Study of Monkey Brain Explains Human Fear of Snake

Fear of snakes is the most common phobia.  In a new finding, scientists explain why ophidiophobia-fear of snakes, is placed among the top fears of humans,  also seen in other primates.

Scientists have found specific brain cells that trigger a rapid warning in response to the slithery creature. The researchers claim that the fear of snake is not innate, but develops early in life.

Earlier, a theory proposed by Lynne Isbell, professor of anthropology at the University of California, Davis, claimed that the evolution of high-quality vision in our ancestors was driven by the threat of snakes. In this finding, neuroscientists from  Japan and Brazil test the notion.

Isbell identified the neurons in the Japanese macaque brain that responded selectively to the images of snake, the team in their present finding implanted electrodes into the brains of two adult macaques (one male and one female) that were raised at the national monkey farm in Amami Island, Japan.

The monkey's pulvinar neuronal activity was recorded via electrodes. The researchers then showed images of monkey faces, monkey hands, geometric shapes and images of snakes. The monkeys had no previous encounter with snakes before the experiment. The researchers noticed that the brains of the monkey displayed a preferential activity of neurons in the medial and dorsolateral pulvinar on seeing images of the snakes. Compared to the other stimuli, snakes extracted the fastest and strongest responses from the neurons.

"We're finding results consistent with the idea that snakes have exerted strong selective pressure on primates," Isbell said in a statement.

Hisao Nishijo at the University of Toyama, Japan, studied the neural mechanism responsible for emotion as well as fear in the macaque monkeys, especially those instinctive responses that occur without learning or memory.

"The results show that the brain has special neural circuits to detect snakes, and this suggests that the neural circuits to detect snakes have been genetically encoded," Nishijo said.

"I don't see another way to explain the sensitivity of these neurons to snakes except through an evolutionary path," Isbell concluded. "I don't do neuroscience and they don't do evolution, but we can put our brains together and I think it brings a wider perspective to neuroscience and new insights for evolution."