Intrinsic functional connectivity alterations in progressive supranuclear palsy: Differential effects in frontal cortex, motor, and midbrain networks.

BACKGROUND: The topography of functional network changes in progressive supranuclear palsy can be mapped by intrinsic functional connectivity MRI. The objective of this study was to study functional connectivity and its clinical and behavioral correlates in dedicated networks comprising the cognition-related default mode and the motor and midbrain functional networks in patients with PSP. METHODS: Whole-brain-based "resting-state" functional MRI and high-resolution T1-weighted magnetic resonance imaging data together with neuropsychological and video-oculographic data from 34 PSP patients (22 with Richardson subtype and 12 with parkinsonian subtype) and 35 matched healthy controls were subjected to network-based functional connectivity and voxel-based morphometry analysis. RESULTS: After correction for global patterns of brain atrophy, the group comparison between PSP patients and controls revealed significantly decreased functional connectivity (P < 0.05, corrected) in the prefrontal cortex, which was significantly correlated with cognitive performance (P = 0.006). Of note, midbrain network connectivity in PSP patients showed increased connectivity with the thalamus, on the one hand, whereas, on the other hand, lower functional connectivity within the midbrain was significantly correlated with vertical gaze impairment, as quantified by video-oculography (P = 0.004). PSP Richardson subtype showed significantly increased functional motor network connectivity with the medial prefrontal gyrus. CONCLUSIONS: PSP-associated neurodegeneration was attributed to both decreased and increased functional connectivity. Decreasing functional connectivity was associated with worse behavioral performance (ie, dementia severity and gaze palsy), whereas the pattern of increased functional connectivity may be a potential adaptive mechanism. © 2017 International Parkinson and Movement Disorder Society.

The functional anatomy of motor imagery after sub-acute stroke.

BACKGROUND: The neural correlates of motor imagery (MI) are tightly coupled with the cortical motor control network. Therefore MI may have therapeutic potential for patients with motor deficits after an ischemic stroke. OBJECTIVE: The aim of our study was to assess the hemispheric balance of the cortical motor network during motor imagery (MI) in patients recovering from stroke in the sub-acute stage. METHODS: We studied 17 patients after cerebral ischemic stroke (sub-acute stage) and 12 healthy subjects using functional Magnetic Resonance Imaging (fMRI) during motor imagery and performance of isometric grip force movements (5 Newton). Laterality indices (LI) were calculated from regional activation analysis to assess hemispheric distribution of activity in pre-specified motor areas. RESULTS: Laterality index (LI) revealed a more balanced cortical activity in MI for both controls (-0.03) and patients (-0.12) in the premotor cortex compared to movement execution (0.48 controls; 0.12 patients) and a trend towards a shift in contra-lesional activity in stroke patients. CONCLUSIONS: Our results indicate a preserved interhemispheric balance of patients in the sub-acute stage when activating the cortical motor areas during MI. This could provide a reasonable physiologic baseline for using MI as an additional rehabilitative therapy for improving functional recovery in the sub-acute stage after stroke.

Neuroimaging of multimodal sensory stimulation in amyotrophic lateral sclerosis.

AIM: Structural and functional imaging techniques were combined to investigate sensory system function in amyotrophic lateral sclerosis (ALS). METHODS: Functional MRI (fMRI) was used to investigate cortical activity during visual, auditory and somatosensory stimulation in 14 ALS patients and 18 control subjects. Changes in amplitude, latency and duration of the blood oxygen level dependent response were modelled. Furthermore, diffusion tensor imaging was used to investigate changes in white matter networks. RESULTS: During visual stimulation, fMRI demonstrated a decreased response in secondary visual areas in ALS, possibly related to demyelination of sensory nerve fibres. Increasing brain activity in associative cortices was linked to a decrease in physical functioning and might represent a compensatory process. Additionally, reduced white matter functioning became evident for fibres projecting to the extrastriate visual cortex. For auditory stimulation, a delayed response in secondary auditory areas probably linked to prolonged nerve conductance time and an altered cortical pattern in areas involved in target processing/detection became evident in ALS patients. Structural white matter changes in the primary and secondary auditory cortices were observed. For somatosensory stimulation, a prolonged/reduced response in sensory integration areas of the parietal lobe was observed, perhaps linked to the reduced visceral inflow due to immobility. CONCLUSION: Multiparametric MRI suggests a progressive functional deficit in secondary/higher order sensory processing areas in ALS, probably associated with reduction of re-afferent information flow due to progressive immobility. The changes described might also represent an expression of the disease process itself. Evidence for compensatory processes in multimodal associative cortices was found.