Crows Match Monkeys' Decision-Making Logic, but Twice as Fast

Much of what scientists know about how brains make decisions comes from experiments in which monkeys watch moving dots. A new study has put birds through the same test, and the results suggest that crows reach decisions much like primates do, only faster.

The experiment is known as the random-dot-motion task. A cloud of flickering specks drifts weakly in one direction, and the subject must work out whether it is moving and which way. In primates, the task has shown that neurons in the neocortex collect visual evidence over time. Their firing rates climb until they cross a threshold, at which point the animal commits to a choice.

Birds, however, have no neocortex, which left open how their brains handle similar decisions. "This was the big question," said Andreas Nieder, a neurobiologist at the University of Tübingen. "How [would] a differently organized avian brain encode decisions?"

To find out, Nieder and colleague Philipp Schmidbauer gave the same task to two hand-raised carrion crows and recorded their brain activity as they worked. The birds sat in front of a touch-sensitive monitor showing white dots on a black background. Some fraction of the dots drifted together to the left, right, up or down, and the crows reported the direction by pecking one of the targets flanking the display. A correct answer earned a mealworm.

Nieder said the team deliberately kept the setup identical to the monkey version. "We intentionally wanted to have exactly the same random-dot motion task," he said. "The only difference was that the crows had to peck to indicate their decision, whereas monkeys were indicating by making an eye movement."

The researchers varied the difficulty by changing how many dots moved together. At the easy end, 81 percent of the dots moved coherently, which is trivially easy to read. At the hardest end, 3 percent did, barely distinguishable from noise. The team also included a zero percent condition, in which there was no correct answer.

The crows ultimately solved the task in the same way primates do, using the same mathematical logic even though their brains are organized very differently. They also did it twice as fast as the monkeys. The finding indicates that a brain without a neocortex can arrive at decisions through a comparable process.