Motor Preparation Rather Than Decision-Making Differentiates Parkinson’s Disease Patients With And Without Freezing of Gait

Objective: Freezing of gait (FOG) is a brief, episodic phenomenon affecting over half of people with Parkinson’s disease (PD) and leads to significant morbidity. The pathophysiology of FOG remains poorly understood but is associated with deficits in cognitive function and motor preparation. Method: We studied 20 people with PD (10 with FOG, 10 without FOG) and performed a timed response target detection task while electroencephalographic data were acquired. We analysed the data to detect and examine cortical markers of cognitive decision making (P3b or centroparietal positivity, CPP) and motor readiness potential. We analysed current source density (CSD) to increase spatial resolution and allow identification of distinct signals. Results: There was no difference in the P3b/CPP response between people with PD with and without FOG, suggesting equivalent cognitive processing with respect to decision-making. However, the FOG group had significant difference with an earlier onset and larger amplitude of the lateralized readiness potential. Furthermore, the amplitude of the lateralised readiness potential correlated strongly with total Frontal Assessment Battery score. Conclusions: The difference in lateralized readiness potentials may reflect excessive recruitment of lateral premotor areas to compensate for dysfunction of the supplementary motor area and resultant loss of automatic motor control. This early, excessive recruitment of frontal networks occurs in spite of equivalent motor scores and reaction times between groups. Significance: The saturation of frontal processing mechanisms could help explain deficits in attentional set-shifting, dual-tasking and response inhibition which are frequently reported in FOG

Programming parameters of subthalamic deep brain stimulators in Parkinson's disease from a controlled trial

Background: Programming algorithms have never been tested for outcome. The EARLYSTIM study showed superior outcomes of deep brain stimulation of the subthalamic nucleus (STN-DBS) over best medical treatment in early Parkinson's disease (PD). Patients were programmed according to common guidelines but customized for each patient. Methods: Stimulation parameters were systematically documented at 1, 5, 12, and 24 month in the cohort of 114 patients who had bilateral STN-DBS at 24 month. We investigated the influence of atypical programming, changes of stimulated electrode contacts and stimulation energy delivered. Outcomes were the Unified Parkinson's Disease Rating Scale (UPDRS) motor and ADL-subscores, health-related quality of life (PDQ-39) summary index and mobility- and ADL-subscores. Results: At 1/5/12/24 months follow up, mean amplitude (1.8/2.5/2.6/2.8 V), impedance (1107/1286/1229/1189 Omega) and TEED (33.7/69.0/84.4/93.0 V2*mu s*Hz/Omega) mainly increased in the first 5 months, while mean pulse width (60.0/62.5/65.1/65.8 mu s), frequency (130/137.7/139.1/142.7 Hz) remained relatively stable. Typical programming (single monopolar electrode contact) was used in 80.7% of electrodes. Double monopolar (11/114) and bipolar (2/114) stimulation was only rarely required. There was no significant difference in clinical outcomes between the patient groups requiring contact changes (n = 32/28.1%) nor between (n = 83/72.8%) versus non-typical programming. Energy used for STN-DBS was higher for the dominant side of PD. Conclusion: In the first 5 months an increase in amplitude is required to compensate for various factors. Monopolar stimulation is sufficient in 80% of patients at 24 months. Homogeneous stimulation strategies can account for the favorable outcomes reported in the Earlystim study