Presaccadic spike potential with vertical saccades.

Presaccadic spike potentials were recorded from four electrodes placed around the eyes for 20 degree vertical saccadic eye movements. Twenty upward and 20 downward saccades were recorded using electro-oculography and the spike potentials back-averaged from the start of the eye movement. Separate average waveforms were obtained for upward and downward saccades. The onset of the spike was between 17.3 and 6.8 ms before the start of the saccade with downward saccades having earlier onsets than upward saccades. This difference was only significant in the right eye (P less than 0.025). The peak occurred between 3.4 ms before to 5.2 ms after the start of the eye movement and was earlier with downward saccades. This was only significant in the right eye (P less than 0.025). The onset to peak amplitude measured between 15.9 and 42.3 microV with no statistical difference between upward and downward saccades. It was found, however, that the electrodes placed below the eyes recorded larger amplitudes for upward saccades than the other electrode-recording positions (right eye P less than 0.05, left eye P less than 0.025). A second component to the spike potential waveform was observed in many of the recordings and a possible origin of this component due to eyelid activity is hypothesized.