Cognitive correlates of psychosis in patients with Parkinson's disease.
BACKGROUND
Psychosis and hallucinations occur in 20-30% of patients with Parkinson's disease (PD). In the current study, we investigate cognitive functions in relation to the occurrence of psychosis in PD patients.


METHODS
We tested three groups of subjects - PD with psychosis, PD without psychosis and healthy controls - on working memory, learning and transitive inference tasks, which are known to assess prefrontal, basal ganglia and hippocampal functions.


RESULTS
In the working memory task, results show that patients with and without psychosis were more impaired than the healthy control group. In the transitive inference task, we did not find any difference among the groups in the learning phase performance. Importantly, PD patients with psychosis were more impaired than both PD patients without psychosis and controls at transitive inference. We also found that the severity of psychotic symptoms in PD patients [as measured by the Unified Parkinson Disease Rating Scale Thought Disorder (UPDRS TD) item] is directly associated with the severity of cognitive impairment [as measured by the mini-mental status exam (MMSE)], sleep disturbance [as measured by the Scales for Outcome in Parkinson Disease (SCOPA) sleep scale] and transitive inference (although the latter did not reach significance).


CONCLUSIONS
Although hypothetical, our data may suggest that the hippocampus is a neural substrate underlying the occurrence of psychosis, sleep disturbance and cognitive impairment in PD patients.
a Department of Veterans Affairs , New Jersey Health Care System , East Orange , NJ , USA.
Ahmed A
AA
Moustafa
Rakhee
R
Krishna
Michael J
MJ
Frank
Abeer M
AM
Eissa
Doaa H
DH
Hewedi
D000368:Aged; D001479:Basal Ganglia / Q000503:physiopathology; D016022:Case-Control Studies; D003071:Cognition / Q000502:physiology*; D003072:Cognition Disorders / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D005260:Female; D006624:Hippocampus / Q000503:physiopathology; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000150:complications* / Q000503:physiopathology / Q000523:psychology*; D017397:Prefrontal Cortex / Q000503:physiopathology; D011618:Psychotic Disorders / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D012890:Sleep / Q000502:physiology; D012893:Sleep Wake Disorders / Q000150:complications / Q000503:physiopathology; D013850:Thinking / Q000502:physiology; D013997:Time Factors
Parkinson's disease; cognition; learning; psychosis; transitive inference; working memory