Biomedical Engineering Reference
In-Depth Information
9.4.4 Phase-Informed Time-Frequency Map
A “phase-informed” time-frequency map is the time-frequency map of the HF signal
x
H
(
t
)
displayed with the overlay of the sinusoidal time course cos
(ʸ
L
(
t
))
.Bydis-
playing the time-frequency map of
x
H
(
in this manner, the relationship between
the amplitude of the HF signal and the phase of the LF signal can be visualized in an
intuitive manner. Particularly, the preference of the HF signal amplitude to the phase
of the LF signal is clearly shown. This type of map was first introduced by Canolty
et al. [
11
] and it is often called as the Canolty map. Examples of the phase-informed
TF map obtained using hand-motor MEG data are shown in Sect.
9.5
.
t
)
9.5 Source Space PAC Analysis: An Example Study Using
Hand-Motor MEG Data
9.5.1 Experimental Design and Recordings
Here, we present results of an example study to demonstrate the noninvasive detection
of PAC using the MEG source space analysis. We used a hand-motor task similar to
thetaskusedin[
16
]. A healthy, right-handed subject (30 years old male) participated
in the MEG study.
2
The subject was asked to perform grasping movements (grasping
a soft toy) with his left hand every 10 s. An auditory cue was provided to inform the
grasp timing. The subject repeated grasping 64 times with his eyes open.
MEG data was acquired using a whole-head 160-channel MEG system (PQA160C,
Yokogawa Electric Corporation, Japan) with a sample rate of 2,000 Hz. A band-pass
filter with a bandwidth of 0.16-500 Hz was applied. Electromyogram was recorded
from the subject's left forearm to monitor subject's hand movements. During the
recordings, the subject lay in the supine position on a bed in a magnetically shielded
room. The subject's T1-weighted MRI was obtained, which consists of 166 slices
of 1.2 mm thickness. A single-slice image has 512
×
512 voxels in a field of view of
261
×
261 mm.
9.5.2 Data Analysis
9.5.2.1 Preprocessing
An ICA-based interference removal procedure was applied to remove eyeblink and
MCG artifacts. An offline digital notch filter with the frequency of 60, 120, and 180 Hz
2
Informed consent was obtained from the subject before the experiment. Handedness was deter-
mined using the Edinburgh Handedness Inventory [
17
].
