Abstract
BackgroundDistinctive patterns of functional connectivity (FC) abnormalities in neural circuitry has been reported in patients with bipolar depression (BD) and unipolar depression (UD). However, it is unclear that whether this distinct functional connectivity patterns are diagnosis specific between BD and UD. This study aimed to compare patterns of functional connectivity among BD, UD and healthy controls (HC) and determine the distinct functional connectivity patterns which can differentiate BD from UD.MethodTotally 23 BD, 22 UD, and 24 HC were recruited to undergo resting-state fMRI scanning. FC between each pair of brain regions was calculated and compared among the three groups, the associations of FC with depressive symptom were also analyzed.ResultsBoth patient groups showed significantly decreased cerebral-limbic FC located between the default mode network [posterior cingulated gyrus (PCG) and precuneus] and limbic regions (hippocampus, amygdala and thalamus) than HC. Moreover, the BD group exhibited more decreased FC mainly in the cortical regions (middle temporal gyrus, PCG, medial superior frontal gyrus, inferior occipital gyrus and superior temporal gyrus), but the UD group is more associated with limbic alterations. These decreased FCs were negatively correlated with HAMD scores in both BD and UD patients.ConclusionsBD and UD patients demonstrate different patterns of abnormal cerebral-limbic FC, reflected by decreased FC within cerebral cortex and limbic regions in BD and UD, respectively. The distinct FC abnormal pattern of the cerebral-limbic circuit might be applied as biomarkers to differentiate these two depressive patient groups.
Highlights
Distinctive patterns of functional connectivity (FC) abnormalities in neural circuitry has been reported in patients with bipolar depression (BD) and unipolar depression (UD)
Both patient groups showed significantly decreased cerebral-limbic FC located between the default mode network [posterior cingulated gyrus (PCG) and precuneus] and limbic regions than healthy controls (HC)
The BD group exhibited more decreased FC mainly in the cortical regions, but the UD group is more associated with limbic alterations
Summary
Distinctive patterns of functional connectivity (FC) abnormalities in neural circuitry has been reported in patients with bipolar depression (BD) and unipolar depression (UD). Glutamate-related magnetic resonance spectroscopy (MRS) measures have reported that Glx (composed mainly of glutamate and glutamine) reduced in prefrontal and subcortical regions in unipolar depression, but increased in all mood states in bipolar disorder [21, 22]. Taken together, these evidence suggest that the neuropathology of depression involves dysfunctions within a neuroanatomical circuit including the frontal cortex and limbic structures [23, 24], but the specific pattern of neural changes are different between unipolar and bipolar depression in this circuit. Most existing studies had a major shortcoming that the recruited BD patients included a manic phase, depressive phase or remission phase, which cannot rule out the interference of various disease states [15, 19]
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