Enhanced functional connectivity between putamen and supplementary motor area in Parkinson's disease patients

Psychomotor symptoms of schizophrenia map on the cerebral motor circuit

Schizophrenia is a devastating disorder thought to result mainly from cerebral pathology. Neuroimaging studies have provided a wealth of findings of brain dysfunction in schizophrenia. However, we are still far from understanding how particular symptoms can result from aberrant brain function. In this context, the high prevalence of motor symptoms in schizophrenia such as catatonia, neurological soft signs, parkinsonism, and abnormal involuntary movements is of particular interest. Here, the neuroimaging correlates of these motor symptoms are reviewed. For all investigated motor symptoms, neural correlates were found within the cerebral motor system. However, only a limited set of results exists for hypokinesia and neurological soft signs, while catatonia, abnormal involuntary movements and parkinsonian signs still remain understudied with neuroimaging methods. Soft signs have been associated with altered brain structure and function in cortical premotor and motor areas as well as cerebellum and thalamus. Hypokinesia is suggested to result from insufficient interaction of thalamocortical loops within the motor system. Future studies are needed to address the neural correlates of motor abnormalities in prodromal states, changes during the course of the illness, and the specific pathophysiology of catatonia, dyskinesia and parkinsonism in schizophrenia.

Role of local and distant functional connectivity density in the development of minimal hepatic encephalopathy

The progression of functional connectivity (FC) patterns from non-hepatic encephalopathy (non-HE) to minimal HE (MHE) is not well known. This resting-state functional magnetic resonance imaging (rs-fMRI) study investigated the evolution of intrinsic FC patterns from non-HE to MHE. A total of 103 cirrhotic patients (MHE, n = 34 and non-HE, n = 69) and 103 healthy controls underwent rs-fMRI scanning. Maps of distant and local FC density (dFCD and lFCD, respectively) were compared among MHE, non-HE, and healthy control groups. Decreased lFCD in anterior cingulate cortex, pre- and postcentral gyri, cuneus, lingual gyrus, and putamen was observed in both MHE and non-HE patients relative to controls. There was no difference in lFCD between MHE and non-HE groups. The latter showed decreased dFCD in inferior parietal lobule, cuneus, and medial frontal cortex relative to controls; however, MHE patients showed decreased dFCD in frontal and parietal cortices as well as increased dFCD in thalamus and caudate head relative to control and non-HE groups. Abnormal FCD values in some regions correlated with MHE patients’ neuropsychological performance. In conclusion, lFCD and dFCD were perturbed in MHE. Impaired dFCD in regions within the cortico-striato-thalamic circuit may be more closely associated with the development of MHE.

A Window into the Brain: Advances in Psychiatric fMRI

Functional magnetic resonance imaging (fMRI) plays a key role in modern psychiatric research. It provides a means to assay differences in brain systems that underlie psychiatric illness, treatment response, and properties of brain structure and function that convey risk factor for mental diseases. Here we review recent advances in fMRI methods in general use and progress made in understanding the neural basis of mental illness. Drawing on concepts and findings from psychiatric fMRI, we propose that mental illness may not be associated with abnormalities in specific local regions but rather corresponds to variation in the overall organization of functional communication throughout the brain network. Future research may need to integrate neuroimaging information drawn from different analysis methods and delineate spatial and temporal patterns of brain responses that are specific to certain types of psychiatric disorders.

Resting-state functional brain networks in Parkinson's disease

The network approach is increasingly being applied to the investigation of normal brain function and its impairment. In the present review, we introduce the main methodological approaches employed for the analysis of resting‐state neuroimaging data in Parkinson's disease studies. We then summarize the results of recent studies that used a functional network perspective to evaluate the changes underlying different manifestations of Parkinson's disease, with an emphasis on its cognitive symptoms. Despite the variability reported by many studies, these methods show promise as tools for shedding light on the pathophysiological substrates of different aspects of Parkinson's disease, as well as for differential diagnosis, treatment monitoring and establishment of imaging biomarkers for more severe clinical outcomes.

Increased connectivity between sensorimotor and attentional areas in Parkinson's disease

INTRODUCTION

Our study is using Independent Component Analysis (ICA) to evaluate functional connectivity changes in Parkinson's disease (PD) in an unbiased manner.

METHODS

Resting-state functional magnetic resonance imaging (rs-fMRI) data was collected for 27 PD patients and 16 healthy subjects. Differences for intra- and inter-network connectivity between healthy subjects and patients were investigated using FMRIB Software Library (FSL) tools (Melodic ICA, dual regression, FSLNets).

RESULTS

Twenty-three ICA maps were identified as components of neuronal origin. For intra-network connectivity changes, eight components showed a significant connectivity increase in patients (p < 0.05); these were correlated with clinical scores and were largest for (sensori)motor networks. For inter-network connectivity changes, we found higher connectivity between the sensorimotor network and the spatial attention network (p = 0.0098) and lower connectivity between anterior and posterior default mode networks (DMN) (p =  0.024), anterior DMN and visual recognition networks (p = 0.026), as well as between visual attention and main dorsal attention networks (p = 0.03), for patients as compared to healthy subjects. The area under the Receiver Operating Characteristics (ROC) curve for the best predictor (partial correlation between sensorimotor and spatial attention networks) was 0.772. These functional alterations were not associated with any gray or white matter structural changes.

CONCLUSION

Our results show higher connectivity between sensorimotor and spatial attention areas in patients that may be related to the reduced movement automaticity in PD.

Putamen-midbrain functional connectivity is related to striatal dopamine transporter availability in patients with Lewy body diseases

Prior work has shown that functional connectivity between the midbrain and putamen is altered in patients with impairments in the dopamine system. This study examines whether individual differences in midbrain-striatal connectivity are proportional to the integrity of the dopamine system in patients with nigrostriatal dopamine loss (Parkinson's disease and dementia with Lewy bodies). We assessed functional connectivity of the putamen during resting state fMRI and dopamine transporter (DAT) availability in the striatum using 11C-Altropane PET in twenty patients. In line with the hypothesis that functional connectivity between the midbrain and the putamen reflects the integrity of the dopaminergic neurotransmitter system, putamen-midbrain functional connectivity was significantly correlated with striatal DAT availability even after stringent control for effects of head motion. DAT availability did not relate to functional connectivity between the caudate and thalamus/prefrontal areas. As such, resting state functional connectivity in the midbrain-striatal pathway may provide a useful indicator of underlying pathology in patients with nigrostriatal dopamine loss.

Discriminative analysis of Parkinson's disease based on whole-brain functional connectivity

Recently, there has been an increasing emphasis on applications of pattern recognition and neuroimaging techniques in the effective and accurate diagnosis of psychiatric or neurological disorders. In the present study, we investigated the whole-brain resting-state functional connectivity patterns of Parkinson's disease (PD), which are expected to provide additional information for the clinical diagnosis and treatment of this disease. First, we computed the functional connectivity between each pair of 116 regions of interest derived from a prior atlas. The most discriminative features based on Kendall tau correlation coefficient were then selected. A support vector machine classifier was employed to classify 21 PD patients with 26 demographically matched healthy controls. This method achieved a classification accuracy of 93.62% using leave-one-out cross-validation, with a sensitivity of 90.47% and a specificity of 96.15%. The majority of the most discriminative functional connections were located within or across the default mode, cingulo-opercular and frontal-parietal networks and the cerebellum. These disease-related resting-state network alterations might play important roles in the pathophysiology of this disease. Our results suggest that analyses of whole-brain resting-state functional connectivity patterns have the potential to improve the clinical diagnosis and treatment evaluation of PD.

Speech hastening during electrical stimulation of left premotor cortex

Cortical and axonal electrical stimulation of left premotor cortex and SMA during awake brain surgery yielded unique behavioral responses. In two patients, there was involuntary acceleration of speech (i.e., speech hastening) during a counting or picture naming task. In one patient, stimulation led to a deceleration of the rate with which three different tasks were performed (arm movements, finger tapping and counting). Possible explanatory mechanisms are discussed, and the literature on so-called "negative motor areas" is shortly reviewed. It is argued that the function of loops between cortex and basal ganglia were modulated via stimulation of frontostriatal and/or fronto-opercular pathways.

Reduced topological efficiency in cortical-basal Ganglia motor network of Parkinson's disease: a resting state fMRI study

Parkinson's disease (PD) is mainly characterized by dopamine depletion of the cortico-basal ganglia (CBG) motor circuit. Given that dopamine dysfunction could affect functional brain network efficiency, the present study utilized resting-state fMRI (rs-fMRI) and graph theoretical approach to investigate the topological efficiency changes of the CBG motor network in patients with PD during a relatively hypodopaminergic state (12 hours after a last dose of dopamimetic treatment). We found that PD compared with controls had remarkable decreased efficiency in the CBG motor network, with the most pronounced changes observed in rostral supplementary motor area (pre-SMA), caudal SMA (SMA-proper), primary motor cortex (M1), primary somatosensory cortex (S1), thalamus (THA), globus pallidus (GP), and putamen (PUT). Furthermore, reduced efficiency in pre-SMA, M1, THA and GP was significantly correlated with Unified Parkinson's Disease Rating Scale (UPDRS) motor scores in PD patients. Together, our results demonstrate that individuals with PD appear to be less effective at information transfer within the CBG motor pathway, which provides a novel perspective on neurobiological explanation for the motor symptoms in patients. These findings are in line with the pathophysiology of PD, suggesting that network efficiency metrics may be used to identify and track the pathology of PD.

Nicotinic acetylcholine receptor density in cognitively intact subjects at an early stage of Parkinson's disease

We investigated in vivo brain nicotinic acetylcholine receptor (nAChR) distribution in cognitively intact subjects with Parkinson’s disease (PD) at an early stage of the disease. Fourteen patients and 13 healthy subjects were imaged with single photon emission computed tomography and the radiotracer 5-[¹²³I]iodo-3-[2(S)-2-azetidinylmethoxy]pyridine ([¹²³I]5IA). Patients were selected according to several criteria, including short duration of motor signs (<7 years) and normal scores at an extensive neuropsychological evaluation. In PD patients, nAChR density was significantly higher in the putamen, the insular cortex and the supplementary motor area and lower in the caudate nucleus, the orbitofrontal cortex, and the middle temporal gyrus. Disease duration positively correlated with nAChR density in the putamen ipsilateral (ρ = 0.56, p < 0.05) but not contralateral (ρ = 0.49, p = 0.07) to the clinically most affected hemibody. We observed, for the first time in vivo, higher nAChR density in brain regions of the motor and limbic basal ganglia circuits of subjects with PD. Our findings support the notion of an up-regulated cholinergic activity at the striatal and possibly cortical level in cognitively intact PD patients at an early stage of disease.

Cortico-striatal-thalamic network functional connectivity in hemiparkinsonism

Cortico-striatal-thalamic network functional connectivity (FC) and its relationship with levodopa (L-dopa) were investigated in 69 patients with hemiparkinsonism (25 drug-naïve [n-PD] and 44 under stable/optimized dopaminergic treatment [t-PD]) and 27 controls. Relative to controls, n-PD patients showed an increased FC between the left and the right basal ganglia, and a decreased connectivity of the affected caudate nucleus and thalamus with the ipsilateral frontal and insular cortices. Compared with both controls and n-PD patients, t-PD patients showed a decreased FC among the striatal and thalamic regions, and an increased FC between the striatum and temporal cortex, and between the thalamus and several sensorimotor, parietal, temporal, and occipital regions. In both n-PD and t-PD, patients with more severe motor disability had an increased striatal and/or thalamic FC with temporal, parietal, occipital, and cerebellar regions. Cortico-striatal-thalamic functional abnormalities occur in patients with hemiparkinsonism, antecede the onset of the motor symptoms on the opposite body side and are modulated by L-dopa. In patients with hemiparkinsonism, L-dopa is likely to facilitate a compensation of functional abnormalities possibly through an increased thalamic FC.

Functional neuroimaging of motor control in Parkinson's disease: a meta-analysis

Functional neuroimaging has been widely used to study the activation patterns of the motor network in patients with Parkinson's disease (PD), but these studies have yielded conflicting results. This meta-analysis of previous neuroimaging studies was performed to identify patterns of abnormal movement-related activation in PD that were consistent across studies. We applied activation likelihood estimation (ALE) of functional neuroimaging studies probing motor function in patients with PD. The meta-analysis encompassed data from 283 patients with PD reported in 24 functional neuroimaging studies and yielded consistent alterations in neural activity in patients with PD. Differences in cortical activation between PD patients and healthy controls converged in a left-lateralized fronto-parietal network comprising the presupplementary motor area, primary motor cortex, inferior parietal cortex, and superior parietal lobule. Both, increases as well as decreases in motor cortical activity, which were related to differences in movement timing and selection in the applied motor tasks, were reported in these cortical areas. In the basal ganglia, PD patients expressed a decrease of motor activation in the posterior motor putamen, which improved with dopaminergic medication. The likelihood of detecting a decrease in putaminal activity increased with motor impairment. This reduced motor activation of the posterior putamen across previous neuroimaging studies indicates that nigrostriatal dopaminergic denervation affects neural processing in the denervated striatal motor territory. In contrast, fronto-parietal motor areas display both increases as well as decreases in movement related activation. This points to a more complex relationship between altered cortical physiology and nigrostriatal dopaminergic denervation in PD.