Crows are among the planet's most intelligent animals, teaching their young to use tools for foraging and banding together to fight off intruders. Now, the first study of how abstract reasoning works in these birds' brains could shed light on how intelligence works in a truly alien, non-mammal brain.
Illustration by Tiger-tyger
We've studied brain structure pretty extensively in mammals from humans and apes to whales and mice. But German neuroscientists Lena Veit and Andreas Nieder are the first to watch what happens in crow brains as these birds worked their way through a series of brain-teasers. They actually wired the crows' brains up with electrodes, watching as individual neurons fired when the crows did a test that required abstract reasoning. What Veit and Nieder found reveals a lot about what intelligence looks like in a brain that's nothing like our own.
The crow, and some of its relatives in the corvid family (such as jays and magpies), are among the only intelligent species we've encountered outside the world of mammals. But their brains are utterly different from ours. The mammalian seat of reason is in our prefrontal cortex, a thin layer of nerve-riddled tissue on the outside of the front region of our brains. Birds have no prefrontal cortex (PFC). Instead, they have the nidopallium caudolaterale (NCL), which is located toward the middle of their brains. You can see the different regions in the image, below.
The thing that's really interesting about comparing bird and human intelligence is that we did not evolve from a common, intelligent ancestor. Our last common ancestor with birds lived during the Permian period, about 300 million years ago, before the age of dinosaurs. It probably looked like a cross between a reptile and a rodent, and was roughly the size of a big raccoon.
This ancestor's simple brain was ruled by instinct rather than higher-level cognition. Still, lurking inside its rather small skull was a brain part called the pallium, which over millions of years evolved into the PFC in mammals and the NCL in birds. That makes mammal and bird intelligence an excellent example of parallel evolution — both groups of animals developed intelligence independently of one another.
Despite all their differences, the PFC and NCL have a few features in common. Veit and Nieder write in Nature Communications that both regions are involved in "working memory, reversal learning and reward prediction." The areas also "share important properties such as dense innervation by dopaminergic fibres and connectivity patterns with multiple sensory input, limbic and motor output regions." What that means is that the NCL and PFC are both packed with neurons, or nerve cells, that respond to the crucial neurotransmitter dopamine. Its neurons are also connected to the parts of the brain that handle memory, emotion, and body movements. The PFC and NCL are brain command centers, synthesizing information from a vast array of inputs and outputs.
Given that the NCL is the seat of crow intelligence, the researchers decided to see whether they could actually watch in real time as a crow figured out a puzzle. They used crows that had been raised in captivity, and trained to do a test kind of like the Sesame Street "which one doesn't belong?" quiz. The crows had to identify whether two images were different or the same.
First, the researchers put electrodes over the crows' NCL, to watch each neuron firing. Then they would present the crow with an image. Next, the crow would be prompted to choose an image that matched or didn't match that image (they had already been trained to do this with a sound or sign that either meant "match" or "don't match"). Finally, the crow would be presented with two images and have to choose the matching or not matching one.
This is a test that requires abstract reasoning, because the images change all the time and the crows have to apply the abstract idea of "match" or "not match" to a variety of inputs. In addition, this test reveals that the researchers defined intelligence as an ability to do abstract reasoning. Obviously there are many ways to define intelligence, and this is simply one way to do it.
What the researchers found was pretty amazing. They identified what they call "abstract rule neurons" which governed which answer the crows would give. Basically, the birds' brains assigned one rule (match) to one neuron, then the other rule (don't match) to another neuron. When the crows correctly matched an image, the match rule neuron would fire. When the crow gave an incorrect answer, or became confused, the abstract rule neuron fired only very weakly.
Veit and Nieder concluded that this was strong evidence that crows' brains have developed to handle abstract rules, which is why the birds are good at learning and responding to a variety of situations in a flexible way. They note that "the ability to guide behavior by general rules rather than by relying on fixed stimulus-response associations constitutes a survival advantage." This is the same survival advantage conferred on humans due to our intelligence. But our intelligence occupies a very different structure in our brains.
What this experiment suggests is that two dramatically different species might have similar abstract reasoning abilities — even if their brains are completely unlike each other. If we imagine that intelligence can only dwell in a mammal-like brain, we may miss out on discovering smart life forms elsewhere. The crow brain may be the first truly alien intelligence we've been able to study.
The crow brain may also help us better understand what's required to build an artificial intelligence, too. We can look at what the crow and human brain share in common, and speculate about what it might take to create an intelligence that resides in a non-brain structure. As I mentioned earlier, both the PFC and NCL contain many neurons connected to other parts of the brain, and they work a lot with the neurotransmitter dopamine. These regions also appear to deal in abstract rules.
Most of all, we can find hope in the idea that intelligence isn't just a quirk of one type of brain. Many kinds of brains can become intelligent. We are not alone.
Read the scientific paper in Nature Communications
Annalee Newitz is the editor-in-chief of io9. She is also the author of Scatter, Adapt and Remember: How Humans Will Survive a Mass Extinction.