What brain structures are active during emotions? Effects of brain stimulation elicited aversion on c-fos...

Aversive behavior is produced by stimulating some brain structures, such as the dorsal periaqueductal gray and the medial hypothalamus. We have used c-fos immunoreactivity to map brain areas which are influenced by stimulation of these two structures. Stimulation was produced in freely moving rats by electrical stimulation or by microinjections of either excitatory amino acids or GABA blocking drugs. Behavior was monitored to detect emotional changes. The effects on labeling induced by the stimulation of either structure were then compared. Structures labeled include the amygdala, the stria terminalis, the supramamillary area, the hypothalamus, the periaqueductal gray, the superior colliculus, the nucleus cuneiformis, and the locus coeruleus. Regardless whether chemical or electrical stimulation was used or the structure stimulated, there was a large overlap among the brain areas labeled. We then compared our results with data from the literature where other methods of inducing aversion have been used, including pain and stress. There was remarkable similarity in the patterning of labeling irrespective of the type of stimulation (central-peripheral, chemical-electrical). There was, however, one interesting difference produced by central vs. peripheral stimulation. Labeling was unilateral in the former case and bilateral in the latter case. Our results suggest that there is a neural substrate that mediates aversive behavior, no matter how it is produced. Nevertheless, that peripheral stimulation produces mainly bilateral activation of this substrate whereas central stimulation produces mainly unilateral activation suggests that natural peripheral stimuli are also integrated at a higher functional level. Future work could be directed toward explicit comparisons of central versus peripheral stimulation to identify the structures involved in higher level integration of aversive behavior.