Page 11 - JCBP-1-1

Journal of Clinical and
Basic Psychosomatics Brain MRI alterations in MDD

correlated negatively with internal olfactory gray matter a non-task design-driven data processing method, is
thickness and hippocampal volume . Longitudinal applied to obtain multiple-parameter images to study the
[18]
studies have shown that the left frontal, precuneus, mechanisms of brain activity at rest. Two main analytical
supramarginalgyrus gray matter, and hippocampus methods are used: (i) Local brain activity analysis,
volumes were significantly increased in patients with including regional homogeneity (ReHo), amplitude of
MDD after antidepressant treatments [19,20] . Similar results low-frequency fluctuations (ALFF), and fractional ALFF
were reported in a 7.0 T structural MRI study . However, (fALFF) and (ii) brain functional integration, including
[21]
Reed et al. found that the gray matter thickness in the left functional connectivity (FC) and independent component
hemisphere, predominantly in the frontal and temporal analysis (ICA) [9,27] . Task-fMRI utilizes an experimental task
lobes, in patients with MDD significantly decreased after design to analyze the blood oxygen level-dependent signal
[22]
treatment . The differences between studies may be differences between participants with different tasks or the
related to small sample sizes, differences in antidepressant same task [9,27] .
medications, and disease heterogeneity.
Some rs-fMRI studies showed, in patients with MDD
3.2. Possible mechanisms of brain structural before treatment, a significant decrease in ReHo values
changes in the right superior frontal gyrus, right precuneus, and
bilateral cingulate gyrus and a significant increase in ReHo
In patients with MDD, gray matter thinning may be values in the left dorsomedial prefrontal lobe [28,29] . A recent
caused by a decrease in glial cell density and neuronal study found that ReHo values in the right inferior frontal
volume, as gray matter thickness and volume reflect the gyrus triangle and left post-central gyrus were significantly
density, size, and arrangement of neurons . FA values higher in young patients with MDD compared to older
[23]
in the brain’s white matter are related to axonal density patients . Longitudinal studies have indicated that
[30]
and myelin formation, and reduced FA values indicate patients with MDD had significantly increased ReHo
axonal damage and disruption of the white matter values in the right superior frontal and cingulate gyri and
microstructure . The regions that underwent abnormal decreased ReHo values in the left dorsomedial prefrontal
[24]
changes in the studies mentioned above may be key cortex after antidepressant treatment, while ReHo values
brain regions and neural circuits that regulate emotion in the right precuneus remained lower than those in
and cognition. Antidepressants can relieve depression by normal controls [28,31,32] . It has been found that fALFF values
modulating neurotransmitter content and expression of in the dorsolateral prefrontal, dorsomedial prefrontal,
related receptors, enhancing local synaptic connectivity,
exerting anti-inflammatory effects to reverse inflammatory and precuneus of patients with MDD after antidepressant
[33,34]
changes, and increasing neurotrophic factors such as treatment were reduced . Rs-fMRI studies based on
ICA have shown reduced FC within the default mode
brain-derived neurotrophic factor to promoteneuro network (DMN) and between the cerebellum and salience
plasticity, thus altering the microstructure of the brain to networks (SN) in patients with MDD after treatment [35,36] .
normalize the gray matter volume and the white matter
microstructure [4,6,7,25,26] . Large-scale brain network rs-fMRI studies have identified
reduced FC within the DMN and between the DMN and
Thus, the pathological changes in the gray and suprachiasmatic nucleus network [37,38] . However, Fatt et al.
white matter of the brain in patients with MDD reported contrasting results, showing an increase in FC
after pharmacological treatment are reversible. The within the DMN, central executive network (CEN), and
improvement of cognitive and affective symptoms in SN in patients with MDD after treatment, as well as a
patients after treatment suggests that structural changes higher FC within the DMN and between the DMN and
in the gray and white matter of the corresponding brain CEN . Karim et al. found decreased connections in
[39]
regions may be the neuropathological mechanism of MDD. the right pre-central gyrus within the CEN and the right
Future studies may utilize high-field MRI combined with inferior frontal and superior limbic gyrus within the DMN
imaging modalities such as diffusion kurtosis imaging and in older patients with MDD after the treatment . The
[40]
diffusion spectral imaging to further explore the precision variability in findings among the relevant studies may
diagnosis and treatment efficacy of MDD. be attributed to the interaction between the functional
4. Changes in functional brain MRI in MDD networks and the different neural activities induced by
different antidepressants, in addition to the heterogeneity
4.1. Known influences on brain function in MDD of MDD.
fMRI methods for MDD include resting-state fMRI Tasks targeting the emotional regulation circuitry
(rs-fMRI) and task fMRI (task-fMRI) [2,8,9,27] . Rs-fMRI, have been most frequently employed to identify

Volume 1 Issue 1 (2023) 3 https://doi.org/10.36922/jcbp.0896