Global efficiency of the motor network is decreased in Parkinson's disease in comparison with essential tremor and healthy controls.

BACKGROUND: Graph theory (GT) is a mathematical field that analyses complex networks that can be applied to neuroimaging to quantify brain's functional systems in Parkinson's disease (PD) and essential tremor (ET). OBJECTIVES: To evaluate the functional connectivity (FC) measured by the global efficiency (GE) of the motor network in PD and compare it to ET and healthy controls (HC), and correlate it to clinical parameters. METHODS: 103 subjects (54PD, 18ET, 31HC) were submitted to structural and functional MRI. A network was designed with regions of interest (ROIs) involved in motor function, and GT was applied to determine its GE. Clinical parameters were analyzed as covariates to estimate the impact of disease severity and medication on GE. RESULTS: GE of the motor circuit was reduced in PD in comparison with HC (p .042). Areas that most contributed to it were left supplementary motor area (SMA) and bilateral postcentral gyrus. Tremor scores correlated positively with GE of the motor network in PD subgroups. For ET, there was an increase in the connectivity of the anterior cerebellar network to the other ROIs of the motor circuit in comparison with PD. CONCLUSIONS: FC measured by the GE of the motor network is diminished in PD in comparison with HC, especially due to decreased connectivity of left SMA and bilateral postcentral gyrus. This finding supports the theory that there is a global impairment of the motor network in PD, and it does not affect just the basal ganglia, but also areas associated with movement modulation. The ET group presented an increased connectivity of the anterior cerebellar network to the other ROIs of the motor circuit when compared to PD, which reinforces what it is known about its role in this pathology.

Depression in medical school: the influence of morningness-eveningness.

Medical students are at higher risk for depression, affecting not only their lives but also patient care. This article studied a population of medical students engaged in lecture-based learning regarding the presence of depressive symptoms and its relation to morningness-eveningness. Depressive symptoms were assessed by the Beck Depressive Inventory scale (BDI>10), and diurnal preference was assessed by the Horne & Ostberg Morningness/Eveningness Questionnaire (MEQ). Family history of depression and involvement in regular physical activity were also investigated. A total of 161 students, 77 (47.8%) males, aged 19 to 30 yrs (22.1+/-2.1) living in a city close to the equator were evaluated. Fifty-three individuals (32.9%) had depressive symptoms. Depressive individuals showed a trend to be female (p=0.07). Also, female gender showed a non-significant shift toward morningness. Fifty-eight (36.0%) subjects participated in regular physical activity. In 57 cases (35.4%), there was a history of depression in the family. Fifteen individuals (9.3%) were definitely evening type, 42 (26.1%) were moderately evening type, 44 (27.3%) were indifferent, 42 (26.1%) were moderately morning type, and 18 (11.2%) were definitely morning type. Family history of depression (OR=0.29, 95% CI=1.37-6.12) and sedentary life (OR=0.28, 95% CI=0.12-0.65) were associated with depressive symptoms. Eveningness was associated with depressive symptoms (OR=0.66, 95% CI=0.50-0.88), and this association remained significant after adjusting for the presence of familial depression and physical activity (OR=0.71, 95% CI=0.52-0.95). In conclusion, depressive symptoms are independently associated with "eveningness" in medical students. These results should be confirmed by future studies involving a larger number of subjects.