Biomedical Engineering Reference
In-Depth Information
Chapter 9
Detection of Phase-Amplitude Coupling
in MEG Source Space: An Empirical Study
9.1 Introduction
Neural oscillations across multiple frequency bands have consistently been observed
in EEG and MEG recordings. The alpha rhythm (8-13 Hz), the best known brain
oscillation, is observed throughout the brain. Other well-known oscillations include
the delta (1-3 Hz), theta (4-7 Hz), beta (13-30 Hz), and gamma (>30 Hz) bands.
Gamma-band oscillations are considered to be those most closely associated with
firing of cortical neurons [
1
].
Recently, neural substrates responsible for the genesis of such brain rhythms and
their functional role in brain information processing have been the subject of intense
investigations. As a result, a number of hypotheses for explaining the role of neural
oscillations have emerged, some including the concept that sensory input information
is coded using multiple temporal scales [
2
-
6
]. One of these hypotheses claims that
temporal coding through regulation of oscillators' firing is essential for the effective
exchange of information in the mammalian brain [
7
]. Another hypothesis claims
that temporal coding organized by coupled alpha and gamma oscillations prioritizes
visual processing [
8
].
A recent study [
9
] suggests that information gating via selective attention is closely
related to temporal encoding. Another study suggests that temporal encoding com-
bined with the encoding by the phase of firing is expected to carry more information
than temporal encoding by spike rates or spike patterns [
10
]. Therefore, temporal
encoding due to phase of firing is considered to be one of the most plausible expla-
nations behind mechanisms of information processing in the brain.
On the other hand, if the brain uses temporal encoding based on the phase of firing,
there should be an oscillator that regulates neural firing based on its phase. There-
fore, the hypothesis for temporal encoding based on phase of firing suggests a pos-
sible coupling between oscillators with different frequencies. That is, the amplitude
The authors of this chapter are Eiichi Okumura, Ph.D. and Takashi Asakawa, Ph.D. who are
with Neuroscience Project Office, Innovation Headquaters, Yokogawa Electric Corporation.
