Parkinson's disease changes the balance of onset and offset visual responses: an evoked potential study

Objectives: We investigated whether the transient pattern onset and offset visual evoked potential (VEP) can distinguish between patients with Parkins on's disease (PD) and normal subjects. Methods: Two horizontal sinusoidal gratings differing in spatial frequency, i.e. 1 and 4 cycles per degree, were presented to 17 patients with PD and 16 age-matched control subjects. We analyzed the responses in the time-doma in and measured the latencies and amplitudes of N1 and P1 to the onset and the offset of the stimulus: we also derived the measures of offset N1 and P 1 amplitude responses 'normalized' to onset N1 and P1 amplitude values, res pectively (amplitude ratios). Results: Absolute and normalized offset PI amplitude is a distinguishing fe ature of PD patients from controls. Offset P1 amplitude was significantly l arger in PD patients than in controls, particularly to the lower spatial fr equency stimulus (P < 0.01 for absolute and P < 0.001 for normalized values , respectively). Conclusions: We conclude that the pattern onset/offset VEP amplitude provid es a simple measure to evaluate visual processing deficits in PD and could contribute to all understanding of the pathophysiology of these changes. (C ) 2001 Elsevier Science Ireland Ltd. All rights reserved.