The "gap paradigm" leads to express-like saccadic reaction times in Parkinson's disease

Application of the "gap paradigm" reduces mean saccadic reaction time (SRT). It enhances oculomotor response, sometimes showing express-like reactions within about 100-140 ms from target onset, which are called "express saccades." Despite some controversy, there is evidence that express and regular saccades may be controlled by different pathways, but it is still not clear which pathways are involved in the generation of express saccades. It was suggested that the substantia nigra (SN) could take part in the control of these saccades. We compared saccadic reaction times of 14 patients with mild to moderate Parkinson's disease (PD), which commonly affects the SN, with those of nine elderly normal subjects. The results show a clear gap effect and no significant difference between mean saccadic reaction times and reaction time distributions of the PD and the control group. In the gap condition, express saccades are present in several subjects of both groups. Therefore, it is concluded that the deficits in the SN pars compacta due to PD, which affect directly and indirectly the activity of the SN pars reticulata that projects to SC, do not dominantly influence the process of preparing and executing express and regular saccades in patients with mild to moderate PD.