Quiet connections: Reduced fronto‐temporal connectivity in nondemented Parkinson's Disease during working memory encoding

Abstract

Parkinson’s Disease (PD) is a common neurodegenerative disorder characterized primarily by motor symptoms such as bradykinesia, muscle rigidity, and resting tremor. It is now broadly accepted that these motor symptoms frequently co-occur with cognitive impairments, with deficits in working memory and attention being among the most common cognitive sequalae associated with PD. While these cognitive impairments are now recognized, the underlying neural dynamics and precise regions involved remain largely unknown. To this end, we examined the oscillatory dynamics and interregional functional connectivity that serve working memory processing in a group of un-medicated adults with PD and a matched group without PD. Each participant completed a high-load, Sternberg-type working memory task during magnetoencephalography (MEG), and we focused on the encoding and maintenance phases. All data were transformed into the time-frequency domain and significant oscillatory activity was imaged using a beamforming approach. Phase-coherence (connectivity) was also computed among the brain sub-regions exhibiting the strongest responses. Our most important findings were that un-medicated patients with PD had significantly diminished working memory performance (i.e., accuracy), and reduced functional connectivity between left inferior frontal cortices and left supramarginal–superior temporal cortices compared to participants without PD during the encoding phase of working memory processing. We conclude that patients with PD have reduced neural interactions between left prefrontal executive circuits and temporary verbal storage centers in the left supramarginal/superior temporal cortices during the stimulus encoding phase, which may underlie their diminished working memory function.

A systematic review of MEG‐based studies in Parkinson's disease: The motor system and beyond

“…Additional connectivity measures that have been used in source‐space analysis to demonstrate cross‐sectional differences between PD patients and controls include the phase locking value (PLV (Lachaux et al, ); comparable to PLI but sensitive to volume conduction/field spread) and directed Phase Transfer Entropy (dPTE; (Lobier, Siebenhuhner, Palva, & Palva, )), a measure of directed connectivity. The PLV study demonstrated that during a working memory task, PD patients had significantly lower alpha band (9–16 Hz) PLV within the left‐hemispheric fronto‐temporal circuitry compared to controls, which correlated negatively with verbal working memory performance (Wiesman et al, ). The dPTE has been used to reveal lower beta band directed connectivity from posterior cortical brain regions toward frontal and subcortical brain regions in PD versus controls.…”

Spatiotemporal oscillatory dynamics of visual selective attention during a flanker task

“…Based on these analyses, the time-frequency windows containing significant oscillatory events across all participants and conditions were selected for imaging. Note that a similar approach has been used in several recent papers (Heinrichs-Graham and Wilson, 2015, 2016; Wiesman et al, 2016, 2017). …”

Attention training improves aberrant neural dynamics during working memory processing in veterans with PTSD

“…The MEG preprocessing and imaging analysis pipeline was closely based on the methods reported in our recent WM papers (Heinrichs-Graham & Wilson, 2015; McDermott et al, 2015; Proskovec, Heinrichs-Graham, & Wilson, 2016; Wiesman et al, 2016). The continuous magnetic time series was divided into epochs of 6,900 ms duration, with 0 ms being the onset of the encoding grid and the baseline being the −400–0 ms time bin (see Fig.…”