An introductory text reads, you instantly recoil when you spot a snake- then sigh with relief just a moment later when it registers that the snake is a rubber toy. Have you ever wondered why you react with fear when a “threat” turns out to be nothing? Why does it take longer for you to process a threat than react to it? Sensory information (sight, sound) entering the brain travels to the thalamus and is then routed to the cortex for processing. Sensory information can also go directly to the amygdala. In the case of a threat, the amygdala alerts other areas of the brain and the endocrine system instantly without waiting for a conscious command. This enables a response to fear before you are even fully aware of what you are reacting to.
A schematic shows a woman looking at a snake hanging in a branch; parts of her brain are highlighted and labeled. Two ovoid structures attached to each other at center is labeled thalamus, an almond-shaped structure attached at the end of a C-shaped structure is labeled amygdala, a small region in the occipital lobe is labeled visual cortex.
The pathways of the information through brain are as follows, the path from eyes to thalamus and its corresponding callout reads, visual information goes directly to the thalamus; the path from thalamus to amygdala is labeled direct path and its corresponding callout reads, basic information about threat is conveyed directly to the amygdala, enabling rapid response; the path from thalamus to visual cortex is labeled indirect cortex and the corresponding callout reads, it takes longer for neural information to go to the visual cortex for processing; the path from visual cortex to amygdala is labeled information about threat and corresponding callout reads, if it’s been determined that the threat is a false alarm, this message will instruct the amygdala to inhibit the fear reaction. A callout from amygdala reads, after receiving information about threat, the amygdala: instructs hypothalamus and medulla to alert sympathetic nervous system; prompts pituitary gland to secrete stress hormones.
Amygdala leads to an illustration of an enlarged view of the coronal section of brain. Two sub cortical structures are highlighted in red on either sides of brain just over the brain stem. Text below reads, the amygdala, shown here in red, plays a pivotal role in experiencing fear. Information about threats prompts the amygdala to activate the physiological responses that characterize fear.
An illustration below the schematic depicts a mouse close to a cat. A callout beside reads, what happens when the amygdala doesn’t work? Animals with amygdala damage may not exhibit any response to a threat. For example, the mouse in this picture is uncharacteristically comfortable with a predator. Similarly, one study found that people with amygdala damage demonstrated an absence of expected fear behaviors (Feinstein, Adolphs, Damasio, and Tranel, 2011).