Effects of LSD‐25, psilocybin, and psilocin on temporal lobe EEG patterns and learned behavior in the cat

Abstract

The effects of LSD-25, psilocybin, and psilocin have been studied in 18 cats with electrodes chronically implanted in the amygdala, parts of the hippocampus and entorhinal cortex, the thalamic nucleus ventralis anterior, rostral midbrain reticular formation, and primary visual cortex. Certain characteristic changes in general behavior followed administration of LSD-25 in doses of 25 to 100 [mu]g. The animals adopted a wide-based "kangaroo" posture with tail extended, and exhibited staring, head shaking, and sprawling with claws extended. There was a loss of normal affective responses. With LSD-25 dosage around 25 u.g. per kilogram, brief seizure-like episodes were seen in EEG records in a quiet environment. They were maximal in amplitude and longest in duration in dorsal hippocampal and entorhinal cortex, and appeared variably in the thalamus and midbrain reticular formation. These seizures seemed critically dependent on reduction of visual and auditory sensory influences. At higher doses of LSD-25 in the vicinity of 100 ug. per kilogram, seizures persisted in a well-lit environment and disrupted a delayed response performance when the seizure episode encroached on the period when a discriminative performance was required. Unlike visual and auditory stimuli, ingestion of food during the action of LSD-25 was frequently associated with wave and wave-and-spike seizure activity, confined in some instances to hippocampal and amygdaloid systems. Tolerance to LSD appeared with doses repeated at more frequent intervals than seven to ten days. Psilocybin and psilocin resembled LSD-25 in their general effects but differed in the brevity of their action and the frequent occurrence of severe autono-mic reactions, including vomiting, micturition, and pupillary dilatation. The relationship of these findings to physiologic mechanisms in the memory trace and to problems of sensory deprivation, such as may occur in the space environment, is discussed.