Unconditioned aggressive or ESCAPE responses that an animal displays when it is exposed to an AVERSIVE STIMULUS. Cannon (1871–1945) introduced the phrase ‘fight-orflight response’ in the early 1900s to refer to the physiological reactions that prepare the individual for performing fight or flight. The UNCONDITIONED RESPONSE to a PUNISHMENT may be either defensive attacks or attempts to escape. However, fight-or-flight does not depend on the actual punishment delivered but on other stimuli present at the time of punishment. Where effective escape is impossible and there is nothing suitable to ATTACK in the environment, punishing stimuli (such as electric shock) produce unconditioned escape behaviour. However, if a suitable object is present (another animal or small inanimate object for instance) the most likely response is an attack, even though there is no causal relationship between the shock and the object. Given the choice between fight or flight, animals appear to prefer fight. The preference for fight is so great that animals will even work to provide themselves with a suitable stimulus to attack.
It is well known that these situations activate the peripheral SYMPATHETIC NERVOUS SYSTEM resulting in AROUSAL, increased heart rate, ADRENAL GLAND release of ADRENALINE, and suppression of digestive activity. However, less is known about central mechanisms underlying these behavioural responses.
Experimental evidence (see Gray, 1987) suggests three separate brain systems that mediate emotional responses: (1) the REWARD system that responds to rewarding (non-punishment) stimuli by activating approach behaviour (positive emotional states); (2) the BEHAVIOURAL INHIBITION SYSTEM that responds to punishing stimuli by suppressing behaviour (passive negative states); and (3) the fight-or-flight system that responds to unconditioned punishment (non-rewards) by activating escape or aggressive behaviour (negative states). The AMYGDALA, HYPOTHALAMUS, and midbrain CENTRAL GREY are thought to be the central components of the fight-or-flight system. The amygdala projects to the medial hypothalamus and then to the central grey to serve as the final fight-or-flight common pathway. The central grey is under inhibitory control from the medial hypothalamus which may be disinhibited by activity from the amygdala. Upon initial exposure to novel stimuli, the behavioural inhibitory system dominates and inhibition of both approach and fight-or-flight is maintained. Attachment of rewarding or punishing significance to these stimuli evokes a change in the medial hypotha-lamus via the amygdala until either approach or fight-or-flight behaviour dominates.
