Abstract
BackgroundAbnormalities in large-scale, structural and functional brain connectivity have been increasingly reported in patients with major depressive disorder (MDD). However, MDD-related alterations in functional interaction between the cerebral hemispheres are still not well understood. Resting state fMRI, which reveals spontaneous neural fluctuations in blood oxygen level dependent signals, provides a means to detect interhemispheric functional coherence. We examined the resting state functional connectivity (RSFC) between the two hemispheres and its relationships with clinical characteristics in MDD patients using a recently proposed measurement named “voxel-mirrored homotopic connectivity (VMHC)”.Methodology/Principal FindingsWe compared the interhemispheric RSFC, computed using the VMHC approach, of seventeen first-episode drug-naive patients with MDD and seventeen healthy controls. Compared to the controls, MDD patients showed significant VMHC decreases in the medial orbitofrontal gyrus, parahippocampal gyrus, fusiform gyrus, and occipital regions including the middle occipital gyrus and cuneus. In MDD patients, a negative correlation was found between VMHC of the fusiform gyrus and illness duration. Moreover, there were several regions whose VMHC showed significant negative correlations with the severity of cognitive disturbance, including the prefrontal regions, such as middle and inferior frontal gyri, and two regions in the cereballar crus.Conclusions/SignificanceThese findings suggest that the functional coordination between homotopic brain regions is impaired in MDD patients, thereby providing new evidence supporting the interhemispheric connectivity deficits of MDD. The significant correlations between the VMHC and clinical characteristics in MDD patients suggest potential clinical implication of VMHC measures for MDD. Interhemispheric RSFC may serve as a useful screening method for evaluating MDD where neural connectivity is implicated in the pathophysiology.
Highlights
Abnormalities in large-scale, brain connectivity have been increasingly reported in patients with major depressive disorder (MDD)
voxel-mirrored homotopic connectivity (VMHC) Differences between Groups Compared to the controls, the MDD patients showed significant decreases in VMHC, but no increase, in the medial orbitofrontal gyrus, parahippocampal gyrus/fusiform gyrus, and occipital regions including the middle occipital gyrus and cuneus
The primary findings of this study are: (1) MDD patients showed significant decreases in the homologous resting state functional connectivity (RSFC) in regions including the medial orbitofrontal gyrus, parahippocampal gyrus, fusiform gyrus, and the occipital regions. These results are in agreement with the above-reviewed studies showing alterations of interhemispheric interaction in MDD; (2) there was some evidence to suggest inverse relationships between the degree of cognitive disturbance and VMHC in the prefrontal and cerebellar regions, and between the illness duration and VMHC of the fusiform gyrus in MDD patients
Summary
Abnormalities in large-scale, brain connectivity have been increasingly reported in patients with major depressive disorder (MDD). Resting state studies have shown specific network alterations in MDD patients, typically involving the default mode network [5] and the cognitive control network [6]. MDD-related alterations in the functional interaction between the cerebral hemispheres are still pooly understood. Split-brain studies has demonstrated that humans with sectioned corpus callosum (CC, the largest white-matter connection between the hemispheres) had deficits in the sensory, motor, and language processing [12,13,14] as well as cognitive function, such as impairment in attentional maintenance [15,16]. Abnormalities in large-scale, structural and functional brain connectivity have been increasingly reported in patients with major depressive disorder (MDD). We examined the resting state functional connectivity (RSFC) between the two hemispheres and its relationships with clinical characteristics in MDD patients using a recently proposed measurement named ‘‘voxel-mirrored homotopic connectivity (VMHC)’’
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