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 Parkinson'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-domain 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 P1 amplitude responses 'normalized' to onset N1 and P1 amplitude values, respectively (amplitude ratios).

RESULTS

Absolute and normalized offset P1 amplitude is a distinguishing feature of PD patients from controls. Offset P1 amplitude was significantly larger in PD patients than in controls, particularly to the lower spatial frequency stimulus (P<0.01 for absolute and P<0.001 for normalized values, respectively).

CONCLUSIONS

We conclude that the pattern onset/offset VEP amplitude provides a simple measure to evaluate visual processing deficits in PD and could contribute to an understanding of the pathophysiology of these changes.