Some attentional effects of unilateral frontal lesions in the rat

Visual learning, sensory neglect and motor behaviour were studied in rats with unilateral lesions of anteromedial (AM) or dorsolateral (DL) frontal cortex. The purpose was to determine whether the principal features of the syndrome seen after unilateral frontal eye field lesions in primates appear in the rat. In the first two experiments, rats were trained on a visual discrimination using shock avoidance. AM lesions greatly prolonged choice latency but did not increase errors, and this held both for binocular performance and for monocular performance with the contralateral eye. One group of AM-lesion animals was postoperatively maintained in the dark, and their latencies, binocular and monocular, did not differ from the DL controls. Thus, deprivation of visual experience prevented the effects of the AM lesion. The second experiment used simple sensory stimuli to test for visual, auditory and tactile neglect. Ipsiversive circling was also investigated. All rats with AM lesions neglected contralaterally and circled in the first postoperative week. Recovery was underway by the second week and complete in three weeks. The animals were trained preoperatively on a conditioned avoidance problem in which shock was signalled from various points in the visual field. Tested postoperatively, the AM-lesion rats avoided normally. The findings of the two experiments strongly suggest that the functions of AM cortex in the rat are similar to those of the frontal eye field in primates. This cortical region appears to be part of a system which prominently includes the superior colliculus and serves attentional/orienting functions.