Carrion crows can evaluate a cloud of moving dots and decide which way it is drifting using the same core mathematical strategy that primate brains use for the task — and they do it roughly twice as fast, according to new research from the University of Tübingen.
Much of what scientists know about how brains make perceptual decisions comes from a classic test called the random-dot-motion task, in which a subject watches a cloud of flickering dots, some fraction of which drift together in one direction, and has to report which way the coherent motion is heading. In primates, neurons in the neocortex accumulate visual evidence over time, with firing rates climbing until they cross a threshold and the animal commits to an answer. Birds have no neocortex at all, so it was not obvious whether they could solve the same problem the same way.
Researchers Andreas Nieder and Philipp Schmidbauer put two hand-raised crows through an identical version of the task, recording from 248 neurons in a brain region called the NCL — widely regarded as the bird-brain functional counterpart to the primate prefrontal cortex, despite evolving along a completely different architecture. Both birds performed better than chance even when only 3% of the dots moved coherently, barely distinguishable from random noise, and their neural activity climbed toward a decision threshold just as primate neurons do. "This was the big question," Nieder said. "How would a differently organized avian brain encode decisions?" The answer, the team found, is that it uses essentially the same logic — just compressed into roughly half the time primates take.
Birds and mammals diverged evolutionarily more than 360 million years ago, making the shared computational strategy, arrived at through entirely different brain architecture, a striking example of convergent evolution in how nervous systems solve the same basic problem.