Cortical potentials preceding centrifugal and centripetal self-paced horizontal saccades

Cortical potentials preceding self-paced centrifugal and centripetal saccades were recorded in 15 subjects from F3, Fz, F4, C3, Cz, C4, P3, Pz and P4 versus linked mastoid electrodes. A negative potential starting about 1.0 sec prior to saccade onset, reaching a peak amplitude of 6.8 microV on average, preceded centrifugal saccades. In contrast the negativity preceded centripetal saccades by only 500 msec, and its peak amplitude was smaller (4.6 microV). We conclude that these differences reflect the fact that less 'effort' is needed with centripetal as compared to centrifugal saccades.