007 by The National Academy of Sciences of the USA
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