Verbal memory in drug-naive, newly diagnosed Parkinson's disease. The retrieval deficit hypothesis revisited.
OBJECTIVE
The retrieval deficit hypothesis on memory impairment in patients with Parkinson's disease (PD) implies a selective impairment in recall of learned material with normal encoding, retention, and recognition. This hypothesis has been challenged by new data. We have therefore investigated verbal memory and learning in a large sample of newly diagnosed, drug naïve, non-demented patients with PD.


METHODS
From a sample of patients with PD from the Norwegian ParkWest study, 133 PD patients and 133 controls matched on sex, age, and education were included. The California Verbal Learning Test-2 (CVLT-2) was used to assess verbal memory.


RESULTS
Patients performed significantly worse than controls on free and cued recall as well as on recognition memory. Patients used the semantic clustering learning strategy significantly less extensively than the controls and the learning slope of the PD patients was significantly less steep. There was no difference in retention when controlling for encoding. Patients did not perform better on the recognition measure or on cued recall (d-prime), as compared to free recall. Executive functions explained a substantial part of the memory deficits.


CONCLUSIONS
This study suggests that memory impairment in drug naïve early PD to a large degree is a deficit of learning/ encoding and not of retention or retrieval. An implication is that the retrieval deficit hypothesis should be moderated in its general form. Executive deficits and less extensive use of the efficient semantic clustering learning strategy had a strong impact on learning and memory.
Norwegian Centre for Movement Disorders, Stavanger University Hospital. bronnick@gmail.com
Kolbjørn
K
Brønnick
Guido
G
Alves
Dag
D
Aarsland
Ole-Bjørn
OB
Tysnes
Jan Petter
JP
Larsen
D000368:Aged; D000704:Analysis of Variance; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007391:International Cooperation; D008297:Male; D008569:Memory Disorders / Q000175:diagnosis* / Q000209:etiology*; D011939:Mental Recall / Q000502:physiology*; D008875:Middle Aged; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000150:complications*; D011569:Psychiatric Status Rating Scales; D014706:Verbal Learning / Q000502:physiology*