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In association with the lab's move to Nanotalo at the end of 2007, our MEG operations moved very smoothly to a new facility. Our brand-new three-layered magnetically shielded room provides several technical improvements compared with the old two-layered magnetically shielded room. During the design and construction phase, special attention was paid to passive shielding of environmental noise. As a part of the BRU's research agreement with Elekta-Neuromag, the MEG sensors and the data acquisition system were upgraded to the newest technology, allowing sampling frequencies up to 5000 Hz. As a result of the upgrade, our MEG facility is one of the most advanced sites in the world, with gratifying low noise figures.
The new location of the BRU provides better working facilities and more closely located office space, which greatly improves group cohesion.
We list below our achievements from 2007 in the form of published papers.
HUMAN SYSTEMS NEUROSCIENCE
Caetano G, Jousmäki V, and Hari R: Actor’s and viewer’s primary motor cortices stabilize similarly after seen or heard motor actions. Proc Nat Acad Sci USA 2007, 104: 9058–9062.
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 approximately 20-Hz brain rhythms started to decrease, as a sign of M1 activation, approximately 2 s before the action and then increased, with a clear rebound approximately 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 approximately 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 approximately 10-Hz somatosensory rhythm, which also started to decrease before own and viewed actions, returned to the baseline level approximately 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.
Huang MX, Song T, Hagler DJ Jr, Podgorny I, Jousmäki V, Cui L, Gaa K, Harrington DL, Dale AM, Lee RR, Elman J, and Halgren E: A novel integrated MEG and EEG analysis method for dipolar sources. NeuroImage 2007, 37: 731–748.
The ability of magnetoencephalography (MEG) to accurately localize neuronal currents and obtain tangential components of the source is largely due to MEG's insensitivity to the conductivity profile of the head tissues. However, MEG cannot reliably detect the radial component of the neuronal current. In contrast, the localization accuracy of electroencephalography (EEG) is not as good as MEG, but EEG can detect both the tangential and radial components of the source. In the
Annual Report 2007