Neural synchronization tomography

A new brain-imaging method, pioneered by a research group from several institutions in Germany, can not only localize active areas in the brain but also show their correlations when test subjects perform physical tasks. The technique begins with standard magnetoencephalography: The researchers used a helmet with 148 SQUID sensors to map the fluctuating magnetic fields produced by tiny electrical currents in the brain. But then, those magnetic fields are inverted to produce a three-dimensional reconstruction of the current source density within the brain. Phase synchronization of the current source densities in different areas of the brain indicates interactions. The researchers demonstrated the technique, dubbed synchronization tomography, by asking test subjects to tap their finger in time to a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The resulting images showed that the same regions of the brain were active whether people tapped to an external beat or paced the tapping themselves, but that the synchronization between the different brain areas was dramatically different without external pacing. Other brain imaging methods, including functional magnetic resonance imaging and positron emission tomography, can also provide insight into brain activity, but their time resolution is too low to disclose how the brain regions interact with each other. (P. A. Tass et al., Phys. Rev. Lett., in press.)