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S.-H. Lee and Y. Park
symptomatology and etiologies of the involved disorders [95]. Source analysis of
MMN in EEG and MEG signals localizes MMN to the auditory cortex, adjacent
areas of the superior temporal lobe, middle and inferior frontal gyrus, and anterior
cingulate cortex.
Furthermore, MMN has several clinical implications. For example, it correlates
with disease severity, cognitive dysfunction, impaired social functioning, and brain
alterations such as reductions in gray matter. Reductions in MMN may imply deficits
in NMDA receptors, which function abnormally in patients with schizophrenia. It
has been reported that individuals with chronic schizophrenia exhibit reduced MMN
amplitudes, 0.94 standard deviation (SD) smaller for pitch deviants and 1.23 SDs
smaller for duration deviants, compared with healthy controls. Moreover, MMN
deficits also appear to be more severe in schizophrenia compared to individuals with
bipolar disorder or Alzheimer’s disease.
7.2.6 Alpha Asymmetry
Alpha asymmetry has been extensively studied in both clinical and nonclinical samples. Among various psychiatric disorders, it has been studied mostly in depression
and anxiety disorders. Alpha asymmetry is characterized by an asymmetrical alphaband activity (8–12 Hz) in the left and right hemispheres [36], and known to be a
reflection of cortical activity [18]. Thus, increased alpha indicates decreased cortical activity and decreased alpha indicates increased cortical activity. Studies have
identified alpha asymmetry mostly in the frontal and the parietal regions of the brain.
Perhaps, the most referred explanation of the relationship between alpha asymmetry and psychiatric disorders is the behavioral activation/inhibition systems
(BAS/BIS). Initially proposed by Gray to understand the psychophysiology of personality configurations [32], the BAS/BIS have been applied to studies examining different psychopathologies. For example, empirical research has suggested that
depression is characterized by hypofunctioning of the BAS, which signifies that
depressive individuals demonstrate an indifference towards positive stimuli [56].
Davidson argued that both the BAS and BIS are lateralized hemispherically, whereby
the left hemisphere regulates the BAS and the right hemisphere regulates the BIS [19].
Results supporting the relationship between alpha asymmetry and BAS have been
more constant that those between alpha asymmetry and BIS [16, 36, 129]. There are
still inconstant reports about alpha symmetry and major depressive disorder. Comorbid anxiety disorder, subtype of depressive disorder considering individual variance
of characteristics in terms of BIA/BAS, and the presence of suicidal ideation should
possibly be considered to obtain more coherent findings in future. Nonetheless, alpha
asymmetry seems to have promising value as a marker of psychiatric disorders.
S.-H. Lee and Y. Park
symptomatology and etiologies of the involved disorders [95]. Source analysis of
MMN in EEG and MEG signals localizes MMN to the auditory cortex, adjacent
areas of the superior temporal lobe, middle and inferior frontal gyrus, and anterior
cingulate cortex.
Furthermore, MMN has several clinical implications. For example, it correlates
with disease severity, cognitive dysfunction, impaired social functioning, and brain
alterations such as reductions in gray matter. Reductions in MMN may imply deficits
in NMDA receptors, which function abnormally in patients with schizophrenia. It
has been reported that individuals with chronic schizophrenia exhibit reduced MMN
amplitudes, 0.94 standard deviation (SD) smaller for pitch deviants and 1.23 SDs
smaller for duration deviants, compared with healthy controls. Moreover, MMN
deficits also appear to be more severe in schizophrenia compared to individuals with
bipolar disorder or Alzheimer’s disease.
7.2.6 Alpha Asymmetry
Alpha asymmetry has been extensively studied in both clinical and nonclinical samples. Among various psychiatric disorders, it has been studied mostly in depression
and anxiety disorders. Alpha asymmetry is characterized by an asymmetrical alphaband activity (8–12 Hz) in the left and right hemispheres [36], and known to be a
reflection of cortical activity [18]. Thus, increased alpha indicates decreased cortical activity and decreased alpha indicates increased cortical activity. Studies have
identified alpha asymmetry mostly in the frontal and the parietal regions of the brain.
Perhaps, the most referred explanation of the relationship between alpha asymmetry and psychiatric disorders is the behavioral activation/inhibition systems
(BAS/BIS). Initially proposed by Gray to understand the psychophysiology of personality configurations [32], the BAS/BIS have been applied to studies examining different psychopathologies. For example, empirical research has suggested that
depression is characterized by hypofunctioning of the BAS, which signifies that
depressive individuals demonstrate an indifference towards positive stimuli [56].
Davidson argued that both the BAS and BIS are lateralized hemispherically, whereby
the left hemisphere regulates the BAS and the right hemisphere regulates the BIS [19].
Results supporting the relationship between alpha asymmetry and BAS have been
more constant that those between alpha asymmetry and BIS [16, 36, 129]. There are
still inconstant reports about alpha symmetry and major depressive disorder. Comorbid anxiety disorder, subtype of depressive disorder considering individual variance
of characteristics in terms of BIA/BAS, and the presence of suicidal ideation should
possibly be considered to obtain more coherent findings in future. Nonetheless, alpha
asymmetry seems to have promising value as a marker of psychiatric disorders.