Classical eyeblink conditioning in the bilaterally hemispherectomized cat

The classically conditioned eyeblink response was studied in cats with various forebrain lesions, compatible with a growing body of evidence that telencephalic structures are not necessary for the acquisition and maintenance of a classically conditioning response.

Abstract

The classically conditioned eyeblink response was studied in cats with various forebrain lesions. The most extreme of these were three chronically prepared "diencephalic" cats in which the cerebral hemispheres were separated from the thalamus and removed bilaterally. Other animals studied included two animals with frontal cortex ablation, one neodecorticate cat, two animals with bilateral lesions of the caudate nucleus, and one cat with extensive bilateral damage to the thalamic nucleus ventralis posteromedialis. Conditioning was established using a 400-msec duration auditory conditioning stimulus (CS) followed by a brief cutaneous shock to the eyelid as the reinforcing stimulus (US). The EMG was recorded bipolarly from orbicularis oculi, and integrated EMG for the CS interval served as an additional objective measure of conditioned response (CR) magnitude. The conditioned responses were characterized by a burst of EMG activity toward the end of the CS interval (latency 100 msec) which occurred as a result of systematic pairing of CS and US, and did not occur during random presentation of the CS and US, or CS alone. All of the experimental animals learned a conditioned blink response which appeared qualitatively similar to that obtained in the normal animals. All preparations acquired a response, showed extinction when reinforcement was discontinued, discriminated between two stimuli within the same sensory modality, showed discrimination reversal, and retained the acquired response over days. Our results are compatible with a growing body of evidence that telencephalic structures are not necessary for the acquisition and maintenance of a classically conditioned response. Further studies in this laboratory are aimed at investigating conditioning in the chronic decerebrate cat.