198 FRONTAL EYE FIELD LESIONS: OCULAR OR FIELD NEGLECT? CHRISTIE, D. AND STEELE RUSSELL, I. MRC Unit on Neural Mechanisms of Behaviour, 3 Malet Place, London WCIE 7JG, England Recent research has supported the view that the rat anteromedial cortex (AM)is homologous to the monkey Frontal Eye Field (FEF) (I). Unilateral lesions in the FEF produce a visual neglect for sti- muli presented in the contralateral field to the lesion. The neglect is transitory and can be rein- stated in monkey by callosal section (2). A distinguishing feature of the monkey neglect is that the animal suffers from a purely visual field, attentional impairment where there is a failure to react, rather than an inability to detect. Targets in the contralateral visual field are neglected both binocularly and monocularly with either eye. It has been suggested that the rat demonstrates a similar field deficit following uni- lateral AM lesions (3, I). However, the field-dependent nature of this neglect has been recently questioned by Crowne and Pathria (4). They reported an increase in choice latency without any change in error scores. This effect was only reported with the eye contralateral to the lesion. The present study was undertaken to test the generality of the Crowne and Pathria claim that the FEF lesions produce an ocular as opposed to a field neglect. Rats were trained on a similar visual discrimination and were tested for visual neglect after unilateral FEF lesions. Contrary to Crowne and Pathria, neglect was seen in terms of large increase in errors due to the complete loss of detection efficiency in the contralateral field to the lesion. Furthermore this neglect was consistent for either eye during monocular testing. No differences in choice latency were found. These findings support the earlier claims that the functional role of the rat AM cortex is similar to primate FEF cortex. REFERENCES I. Steele Russell, I. and Pereira, S.C. In: Functional Recovery from Brain Damage. M.W. van Hof and G. Mohn (Eds.) Elsevier Biomedical Press, Amsterdam (1981) pp. 209-238. 2. Crowne, D.P., Yeo, C.H. and Steele Russell, I., Behav. Brain Res., 2 (1981) 165-187. 3. Cowey, A. and Bozek, T., Brain Res., 72 (1974) 53-63. 4. Crowne, D.P. and Pathria, M.N., Behav. Brain Res., 6 (1982) 25-39. HABITUATION OF THE EARLY AND MIDDLE LATENCY COMPONENTSOF THE AUDITORY EVOKED POTENTIALS IN FREELY MOVING CAT CSEPE, V . , KARMOS, G., MOLNAR, M. AND WINKLER, I . Dept, of Psychophysiology, Inst. for Psychology of the Hung. Acad. Science, Budapest, Hungary The experiments were designed to investigate the changes of the auditory evoked potentials (AEPs) recorded on the auditory cortex and in the medial geniculate body (MGB) of freely moving cats. Habituation was studied in response to repetitive auditory stimuli for dividing of slow and fast