EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.

quadspectrum). The in-phase component contains volume conduction and
the synchronous activation of local neural generators. The out-of-phase
component contains the network or connectivity contributions from
locations distant to a given source. In other words, the cospectrum = volume
conduction and the quadspectrum = non-volume conduction which can be
separated and analyzed by independently evaluating the cospectrum and
quadspectrum. Figure 7 is an example of the differences between the inphase
and out-of-phase components of the cross-spectrum in a right
hemisphere hematoma patient. The cospectrum shows high focal sources
and little distant zero phase lag relations. This is indicative of a source near
to the surface of the scalp at P4 and C4. The quadspectrum shows high outof-phase
power or network connections between P4 and the distant left
hemisphere and especially F3 that are highly out-of-phase. In general the
right parietal lobe is out of phase with respect to the spatially distant left
hemisphere.
Fig. 7 – Left is the cospectral power or In-Phase power in all 171 electrode combinations
of the 10/20 system. Right is the quadspectral power or Out-of-Phase relationships. P4
and C4 are near to the location of the right hemisphere hematoma. P4 is out-of-phase
with a large number of locations, especially the left hemisphere (from NeuroGuide