Effects of caudate nuclei or frontal cortex ablations in cats. II. Sleep-wakefulness, EEG, and motor activity.

The effects of caudate nuclei ablation or frontal cortex removal on the percentages of wakefulness and sleep stages, spontaneous motor activity, and the EEG were studied in cats by means of 24-hr polygraphic recordings for a 6-month period. A significant, permanent, reduction of sleep (particularly REM sleep) and an increase in motor activity were observed in cats with removal of most of the frontal tissue in front of the A22 stereotaxic plane. A similar decrease in sleep was also observed in animals with bilateral, almost total, removal of the caudate nuclei, but this reduction almost fully recovered after the second postlesion month. Motor hyperactivity was more marked in cats with caudate ablations than in cats with frontal ablations and persisted indefinitely. No marked or lasting effects on the EEG were observed. Sham-operated cats and those with unilateral caudate removal behaved like intact cats. It is concluded that both the frontal cortex and the caudate nuclei are parts of a postulated, complex, forebrain system modularing brain stem activating-deactivating central nervous system mechanisms.