Sequential motor learning in parkinsonian patients with freezing of gait

Objective: To evaluate explicit motor sequence learning task in parkinsonian patients with (PD/F1) and without (PD/F-) FOG and in aged-matched normal controls (NC). Background: Freezing of gait (FOG) is a common and disabling gait disorder in patients with advanced Parkinson’s disease (PD). Poor responsiveness to dopaminergic treatment as well as trigger sensitivity suggests that the pathophysiology of this phenomenon is complex and possibly reflects a more general motor control deficit. Indeed, FOG has been recently associated to cognitive decline (executive functions impairment) even in the early stages of the disease. Methods: 6 subjects for each group were recruited and executed planar reaching movements of the right dominant hand on a digitizing tablet. The tasks were: 1. CCW, a timed-response task where targets appeared in a predictable counterclockwise order; 2. RAN, a reaction time task where targets were random and unpredictable; SEQ, a sequence (5 blocks of 80 elements) that the subjects had to learn while reaching for targets. A verbal or declarative score (from 0, unable to repeat the sequence, to 8 complete knowledge of sequence) was computed. Motor learning performance was correlated with neuropsychological evaluation. Results: Reaction times during SEQ task were significantly longer in PD/F1. The verbal score was significantly lower in PD/F1 who presented less anticipatory movements. Motor learning impairment was correlated to executive dysfunction. Conclusions: PD patients with FOG showed greater difficulties in explicit sequence learning. This observation supports the hypothesis that FOG is associated with frontal lobe cognitive dysfunction. It might be postulated that the occurrence of FOG in PD could is the result of primary perceptual/cognitive impairment rather than a pure motor disturbance.