Years of either running from or running after animals left its mark in the human brain -- even just looking at a photo of an animal jolts our brains into action.
No matter how high tech and urban we may become, animals continue to affect our brains like no other person, place or thing, shows new research in the latest issue of Nature Neuroscience.
Co-author Ralph Adolphs explained to Discovery News "that it is important for the brain to be able to rapidly detect animals. The reasons for this are probably several, but would likely include the need to avoid predators and catch prey."
"These abilities are at once critically important to survival and yet very difficult to do," added Adolphs, a professor of psychology, neuroscience and biology at the California Institute of Technology. "Both predator and prey detection requires fast, real-time detection of shapes that are often camouflaged in a cluttered environment."
Adolphs, project leader Florian Mormann, and their colleagues recorded how the brains of 41 neurosurgical patients undergoing epilepsy monitoring responded to images of people, landmarks, animals, or objects. During 111 experimental sessions, the researchers monitored the subjects' brain activity as they sat in bed while viewing about 100 images per session. The monitoring was quite precise, showing how even individual neurons reacted.
The scientists found that neurons in the right amygdala responded preferentially to pictures of animals, whether they were of cute little critters or threatening big beasts. The amygdalae are two almond-shaped groups of neurons located deep within the brain.
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."
Outside of an experimental setting, humans, of course, don't just see animals. We hear them and they affect our other senses too. Although the study just involved photographs, the researchers suspect the amygdala would have also been jolted into action by animal calls.
Even though we may not feel particularly moved by animal images, the researchers say the resulting brain activity occurs at a conscious level. The researchers stop short of saying that animals inherently trigger our emotions, but it's possible that they do affect our fear and arousal responses in unique ways.
Prior studies have supported that early in vertebrate evolution, "the right brain hemisphere became specialized in dealing with unexpected and behaviorally relevant stimuli," Mormann said. This latest study strengthens that theory.
The level of specialization is intense, especially considering how the human brain springs into action after just seeing a photo of an animal.
Animal images, 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."
For our early human ancestors, that response would likely have been to run for their lives, hide, admire, or go in for the dinner kill.