Electrographic aspects of an “arousal” or attention reaction induced in the unanesthetized rabbit by the presence of a human being

Abstract An EEG response recorded simulataneously in the cortex, the medial and lateral thalamus, the rhinencephalon and the midbrain reticular formation of unanesthetized rabbits is described. It consists of: ( a ) suppression of slow waves and bursts in the cortex, and appearance of a low voltage fast activity predominant in the sensorimotor areas; ( b ) slight increase in frequency and regularity (5–7 c/sec. instead of 4–5 c/sec.) of the thalamic basic activity, with a tendency to generalization all over the brain, especially in the occipital cortex; ( c ) slight increase in frequency and regularity of the slow rhinencephalic rhythms (5–7 instead of 4–5 c/sec.) synchronized with the thalamic basic activity, and increase in voltage of the rhinencephalic fast components; ( d ) slight increase in voltage of the low voltage fast activities in the midbrain reticular formation appearing simultaneously with the cortical desynchronization. The electrical pattern of this response appears identical with the “arousal” reaction induced by stimulation of the brain-stem reticular formation. Electrographic evidence is given that the so-called “arousal” system involves at least three mechanism: (1) a reticulo-cortical desynchronizing mechanism; (2) a thalamo-cortical synchronizing mechanism, leading to an acceleration and an increase in regularity of the thalamic rhythmic activity, with extension of this rhythm (5–7 c/sec.) all over the brain, even to the midbrain reticular formation; (3) a rhinencephalic mechanism showing high voltage fast activity and an acceleration of the slower rhinencephalic rhythmic activity (5–7 instead of 4–5 c/sec.), synchronized with the thalamic rhythm. These wide-spread electrographic changes and the responsiveness of the so-called “arousal” system to more elaborate, cortical processes, involving increased attention and possibly some emotional components (visual perception of a moving being) suggest that this system may be activated by sensory afferents, but also by higher, cortico-diencephalic and rhinencephalic systems concerned with the control of attention and emotional behaviour. The usefulness of such electrographic data for experimental psychology is pointed out.