Counting Crows: Neural Basis of Numerical Ability in Crows Discovered

Tübingen neurobiologists discover cells in the crow brain that respond to a specific number of items.

An old story says that crows have the ability to count. Three hunters go into a blind situated near a field where watchful crows roam. They wait, but the crows refuse to move into shooting range. One hunter leaves the blind, but the crows won’t appear. The second hunter leaves the blind, but the crows still won’t budge. Only when the third hunter leaves, the crows realize that the coast is clear and resume their normal feeding activity.

Helen Ditz and Professor Andreas Nieder of the University of Tübingen found the neuronal basis of this numerical ability in crows. They trained crows to discriminate groups of dots. During performance, the team recorded the responses of individual neurons in an integrative area of the crow endbrain. This area also receives inputs from the visual system. The neurons ignore the dots’ size, shape and arrangement and only extract their number. Each cell’s response peaks at its respective preferred number.

Image shows a crow pecking dots on a computer screen.
Crows recognized the number of dots shown in computer displays. Tübingen researchers discovered ‘number neurons’ in the crow’s end-brain that responded to a specific number of items. Image credit: Andreas Nieder.

The study published in PNAS provides valuable insights into the biological roots of counting capabilities. “When a crow looks at three dots, grains or hunters, single neurons recognize the groups’ ‘threeness’ “, says Helen Ditz. “This discovery shows that the ability to deal with abstract numerical concepts can be traced back to individual nerve cells in corvids.” What makes this finding even more interesting is that a long evolutionary history separates us from birds. As a consequence, the brains of crows and humans are designed very differently. “Surprisingly, we find the very same representation for numbers as we have previously discovered in the primate cortex,” Prof. Andreas Nieder says. “It seems as if corvids and primates with independently und distinctively developed endbrains have found the same solution to process numbers.” Even abstract behavior which we think of as sophisticated mental feats ultimately has biological roots.

About this neuroscience research

Source: Universitaet Tübingen
Image Credit: The image is credited to Andreas Nieder
Original Research: Abstract for “Neurons selective to the number of visual items in the corvid songbird endbrain” by Helen M. Ditz and Andreas Nieder in PNAS. Published online May 11 2015 doi:10.1073/pnas.1504245112


Neurons selective to the number of visual items in the corvid songbird endbrain

It is unknown whether anatomical specializations in the endbrains of different vertebrates determine the neuronal code to represent numerical quantity. Therefore, we recorded single-neuron activity from the endbrain of crows trained to judge the number of items in displays. Many neurons were tuned for numerosities irrespective of the physical appearance of the items, and their activity correlated with performance outcome. Comparison of both behavioral and neuronal representations of numerosity revealed that the data are best described by a logarithmically compressed scaling of numerical information, as postulated by the Weber–Fechner law. The behavioral and neuronal numerosity representations in the crow reflect surprisingly well those found in the primate association cortex. This finding suggests that distantly related vertebrates with independently developed endbrains adopted similar neuronal solutions to process quantity.

“Neurons selective to the number of visual items in the corvid songbird endbrain” by Helen M. Ditz and Andreas Nieder in PNAS. Published online May 11 2015 doi:10.1073/pnas.1504245112

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  1. I often hear crows call to each other first thing in the morning (usually when I’m trying to either stay asleep or concentrate), not quite the dawn chorus I appreciate. One morning after a particularly large, noisy flock had been disbursed by city workers I noticed the conversation changed. Instead of the usual mobbing cacophony all at once, they were taking turns. Having voices that were either farther away or closer to me I found I could make out that each bird had a unique voice, much as we do. Then I realized with a shock that each one of those voices was consistently cawing a number, and would repeat that number until it heard another bird starting to count. It would then repeat the other bird’s number back, pause, then proclaim its own again. It sounded for all the world like, “I am over here and I am #5. I am #5. I am #5… I hear you #4. …I am over here and I am #5.”  As the voices came closer together again the tone of voice and turn-taking would stop as if no longer necessary. I’ve noticed this behavior every so often since. Having read this article I don’t think this is such a daft observation after all, even if it means we have to start thinking of birds as both skilled and self-aware. As to being self-aware, my own parrot tends to think out loud when she is contemplating doing something we’ve taught her not to do. Hearing our bird start saying, “Bad, bad, baaadddd,” has kept her out of a lot of trouble over the years. I doubt one could contemplate future action without being self-aware?

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