Determination of ECoG information flow activity based on Granger causality and Hilbert transformation
Demirer, R. Murat and Ozerdem, Mehmet Sirac and Bayrak, Coskun and
Mendi, Engin
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Abstract
Analysis of directional information flow patterns among different
regions of the brain is important for investigating the relation between
ECoG (electrocorticographic) and mental activity. The objective is to
study and evaluate the information flow activity at different
frequencies in the primary motor cortex. We employed Granger causality
for capturing the future state of the propagation path and direction
between recording electrode sites on the cerebral cortex. A grid covered
the right motor cortex completely due to its size (approx. 8 cm x 8 cm)
but grid area extends to the surrounding cortex areas. During the
experiment, a subject was asked to imagine performing two activities:
movement of the left small finger and/or movement of the tongue. The
time series of the electrical brain activity was recorded during these
trials using an 8 x 8 (0.016-300 Hz band with) ECoG platinum electrode
grid, which was placed on the contralateral (right) motor cortex. For
detection of information flow activity and communication frequencies
among the electrodes, we have proposed a method based on following
steps: (i) calculation of analytical time series such as amplitude and
phase difference acquired from Hilbert transformation, (ii) selection of
frequency having highest interdependence for the electrode pairs for the
concerned time series over a sliding window in which we assumed time
series were stationary, (iii) calculation of Granger causality values
for each pair with selected frequency. The information flow (causal
influence) activity and communication frequencies between the electrodes
in grid were determined and shown successfully. It is supposed that
information flow activity and communication frequencies between the
electrodes in the grid are approximately the same for the same pattern.
The successful employment of Granger causality and Hilbert
transformation for the detection of the propagation path and direction
of each component of ECoG among different subcortex areas were capable
of determining the information flow (causal influence) activity and
communication frequencies between the populations of neurons
successfully. (C) 2013 Elsevier Ireland Ltd. All rights reserved.... Show more Show less