Depression and apathy are among the most common neuropsychiatric disturbances in Parkinson's disease (PD), and among the most important factors associated with a poor quality of life. However, their neural bases remain unclear. The results of the magnetic resonance imaging (MRI) studies on depression in PD differ dramatically. Some of them proposed a role of morphologic changes in the mediodorsal thalamus. In contrast to previous voxel-based morphometry (VBM) data, our study did not confirm a decrease in gray matter (GM) density in any brain region of depressed PD patients. Instead, a more severe white matter (WM) loss in the right frontal lobe was found, including the anterior cingulate bundle and the inferior orbitofrontal (OF) region. We suggested that the negative correlation between the severity of depression and WM density in the right OF region reinforces the hypothesis of depression in PD as a "disconnection syndrome". Only one MRI study using VBM found that high apathy scores correlated with low GM density values in the right (posterior) cingulate gyrus and the bilateral inferior frontal gyrus, in line with the findings in Alzheimer's disease and elderly adults with major depression.

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