Cognitive slowing in Parkinson's disease is related to frontostriatal dopaminergic dysfunction

BackgroundFrontostriatal and cognitive dysfunctions in Parkinson's disease (PD) are hypothesized to be linked predominately to dopaminergic dysfunction within neural networks linking dorsal striatum to dorsolateral prefrontal cortex.MethodsThe authors evaluated the relationship between frontostriatal dopaminergic function and cognitive performance, especially cognitive processing speed by performing [18F]fluorodopa PET and computerized tests of automatic and controlled cognitive processing speed (CogniSpeed) in 23 newly diagnosed and unmedicated PD patients and 14 controls.ResultsPD patients were slower than the controls in all the CogniSpeed measures studied. The Fdopa uptake in caudate nucleus correlated negatively with slowing on all the tests. Slower performance in relatively automatic processes measured by choice reaction tasks as well as in more controlled processes measured by a calculation task was related to reduced Fdopa uptake in the anterior cingulate gyrus. The reduced dopaminergic function in the thalamus was associated with the slower performance in the subtraction test.ConclusionOur study indicates that dopaminergic dysfunction within neural networks linking striatum to prefrontal cortex is involved in the slowing of both automatic and controlled cognitive processing in PD patients.