Abstract
Parkinson's disease (PD) related dementia (PDD) develops in up to 80% of PD patients. The present study was performed to further unravel the underlying pathophysiological mechanisms by applying a new analysis approach that uses an atlas-based MEG beamformer to provide a detailed anatomical mapping of cortical rhythms and functional interactions. Importantly, we used the phase lag index (PLI) as a measure of functional connectivity to avoid any biases due to effects of volume conduction.MEG recordings were obtained in 13 PDD and 13 non-demented PD patients. Beamforming was used to estimate spectral power and PLI in delta, theta, alpha, beta and gamma frequency bands. Compared to PD patients, PDD patients had more delta and theta power in parieto-occipital and fronto-parietal areas, respectively. The PDD patients had less alpha and beta power in parieto-temporo-occipital and frontal areas, respectively. Compared to PD patients, PDD patients had lower mean PLI values in the delta and alpha bands in fronto-temporal and parieto-temporo-occipital areas, respectively. In addition, in PDD patients connectivity between pairs of regions of interest (Brodmann areas) was stronger in the theta band and weaker in the delta, alpha and beta bands.The added value of the present results over previous studies analysing frequency-specific changes in neuronal activity in PD patients, is the anatomical framework in which we demonstrated a slowing in neuronal activity and a reduction in functional connectivity in PD related dementia. Moreover, this study shows a widespread reduction in functional connectivity between different regions in PDD.
Highlights
Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with both motor and a variety of non-motor symptoms including cognitive dysfunction and dementia
Connectivity was stronger for some and weaker for other pairs of ROIs in the Parkinson's disease related dementia (PDD) group. This is the first study to use MEG recordings projected to an atlas-based source space to provide a 3D anatomical view of differences in oscillatory power and functional connectivity between PD and PDD patients
Our main findings are: i) stronger activation in PDD compared to PD in the delta and theta bands, in respectively the parieto-occipital and fronto-parietal areas; ii) in the alpha and beta bands, less power was found in PDD patients compared to PD in respectively the occipito-parieto-temporal and frontal areas; iii) functional connectivity was weaker in the delta and alpha bands in respectively the fronto-temporal and occipito-parieto-temporal areas; iv) a more detailed analysis revealed that functional connectivity between pairs of ROIs was generally weaker in PDD patients compared to PD patients in the delta, alpha and to a lesser extent beta bands, whereas functional connectivity between pairs of ROIs was stronger in the theta band
Summary
Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with both motor and a variety of non-motor symptoms including cognitive dysfunction and dementia. Parkinson's disease related dementia (PDD) develops in up to 80% of PD patients (Aarsland and Kurz, 2010; Reid et al, 2011) and is characterized by executive dysfunction and memory deficits, often in combination with. The involvement of multiple projection systems is supported by the neuropathological findings by Braak et al (2003), indicating that PD specific brain pathology extends beyond the nigrostriatal dopaminergic system. Several MEG and EEG studies have demonstrated a slowing of background oscillatory activity in PDD patients (Bosboom et al, 2006; Kotini et al, 2005; Neufeld et al, 1988, 1994; Soikkeli et al, 1991; Stoffers et al, 2007; Tanaka et al, 2000), and a recent study
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