DISSOCIATION OF SACCADE-RELATED AND PURSUIT-RELATED ACTIVATION IN HUMAN FRONTAL EYE FIELDS AS REVEALED BY FMRI

The location of the human frontal eye fields (FEFs) underlying horizon tal visually guided saccadic and pursuit eye movements was investigate d with the use of functional magnetic resonance imaging in five health y humans. Execution of both saccadic and pursuit eye movements induced bilateral FEF activation located medially at the junction of the prec entral sulcus and the superior frontal sulcus and extending laterally to the precentral gyrus. These findings extend previous functional ima ging studies by providing the first functional imaging evidence of a s pecific activation in the FEF during smooth pursuit eye movements in h ealthy humans. FEF activation during smooth pursuit performance was sm aller than during saccades. This finding, which may reflect the presen ce of a smaller pursuit-related region area in human FEF than the sacc ade-related region, is consistent with their relative size observed in the monkey. The mean location of the pursuit-related FEF was more inf erior rind. lateral than the location of the saccade-related FEF. Thes e results provide the first evidence that there are different subregio ns in the human FEF that are involved in the execution of two differen t types of eye movements, namely saccadic and pursuit eye movements. M oreover, this study provides additional evidence that the human FEF is located in Brodmann's area 6, unlike the monkey FEF which is located in the posterior part of Brodmann's area 8.