CORTICAL POTENTIALS DURING THE GAP PRIOR TO EXPRESS SACCADES AND FASTREGULAR SACCADES

When a temporal gap is introduced between the offset of the central fi xation point and the appearance of a new target, saccadic reaction tim e is reduced (Sap effect) and a special population of extremely fast s accades occurs (express saccades). It has been hypothesized that the g ap triggers a readiness signal, which is responsible for the reduced s accadic reaction times. Here, we recorded event-related potentials dur ing the gap to investigate the central precesses associated with the g eneration of fast regular saccades and express saccades. Prior to the execution of fast regular saccades, subjects produced a slow negative shift, with a maximum at frontal and central channels that started 40 ms after fixation offset. This widespread negativity is similar to a r eadiness potential. Anticipatory saccades were preceded by an increase d frontal and parietal negativity. Prior to express saccades, a fronta l negativity was observed, which started 135 ms after the disappearanc e of the fixation point. It is assumed that the frontal negativity pri or to express saccades corresponds to the fixation-disengagement disch arge described in the frontal eye field of monkeys. Therefore, we hypo thesize that fast regular saccades are the result of an increased read iness signal, while express saccades are the result of specific prepar atory processes.