Does implicit learning in non-demented Parkinson's disease depend on the level of cognitive functioning?

We investigated the influence of the level of cognitive functioning on sequence-specific learning in Parkinson's disease (PD). This was done by examining the relationship between the scales for outcomes in Parkinson's disease-cognition [SCOPA-COG, Marinus, J., Visser, M., Verwey, N. A., Verhey, F. R. J., Middelkoop, H. A. M.,Stiggelbout, A., et al. (2003). Assessment of cognition in Parkinson's disease. Neurology, 61, 1222-1228] and the serial reaction time (SRT) task [Nissen, M. J., & Bullemer, P. T. (1987). Attentional requirements for learning: Evidence from performance measures. Cognitive Psychology, 19, 1-32] in a homogeneous sample, consisting of 25 PD patients diagnosed in Stage 3 of the Hoehn and Yahr [Hoehn, M. M., & Yahr, M. D. (1967). Parkinsonism: onset, progression, and mortality. Neurology, 17, 427-442] scale. Six patients in the low scoring cognitive group, 11 patients in the average scoring and eight patients in the high scoring group, conducted a SRT task with a deterministic sequence. Sequence-specific learning was assessed by inserting a random block to determine whether the acquisition of sequence movements differed between groups. Our results indicate an association between cognitive functioning in PD patients and sequence learning. These findings emphasize the use of assessing cognition in addition to the well-known motor aspects in PD.