A BS TRACT: Background: Action observation training and motor imagery may improve motor learning in Parkinson's disease (PD). Objectives: The objectives of this study were to assess mobility and balance (performing motor and dual tasks) and brain functional reorganization following 6 weeks of action observation training and motor imagery associated with dual-task gait/balance exercises in PD patients with postural instability and gait disorders relative to dual-task training alone. Methods: Twenty-five PD-postural instability and gait disorder patients were randomized into 2 groups: the DUAL-TASK+AOT-MI group performed a 6-week gait/balance training consisting of action observation training-motor imagery combined with practicing the observed-imagined exercises; the DUAL-TASK group performed the same exercises combined with watching landscape videos. Exercises were increasingly difficult to include the dual task. At baseline and at 6 weeks, patients underwent: mobility, gait, and balance evaluations (also repeated 2 months after training), cognitive assessment, and functional MRI, including motor and dual tasks. Results: Dual-task gait/balance training enhanced mobility, during both single-and dual-task conditions, and executive functions in PD-postural instability and gait disorders, with a long-lasting effect at 14 weeks. When exercises were preceded by action observation trainingmotor imagery, PD-postural instability and gait disorders showed greater improvement of balance and gait velocity both with and without the dual task, particularly during the turning phase. After training, the DUAL-TASK+AOT-MI group showed reduced recruitment of frontal areas and increased activity of cerebellum during functional-MRI motor and dual task, correlating with balance/turning velocity and executive improvements, respectively. The DUAL-TASK group showed reduced activity of supplementary motor area and increased recruitment of temporo-parietal areas during the dual task and decreased cerebellar activity during the motor task correlating with faster turning velocity. Functional MRI results were not corrected for multiple comparisons and should be interpreted carefully. Conclusions: Adding action observation training-motor imagery to dual-task gait/balance training promotes specific functional reorganization of brain areas involved in motor control and executive-attentive abilities and more long-lasting effects on dual-task mobility and balance in PD-postural instability and gait disorders.

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The purpose of the present review is to provide an update of the available recent scientific literature on the use of magnetic resonance imaging (MRI) in Alzheimer’s disease (AD). MRI is playing an increasingly important role in the characterization of the AD signatures, which can be useful in both the diagnostic process and monitoring of disease progression. Furthermore, this technique is unique in assessing brain structure and function and provides a deep understanding of in vivo evolution of cerebral pathology. In the reviewing process, we established a priori criteria and we thoroughly searched the very recent scientific literature (January 2018–March 2020) for relevant articles on this topic. In summary, we selected 73 articles out of 1654 publications retrieved from PubMed. Based on this selection, this review summarizes the recent application of MRI in clinical trials, defining the predementia stages of AD, the clinical utility of MRI, proposal of novel biomarkers and brain regions of interest, and assessing the relationship between MRI and cognitive features, risk and protective factors of AD. Finally, the value of a multiparametric approach in clinical and preclinical stages of AD is discussed.