Review article
Implicit learning in Parkinson’s disease

Parkinson’s disease is the second most common neurodegenerative disease in the population, which mainly affects older people. The disease is a result of loss of dopaminergic input to the striatum due to a reduction in dopamine neurons in the substantia nigra compacta. The core symptoms of the disease include motor symptoms, especially resting tremor, rigidity and bradykinesia as well as vegetative, cognitive and emotional symptoms. One of the cognitive dysfunctions in Parkinson’s disease is impairment in implicit learning involving the acquisition of complex knowledge in an involuntary manner, without control of the process. The results of implicit learning are difficult or impossible to verbalize but can be observed in progressive, gradual improvement across many trials in performance on implicit learning tasks. The medial temporal lobe and the hippocampus although critical for many kinds of learning probably are not necessary for implicit learning. Amnestic patients exhibit impaired explicit (fact-and-event) learning and memory but various forms of implicit learning and memory remain intact. The review of research on implicit learning in Parkinson’s disease presented in the article shows performance deficits of the tasks with motor component, while performance of most of the implicit non-motor tasks is not disrupted in patients with PD. Implicit motor learning impairment in patients with Parkinson’s disease is a subject worthy of exploration and inclusion in clinical practice because it can significantly affect the daily functioning of patients, impede rehabilitation and reduce their quality of life.