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.

Reduced benefit from mnemonic strategies in early-stage Alzheimer's disease: a brief testing-the-limits paradigm for clinical practice.

Discriminating incipient Alzheimer's disease (AD) from major depression (MD) and age related memory decline is a challenge in clinical practice. Since AD is characterized by an early loss of neuronal and functional plasticity, a dynamic test strategy, such as the testing-the-limits (TtL) approach, that measures learning capacity can be a helpful diagnostic tool. To evaluate this, a short recognition paradigm consisting of a pre-test (baseline) and two post-test conditions with an interposed encoding instruction was developed and administered to individuals with incipient AD (n = 19; Mini Mental Status Examination (MMSE) 26.5), patients with depressive disorders (n = 11; MMSE 30), and healthy controls (n = 11; MMSE 30). In addition, participants completed a set of traditional neuropsychological tests that focused on the subjects' cognitive baseline performance. Intergroup comparisons (Kruskal-Wallis, U test) revealed significantly higher post-test failure rates in AD patients. Pre-test performance of MD and AD patients did not differ. Intra-group comparisons (Friedman, Wilcoxon test) showed that all three subject samples benefit from intervention in post-test 1. In contrast to MD and healthy individuals, who revealed significantly lower failure rates in post-test 2 compared to the pre-test, AD patients did not improve. Out of the 15 traditional test scores obtained, only two discriminated simultaneously between AD and each of the other groups. Our data confirm the finding of an impaired cognitive plasticity already present in very early stages of AD and illustrate the efficiency of a dynamic test approach in identifying incipient dementia.