Cognitive Impact of ß-Amyloid Load in the Rapid Eye Movement Sleep Behavior Disorder-Lewy Body Disease Continuum.

BACKGROUND: Rapid eye movement sleep behavior disorder (RBD) is linked to the diffuse-malignant subtype and higher cognitive burden in Lewy body disease (LBD). OBJECTIVE: This study explores brain ß-amyloid deposition and its association with cognitive decline across the RBD-LBD continuum. METHODS: Patients with isolated RBD (iRBD), Parkinson's disease with probable RBD (PDRBD), and dementia with Lewy bodies with probable RBD (DLBRBD) underwent 18F-florbetaben positron emission tomography, 3T magnetic resonance imaging scans, and comprehensive neuropsychological assessments. Subjects were categorized as cognitively normal (NC), mild cognitive impairment (MCI), or dementia. Global and regional standardized uptake value ratios (SUVR) were estimated in predefined cognitive volumes of interest (VOI) derived from voxel-wise comparison analysis among the cognitive groups, namely the prefrontal, parietal, precentral cortices, lingual gyrus, and supplementary motor area. Generalized linear models assessed the relationship between 18F-florbetaben SUVRs and neuropsychological testing, adjusting for age and sex. Subgroup analysis focused on the polysomnography-confirmed iRBD-continuum subset (n = 41) encompassing phenoconverters and nonconverters in our prospective iRBD cohort. RESULTS: Eighty-six subjects were classified as follows: 14 NC, 54 MCI, and 18 dementia. The proportion of positive ß-amyloid scans increased with advanced cognitive stages (P = 0.038). ß-Amyloid signals in cognitive VOIs were elevated in subgroups showing impairment in Trail-Making Test B (TMT-B). A linear association between TMT-B z score and global cortical ß-amyloid levels was observed in the iRBD-continuum subset (P = 0.013). CONCLUSION: Cortical ß-amyloid accumulates with declines in executive function within the RBD-LBD continuum. TMT-B performance may be a useful marker associating with ß-amyloid load, particularly in the iRBD population. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Monoaminergic Degeneration and Ocular Motor Abnormalities in De Novo Parkinson's Disease.

BACKGROUND: Evaluating eye movements in Parkinson's disease (PD) provides valuable insights into the underlying pathophysiological changes. OBJECTIVE: The aim was to investigate the relationship between monoaminergic degeneration and ocular motor abnormalities in de novo PD. METHODS: Drug-naive PD patients who underwent N-(3-[18 F]fluoropropyl)-2-carbomethoxy-3-(4-iodophenyl) nortropane positron emission tomography scans and video-oculography at diagnosis were eligible. Measurements of saccadic accuracy, latency, and smooth pursuit gain and square wave jerk frequency were collected. Patients underwent Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and detailed cognitive tests. We investigated the associations between ocular motor measurements and specific tracer uptake ratios (SUR) in the caudate nucleus, anterior and posterior putamen, thalamus, and dorsal raphe nuclei, along with motor and cognitive symptoms. RESULTS: One-hundred twenty-four subjects were included in this study. Saccadic accuracy was positively associated with parkinsonian motor severity expressed as Hoehn and Yahr stages, MDS-UPDRS Part III scores, and subscores for bradykinesia and rigidity but not with tremor scores (PFDR < 0.05). Saccadic accuracy correlated with poor performances in the Rey-Complex-Figure copy, and latency with the Digit Symbol Coding and the Montreal Cognitive Assessment scores (PFDR < 0.05). Prolonged saccadic latency correlated with reduced thalamic SUR, whereas decreased saccadic accuracy correlated with reduced SUR in the anterior and posterior putamen (PFDR < 0.05). Reduced smooth pursuit gain showed associations with reduced SUR in the dorsal raphe, a serotonin-predominant region, but did not correlate with parkinsonism severity scores. CONCLUSION: Defective dopaminergic and nondopaminergic neural systems may discretely influence ocular motor function in de novo PD patients. © 2023 International Parkinson and Movement Disorder Society.

Validation of the REM behaviour disorder phenoconversion-related pattern in an independent cohort.

BACKGROUND: A brain glucose metabolism pattern related to phenoconversion in patients with idiopathic/isolated REM sleep behaviour disorder (iRBDconvRP) was recently identified. However, the validation of the iRBDconvRP in an external, independent group of iRBD patients is needed to verify the reproducibility of such pattern, so to increase its importance in clinical and research settings. The aim of this work was to validate the iRBDconvRP in an independent group of iRBD patients. METHODS: Forty iRBD patients (70 ± 5.59 years, 19 females) underwent brain [18F]FDG-PET in Seoul National University. Thirteen patients phenoconverted at follow-up (7 Parkinson disease, 5 Dementia with Lewy bodies, 1 Multiple system atrophy; follow-up time 35 ± 20.56 months) and 27 patients were still free from parkinsonism/dementia after 62 ± 29.49 months from baseline. We applied the previously identified iRBDconvRP to validate its phenoconversion prediction power. RESULTS: The iRBDconvRP significantly discriminated converters from non-converters iRBD patients (p = 0.016; Area under the Curve 0.74, Sensitivity 0.69, Specificity 0.78), and it significantly predicted phenoconversion (Hazard ratio 4.26, C.I.95%: 1.18-15.39). CONCLUSIONS: The iRBDconvRP confirmed its robustness in predicting phenoconversion in an independent group of iRBD patients, suggesting its potential role as a stratification biomarker for disease-modifying trials.

Brain Metabolic Correlates of Dopaminergic Denervation in Prodromal and Early Parkinson's Disease.

BACKGROUND: It remains unclear how brain metabolic activities transform in response to dopamine deficiency in the prodromal and early phases of Parkinson's disease (PD). OBJECTIVE: To investigate the relationship between nigrostriatal dopaminergic denervation and brain glucose metabolism in patients with isolated rapid eye movement sleep behavior disorder (iRBD) and early PD. METHODS: This cohort study included 28 patients with polysomnography-confirmed iRBD, 24 patients with de novo PD with probable rapid eye movement sleep behavior disorder (denovo PD), and 28 healthy controls (HCs) who underwent two positron emission tomography scans with 18 F-fluorodeoxyglucose (all participants) and 18 F-N-3-fluoropropyl-2ß-carboxymethoxy-3ß-(4-iodophenyl)-nortropane (except for one denovo PD patient and 15 HCs). We analyzed striatal and voxel-wise whole-brain glucose metabolism in relation to nigrostriatal dopaminergic integrity and comparatively investigated the whole-brain metabolic connectivity among the groups. We also assessed longitudinal metabolic changes against progressive dopaminergic denervation over 4 years in the iRBD group. RESULTS: From HCs to iRBD and finally to the denovo PD, dopaminergic integrity positively correlated with metabolic activity in the caudate, whereas a negative correlation was observed in the posterior putamen. In the iRBD group, there was a metabolic increase in the inferior orbitofrontal cortex against putaminal dopaminergic denervation at baseline, but negative correlations were newly observed in the superior orbitofrontal cortex and superior frontal gyrus at the 4-year follow-up. The denovo PD group showed negative correlations in the cerebellum and fusiform gyrus. Intra- and inter-regional metabolic connectivities in the parieto-occipital cortices were enhanced in the iRBD group compared with the denovo PD and HC groups. In the iRBD group, overall metabolic connectivity was strengthened along with enhanced basal ganglia-frontal connection by advancing dopaminergic denervation. CONCLUSIONS: Our findings suggest diverse trajectories of metabolic responses associated with dopaminergic denervation between individual brain areas in the prodromal and early PD stages. © 2022 International Parkinson and Movement Disorder Society.

Longitudinal Changes in Isolated Rapid Eye Movement Sleep Behavior Disorder-Related Metabolic Pattern Expression.

BACKGROUND: It remains unclear whether and how the isolated rapid eye movement (REM) sleep behavior disorder (iRBD)-related metabolic pattern (RBDRP) changes with disease progression in iRBD. OBJECTIVE: To examine longitudinal changes in RBDRP expression in iRBD patients and to explore trajectories of relative metabolic activities of individual brain regions constituting RBDRP. METHODS: In this cohort study, 25 iRBD patients (mean age [±standard deviation], 69.2 ± 5.3 years; 12 [48%] patients were men) and 24 age-matched healthy controls were included. The patients underwent at least two 18 F-fluorodeoxyglucose positron emission tomography scans at baseline and at the 2-year and/or 4-year follow-ups. We measured the RBDRP expression of the patients and controls which was validated by reproduction in a separate iRBD cohort (n = 13). RESULTS: At baseline, the RBDRP expression discriminated iRBD patients from healthy controls. However, the RBDRP expression z scores tended to decrease over time in the patients, especially with longer follow-ups, and this tendency was observed even in patients with high-risk of phenoconversion. Furthermore, the degree of RBDRP expression at baseline did not predict the disease conversion. The RBDRP breakdown was mainly provoked by the attenuation of relative hypermetabolism in the frontal cortex including premotor areas and relative hypometabolism in the occipital cortex. The putaminal metabolic activity increased steadily with the disease progression. CONCLUSIONS: The RBDRP expression in iRBD patients was altered significantly over time. Some of the brain metabolic changes seem to represent attempted functional compensation against ongoing neurodegeneration. The RBDRP expression measurement at one time point may not be a reliable biomarker for predicting disease conversion. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cognitive signature of brain FDG PET based on deep learning: domain transfer from Alzheimer's disease to Parkinson's disease.

PURPOSE: Although functional brain imaging has been used for the early and objective assessment of cognitive dysfunction, there is a lack of generalized image-based biomarker which can evaluate individual's cognitive dysfunction in various disorders. To this end, we developed a deep learning-based cognitive signature of FDG brain PET adaptable for Parkinson's disease (PD) as well as Alzheimer's disease (AD). METHODS: A deep learning model for discriminating AD from normal controls (NCs) was built by a training set consisting of 636 FDG PET obtained from Alzheimer's Disease Neuroimaging Initiative database. The model was directly transferred to images of mild cognitive impairment (MCI) patients (n = 666) for identifying who would rapidly convert to AD and another independent cohort consisting of 62 PD patients to differentiate PD patients with dementia. The model accuracy was measured by area under curve (AUC) of receiver operating characteristic (ROC) analysis. The relationship between all images was visualized by two-dimensional projection of the deep learning-based features. The model was also designed to predict cognitive score of the subjects and validated in PD patients. Cognitive dysfunction-related regions were visualized by feature maps of the deep CNN model. RESULTS: AUC of ROC for differentiating AD from NC was 0.94 (95% CI 0.89-0.98). The transfer of the model could differentiate MCI patients who would convert to AD (AUC = 0.82) and PD with dementia (AUC = 0.81). The two-dimensional projection mapping visualized the degree of cognitive dysfunction compared with normal brains regardless of different disease cohorts. Predicted cognitive score, an output of the model, was highly correlated with the mini-mental status exam scores. Individual cognitive dysfunction-related regions included cingulate and high frontoparietal cortices, while they showed individual variability. CONCLUSION: The deep learning-based cognitive function evaluation model could be successfully transferred to multiple disease domains. We suggest that this approach might be extended to an objective cognitive signature that provides quantitative biomarker for cognitive dysfunction across various neurodegenerative disorders.

Macular ganglion-cell-complex layer thinning and optic nerve integrity in drug-naïve Parkinson's disease.

To reveal the macular inner retinal change linked to axonal degeneration in Parkinson's disease (PD), we performed macular optical coherence tomography scan and diffusion tensor imaging of the retrobulbar optic nerve on both eyes of 36 drug-naïve PD patients. Thicknesses of inner retinal layers were automatically measured, and correlation analysis was conducted between the retinal thickness and diffusion parameters of the optic nerve. PD patients showed thinning of the inner retinal layers compared to control data. Thicknesses of the ganglion cell and inner plexiform layers were both correlated positively with fractional anisotropy and negatively with diffusivity indices of ipsilateral optic nerve (FDR-adjusted p < 0.05). This study revealed a novel in vivo connection between macular parafoveal ganglion cell change and integrity in the retrobulbar optic nerve in drug-naïve PD.

Visual Hallucination and Pattern of Brain Degeneration in Parkinson's Disease.

BACKGROUND AND OBJECTIVES: The incidence of visual hallucination (VH) increases with Parkinson's disease (PD) progression, and its development is thought to be related to a specific neurodegenerative process in PD. This study aimed to reveal brain degeneration related to VH in PD by analyzing neuroimaging data obtained from patients in their different stages of PD. METHODS: Data from 48 PD patients - 21 nondemented without VH (PNV group), 10 nondemented with VH (PV group), and 17 demented with VH (PVD group) - and 30 age-matched healthy controls (HC group) were analyzed. Voxel-based morphometry and tract-based spatial statistics were conducted. Previous magnetic resonance volumetric studies on VH in PD were collectively reviewed. RESULTS: The PV group showed gray matter atrophy in the right inferior parietal lobule and supramarginal gyrus compared with the HC and PNV groups. The PVD group showed a wider range of gray matter atrophies in the temporo-parieto-occipital regions than those in the PV group. White matter changes seemed to be an earlier event than gray matter changes. Fractional anisotropy values diffusely decreased in all three PD subgroups compared with the HC group without significant differences between the PD subgroups. Mean diffusivity was not different between the PNV and HC groups but increased in the parieto-temporal region in the PV group and increased diffusely in the PVD group, additionally including the fronto-occipital regions. A review of previous studies supported our observations. CONCLUSIONS: Gray matter degenerations from the parieto-temporal junction to the parieto-occipital and temporo-occipital regions may be responsible for VH on the typical timeline of PD progression.

Lateral geniculate atrophy in Parkinson's with visual hallucination: A trans-synaptic degeneration?

INTRODUCTION: Defective visual information processing contributes to visual hallucination in PD, for which "top-down" and "bottom-up" impairment are suggested mechanisms. This study was aimed to investigate macro- and microstructural neural changes in afferent visual pathways in relation to visual hallucination in nondemented PD patients. METHODS: This study included 24 nondemented, nondepressed PD patients (10 hallucinating and 14 nonhallucinating) and 15 age-matched healthy controls. We analyzed volumetric and diffusion tensor MRI data by applying region of interest analyses on the visual pathways, including the optic chiasm, bilateral optic nerves, lateral geniculate bodies, optic radiations, and primary visual cortex. RESULTS: Patients' demographic characteristics, daily medication doses, as well as duration and motor severity of PD were similar in the two PD groups. Compared to PD patients without hallucination, those with hallucination had fractional anisotropy decrease in the left optic nerve and showed atrophy of lateral geniculate bodies, especially in the left side. In addition, the PD with hallucination group had diffusivity increase in the left optic radiation compared to that in the PD without hallucination and healthy control groups. There were no differences in the primary visual cortex volume among the study groups. CONCLUSIONS: We found microstructural alterations in visual pathways in nondemented PD patients with hallucination, mainly in first-order neurons and atrophy in the lateral geniculate body where the retinal ganglion cells synapse to second-order neurons. Afferent visual pathway degeneration may occur in a trans-synaptic way in PD. Further studies warrant to be conducted.

Association Between Serum Triglycerides and Cerebral Amyloidosis in Cognitively Normal Elderly.

OBJECTIVES: Although many preclinical studies have suggested the possible linkage between dyslipidemia and cerebral amyloid deposition, the association between serum lipid measures and cerebral amyloid-beta (Aß) deposition in human brain is still poorly known. We aimed to investigate the association in cognitively normal (CN) elderly individuals. DESIGN: Cross-sectional study. SETTING: University hospital dementia clinic. PARTICIPANTS: 59 CN elderly. MEASUREMENTS: The study measures included comprehensive clinical and neuropsychological assessment based on the CERAD protocol, magnetic resonance imaging and (11)C-labelled Pittsburgh Compound B positron emission tomography scans, and quantification for serum lipid biomarkers. RESULTS: Multiple linear regression analyses showed that a higher serum triglycerides level was associated with heavier global cerebral Aß deposition even after controlling age, sex, and apolipoprotein E ε4 genotype. Serum apolipoprotein B also showed significant positive association with global cerebral Aß deposition, but the significance disappeared after controlling serum triglycerides level. No association was found between other lipid measures and global cerebral Aß deposition. CONCLUSIONS: The findings suggest that serum triglycerides are closely associated with cerebral amyloidosis, although population-based prospective studies are needed to provide further evidence of the causative effect of triglycerides on cerebral amyloidosis.

Ultrafast generation of fundamental and multiple-order phonon excitations in highly enriched (6,5) single-wall carbon nanotubes.

Using a macroscopic ensemble of highly enriched (6,5) single-wall carbon nanotubes, combined with high signal-to-noise ratio and time-dependent differential transmission spectroscopy, we have generated vibrational modes in an ultrawide spectral range (10-3000 cm(-1)). A total of 14 modes were clearly resolved and identified, including fundamental modes of A, E1, and E2 symmetries and their combinational modes involving two and three phonons. Through comparison with continuous wave Raman spectra as well as calculations based on an extended tight-binding model, we were able to identify all the observed peaks and determine the frequencies of the individual and combined modes. We provide a full summary of phonon frequencies for (6,5) nanotubes that can serve as a basic reference with which to refine our understanding of nanotube phonon spectra as well as a testbed for new theoretical models.

Progression trajectories from prodromal to overt synucleinopathies: a longitudinal, multicentric brain [18F]FDG-PET study.

The phenoconversion trajectory from idiopathic/isolated Rapid eye movement (REM) sleep behavior disorder (iRBD) towards either Parkinson's Disease (PD) or Dementia with Lewy Bodies (DLB) is currently uncertain. We investigated the capability of baseline brain [18F]FDG-PET in differentiating between iRBD patients eventually phenoconverting to PD or DLB, by deriving the denovoPDRBD-related pattern (denovoPDRBD-RP) from 32 de novo PD patients; and the denovoDLBRBD-RP from 30 de novo DLB patients, both with evidence of RBD at diagnosis. To explore [18F]FDG-PET phenoconversion trajectories prediction power, we applied these two patterns on a group of 115 iRBD patients followed longitudinally. At follow-up (25.6 ± 17.2 months), 42 iRBD patients progressed through overt alpha-synucleinopathy (21 iRBD-PD and 21 iRBD-DLB converters), while 73 patients remained stable at the last follow-up visit (43.2 ± 27.6 months). At survival analysis, both patterns were significantly associated with the phenoconversion trajectories. Brain [18F]FDG-PET is a promising biomarker to study progression trajectories in the alpha-synucleinopathy continuum.

Brain olfactory-related atrophy in isolated rapid eye movement sleep behavior disorder.

OBJECTIVE: To investigate structural and functional connectivity changes in brain olfactory-related structures in a longitudinal prospective cohort of isolated REM sleep behavior disorder (iRBD) and their clinical correlations, longitudinal evolution, and predictive values for phenoconversion to overt synucleinopathies, especially Lewy body diseases. METHODS: The cohort included polysomnography-confirmed iRBD patients and controls. Participants underwent baseline assessments including olfactory tests, neuropsychological evaluations, the Movement Disorders Society-Unified Parkinson's Disease Rating Scale, 3T brain MRI, and 18 F-FP-CIT PET scans. Voxel-based morphometry (VBM) was performed to identify regions of atrophy in iRBD, and volumes of relevant olfactory-related regions of interest (ROI) were estimated. Subgroups of patients underwent repeated volumetric MRI and resting-state functional MRI (fMRI) scans after four years. RESULTS: A total of 51 iRBD patients were included, with 20 of them converting to synucleinopathy (mean time to conversion 3.08 years). Baseline VBM analysis revealed atrophy in the right olfactory cortex and gyrus rectus in iRBD. Subsequent ROI comparisons with controls showed atrophy in the amygdala. These olfactory-related atrophies tended to be associated with worse depression, anxiety, and urinary problems in iRBD. Amygdala 18 F-FP-CIT uptake tended to be reduced in iRBD patients with hyposmia (nonsignificant after multiple comparison correction) and correlated with urinary problems. Resting-state fMRI of 23 patients and 32 controls revealed multiple clusters with aberrant olfactory-related functional connectivity. Hypoconnectivity between the putamen and olfactory cortex was associated with mild parkinsonian signs in iRBD. Longitudinal analysis of volumetric volumetric MRI in 22 iRBD patients demonstrated four-year progression of olfactory-related atrophy. Cox regression analysis revealed that this atrophy significantly predicted phenoconversion. INTERPRETATION: Progressive atrophy of central olfactory structures may be a potential indicator of Lewy body disease progression in iRBD.

Longitudinal evolution of cortical thickness signature reflecting Lewy body dementia in isolated REM sleep behavior disorder: a prospective cohort study.

BACKGROUND: The isolated rapid-eye-movement sleep behavior disorder (iRBD) is a prodromal condition of Lewy body disease including Parkinson's disease and dementia with Lewy bodies (DLB). We aim to investigate the longitudinal evolution of DLB-related cortical thickness signature in a prospective iRBD cohort and evaluate the possible predictive value of the cortical signature index in predicting dementia-first phenoconversion in individuals with iRBD. METHODS: We enrolled 22 DLB patients, 44 healthy controls, and 50 video polysomnography-proven iRBD patients. Participants underwent 3-T magnetic resonance imaging (MRI) and clinical/neuropsychological evaluations. We characterized DLB-related whole-brain cortical thickness spatial covariance pattern (DLB-pattern) using scaled subprofile model of principal components analysis that best differentiated DLB patients from age-matched controls. We analyzed clinical and neuropsychological correlates of the DLB-pattern expression scores and the mean values of the whole-brain cortical thickness in DLB and iRBD patients. With repeated MRI data during the follow-up in our prospective iRBD cohort, we investigated the longitudinal evolution of the cortical thickness signature toward Lewy body dementia. Finally, we analyzed the potential predictive value of cortical thickness signature as a biomarker of phenoconversion in iRBD cohort. RESULTS: The DLB-pattern was characterized by thinning of the temporal, orbitofrontal, and insular cortices and relative preservation of the precentral and inferior parietal cortices. The DLB-pattern expression scores correlated with attentional and frontal executive dysfunction (Trail Making Test-A and B: R = - 0.55, P = 0.024 and R = - 0.56, P = 0.036, respectively) as well as visuospatial impairment (Rey-figure copy test: R = - 0.54, P = 0.0047). The longitudinal trajectory of DLB-pattern revealed an increasing pattern above the cut-off in the dementia-first phenoconverters (Pearson's correlation, R = 0.74, P = 6.8 × 10-4) but no significant change in parkinsonism-first phenoconverters (R = 0.0063, P = 0.98). The mean value of the whole-brain cortical thickness predicted phenoconversion in iRBD patients with hazard ratio of 9.33 [1.16-74.12]. The increase in DLB-pattern expression score discriminated dementia-first from parkinsonism-first phenoconversions with 88.2% accuracy. CONCLUSION: Cortical thickness signature can effectively reflect the longitudinal evolution of Lewy body dementia in the iRBD population. Replication studies would further validate the utility of this imaging marker in iRBD.

Metabolic changes of cerebrum by repetitive transcranial magnetic stimulation over lateral cerebellum: a study with FDG PET.

To better understand the functional role of cerebellum within the large-scale cerebellocerebral neural network, we investigated the changes of neuronal activity elicited by cerebellar repetitive transcranial magnetic stimulation (rTMS) using (18)F-fluorodeoxyglucose (FDG) and positron emission tomography (PET). Twelve right-handed healthy volunteers were studied with brain FDG PET under two conditions: active rTMS of 1 Hz frequency over the left lateral cerebellum and sham stimulation. Compared to the sham condition, active rTMS induced decreased glucose metabolism in the stimulated left lateral cerebellum, the areas known to be involved in voluntary motor movement (supplementary motor area and posterior parietal cortex) in the right cerebral hemisphere, and the areas known to be involved in cognition and emotion (orbitofrontal, medial frontal, and anterior cingulate gyri) in the left cerebral hemisphere. Increased metabolism was found in cognition- and language-related brain regions such as the left inferior frontal gyrus including Broca's area, bilateral superior temporal gyri including Wernicke's area, and bilateral middle temporal gyri. Left cerebellar rTMS also led to increased metabolism in the left cerebellar dentate nucleus and pons. These results demonstrate that rTMS over the left lateral cerebellum modulates not only the target region excitability but also excitability of remote, but interconnected, motor-, language-, cognition-, and emotion-related cerebral regions. They provide further evidence that the cerebellum is involved not only in motor-related functions but also in higher cognitive abilities and emotion through the large-scale cerebellocereberal neural network.

Repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex improves probabilistic category learning.

Traditionally, it has been thought that probabilistic category learning, one of the implicit memory functions, is dependent on the basal ganglia. However, there is growing evidence indicating the involvement of the dorsolateral prefrontal cortex (DLPFC) in probabilistic category learning. In order to identify the causal role of DLPFC in probabilistic category learning, we investigated whether repetitive transcranial magnetic stimulation (rTMS) over the left DLPFC influences the learning ability in healthy subjects using the weather prediction task (WPT). Application of 10 Hz rTMS over the left DLPFC induced significant improvement in the total hit rate during the total trials of the WPT, compared with sham stimulation. Specifically, the improvement was significant in the early and late learning blocks of the WPT, but not in the intermediate block of learning. These results indicate that the left DLPFC may play an important role in probabilistic category learning, possibly by influencing not only on embodied information application in late stage of the learning but also on memory encoding for working memory demands in early stage of the learning via frontostriatal and frontohippocampal circuits, respectively. They also may lend support to the possibility that rTMS can improve implicit learning ability in patients with basal ganglia disorders.

Mild behavioral impairment linked to progression to Alzheimer's disease and cortical thinning in amnestic mild cognitive impairment.

Background: Mild behavioral impairment (MBI) is a neurobehavioral syndrome characterized by later life emergence of sustained neuropsychiatric symptoms, as an at-risk state for dementia. However, the associations between MBI and a risk of progression to Alzheimer's disease (AD) and its neuroanatomical correlates in mild cognitive impairment (MCI) are still unclear. Method: A total 1,184 older adults with amnestic MCI was followed for a mean of 3.1 ± 2.0 years. MBI was approximated using a transformation algorithm for the Neuropsychiatric Inventory at baseline. A two-step cluster analysis was used to identify subgroups of individuals with amnestic MCI based on profiles of 5 MBI domain symptoms (decreased motivation, affective dysregulation, impulse dyscontrol, social inappropriateness, abnormal perception/thought content). A Cox regression analysis was applied to investigate differences in the risk of progression to AD between subgroups. A subset of participants (n = 202) underwent 3D T1-weighted MRI scans at baseline and cortical thickness was compared between the subgroups of amnestic MCI patients. Result: The cluster analysis classified the patients into 3 groups: (1) patients without any MBI domain symptoms (47.4%, asymptomatic group); (2) those with only affective dysregulation (29.4%, affective dysregulation group); (3) those with multiple MBI domain symptoms, particularly affective dysregulation, decreased motivation and impulse dyscontrol (23.2%, complex group). Compared to the asymptomatic group, the complex group was associated with a higher risk of progression to AD (hazard ratio = 2.541 [1.904-3.392], p < 0.001), but the affective dysregulation group was not (1.214 [0.883-1.670], p = 0.232). In cortical thickness analysis, the complex group revealed cortical thinning bilaterally in the inferior parietal, lateral occipital, lateral superior temporal, and frontopolar regions compared with the affective dysregulation group. Conclusion: The multiple co-occuring MBI domains in individuals with amnestic MCI are associated with a higher risk of progression to AD and cortical thinning in temporal, parietal and frontal areas. These results suggest that evaluation of MBI could be useful for risk stratification for AD and appropriate intervention in MCI individuals.

Brain Metabolism Related to Mild Cognitive Impairment and Phenoconversion in Patients With Isolated REM Sleep Behavior Disorder.

BACKGROUND AND OBJECTIVES: Mild cognitive impairment (MCI) in isolated REM sleep behavior disorder (iRBD) is a risk factor for subsequent neurodegeneration. We aimed to identify brain metabolism and functional connectivity changes related to MCI in patients with iRBD and the neuroimaging markers' predictive value for phenoconversion. METHODS: This is a prospective cohort study of patients with iRBD with a mean follow-up of 4.2 ± 2.6 years. At baseline, patients with iRBD and age- and sex-matched healthy controls (HCs) underwent 18F-fluorodeoxyglucose (FDG)-PET and resting-state fMRI scans and a comprehensive neuropsychological test battery. Voxel-wise group comparisons for FDG-PET data were performed using a general linear model. Seed-based connectivity maps were computed using brain regions showing significant hypometabolism associated with MCI in patients with iRBD and compared between groups. A Cox regression analysis was applied to investigate the association between brain metabolism and risk of phenoconversion. RESULTS: Forty patients with iRBD, including 21 with MCI (iRBD-MCI) and 19 with normal cognition (iRBD-NC), and 24 HCs were included in the study. The iRBD-MCI group revealed relative hypometabolism in the inferior parietal lobule, lateral and medial occipital, and middle and inferior temporal cortex bilaterally compared with HC and the iRBD-NC group. In seed-based connectivity analyses, the iRBD-MCI group exhibited decreased functional connectivity of the left angular gyrus with the occipital cortex. Of 40 patients with iRBD, 12 patients converted to Parkinson disease (PD) or dementia with Lewy bodies (DLB). Hypometabolism of the occipital pole (hazard ratio [95% CI] 6.652 [1.387-31.987]), medial occipital (4.450 [1.143-17.327]), and precuneus (3.635 [1.009-13.093]) was associated with higher phenoconversion rate to PD/DLB. DISCUSSION: MCI in iRBD is related to functional and metabolic changes in broad brain areas, particularly the occipital and parietal areas. Moreover, hypometabolism in these brain regions was a predictor of phenoconversion to PD or DLB. Evaluation of cognitive function and neuroimaging characteristics could be useful for risk stratification in patients with iRBD.

Relationship of amyloid-ß burden with age-at-onset in Alzheimer disease.

OBJECTIVE: To investigate the relationship between in vivo brain amyloid-beta (Aß) burden, measured by C-labeled Pittsburgh Compound B (C-PiB) retention, and age-at-onset in patients with Alzheimer disease (AD). DESIGN: Cross-sectional study. SETTING: University Dementia Clinic. PARTICIPANTS: Twenty-two AD patients including 11 early-onset AD (EOAD: onset <65 years) and 11 late-onset AD (LOAD: onset ≥65years) cases with matched dementia severity, duration of illness, and apolipoprotein E ε4 allele number. INTERVENTION: C-PiB positron emission tomography scans. MEASUREMENTS: Both region of interest and voxel-based analyses were performed to compare C-PiB retention between EOAD and LOAD groups, and to test linear relationship between age-at-onset and C-PiB retention. RESULTS: Both region of interest (ROI) and voxel-based analyses revealed that EOAD patients had significantly higher C-PIB retentions than LOAD patients in diffuse brain regions including frontal, lateral parietal, lateral temporal, and occipital cortex, and basal ganglia. Subgroup analyses showed that negative correlation between age-at-onset and C-PiB retention was significant in LOAD but not in EOAD. CONCLUSIONS: Our finding of a heavier Aß burden in the brain of living EOAD patients than LOAD patients is in agreement with those from postmortem studies. The inverse relationship between age-at-onset and Aß burden is possibly associated with aging-related decrease of brain or cognitive reserve and with aging-related increase of brain vulnerability.

Probable REM sleep behavior disorder is associated with longitudinal cortical thinning in Parkinson's disease.

REM sleep behavior disorder (RBD) has a poor prognostic implication in both motor and non-motor functions in Parkinson's disease (PD) patients. However, to the best of our knowledge no study to date investigated the longitudinal cerebral changes underlying RBD symptoms in PD. We performed the longitudinal study to investigate the association between probable RBD and cortical and subcortical changes in early, de novo PD patients. We studied 78 participants from the Parkinson's Progression Marker Initiative who underwent structural MRI at baseline and after 2 years. The presence of probable RBD (pRBD) was evaluated using the RBD screening questionnaire. We compared the cross-sectional and longitudinal cortical thickness and subcortical volume changes, between PD patients with and without pRBD. At baseline, we found bilateral inferior temporal cortex thinning in the PD-pRBD group compared with the PD-noRBD group. Longitudinally, the PD-pRBD group revealed a significant increase in the rate of thinning in the left insula compared with the PD-noRBD group, and the increased thinning correlated with decreased cognitive performance. In subcortical volume analyses, the presence of pRBD was linked with volume decrease over time in the left caudate nucleus, pallidum and amygdala. The volume changes in the left caudate nucleus revealed correlations with global cognition. These results support the idea that RBD is an important marker of rapid progression in PD motor and non-motor symptoms and suggest that the atrophy in the left insula and caudate nucleus might be the underlying neurobiological mechanisms of the poorer prognosis in PD patients with RBD.