Introduction: An escape, hide and freeze (EHF) system has been plotted in the chick diencephalon and compared with that described in mammals, with particular reference to the defensive threat and fleeing system described for the cat. It is largely medially distributed and supra-threshold stimulation at different sites in the core of this system can elicit a mix of these behaviours. (These EHF behaviours can also be elicited peripherally. These results emerged from a broadly based study of CNS sites that were investigated for their potential to support electrical self-stimulation.) Results: 1/ The EHF system starts in the rostral anterior hypothalamus and runs backward through the medial dorsal hypothalamus. 2/ A lateral extension occurs at the entry of the hypothalamic component of the Tractus occipito-mesencephalicus (TOM). 3/ Posterior to this TOM junction the system shows a ventral extension, but this does not include the N. ventromedialis: it coincides instead with medial and periventricular fibres. 4/ The preoptic area, lateral hypothalamic and mamillary areas were all free of EHF sites. Conclusions: a - The EHF system thus corresponds well with the distribution of the defensive escape-threat system in mammals. b - In both mammals and birds similar behaviour can be elicited from both the diencephalic escape system and the central mesencephalic gray. The two are probably connected in the bird by periventricular routes, part of which can be identified by EHF sites. c - The discussion also refers to other properties of the EHF system such as its role in vocalisation and activation by non-reinforcement
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