Biomedical Engineering Reference
In-Depth Information
In this figure, significant increases in HF signal amplitudes were observed at
specific phases of the LF signal. For the HF band of 75
±
25 Hz, the amplitude of
105
◦
the HF signal increases significantly near
−
of the LF phase. For the HF band
25 Hz, the amplitude of the HF signal increases significantly near 135
◦
of the LF phase. For the HF band of the 150
of the 100
±
25 Hz, the amplitude of the HF signal
reaches its maximum near 15
◦
of the LF phase.
Figure
9.5
c shows the phase-informed TF map in which three HF components are
observed near 75,100, and 150 Hz. These HF components have different preferred
phases for the LF signal, indicating that the three HF components have different
timing dependencies on the same LF signal. Such LF phase dependence of the HF
signal amplitude across locations suggests the possibility of dynamic multiplexing
neuronal codes that exploit timing differences across regions due to synaptic or
propagation delays.
±
9.6 Summary
We have shown that the phase-amplitude coupling (PAC), both local PAC and cross-
location PAC, can successfully be detected in MEG source space analysis. PAC is
considered to reflect temporal coding of a brain. The measurement of PAC could
therefore be a promising tool for monitoring information processing in the human
brain. Specifically, PAC analysis can provide coupling-related information, including
the frequency of brain rhythms, and the specific phases of LF components, which are
preferred by the HF components. These preferred phases are considered to reflect the
timing of information exchange. We believe that exploring xPAC is one of the most
promising approaches to reveal the mechanisms of brain information processing. Our
studies suggest that MEG source space analysis could be a powerful tool in xPAC
studies, because of MEG's wide coverage of the brain and its noninvasiveness.
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