Animal Instincts

Where is a human not an animal? In your right amygdala, according to new research published yesterday in Nature Neuroscience.

A team of researchers from Caltech monitored the brain activity of 41 epilepsy patients. As the patients relaxed in bed and looked at 100 different pictures of people, places, and animals, the neuroscientists captured the responses of 1,445 neurons in the brain—within the amygdalae and other locations.

The results? Each patient had a reaction to the images of animals in the right amygdala. The animals could be harmless household pets or threatening predators and the reaction was the same. No other image, including people, brought the same reaction.

The amygdalae regulate memory and emotion—whether fear, pleasure, or anger. (It features prominently in our video, How We Decide.)

This particular reaction leads the researchers to believe these reactions are hard-wired from our evolutionary past. From Discovery News:

[Lead author Florian] Mormann told Discovery News that the right amygdala “has previously been implicated in the processing both of stimuli that are aversive and of stimuli that are rewarding. During our evolutionary past, animals could have represented either predator (aversive) or prey (rewarding). In either case, their behavioral relevance was pretty high.”

…Animal images, [co-author Ralph] Adolphs explained, “mobilize the brain's resources to process information about them. The amygdala helps us to detect that there is an animal out there, and we can then pay attention to it, encode it into memory, and mount a behavior response.”

Interestingly enough, the patients had the same “animal” response to Yoda and Shrek, but not Brad Pitt, Julia Roberts, former President Bill Clinton, or Mother Teresa. (Download a pdf here to see all the images.) Makes you think…