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We recorded smooth pursuit in 4 patients with small, discrete unilateral frontal lobe lesions and in 13 normal subjects. In all cases the lesions affected the frontal eye fields (FEF). The use of step ramp stimuli enabled the measurement of different parameters. Initial acceleration was measured to assess the open loop response, maximum and mean gain was an index of the closed loop response and inaccuracy was used to assess the ability of the saccadic system to refoveate. Patients showed a decreased gain towards the side of the lesion, with significant asymmetry. In contrast, acceleration was reduced in both directions without significant asymmetry. In the monkey, it has been shown that the middle temporal area (MT) codes motion in the contralateral side of space in both directions equally, whereas the posterior parietal cortex (PPC) contains cells which encode velocity asymetrically. Our findings would, therefore, be consistent with the hypothesis that there are two pathways from the homolog of MT in the occipito-tempero-parietal pit to the FEF; a direct pathway and an indirect pathway, via the PPC. The direct pathway might encode target velocity in a retinotopic reference frame without directional asymmetry and be responsible for initial acceleration. The indirect pathway might encode target velocity in a non-retinal frame and be responsible for the predictive mechanisms for maintaining pursuit. © 1995, Elsevier B.V.

Original publication

DOI

10.1016/S0926-907X(05)80023-6

Type

Journal article

Publication Date

01/01/1995

Volume

6

Pages

269 - 280