[Cortical control of saccadic eye movements: a clinical electrophysiological study of antisaccades]

An antisaccadic paradigm in which saccades are directed towards the mirror location opposite to that of target appearance has been thought to reflect frontal lobe function and a saccade-inhibitory mechanism. In order to clarify now the cortical mechanism differs between antisaccades (AS) and reflexive visually guided saccades (VS), we measured scalp EEG potentials preceding AS and VS in 9 young normal subjects, as well as the magnetic brain activities during AS and VS in 1 of them. Prior to the right and left saccades in both paradigms, our measurements revealed the appearance of a slowly developing negative potential, the presaccadic negativity (PSN), and then a steeper negative potential, the presaccadic steep negativity (PSSN). The onset of PSSN was significantly earlier and the maximum amplitude of PSSN was significantly greater in AS than in VS. The peak amplitude of PSSN at each middle electrode (Fz, Cz, Pz) was generally greater in AS than in VS in both directions of saccades. In one normal subject, the difference between AS and VS in the magnetic field distribution just prior to saccades in both directions was demonstrated as current dipoles on the bilateral frontal areas. Our results suggest that the activation of the bilateral frontal lobes is greater prior to AS than it is prior to VS.