| Background Parkinson’s disease(PD) is a progressive neurological degenerative disorder. Although the pathophysiology of PD has been extensively investigated, much remains unclear. Pathophysiological mechanisms underlying different motor deficits are different. Based on the predominant motor symptoms, PD can be classified into tremor-dominant(TD) and akinetic/rigid- dominant(ARD) subtypes. It has been recognized that the ventral intermediate nucleus of thalamus(Vim) is involved in the tremor. However, the role of the Vim in these two subtypes has not been investigated. Resting state functional MRI(RS-f MRI)can investigate neural network connectivity between different regions, and has been increasingly used in PD studies. However, previous studies only focused on the traditional low frequency bands, as highfrequency bands were considered as reflecting high-frequency physiological noises. Recently, it has been recognized that neural disorder specific changes could be detected at high-frequency band. However, so far, PD-related neural activity in high-frequency band has not been investigated. Amplitude of low frequency fluctuation(ALFF), which has been widely applied to explore PD-related brain activity, can be used to investigate spontaneous neural activity across different frequency bands.Objective This study applied RS-f MRI : 1) to investigate the involvement of Vim nucleus in the tremor- and akinetic/rigid-related networks. 2) to investigate spontaneous neural activity across the low- and high-frequency bands in PD patients.Methods 1. This study included 84 PD patients(42 TD and 42 ARD patients) and 42 normal control subjects. All subjects were scanned by a 3T MR scanner. One-sample t test was applied to investigate functional connectivity within each group. A one-way analysis of covariance(ANCOVA) was performed to examine differences of connectivity in the Vim among the three groups, with age and gender taken as covariant factors. A subsequent post hoc analysis was applied to explore the differences between the groups. A correlation analysis of functional connectivity results against the tremor scores in the TD group, or against the akinetic-rigidity scores in the ARD group was performed to explore whether the interactions of brain networks correlate with the severity of clinical symptoms. 2.The ALFF method was used to examine local brain activity in 39 patients and 37 normal controls in full frequency bands [slow-6(0-0.01Hz), slow-5(0.01–0.027 Hz), slow-4(0.027–0.073 Hz), slow-3(0.073–0.198 Hz), and slow-2(0.198–0.25 Hz)]. A repeated-measures analysis of variance and Post hoc t-tests were performed to detect differences of spontaneous activity between two groups in different frequency bands. A correlation analysis was examined between Unified Parkinson’s Disease Rating Scale(UPDRS) motor score and ALFF in patients with PD in each frequency band to discover the relationship between disease severity and spontaneous neural activity.Results 1. In the TD patients, the Vim nucleus exhibited increased connectivity with the cerebellum/dentate nucleus, primary motor cortex(M1), supplementary motor area(SMA), premotor cortex, thalamus, globus pallidus, putamen and parietal cortex compared to the controls; while the connections between the Vim nucleus and M1 and cerebellum/dentate nucleus had positive correlations with the tremor scores. In the ARD patients, the Vim nucleus only showed enhanced connectivity with the globus pallidus and limbic lobe compared to the controls, and no connectivity showed correlation against the akinetic-rigidity scores. TD patients had increased connectivity with the Vim nucleus in the cerebellum, M1, SMA, thalamus, globus pallidus, putamen and parietal cortex compared to ARD patients. 2. Compared with contols, PD patients had decreased ALFF in the putamen in the slow-3, slow-4 and slow-5, and had decreased ALFF in the left precentral gyrus and right SMA in all frequency bands except for the slow-5. Increased ALFF in the cerebellum was found in all frequency bands. The ALFF increased in the regions within the default mode network mainly in the slow-3 and slow-4.Conclusion This study demonstrates that 1) the Vim nucleus has an important role in the tremor-related network, but not in the akinetic/rigid-related network. This finding is helpful to explain the selective effect of Vim deep brain stimulation in PD. 2) The abnormal activity in the striatum is significant in the slow-3, slow-4 and slow-5. Most frequency bands except the slow-5 are helpful in detecting neural changes in cortical motor areas. The increased activity in the cerebellum is the common findings in all frequency bands. Multiple frequency analysis may provide insight into the pathophysiological mechanisms of PD. |
PDF Full Text Request