Effects of Parkinson's disease and dopamine on digit span measures of working memory.

RATIONALE: Parkinson's disease (PD) impairs working memory (WM)-the ability to maintain items in memory for short periods of time and manipulate them. There is conflicting evidence on the nature of the deficits caused by the disease, and the potential beneficial and detrimental effects of dopaminergic medication on different WM processes. OBJECTIVES: We hypothesised that PD impairs both maintenance and manipulation of items in WM and dopaminergic medications improve this in PD patients but impair it in healthy older adults. METHODS: We tested 68 PD patients ON and OFF their dopaminergic medication, 83 healthy age-matched controls, and 30 healthy older adults after placebo and levodopa administration. We used the digit span, a WM test with three components (forwards, backwards, and sequence recall) that differ in the amount of manipulation required. We analysed the maximum spans and the percentage of lists correctly recalled, which probe capacity of WM and the accuracy of the memory processes within this capacity, respectively. RESULTS: PD patients had lower WM capacity across all three digit span components, but only showed reduced percentage accuracy on the components requiring manipulation (backwards and sequence spans). Dopaminergic medication did not affect performance in PD patients. In healthy older adults, levodopa did not affect capacity, but did impair accuracy on one of the manipulation components (sequence), without affecting the other (backwards). CONCLUSIONS: This suggests that the deficit of maintenance capacity and manipulation accuracy in PD patients is not primarily a dopaminergic one and supports a potential "overdosing" of intact manipulation mechanisms in healthy older adults by levodopa.

Subjective Memory Complaints: Symptoms and Outcome in Different Research Settings.

Subjective memory complaints (SMC) are important and may, in certain individuals, herald the onset of neurodegenerative diseases such Alzheimer's disease. However, they are very common and in some individuals will result from mood disorders/personality factors or systemic illnesses. Research has been hampered by the wide variety of criteria and neuropsychological tests used to define this disorder. Different terminology has also hindered the ability to generate generalizable results. We evaluate how subjects with SMC are defined within different research settings (community, primary care, and memory clinic), their rates of progression to mild cognitive impairment and dementia, and how individuals within these contexts differ in terms of complaints, personal characteristics, and help-seeking behavior.