EXPERIMENTAL CONTRIBUTIONS TO PROBLEM OF CONSCIOUSNESS

Abstract

In the intact, anesthetized animal physiological sensory stimuli (nociceptive, proprioceptive, and auditory) can elicit a generalized cortical reaction which is characterized by bilateral activation of specific and non-specific projection and association cortical areas; this response can be regarded as an awakening reaction. Usually the specific cortical area related to the type of stimulation used shows a greater degree of excitation than the non-specific areas. Whether or not an awakening response is elicited depends on the level of anesthesia of the animal and the type of stimulus used. The sequence of the sensory stimuli listed in decreasing order of ability to produce an arousal reaction are: (1) pain (most effective); (2) proprio-ception; (3) auditory stimulation; (4) optic stimulation (least effective). The cortical reactions to these stimuli were evaluated according to the following: (1) number of specific and non-specific cortical areas activated; (2) degree of excitation in activated areas, the highest degree of excitation in a Dial animal being indicated by a disappearance of Dial bursts and an increase in frequency and amplitude (asynchrony and recruitment); (3) duration of excitation (a strong response frequently outlasting the stimulation period). In response to sensory stimulation there is a high correlation between the generalized cortical response and activation of the hypothalamus, while specific cortical responses do not involve excitation of the hypothalamus in most cases. Hypothalamic activation occurring simultaneously with generalized cortical responses supports the view that the hypothalamus takes an active part in the awakening reaction. It is suggested that normally the hypothalamus is responsible for the generalized cortical or arousal reaction. Sensory stimulation (involving nociceptors, proprioceptors, and acoustic receptors in decreasing order of effectiveness) and hypothalamic activity have been related to the awakening response.