Chapter 8 Neurobiological correlates of defensive behaviors

Abstract

In an attempt to understand the basic neural mechanisms underlying psychiatric conditions involving fear and anxiety, this chapter is focused on identifying the ontogeny and neural substrates of defensive behaviors. Defensive behaviors are exhibited by a wide array of species, including rats, non-human primates, and humans in response to perceived threats from the environment, and are essential components of an organism's behavioral repertoire that ensure its protection and survival. Although the specific behavioral responses that comprise “defensive behaviors” are dependent on the environmental context and vary from species to species, a common element that unites this cross-species phenomenon is that defensive behaviors represent an organism's behavioral response to fear. For example, vertebrates have evolved defensive behavioral responses that facilitate survival from threatening stimuli, such as predators. Because defensive behaviors are expressed in response to an immediate threat, they characteristically supercede and interrupt the expression of other normal homeostatic behaviors, such as feeding and reproduction that the organism may be engaging in at the time of the perceived threat. One defensive response pattern expressed by many species is to inhibit all body movements and assume an immobile or freezing posture. This phenomenon of behavioral inhibition is effective in preventing detection and attack by predators, may have special relevance for understanding psychopathology, and is discussed in detail in this chapter.