Functional organization in the monkey frontal eye field particularly in the deep region of the anterior arcuate bank

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In a monkey, the cortical region rostral to the arcuate sulcus is called the frontal eye field (FEF), because saccadic eye movements are elicited by electrical stimulation. Purposes of this study are to reveal the exact extent of the FEF by exploring up to the bottom of the anterior arcuate bank, and to show the relationship between the stimulating site in the FEF and elicited saccade vector. Awake Japanese monkeys were sat in primate chairs with their heads tightly fixed. An Elgiloy microelectrode was inserted into the brain through the dura with a selected direction of the electrode, and intracortical electrical microstimulation was done with the electrode to elicite saccades. Results were as follows: 1. The FEF extended rostrocaudally from the caudal end of the principal sulcus to the bottom of the arcuate sulcus, with a mediolateral width of 7-10 mm. 2. When the stimulating site was moved along a radial cell array of the FEF, vector of the elicited saccade remained constant irrespective of the cortical layer of the stimulating site. However, the vector changed gradually with a shift of the stimulating sites along the cortical surface. The saccade amplitude was below 30ﾟ and its direction was contralateral to the stimulating FEF with varying degrees of the vertical component. 3. Amplitude of the saccade is increased gradually, when the stimulating site was moved from medial to lateral FEF. In contrast, saccade direction changed successively with a rostrocaudal shift of the stimulating site. Usually the same saccade direction was found twice or more in distant areas in the FEF. Based on the findings, we discussed the role of the FEF on saccadic eye movements of the animal.