Biomarkers in Major Depressive Disorder – 3

In the first installment of the article series titled “Biomarkers in Major Depressive Disorder”, the topics mentioned included what biomarkers are, as well as why and how they are used in the diagnosis of depression and in the prediction of response to treatment, while the second installment covered the biomarkers acquired through the magnetic resonance imaging methods for diagnosing major depression. Have a look at those articles from the links below:

https://www.kemalarikan.com/en/biomarkers-in-major-depressive-disorder-1.html

https://www.kemalarikan.com/en/biomarkers-in-major-depressive-disorder-2.html

In this latest installment of the series, we will discuss the biomarkers that are obtained through the prominent methods of EEG and PET in the diagnosis of major depression.

Quantitative Electroencephalography (QEEG)

Electroencephalogram (EEG) is a noninvasive, painless method of diagnosis with no side effects, through which the electrical activity of the brain is monitored with the help of metal disks attached on the scalp. It is among the methods of diagnosis that are still used commonly in neuropsychiatry due to the fact that it is a fast and cheap method that can be administered easily on every patient.

Studies on the resting-state EGG in the diagnosis of Major Depression put forward that, among the brain waves at various frequencies, the absolute power of the alpha (8-12) waves can distinguish depression patients from healthy control elements (Olbrich, 2013). Pieces of EEG research conducted on depression patients found out that:

• The absolute power of the EEG alpha was at higher levels in depression patients compared to healthy elements (Begi ć et al.; 2011; Jaworska et al., 2012);
• Instead of the absolute power of the alpha waves, the relative power was higher in depression patients as reported by some pieces of research (John et al., 1988; Prichep & John, 1992);
• This difference particularly occurs in the frontal and parietal or occipital regions of the brain (Grin-Yatsenko et al., 2009; Jaworska et al., 2012; Bruder et al.,2008).
• Nevertheless, some studies reported the exact opposite, or that the low-frequency theta wave, along with the alpha wave, manifests itself in the early stages of depression (Grin-Yatsenko et al., 2010).
• The differences in electrophysiological activities in the right and left hemispheres of the brain are defined as asymmetry in EEG. In EEG, the alpha asymmetry pattern with bigger right lateral activities has become a biomarker which is studied quite a lot for depression (Gordon et al., 2010).
• It was shown that Gamma waves, a fast frequency band (> 30Hz) in EEG, could distinguish depression from healthy elements and bipolar depression, and that antidepressants, along with the treatment, could change the gamma activity (Fitzgerald and Watson, 2018).

Positron Emission Tomography (PET)

This is an imaging technique, which scans the normal or pathological tissues on which metabolic radioactive agents injected intravenously accumulate, and it is used for metabolic or functional imaging. Functional changes that occur in the brain due to Major Depression can be easily analyzed by means of PET. PET-related studies demonstrated that the serotonergic, neuro-inflammation and amyloids in the brain pose a risk for the onset of depression. For instance,

• Serotonergic irregularities in the fronto-limbic regions of the brain indicate a tendency to depression (Frokjaer et al., 2008).
• It was seen that there was a lower potential of serotonin transporter binding, which supports the effects of the serotonergic irregularity in the forebrain, brain stem and putamen of MDD patients making suicide attempts (Nye et al., 2013).
• Biomarkers, which support neuro-inflammation, were spotted in the subgenual anterior cingulate cortex regions of drug-free major depression patients. In untreated patients, however, these indicators were higher (Richards et al., 2018).
• According to the Amyloid PET-related study, in major depression patients with slight cognitive disorders, amyloid plaques were observed to have accumulated in the hippocampus region, which plays a key part in the memory (Wu et al., 2018).

In conclusion, biomarkers obtained by means of both EEG and PET show that major depression is characterized by the deteriorations in cognitive functions, in addition to those in the function of emotion regulation.

REFERENCES:
– The studies mentioned in the article are included in Dr. Lai’s compilation of articles titled “Fronto-limbic neuroimaging biomarkers for diagnosis and prediction of treatment responses in major depressive disorder” (2021), and Dr. Olbrich’s compilation of articles titled “EEG biomarkers in Major Depressive Disorder: Discriminative power and prediction of treatment response” (2013).
– Olbrich, Sebastian; Arns, Martijn (2013). EEG biomarkers in major depressive disorder: Discriminative power and prediction of treatment response. International Review of Psychiatry, 25(5), 604–618. doi:10.3109/09540261.2013.816269.
– Lai, C. H. (2021). Fronto-limbic neuroimaging biomarkers for diagnosis and prediction of treatment responses in major depressive disorder. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 107, 110234.