Indiana Jones and the Overactive Amygdala

For Indiana Jones, there was no villain as menacing and no foe as treacherous as the writhing snakes in Raiders of the Lost Ark. Audiences saw their archaeologist champion paralyzed by fear and almost vanquished by his reptilian adversary. Heroic Indy is not alone! Approximately one third of adults report being ophidiophobic, or terrified of even the thought of snakes. The laboratory of Dr. Öhman at the Karolinska Institute examines how evolutionarily engrained fear-relevant stimuli (i.e. pictures of snakes) influence attention and emotion. If Indiana Jones had been a subject, it is likely that in response to pictures of snakes he would have exhibited a strong psychophysiological response, including an accelerated heart rate, increased blood pressure, enhanced skin conductance, and activation of the startle reflex [1]. It is easy to be sympathetic to Indy’s condition, since we know that attacks by venomous snakes can be fatal. It is more challenging to understand why a picture of a snake – and not just the snake itself – can invoke such a powerful physiological reaction.

Fear is defined as an activated aversive emotional state that motivates an organism to cope with threatening stimuli. Defensive mechanisms often include freezing, escape, or attack. It is thought that fear is controlled by evolutionarily-conserved systems in the brain, primarily the amygdala.

The inability to extinguish fear responses after an immediate threat has diminished is characteristic of anxiety disorders. Uncontrollable states of fear that no longer provide an evolutionary advantage include post-traumatic stress disorder, panic disorders, and phobias. For people who have experienced trauma in response to a particular stimulus (e.g. a snake bite), it is likely that, in response to a quickly moving rustling in the grass, they would react with exaggerated startle, hypervigilance, elevated perspiration, and shortness of breath – a metabolically costly state for the body to exist in long-term. Fortunately for the more than 18% of U.S. adults who suffer from anxiety disorders, the neural circuitry involved in fear responses has been identified [2]. The challenge that remains involves understanding how to shift a pathologically dysregulated fear response to one that is advantageous for avoiding snakes in the way of uncovering that mysterious and long-lost artifact in the Temple of Doom.