It
is commonly agreed in the scientific community that the brain's nerve cells
communicate with each other by means of electric signals, the so-called action
potentials. The simultaneous activity of hundreds of neurons is required to
cause one single neuron to respond and send out a signal itself. Thus network
operations seem to be the carrier of information processing in the brain. These
operations can be 'observed' from the outside by means of measuring the electric
and magnetic activity caused by the processing of electric nerve signals of
the networks. The electric potentials on the skull measured by electroencephalography
(EEG) and magnetic fields around the skull measured by magnetoencephalography
(MEG) are primarily generated by neocortical sources and display a rich spatiotemporal
dynamics on the scale of millimeter and milliseconds. They are the ideal tool
to study human brain dynamics non-invasively. The complexity of these data requires
application of sophisticated data analysis, as well as guidance by theories
and models.