Broad-band magnetic brain activity

Humans are able to generate and maintain rhythmic activity (as in running or beating a drum) and can also synchronize an internally generated rhythm with an external one. Brain functions involved in this ability include at least: internal rhythm generation, prediction of anticipated rhythmic stimuli, movement planning and timing, and coordination of the brain areas responsible for these functions. Several magnetoencephalographic (MEG) studies have implicated various brain areas in the ability to perform rhythmic tasks, including right frontal cortex [1], primary and secondary auditory cortices [2], and right frontal, premotor, and secondary auditory areas [3]. Functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and lesion studies [4, 5, 6] have also demonstrated the involvement of these areas during timing and synchronization tasks. In this paper, we investigate the magnetic brain activity of subjects performing two rhythmic tapping and synchronization tasks. We use an adaptive linearfiltering technique known as differential syntheticaperture magnetometry (dSAM) to locate sources of activity that have high signal-to-noise power ratios in various frequency bands. We then project the whole brain activity onto the individual sources with SAM spatial filters and examine the projections for evidence of phase-synchrony between the different sources. By isolating the oscillatory electromagnetic signals produced by the brain during performance, we can investigate the hypothesis that coordination between brain areas may be accomplished via phaselocking of the oscillatory activity.