Comparison of electrographic effects of stimulation of the amygdala and brain stem reticular formation in cats

Abstract

1. 1. A comparison of the electrographic effects of stimulation of the amygdaloid nucleus and the brain stem reticular formation was made in 15 cats under Nembutal anaesthesia. 2. 2. Stimulation of the amygdala can produce a diffuse electrographic effect consisting of a low voltage, fast, asynchronous activity, having all the characteristics of the “arousal” pattern as produced by stimulation of the brain stem reticular formation. During such a response the barbiturate spindles are blocked and abnormal activities such as delta waves and strychnine spikes may be eliminated. A more restricted activation confined to certain cortical areas, particularly the temporal and sensori-motor cortex, is sometimes produced and more often from the amygdala than from the brain stem reticular formation. 3. 3. The electrical activity of the amygdala itself is activated in an identical way by stimulation of the reticular formation or of the opposite amygdala. This effect consists mainly in the production of a fast rhythmical type of activity, occurring often in spindles, which may represent the arousal pattern of the amygdala. This effect may occur with or without generalized cortical activation. 4. 4. Although it is as yet not possible to ascribe this activation effect to a stimulation of any particular nuclear subdivision of the amygdaloid complex, it seems clear that this effect is not obtainable from the whole amygdaloid complex, nor does it necessarily involve those nuclei receiving direct olfactory connections. 5. 5. These experimental results suggest that the amygdala, like the brain stem reticular formation and the intralaminar system of the thalamus, represents a structure capable of exerting diffuse regulatory effects on other cerebral regions. 6. 6. The role of the amygdala in epileptic automatism is discussed in the light of these findings.