Oh look, little animal!

Man is an amazing creature and still brings surprises to his researchers. Just recently, specialists from the California Institute of Technology (Caltech) and the University of California (University of California, Los Angeles - UCLA) discovered a special area in the human brain for quickly responding to any animal they see. This region turned out to be the right amygdala, a cluster of almond-shaped neurons located deep in the middle temporal lobe of the brain.

It all started at Ronald Reagan University Medical Center. Neurosurgeons prepared for surgery patients with epilepsy who were not helped by drug treatment. In preparation, patients have electrodes implanted in the temporal lobes of their brains for several days to determine which neurons fire during seizures and what surgical intervention should be performed. Caltech biologists took advantage of this situation: since patients are densely covered with electrodes anyway, why not use them to study the activity of nerve cells in the temporal lobes in response to a variety of visual stimuli. 41 patients were involved in the study, and their voluntary informed consent was obtained. But who would refuse a doctor such a request before an operation?

Patients were shown photographs of people, animals, landscapes and architectural objects, while the activity of 489 neurons in the amygdala, 549 cells in the hippocampus and 407 neurons in the entorhinal cortex was recorded. The researchers were surprised by the result: it turned out that the nerve cells of the right amygdala react violently to pictures depicting animals, any kind, be it a fluffy rabbit or a snake, a fish or a bird, or even a rhinoceros. Neurons in the left amygdala and other brain regions studied do not have such selectivity and fire slightly in response to each stimulus.

Using nuclear magnetic resonance imaging, researchers were convinced that a specific reaction of the right amygdala to images of animals occurs not only in patients with epilepsy, but also in healthy people. Noting how fruitful the collaboration between fundamental science and clinical medicine can be, the scientists began to discuss the results. In their opinion, the discovered phenomenon arose in prehistoric times, when every animal that appeared in a person’s field of vision posed either a threat or potential prey to him. In both cases, one had to act quickly: catch prey, run away from a predator, and part of the brain was specialized specifically to provide an immediate reaction. This specialized area was the right amygdala, but its role had until now gone unnoticed by researchers because neuroscientists studying the functions of the amygdala had never before shown subjects images of animals.

The fact that the left amygdala is devoid of increased animal sensitivity does not surprise researchers. Interhemispheric asymmetry is a well-known phenomenon. The right hemisphere plays a leading role in visual-spatial orientation and reaction to all sorts of surprises and biologically significant external stimuli, and the discovered specialization of the right amygdala fits well into the existing principles of physiology.

The hypothesis proposed by Californian scientists needs confirmation, but for now we will venture to propose another one. The amygdala is the part of the brain responsible for emotions, and all human culture is inextricably linked with the emotional perception of animals. Since ancient times, they have personified certain qualities. The jackal is a symbol of cowardice, the fox embodies cunning, the snake and raven are wisdom, the worm is insignificance. The lion is the king of animals, the deer is a noble animal. Animals and birds are tribal totems, characters in legends, fairy tales and fables. The ancient world rested not on a stone, but on a huge turtle (whales, elephants). Nowadays, animals arouse genuine interest among a variety of people; it is supported by numerous popular programs, books and films. More than one generation has grown up on the program “In the World of Animals,” wonderful BBC films, and Darrell’s books. Advertisers are well aware of the emotions that animals evoke in people. Without studying the functions of the tonsils, they use animals in advertising for household appliances and cars. So how can a person remain indifferent after all this when they are shown a photograph of a rabbit or an eagle?

Meanwhile, Californian researchers are going to test how other types of “brutal” stimuli affect the brain: the smells of animals and the sounds they make.

Natalia Reznik

Press release: http://mr.caltech.edu/press_releases/13449

Florian Mormann, Julien Dubois, Simon Kornblith, Milica Milosavljevic, Moran Cerf, Matthias Ison, Naotsugu Tsuchiya, Alexander Kraskov, Rodrigo Quian Quiroga, Ralph Adolphs, Itzhak Fried, Christof Koch. A category-specific response to animals in the right human amygdala. Nature Neuroscience, 2011; DOI: 10.1038/nn.2899.