Electroencephalographic-behavioral dissociations during animal hypnosis

Abstract

1. 1. Seventeen New Zealand White rabbits, with referential or bipolar electrodes in the motor cortex and various subcortical brain areas, were studied before and during hypnosis in 76 test sessions. 2. 2. Hypnosis was typically characterized by a reversible tonic immobility, relative unresponsiveness, decrease in muscle tone, and “arousal” EEG patterns. This state, although superficially similar to paradoxical sleep, was not the same, inasmuch as muscle tone was still present and there were no rapid eye movements, eyelid twitches, or phasic limb movements. 3. 3. After hypnosis was sustained for several minutes, a more “relaxed” state commonly occurred, wherein heart and respiratory rates decreased, muscle tone decreased further, and the EEG was of high voltage, slow activity. 4. 4. On 8 occasions in six rabbits, brief episodes of electrographic seizures occurred during hypnosis, without interrupting the tonic immobility. Seizures were induced in all rabbits with amphetamine, pentylenetetrazol, and the local anesthetic, dyclonine. Whether the drugs were injected before or during hypnosis, the motor component of the seizures was abolished by hypnosis, yet epileptiform EEG activity persisted during the apparent behavioral “sedation”. 5. 5. The “arousal” EEG, and especially the electrographic seizures, represented a conspicuous example of EEG-behavioral dissociation. Other similar dissociations have been reported in recent years, the best known of which are seen with paradoxical sleep, high doses of reserpine, certain neurological disorders, and physostigmine injection into chlorpromazine-sedated animals. 6. 6. The functional disconnection of motor activity in these states have common mechanisms. The existence of these several dissociation states emphasizes the limitations of current knowledge and the need for better understanding of sensori-motor interrelations.