U. WASHINGTON-SEATTLE (US) — Instinctively knowing how to avert danger and stay safe—or not—may depend on a brain area known as the amygdala in both humans and animals.
A study with rats—and one nasty LEGO predator—sheds light on how rats weigh their odds when trying to retrieve food pellets. Neuroscientists studied how the amygdale—known to be an important brain area for perceiving and reacting to fear—was involved in the rats’ decisions to risk their safety for food. The findings are reported in the Proceedings of the National Academy of Sciences.
In humans, impaired amygdala activity has been linked to risky decision-making, such as gambling. And an overactive amygdala could explain anxiety disorders, including post-traumatic stress disorder and phobias.
“When animals go out to forage, they’re taking a risk,” says Jeansok Kim, a University of Washington psychology professor. “They’re leaving the safety of their nests, venturing out where there may be predators that could eat them.”
Kim and co-author June-Seek Choi, a visiting professor from Korea University, trained male rats to retrieve a food pellet placed at varying distances from a safety zone, or nest. The rats, hungry from a restricted food supply for several days, quickly learned to retrieve the food pellets.
The researchers introduced a “predator,” an alligator-shaped robot that was programmed to snap its jaws and surge at the rats. The LEGO Mindstorms Robogator was about twice the size of the rats. The researchers programmed the robot to lurch forward about 9 inches, open and shut its mouth and then return to its resting spot far away from the rats’ nest.
With the robot in place, the rats began foraging as usual. When they neared the food, the Robogator quickly moved toward the rats and snapped its jaws. The rats scurried back to the safety of the nest and then momentarily froze—a typical fear response.
Still hungry, the rats paced back in forth in the nest areas, hidden from the Robogator. Slowly they re-emerged and cautiously approached the food, while the Robogator continued its aggressive movements whenever the rats neared the food pellet.
Most rats learned that they could safely retrieve the food pellet placed closest, 10 inches, from their nest and not intersect the robot’s path. None of the rats obtained the pellet nearer the Robogator, about 30 inches from the nest.
Then researchers created amygdala lesions and observed the rats’ subsequent interactions with the robot. Rats with lesions were unperturbed by the Robogator, and when food was placed near the predator the rats ran straight for the food, barely flinching when the Robogator lunged and snapped.
When Kim and Choi increased the amygdala activity, the rats showed greater fear. Even when the food was at a safe distance from the robot, rats treated with the drug bicuculline, which increases neural activity, were too afraid to venture out for the pellet.
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