Effects of caudate nuclei or frontal cortical ablations in cats. I. Neurology and gross behavior.

Abstract Methods are described for performing one-stage ablation of the caudate nuclei through a midline approach in cats, for maintaining the animals indefinitely, and for their neurological and gross behavioral evaluation. Sixteen cats with extensive bilateral caudate lesions, 13 with extensive unilateral caudatectomy, 14 with bilateral removal of the frontal cortical areas, and eight sham-operated animals, were studied for months. The results of anatomical, neurological, and gross behavioral observations are described in this first paper. A behavioral change labeled “compulsory approaching syndrome” was observed following surgery in all cats with bilateral caudate ablation. This was a long-lasting effect persisting even under unusual conditions. The “syndrome” was characterized by stereotyped and prolonged approaching and/or following of persons, cats, or objects. Visual cues were most effective in eliciting the syndrome but acoustic and tactile stimuli were also adequate. Other components of the syndrome were marked passivity, exaggerated forelimb treading, marked purring, rooting, hyperactivity, hyperreactivity, and sexual changes. The magnitude and duration of the syndrome appeared to be related to the extent of the ablation with its essential features persisting for over 1 yr in cats with the largest ablations (70 to 100% of the nuclei). The syndrome was not observed in sham-operated cats. Bilaterally acaudate cats were remarkably free of permanent gross neurological deficits. Deficits such as motor weakness, faulty awareness, and defective eating and drinking were seen in the early postoperative period. Only moderate hyperactivity along with the compulsory approaching syndrome and some impoverishment and slowness of movements persisted in the chronic state. In all unilaterally acaudate cats, there was an absence of any permanent gross neurological or behavioral changes including the compulsory approaching. Our findings suggest that the caudate nuclei do not have any gross lateralized behavioral or neurological function and indicate a large functional reserve. The cats with bilateral frontal cortical areas removed exhibited early, short-lasting visual tracking, but none of the characteristics of the compulsory approaching syndrome was present (except in three animals, where the characteristics appeared transiently and combined with aggressiveness). Other neurological defects of frontally-operated cats were consequences of ablation of the sensory-motor areas. The syndrome is discussed in terms of the specificity of the caudate ablation in its production and it is tentatively explained as resulting from absence of an inhibitory caudate modulatory influence on polysensory inputs. It is concluded that total ablation of the caudate nuclei in cats is possible and produces a characteristic behavioral change of which the exact nature remains to be elucidated. The caudate does not appear to have an essential role in the control of basic metabolic functions, elementary sensory-motor functions, or elementary cognitive processes as previously postulated.