Dissociation of Electrocortical Activation and Behavioural Arousal

The present experiments were designed to test the following hypothesis: while the ascending reticular system mediates electrocortical ‘tone’, the posterior hypothalamic region has a functionally separable role in maintaining the waking state.

Abstract

THE fact that electrocortical 'activation' and behavioural 'arousal' are often correlated has led to interchangeable use of these terms in recent years. This identity stems from the extensive research of Magoun and Lindsley1, who have put forward the unifying hypothesis that both wakefulness and low-voltage, fast electro-corticographic (EGG) activity depend on the 'tonic' facilitatory effect of the ascending reticular system on the cerebral cortex. Early work by Hanson2 and Hess3 had demonstrated that: (a) stimulation of the posterior hypothalamus results in behavioural arousal from sleep; (b) bilateral lesions of this region are accompanied by a chronic state of somnolence, or coma. Such effects were later duplicated by: (1) stimulation or (2) extensive destruction of the midbrain reticular formation1. In the interest of parsimony it was proposed that the posterior hypothalamus is involved in maintaining the waking state only in so far as it is a part of the ascending reticular system1. The present experiments were designed to test the following hypothesis: while the ascending reticular system mediates electrocortical 'tone', the posterior hypothalamic region has a functionally separable role in maintaining the waking state.