Roles of caudal frontal eye fields (FEF) in representation of visual information in space : Comparison with MT/MST.

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Recent studies show that caudal parts of the frontal eye fields(FEF)contain smooth pursuit neurons. FEF has reciprocal connections with the cortical MT and MST. To understand the FEF role in representation of visual information and pursuit eye movements in space, I examined whether FEF pursuit neurons also respond to vergence eye movements and compared their activity with that in MT/MST. Head-fixed Japanese monkeys were trained to pursue a spot that moved in frontal planes and depth. I tested 155 neurons in FEF and 143 neurons in MT/MST during both frontal pursuit and vergence(I. E. depth pursuit). Majority of FEF neurons(66%)modulated strongly during both frontal and depth pursuit, resulting in three dimensional(3D) Cartesian representation of eye movements. Although MT/MST contained neurons that responded during both frontal and depth pursuit, the percentage of such neurons was much less(12%)compared to that in FEF. Majority of MT/MST neurons responded only during frontal pursuit(76% vs 26% in FEF). Visual response to sinusoidal motion of a virtual spot or optic flow was compared while the animals fixated a stationary spot. Majority of FEF neurons tested(33/61)responded to spot motion and flow in frontal plane and/or depth with visual preferred directions similar to those during pursuit. In contrast, majority of MT/MST neurons tested(57/106)responded to optic flow and spot motion with preferred directions opposite to those during pursuit. These differences between neurons in FEF and MT/MST suggest different roles for the two cortical areas in pursuit and support the view that 3D pursuit signals are synthesized mainly in FEF.