Human spike potentials prior to saccades and optokinetic nystagmus fast phases: effects of instructions, eye movement direction and electrode laterality.

Presaccadic potentials in humans consist of 3 components, a slow negative shift, a positive antecedent potential and a spike potential (SP). This study demonstrated the presence of the SP before another class of rapid eye movements, fast phases of optokinetic nystagmus (OKN), in 11 right-handed, normal human subjects and compared the amplitude of the averaged SP for OKN fast phases, recorded at P3 and P4 (International 10/20 System), with the SP amplitude for 10 degrees self-paced saccades between two red light-emitting diodes. In particular, the effects of electrode laterality, rapid eye movement direction and two sets of instructions during the OKN task were assessed. Subjects were told to either 'look at the screen' (OKN1 paradigm) or to 'try to slow or stop the motion of the pattern' (OKN2 paradigm) during presentation of optokinetic stimulation. As in the case of saccades, the OKN fast phase velocity spike was used to trigger the signal averager (Nicolet (CA-1000]. There were two significant differences in SP amplitude prior to saccades and OKN fast phases. First, 3-way analysis of variance (ANOVA) and Newman-Keuls comparisons revealed that the SP was attenuated significantly for OKN for either eye movement direction over either left or right recording sites (F = 16.045, P less than 0.001). This effect was not related to amplitude differences in eye movements in the different tasks, although a contribution of variance in the OKN fast phase amplitudes cannot be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)