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esis of an active inhibition role in motor tasks played by right inferior frontal cortex
and pre-supplementary motor area. The animations of propagation during a CAT test
The results obtained by means of SDTF in experiments involving working mem-
ory were compatible with fMRI studies on the localization of the active sites and
supplied the information concerning the temporal interaction between them [Brzez-
icka et al., 2011, Blinowska et al., 2010b].
The above described experiments point out that by means of SDTF estimated from
scalp recorded EEG a very clear-cut and consistent evidence concerning the activity
propagation may be found. The findings are compatible with the known facts and at
the same time they have supplied new evidence concerning the information process-
ing in the brain.
4.1.7.3.6 Functional connectivity estimation from intracranial electrical activ-
ity
The study of intracranial EEG (iEEG) gives the opportunity to record the elec-
trical activity, practically free of artifacts, directly from the brain structures. In the
past, this research was mostly concentrated on the analysis of spike trains; the role of
slow cortical activity was mostly neglected. Nowadays, the role of oscillatory activ-
ity of neural networks has become more and more recognized. There is a consensus
that the higher cortical functions depend on dynamic interplay between spatially dis-
tributed multiple cortical regions coupled by the transmission of oscillatory activity,
e.g., [Singer, 1993, Buzsaki and Draguhn, 2004].
The most popular method to study the interaction between cortical areas is coher-
ence (in spite of the limitations of bivariate coherence). To investigate the dynamics
of interactions between brain structures, temporal fluctuations in coherence were
studied, e.g., by [Bullock et al., 1995], and oscillatory synchrony was considered
by [Tallon-Baudry, 2003]. Recently attention has focused on the directionality of
interactions between brain regions. Among the methods used for the study of direc-
tionality, those based on Granger causality seem to be the most appropriate.
For the analysis of signals recorded from specific brain structures it is important
to determine the direct interaction. Direct directed transfer function (Sect. 3.3.2.3.1)
was introduced by [Korzeniewska et al., 2003] for the purpose of investigating the
propagation of LFP recorded from electrodes chronically implanted in the brain of a
behaving animal. The patterns of propagation were recorded from four brain struc-
tures involved in processing of emotions. The patterns of transmission were studied
for an animal walking on a runway and for walking on a runway accompanied by a
stressful stimulus (bell ringing). More flows between the brain structures appeared
in the case of the stressful stimulus and most of them were reciprocal.
The investigation of the intracranial human EEG is limited to cases of patients
who are being prepared for surgical intervention. The limitations in the iEEG re-
search are caused by the fact that the electrode placement is dictated solely by clin-
ical concerns. However, the area covered by electrodes is usually not confined to
the location of the diseased tissue because this location is not precisely determined
before implantation and also the neighboring areas have to be checked to be sure
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