The purpose of this study was to compare the effects of fornix lesions with the deficits known to follow septum lesions in cats learning visual object discriminations. In Experiment 1 when eight cats with aspiration lesions of the fornix performed successive discrimination problems, acquisition was greatly facilitated, but first- and second-reversal scores were normal by comparison with eight normal cats and two operated corpus callosum-control cats without fornix damage. Four corpus callosum-damaged cats with secondary degeneration in the medial fornix also learned the initial problem faster than normals. In Experiment 2 in a simultaneous paradigm, eight cats with fornix lesions scored like five normal controls, although they perseverated in early stages of reversal problems. The authors hypothesize that medial fornix damage, in contrast with septum lesions, enhances both initiation and maintenance of response inhibition.
