Role of the hemigiant neurons in the crayfish defense response

The medial and lateral hemigiant neurons of the crayfish were isolated in the circumesophageal connective and electrically stimulated to examine their ability to elicit a defense response. In contrast to previous reports, neither a defense response nor any other thoracic or abdominal movements were observed following stimulation of either hemigiant. Small fibers that lie adjacent to the hemigiants in the circumesophageal connective evoked defense responses when they were electrically stimulated. Two types of defense responses could be evoked by stimulation of small fibers.