Visual processing deficit in Parkinson's disease

Background Recent neuropsychiatric and electrophysiological evidence suggests that visuocognitive dysfunction exists prior to dementia in Parkinson disease (PD) patients. Methods. We have evaluated concurrent evoked potential responses to sinusoidal grating stimuli of 1 and 4 cpd, presented in a typical oddball paradigm in 25 nondemented PD patients and 20 age-matched controls. The 4 cpd pattern is weighted towards retinal dopaminergic mechanisms. Each pattern was explored both ways as a "frequent" and as a "rare" stimulus. P300 latencies and amplitudes were "normalized" to the VEP. Wavelet analysis was performed on appropriate windows of the concurrently recorded primary and cognitive evoked potentials to 4 cpd stimuli in 11 of the patients and 11 of the controls. Results/Conclusions. The current study confirms that younger (< 60 years) patients are distinguished from their controls both by raw and normalized ERP measures for 1 cpd stimuli. This result did not depend on spatial frequency, suggesting that retinal dopaminergic impairment is not a sufficient explanation for electrophysiological visuocognitive deficits in PD. Wavelet analysis showed that in the "cognitive" time window, high-frequency (17-34 Hz) suppression occurs in normalsbut not in PD patients, suggesting that a different processing of visuocognitive responses may be deficient.