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Festination and freezing of gait (FOG) are sudden episodic inabilities to initiate or sustain locomotion mostly experienced during the later stages of Parkinson's disease (PD) or other higher-level gait disorders. The aim of this study was to develop a clinical rating instrument for short-interval rating of festination and FOG. Foot movements of 33 patients were video taped and rated during 12 episodes in a standardized course on a four-level interval scale according to severity. Motor blocks were provoked in four situations and by three levels of dual-tasking (tasks). Addition of the item scores produced a FOG score. The assessment requires less than 15 min. The inter-rater and re-test reliability of the FOG score is high (Kendall kappa = 0.85-0.92, P < 0.0001). Variability of the item scale due to situations and tasks can be attributed to unidimensional group factors (Cronbach's alpha 0.84 and 0.94). Group comparisons and a logistic regression model show significant effects for both situations and tasks on the item scale (Friedman test: "situation": P < 0.0001, "task": P < 0.0001). Six patients with PD have significantly different scores during mobile (practical ON; 6.2 +/- 3.9) and immobile (practical OFF; 15.8 +/- 4.6) medication states (P < 0.05). The FOG score correlates with the 10 m number of steps (rho = 0.58; P = 0.001) and with the self-evaluation of FOG (rho = 0.51; P < 0.01). Our results encourage the further use of the FOG score to evaluate festination and FOG.

The optimal stimulation site in subthalamic deep brain stimulation (STN-DBS) was evaluated by correlation of the stereotactic position of the stimulation electrode with the electrophysiologically specified dorsal STN border. In a series of 25 electrodes, best clinical results with least energy consumption were found in contacts located in the dorsolateral border zone, whereas contacts within the subthalamic white matter, e.g., zona incerta, were significantly less effective. We suggest that the dorsolateral STN border should be covered by STN-DBS.

The function of low-frequency oscillations as correlates of physiological tremor in supplementary motor area (SMA) and M1 remains unclear. In epicortical recordings from M1 and SMA and surface electromyographic (EMG) recordings in an epileptic patient we found reproducibly significant coherence between all three recording sites in the 6- to 15-Hz band. The partial coherence between SMA and muscle, however, was not significant. There was a constant phase shift between SMA and M1 indicating synchronized activity. We conclude that the cortical correlates of physiological tremor may be involved in linking different cortical motor centers and might therefore play a role in cortical motor planning.