White matter (WM) degeneration is an important feature of Huntington's disease (HD) neuropathology. To investigate WM degeneration we used Diffusion Tensor Imaging and Tract-Based Spatial Statistics to compare Fractional Anisotropy, Mean Diffusivity (MD), parallel diffusivity and perpendicular diffusivity (λ⊥) in WM throughout the whole brain in 17 clinically diagnosed HD patients and 16 matched controls. Significant WM diffusivity abnormalities were identified primarily in the corpus callosum (CC) and external/extreme capsules in HD patients compared to controls. Significant correlations were observed between motor symptoms and MD in the CC body, and between global cognitive impairment and λ⊥ in the CC genu. Probabilistic tractography from these regions revealed degeneration of functionally relevant interhemispheric WM tracts. Our findings suggest that WM degeneration within interhemispheric pathways plays an important role in the deterioration of cognitive and motor function in HD patients, and that improved understanding of WM pathology early in the disease is required.
It appears that microstructural changes influence cognitive status in HD. Although MD was significantly higher in HD compared with controls at both time points, there were no longitudinal changes in either group. This finding does not rule out the possibility that MD could be a sensitive biomarker for detecting early change in preclinical HD.
The study aimed to explore the biological effects of low-frequency repetitive transcranial magnetic stimulation (LFR-TMS) treatment applied to the right prefrontal cortex, comparing this with the effects of high-frequency left-sided (HFL-TMS) in patients with treatment-resistant depression. Twenty-six patients with treatment-resistant depression were randomized to receive either daily LFR-TMS or HFL-TMS treatment for 3 weeks and underwent functional magnetic resonance imaging during a planning task before and after treatment. Patients responded clinically to both forms of treatment with no difference in the degree of response (F1,24 = 0.65;P> 0.05). Low-frequency repetitive transcranial magnetic stimulation resulted in no overall change in task-related activation. However, responders to LFR-TMS demonstrated a bilateral decrease in activity in middle frontal gyrus. In contrast, HFL-TMS produced an increase in activation in left precuneus with responders showing increased activation in several additional regions. Response to LFR-TMS is associated with a bilateral reduction in frontal activation that does not seem to be a nonspecific effect of treatment and differs from the response to HFL-TMS.
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