Contrasting neuronal activity in the supplementary and frontal eye fields during temporal organization of multiple saccades

The organization of a series of actions into an appropriate temporal order is of particular importance in the voluntary control of motor behavior. Previous reports have emphasized the importance of medial motor areas for the temporal organization of movements. The aim of this study was to compare the neuronal activity in the supplementary and frontal eye fields (SEF and FEF) during sequential performance of multiple saccades to clarify the role of the two cortical oculomotor areas in the temporal organization of saccades based on memorized information. We analyzed neuronal activity while monkeys performed three saccades to peripheral targets in orders that were instructed and memorized. We found that activity that reflected saccade sequence or the numerical position of a saccade within a sequence (rank) was more prevalent in the SEF, whereas activity reflecting saccade direction was more dominant in the FEF. Furthermore, a sizeable number of SEF neurons exhibited an increase in activity when the animals were required to discard a current sequence and compose a novel sequence. We propose that the SEF is primarily involved in the process of planning, decoding, and updating saccade sequences, whereas the FEF plays a major role in determining the direction of forthcoming saccades.