EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.
EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.
EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.
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Fig. 4 – The correlation coefficient (<strong>and</strong> coherence) includes at least two possible<br />
couplings <strong>and</strong> mixtures of these two types of coupling: 1- where neuron A<br />
influences neuron B <strong>and</strong> vice versa <strong>and</strong>, 2- where a third neuron ‘C’ influences<br />
neuron A <strong>and</strong> neuron B <strong>and</strong> there is no connection between A <strong>and</strong> B. Comodulation<br />
omits the st<strong>and</strong>ard ‘C’ possibility <strong>and</strong> is limited to where neuron A<br />
influences neuron B <strong>and</strong> vice versa. The limitation of the term “comodulation” is<br />
that without partial correlation analyses or path analyses it is not possible to omit<br />
coupling number 2 which means that the term comodulation can be misleading<br />
unless these additional analyses are conducted.<br />
As discussed by Pikovsky et al (2003) the term modulation is<br />
complicated <strong>and</strong> it is possible for there to be modulation without<br />
synchronization <strong>and</strong> synchronization without modulation. As stated by<br />
Pikovsky et al (2003, p. 77) “Generally, modulation without synchronization<br />
is observed when a force affects oscillations, but cannot adjust their<br />
frequency.” Without further analyses to determine this distinction it is best<br />
to simply refer to amplitude or power correlation.<br />
The distinguishing characteristic of the application of the Pearson<br />
product correlation coefficient is the computation of the time course of the<br />
normalized covariance of spectra over an interval of time: