Visual field defects after frontal eye-field lesions in monkeys

Abstract

Bianchi 6 described a neglect of visual stimuli on the side contralateral to a unilateral frontal lobe lesion in monkeys. This was confirmed by Ferrier and Turner 24 and Jacobsen 27. Kennarda°, al and Kennard and Ectors a2 showed that the neglect occurred after unilateral removal of Brodmann's area 8, which corresponds, though only approximately, to the frontal eye-fields the region of the frontal lobe where electrical stimulation produces highly reproducible contralateral conjugate eye movements, whose precise direction depends on the locus of stimulation. Other frontal lesions did not cause a neglect. Subsequently, Clark and Lashley 13, Welch and Stuteville 4°, Denny-Brown 21,2a and Brucher 1° all found contralateral neglects after unilateral frontal eye-field lesions. This neglect has always been shown by an absence of response to food or frightening visual stimuli. Kennard's 31 technique of recording the order in which the monkey picks up a row of peanuts was a more systematic characterization, but she did not control or measure head and eye movements. Since the other main effect of the lesion is ipsilateral deviation of the head and eyes and circling of the body 1°,25, a0-a2,46 it is possible that the neglect is an indirect result of the oculomotor disturbance. All tests, apart from those using a fear response, have used responses that are spatially related to the stimulus. So a second explanation of the neglect is a disturbance of limb movements to the contralateral side. That there is a motor change of some kind is shown by the fact that these monkeys show a very strong preference for their ipsilateral handel,2a,al, 4e, but whether the visual neglect causes the change in motor behaviour or vice versa, or whether both are a product of something else, is unclear.