Surrounded by technology and urbanity though we may be, the human brain remains profoundly hard-wired to respond to animals.

When people are shown pictures of animals, specific parts of the amygdala – a structure central to pleasure and pain, fear and reward – react almost instantly.

Put another way, glimpsing a bird at the feeder or a shark on Animal Planet, or even a plankitten, could invoke cognitive tricks inherited from ancestors who walked on four legs in shallow water.

The effect is large and consistent, and "may reflect the importance that animals held throughout our evolutionary past," wrote researchers led by California Institute of Technology neurobiologist Florian Mormann in an Aug. 29 Nature Neuroscience paper.

The researchers had access to a unique group of research subjects: 41 people receiving surgery for drug-resistant epilepsy. Prior to surgery, doctors needed to map their minds, a task performed by inserting electrodes into different parts of their brains, then measuring neuron-by-neuron responses to stimuli.

Mormann and colleagues showed the patients pictures of animals, people, landmarks and objects. When patients saw animal pictures, activity spiked in the right amygdala, in the brain's right hemisphere. Full mapping would eventually show those animal-related areas to be uninvolved in each patient's epilepsy.

"As the finding extends across many patients, it would imply something universal," said study co-author Christoph Koch, also a California Institute of Technology neurobiologist. "As universal as the much better-known brain asymmetry for reading text and for comprehending and producing language."

The researchers suspect that animals were so important during evolutionary history as to merit a dedicated processing area in the brain. This doesn't just apply to humans or even primates, however.

Hints of it appear in animals' tendency to favor one eye, and thus one side of their brain, when scanning for food or predators. That behavior has been found in every class of vertebrates, from mammals to fish.

It will be interesting to see whether animal-specific areas and processes exist in earlier stages, before information from our eyes has reached the amygdala, wrote Mormann's team.

Images: 1) A visitor to the Fujifilm giant panda habitat. (woodleywonderworks/Flickr) 2) Red panda at the Brooklyn Zoo. (Brandon Keim/Wired)

See Also:

Citation: "A category-specific response to animals in the right human amygdala." By Florian Mormann, Julien Dubois, Simon Kornblith, Milica Milosavljevic, Moran Cerf, Matias Ison, Naotsugu Tsuchiya, Alexander Kraskov, Rodrigo Quian Quiroga, Ralph Adolphs, Itzhak Fried, & Christof Koch. Nature Neuroscience, Aug. 28, 2011.