The relationship of excessive exploratory behavior in wakefulness to paradoxical sleep without atonia

Abstract

The hypothesis that cats exhibiting paradoxical sleep (PS) without atonia are more active than normal in wakefulness was tested. To provide a quantitative measure of locomotor activity, 15 cats were subjected to an open-field test of activity for 5 one-hour or 10 half-hour sessions before and after placement of bilateral pontine tegmental lesions, which induce PS without atonia. Thirteen of the cats had PS without atonia and showed significant (p < 0.05) increases in open-field activity, which was judged to be exploratory in nature, rather than aimless pacing. Increases ranged from 30-261%. In spite of the abnormal increase in antigravity muscle tone during PS postoperatively, hypertonia was not present during wakefulness. Of the 2 cats without elaborate behavior during PS, 1 had a significant decrease in activity. Its lesion may have damaged a lateral brainstem locomotor region. The same effect was obtained with unilateral damage of this region in 1 of 2 cats subjected to 2-stage operations. The results were used to develop the argument that peripheral motor inhibition during PS depends on suppression of a brainstem locomotor region in addition to direct inhibition of spinal motor neurons.