Fitting Models of Parkinson's Rhythmical Movements Using a Particle Filter
Patients with Parkinson's disease exhibit characteristic abnormalities of rhythmical movements known as "hastening" or "festination" in which frequency is pathologically increased. Rhythmical finger-tapping (MDS-UPDRS item 3.4) is used clinically to quantify these abnormalities. A successful model of the dynamics of Parkinsonian rhythmical movements could serve as the basis for closed loop deep brain stimulation for treatment-refractory symptoms affecting rhythmical activities of daily living such as speech and gait.
We constructed two models of Parkinson's finger-tapping dynamics, one with a single stable limit cycle attractor (single-basin model), and the other with two stable limit cycle attractors, representing normal and festinating movements (double-basin model). In 29 Parkinson's patients and 20 control patients performing finger-tapping we measured motion of the proximal thumb and index finger with angular velocity transducers. We fit the models to the data using a particle filter, assessing goodness of fit by cross-validation. We are interested in comparing goodness-of-fit between the single- and double-basin models in Parkinson's and control subjects, to assess the the filter for detecting transitions between normal and festinating regimes.
Double-basin model: Conditional probability distribution of model parameters as fit by particle filter to patient data. Multidimensional distribution projected onto one- and two-dimensional subspaces.
Cortical Desynchronization and Hasterning/Festination
Reduction (desynchronization) of “idling” EEG and LFP rhythms in the low-beta frequency range is associated with movement initiation; increase in low-beta activity is associated with motor impairment in Parkinson's Disease. Ongoing rhythmical movements in Parkinson's patients may be impaired episodically by “hastening” (“festination”) in which frequency markedy increases, usually in association with reduced amplitude. If incrased low-beta activity anticipated these episodes, it could be used as a biomarker for closed-loop deep brain stimulation aimed at aborting hastening/festination episodes in gait.