Biomedical Engineering Reference
In-Depth Information
Fig. 9.1 a
Typical time
courses of two oscillators
when same-frequency
coupling (SFC) exists.
b
Typical time courses of
two oscillators when phase-
amplitude coupling (PAC)
exists.
c
Typical time courses
of two oscillators when PAC
exists and a common lower
frequency (LF) component
simultaneously drives
the amplitudes of two higher
frequency (HF) oscillators.
In this case, an amplitude-
amplitude coupling (AAC)
between the two HF
oscillations exists even when
they are not directly coupled
(a)
HF
1
HF
2
(b)
HF
PAC
LF
(c)
HF
1
PAC
LF
AAC
PAC
HF
2
the two oscillators exists. Namely, AAC can exist, even when two HF oscillators are
not directly coupled. This situation is depicted in Fig.
9.1
c.
This chapter is based on the hypothesis that, in brain information processing,
the phases of the low-frequency oscillations encode the amplitudes of the high-
frequency oscillations that represent particular neuronal activities. If this hypothesis
is true, analyzing the relationship between the phases of the LF oscillations and
the amplitudes of the HF oscillations, i.e., analyzing the phase-amplitude coupling
(PAC) between the LF and HF signals is extremely important in investigating brain
information processing. Therefore, we focus on the PAC and related topics in this
chapter.
9.3 Local PAC and Cross-Location PAC
When phase-amplitude coupling is observed between the HF and LF signals mea-
sured at the same location in a brain, this PAC is called the local PAC, and termed
lPAC. On the other hand, when the PAC is observed between the HF and LF signals
measured at different locations, this PAC is called the cross-location PAC, and here
termed xPAC.
So far, most studies have investigated lPAC, but some recent studies have extended
their scope to xPAC. For example, in a study using an electrocorticogram (ECoG)
recording, the presence of xPACs during working memory tasks was reported [
12
].
The xPAC between cortical gamma oscillations and an LF oscillation from the
