Electroencephalographic studies in “split brain” cats

Abstract

1. 1. The EEG activities of homologous cortical areas of the cat brain have been recorded in chronic conditions. When the EEG displays slow wave-spindle patterns, the potentials simultaneously recorded from corresponding points of the two hemispheres are essentially similar. 2. 2. The normal EEG bilateral symmetry is disrupted permanently by section of corpus callosum. In the callosotomized animal, however, EEG arousal reactions and onsets of sleep patterns remain synchronous in the two sides. Similar EEG features have been found in a cat with anomalous absence of corpus callosum. 3. 3. When division of all the other forebrain commissures and midsagittal section of the rostral midbrain are added to that of the callosum, a mismatching of the EEG waking and sleeping states in the two hemispheres can be observed for a maximum period of 8–10 days. It has been attributed to asymmetrical parasagittal lesions in the region of the rostral midbrain. Recovery of the normal bilateral matching is always complete. 4. 4. It is concluded that while the corpus callosum is essential for the maintenance of the fine bilateral correspondence of the EEG waves, the sleep-wakefulness cycle in the two separated hemispheres is controlled by the lower brain-stem.