Effects of caudate nuclei or frontal cortical ablations in kittens: Responsiveness to auditory stimuli and comparisons with adult-operated littermates

Abstract

These experiments assess the behavioral responsiveness of adult cats with extensive caudate nuclei or frontal cortical ablations, sustained either neonatally or in adulthood, to presentations of cat vocalizations or of tones. Each subject received 27 presentations, at 1-min intervals, of a 12 s sequence of taped vocalization (calls) on 2 successive days and, 1 week later, a similar series of 2-kHz tones of the same duration and intensity. The behavioral responses were scored using a six-point rating scale and the data were analyzed to compare responsiveness of the groups within each testing day, decrement of responsiveness across the trials of each session (habituation), and retention of habituation across successive days. We found that (a) all acaudate and afrontal cats persisted in responding at higher levels than intact animals in all three testing sessions; (b) the cats with caudate ablations were more responsive than those with frontal ablations to both calls and tones; (c) the hyperresponsiveness was more marked for adult-operated in relation to kitten-operated preparations; (d) in general, the responsiveness of all kitten groups decreased progressively across the three testings; and (e) for the adult-operated cats, there was a decrement between the two call sessions and an increase between the call and the tone sessions. These findings suggest that both the caudate nucleus and the frontal cortex participate in processes controlling the organism's responsiveness to external stimuli with the caudate removal producing the largest defect; they also indicate that, with some qualifications, the lesions sustained by the kitten result in less marked later effects than those sustained by the adult. Furthermore, they may help to explain some of the behavioral changes which we described previously for cats with caudate ablations.