Event-related potentials before saccades and antisaccades and their relation to reaction time.

In the present study, reaction time (RT) was measured in 12 healthy subjects in a saccade and antisaccade task while recording electroencephalographic activity (EEG) from 62 electrodes on the scalp. Event-related potentials averaged both on target appearance and on saccade onset were larger in amplitude (increased negativity) for the antisaccade task compared to the saccade task. The relation of RT variability to EEG amplitude was studied by averaging stimulus-aligned and movement-aligned individual trials for each subject into four RT quartile groups. The analysis showed a relation of EEG amplitude to RT for both saccades and antisaccades. More specifically, the ERP negativity at 100-120 ms after stimulus onset in the saccade task and at 160-200 ms after stimulus onset in the antisaccade task for stimulus-aligned ERPs decreased monotonically with increasing RT as would be expected if this signal would be related to the eye movement preparation processes. This was much more pronounced and wide spread for the antisaccades than for visually triggered saccades. The peak negativity before movement onset for movement-aligned ERPs also covaried with RT suggesting no relation of this activity to movement preparation processes. This study then confirmed that only a particular ERP signal variation was related to the saccadic eye movement preparatory processes while other components of the ERP have no specific relation to the movement preparation. This particular signal was more prominent for antisaccades compared to visually triggered saccades supporting previous evidence for the cortical involvement in the preparation of these voluntary eye movements. In conclusion, this study validates the use of ERPs in the study of the planning and execution of saccadic eye movements.