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S.-H. Lee and Y. Park
sures) differ depending on the independent studies. Critical discussions about the
impact of EEG amplitude and volume conduction on the different connectivity measures might provide meaningful suggestions. The alpha amplitude shows big variance
among individuals, which may reflect unrevealed individual personal characteristics.
If the researchers want to study the resting state alpha activity, the sleepiness during
EEG measurement should be rigorously controlled to rule out contamination of alpha
power by smearing theta power effect on EEG. If these confounding factors could
be well controlled, more uniform results from functional connectivity and network
analysis would be drawn in psychiatric illnesses, including major depressive disorder.
7.3.4 Anxiety Disorder
Most EEG studies have reported alterations of multiple spectral bands in anxiety
disorders. Alterations of the theta (4–8 Hz) and alpha (8–13 Hz) bands are often
observed [5]. However, the beta and gamma band abnormality were also recently
reported in patients with post-traumatic stress disorder (PTSD) [72, 74, 121]. None
of the qEEG alterations are refrained to anxiety disorders. However, they are thought
to be related to symptoms of anxiety disorders and have been targets of neurological
treatments such as neurofeedback training [124]. Among the various anxiety disorders, PTSD and obsessive-compulsive disorder are some that have received the most
empirical attention.
7.3.4.1 Post-traumatic Stress Disorder (PTSD)
Similar to major depressive disorder, frontal alpha asymmetry is a frequently studied
biomarker of PTSD [30, 58]. Relatively greater left frontal activity is regarded as
being related to appetitive motivation, and lower levels of depressive and anxious
symptoms in patients with PTSD [90]. However, the implication of alpha asymmetry
in PTSD is not definitive; a study comparing alpha asymmetry between patients with
PTSD and healthy controls reported no significant differences [30].
Connectivity measures have also been to be of interest when studying EEG
biomarkers of PTSD. Patients with PTSD, when compared with controls, were
found to have decreased resting-state EEG frontal connectivity, especially in beta
and gamma frequency bands. In addition, nodal values (connection strength) of these
two frequency bands were significantly correlated with PTSD symptom severity, and
with depression and increased arousal [72, 74].
In addition, significant associations have been found between PTSD symptoms,
and P200 and P300 ERP components [82]. A recent study by Shu et al. reported
that alterations of ERP components (N200 and P300 amplitudes) accurately classified whether a group of veterans associated with the development of PTSD or not
[123]. Moreover, a source level study by Bae and colleagues reported reduced source
density of P300 in patients with PTSD when compared with healthy controls [4].
S.-H. Lee and Y. Park
sures) differ depending on the independent studies. Critical discussions about the
impact of EEG amplitude and volume conduction on the different connectivity measures might provide meaningful suggestions. The alpha amplitude shows big variance
among individuals, which may reflect unrevealed individual personal characteristics.
If the researchers want to study the resting state alpha activity, the sleepiness during
EEG measurement should be rigorously controlled to rule out contamination of alpha
power by smearing theta power effect on EEG. If these confounding factors could
be well controlled, more uniform results from functional connectivity and network
analysis would be drawn in psychiatric illnesses, including major depressive disorder.
7.3.4 Anxiety Disorder
Most EEG studies have reported alterations of multiple spectral bands in anxiety
disorders. Alterations of the theta (4–8 Hz) and alpha (8–13 Hz) bands are often
observed [5]. However, the beta and gamma band abnormality were also recently
reported in patients with post-traumatic stress disorder (PTSD) [72, 74, 121]. None
of the qEEG alterations are refrained to anxiety disorders. However, they are thought
to be related to symptoms of anxiety disorders and have been targets of neurological
treatments such as neurofeedback training [124]. Among the various anxiety disorders, PTSD and obsessive-compulsive disorder are some that have received the most
empirical attention.
7.3.4.1 Post-traumatic Stress Disorder (PTSD)
Similar to major depressive disorder, frontal alpha asymmetry is a frequently studied
biomarker of PTSD [30, 58]. Relatively greater left frontal activity is regarded as
being related to appetitive motivation, and lower levels of depressive and anxious
symptoms in patients with PTSD [90]. However, the implication of alpha asymmetry
in PTSD is not definitive; a study comparing alpha asymmetry between patients with
PTSD and healthy controls reported no significant differences [30].
Connectivity measures have also been to be of interest when studying EEG
biomarkers of PTSD. Patients with PTSD, when compared with controls, were
found to have decreased resting-state EEG frontal connectivity, especially in beta
and gamma frequency bands. In addition, nodal values (connection strength) of these
two frequency bands were significantly correlated with PTSD symptom severity, and
with depression and increased arousal [72, 74].
In addition, significant associations have been found between PTSD symptoms,
and P200 and P300 ERP components [82]. A recent study by Shu et al. reported
that alterations of ERP components (N200 and P300 amplitudes) accurately classified whether a group of veterans associated with the development of PTSD or not
[123]. Moreover, a source level study by Bae and colleagues reported reduced source
density of P300 in patients with PTSD when compared with healthy controls [4].