Biology subjects

Rousseau, C.

Publications and source records attributed to Rousseau, C..

3 recordsLinked to original sources

bioRxiv2019

Altered hypothalamic diffusivity in Parkinsonian autonomic dysfunction

The pathophysiological basis of autonomic symptoms in Parkinsons disease remains incompletely understood. The hypothalamus plays a key regulatory role in autonomic function and has been shown to be affected in Parkinsons disease. Here, using diffusion magnetic resonance imaging, we investigated whether microstructural properties of the hypothalamus differ in Parkinsons disease patients with high compared to low autonomic symptom burden.\n\nParkinsons disease patients with low (n=25) and high (n=25) autonomic symptom burden were identified from a larger pool, based on scores from a questionnaire assessing autonomic symptoms in Parkinsons disease (SCOPA-AUT). In each patient, we first segmented the hypothalamus manually, based on anatomical landmarks. Diffusivity measures were then extracted from the hypothalamus. Diffusivity measures calculated in the brainstem and the putamen were used to assess the specificity of the results.\n\nRelative to patients with low autonomic symptom burden, patients with high burden showed increased mean, axial, and radial diffusivity in the hypothalamus. In contrast, we did not find significant group differences in any of these measures extracted from the brainstem or the putamen.\n\nThese results reveal consistent differences in the microstructural properties of the hypothalamus between patients with low and high autonomic symptom burden. Hypothalamic diffusivity properties can thus potentially be used as an imaging marker to assist in the identification of therapeutic targets for autonomic dysfunction in Parkinsons disease.

neuroscience↗

bioRxiv2019

Gravity highlights a dual role of the insula in internal models

Movements rely on a mixture of predictive and reactive mechanisms. With experience, the brain builds internal representations of actions in different contexts. Many factors are taken into account in this process among which the immutable presence of gravity. Any displacement of a massive body in the gravitational field generates forces and torques that must be predicted and compensated by appropriate motor commands. Studies have shown that the insular cortex is a key brain area for graviception. However, none attempted to address whether the same internal representation of gravity is shared between reactive and predictive mechanisms. Here, participants either mentally simulated (only predictive) or performed (predictive and reactive) vertical movements of the hand. We found that the posterior part of the insular cortex was engaged when feedback was processed. The anterior insula, however, was activated only in mental simulation of the action. A psychophysical experiment shows participants ability to integrate the effects of gravity. Our results demonstrate a dual internal representation of gravity within the insula and discuss how they can conceptually be linked.

neuroscience↗

bioRxiv2019

Excess significance bias in repetitive transcranial magnetic stimulation literature for neuropsychiatric disorders

IntroductionRepetitive transcranial magnetic stimulation (rTMS) has been widely tested and promoted for use in multiple neuropsychiatric conditions, but as for many other medical devices, some gaps may exist in the literature and the evidence base for rTMS clinical efficacy remains under debate. We aimed to empirically test for an excess number of statistically significant results in the literature on rTMS therapeutic efficacy across a wide range of meta-analyses and to characterize the power of studies included in these meta-analyses.\n\nMethodsBased on power calculations, we computed the expected number of \"positive\" datasets for a medium effect-size (standardized mean difference, SMD=0.30) and compared it with the number of observed \"positive\" datasets. Sensitivity analyses considered small (SMD=0.20), modest (SMD=0.50), and large (SMD=0.80) effect sizes.\n\nResults14 meta-analyses with 228 datasets (110 for neurological disorders and 118 for psychiatric disorders) were assessed. For SMD=0.3, the number of observed \"positive\" studies (n=94) was larger than expected (n=35). We found evidence for an excess of significant findings overall (p<0.0001) and in 8/14 meta-analyses. Evidence for an excess of significant findings was also observed for SMD=0.5 for neurological disorders. 0 (0 %), 0 (0 %), 3 (1 %), and 53 (23 %) of the 228 datasets had power >0.80, respectively for SMDs of 0.30, 0.20, 0.50, and 0.80.\n\nConclusionMost studies in the rTMS literature are underpowered. This results in fragmentation and waste of research efforts. The somewhat high frequency of \"positive\" results seems spurious and may reflect bias.\n\nTrial Registration: PROSPERO 2017 CRD42017056694

scientific communication and education↗