Implicit and explicit memory in patients with Parkinson's disease with and without dementia

Objective: To study explicit and implicit memory processes in patients with Parkinson's disease. Design: Case-control design. All subjects were given a neuropsychological test battery, and the test scores were compared among the groups. Setting: Government-funded research facility. All subjects were examined as outpatients. Patients: We tested nondemented (n=13) and demented (n=5) patients with Parkinson's disease and normal controls (n=12) matched for age, gender, and educational level. Main Outcome Measures: Memory for verbal and pictorial stimuli under both explicit and implicit retrieval conditions. Results: Both nondemented and demented patients with Parkinson's disease exhibited impairment on tests of explicit memory. Their impairment could be graded based on the level of effort required by the task: impaired free recall in nondemented patients and impaired free recall, cued recall, and recognition in demented patients. By contrast, neither group showed evidence of impairment on automatic (modality monitoring and word frequency estimation) or implicit (word and picture fragment identification) memory tasks. Correlation analyses did not support any association between the effortful memory deficits and neurologic variables, mood, or performance on executive function tests. Conclusions: Memory deficits in patients with Parkinson's disease primarily involve the conscious, effortful strategic aspects of searching long-term memory.