Primate brains show fear of snakes
Trait may have kept humans safe
We’re not born with a fear of snakes, but it sure seems to develop early.
Now scientists may be closer to explaining why ophidiophobia ranks among the top fears of humans and seems to be shared with other primates.
Researchers inserted probes into the brains of Japanese macaques and found that neurons in a part of their brains that controls visual attention were more strongly and quickly activated in response to images of snakes, versus other objects.
The results, published online in the journal Proceedings of the National Academy of Sciences, appear to support a theory that early primates developed advanced perception as an evolutionary response to being prey, not as an adaptation that may have made foraging or hunting easier.
Though fear of snakes may not be innate, noticing them more than other phenomena may be hard-wired by evolution, said Lynne Isbell, an evolutionary biologist from the University of California at Davis and one of the authors of the paper. That heightened attention, research has shown, can lead to early and resilient learned behavior, such as fear-mediated avoidance — in other words, getting out of the way of snakes.
“The characteristics we have help us to see them better than other mammals can see them,” Isbell said. “Mammals in general are really good at picking up movement. But snakes lie in wait. They don’t move very much, so it’s crucial to see them before they see us and to avoid them.”
Developing new additions to the brain would have given ancestor primates an advantage. Many scientists assumed the advantage had to do with catching insects for food. But Isbell shookthat viewof primate evolution in 2006.
“They were actually prey,” Isbell said “And the first of the modern predators of primates, and the most persistent, that continued to this day — and that look the same as they did 100 million years ago — are snakes.”
The brain addition that made all the difference for Old Worldmonkeyswas the pulvinar nuclei, Isbell said. Those areas of the thalamus have been found to control such things as eye and head motions toward stimuli — responses known as selective spatial attention.
Researchers inserted probes into the pulvinar nuclei, which receive inputs directly from the retina of the eye and also connect with nearby brain regions associated with threat-relevant behavior and emotional processing.
Electrical pulses fromthe pulvinar neurons occurred about 60 microseconds after the snake was presented to the monkeys — suggesting that the signal might be processed unconsciously. Another pulse came at about 250 microseconds, and that could be associated with feedback from the cortex, where higher cognitive functions are controlled.