Abstract Rule Learning In Human Adults And Parkinson's Disease Patients:A Motor Sequence Learning Study

Abstract rule learning,the ability to extract the abstract rule from the existing sensory sequences to predict the forthcoming stimulus and to generalize to the new instances,has been demonstrated to play an important role in human cognition,especially in the language acquisition.Clinical studies have found that majority of the Parkinson's patients suffer from language problem including spontaneous speech,verbal fluency and verb generation,besides the motor symptoms.However the etiology of the language impairment in PD still remains unclear.Studies using Huntington's disease patients have suggested the role of basal ganglia,and more specifically striatum,in rule application.Further studies need to be carried out to identify the correlation between the deficit in the motor sequence learning and language impairment.However,previous studies only investigated the ability of PD patients on fixed sequence pattern learning,but not the abstract rule acquisition which is more related to language acquisition.Our current project focused on studying the performance of abstract structure learning in motor sequence on PD patients and control adults by designing a novel behavioral paradigm.We found that normal subjects could acquire repetitive and symmetrical rules after a short period practice,but they were unable to acquire substitutional rule after practicing for dozens of times.We further tested the effect of the sequence length on the learning effect,judging by the reaction time.We found that the average reaction time was decreased as the sequence length increased when the subjects were presented with sequences contained repetitive rules.Interestingly,the reaction time was increased with the increment of the sequence length when the sequence contained symmetrical rules.Our studies on PD patients have shown that PD patients could acquire repetitive and symmetrical rules,but it took longer time to learn symmetrical rules as compared with that of repetitive rules.Similar as what we found with normal subjects,the learning effects were more significant with the longer sequences.Moreover,the correct rate of the control group was significantly higher than that of the PD group,and the overall reaction time was significantly lower than that of the PD group.Under most of the conditions,the learning effect of the control group was better than that of the PD group,although not reaching statistically significant.Our study also found a significant correlation between the sequence learning ability of PD patients and their Mini-mental state examination(MMSE)score.Subjects who had lower MMSE score performed poorly in the abstract rule learning task.Our preliminary studies may provide additional evidence that the basal ganglia plays an important role in abstract structure learning.The deficit in abstract rule learning may have correlation with the language problem in PD patients.Our novel abstract rule learning paradigm may have the potential to be used in screening cognitive deficits in PD in the future.