Memory and depression in Parkinson's disease

Disorders of learning and memory are a frequent finding in nondemented Parkinson disease (PD) patients. It is not clear to what extent depression, present in at least half the cases of PD, contributes to these disorders. This paper investigates the possible influence of depression on tests of episodic memory in patients with Parkinson's disease (PD). We studied three groups of 11 subjects each (controls, non-depressed PD, mildly to moderately depressed PD). Neuropsychological tests included tests of short and long-term memory in verbal and non-verbal modalities. The two groups of PD patients performed significantly worse than controls on the memory tests, but there were no differences between the depressed and non-depressed PD patients. This lack of influence of depression on neuropsychological performance is compatible with Starkstein's view that cognitive imnpairment is only found beyond a given threshold of depression severity.