The Crow and the Octopus (or Cognition in the Brain)
Brian size and smarts - corvids and octopuses - Einstein's brain wrinkles
Baby got… brain?
When we were thinking about monkey twins, as one does, we considered human babies’ big brains. That’s how we love to think about ourselves, the big-brained primate, the smartest animal.
And it’s true, we have big brains.
Our so-called ‘encephalization quotient’ (EQ) - a measure of how far brain size deviates from what we’d expect for a given body mass - is about 6.5. For reference, a chimp comes in at around 2.5. Most primates hover around 2, as do many large whales. Second place goes to dolphins at 5-5.5.
This EQ value is thought to reflect differences in ‘intelligence’ (maybe just because that makes us feel good about ourselves). Intelligence is a slippery concept, but looking at the EQ list, it feels intuitively right, doesn’t it? Bigger brain relatively speaking, smarter animal.
If only it were that simple.
For example, an average human with an average-sized brain has an EQ of ~6.5. A very large, overweight person might drop to a 4, simply because of the difference in body weight. Some researchers have claimed that, in non-human primates, we might be better off looking at absolute brain size — later refined into a new metric called the ‘estimate of cognitive brain size based on cognitive equivalence‘. So, bigger brain, smarter animal, after all? Not quite. If we want to compare different groups of animals, we can’t simply rely on brain size either. The brains of the smartest birds (corvids and parrots) weigh between 1 and 25 grams. And yet, in cognitive tests, they appear to do (at least?) as well as chimps with a 400-gram brain1.
Cognitive prowess is not (just) about absolute brain size and it’s not (just) about a fancy formula that correlates brain and body size.
It’s about organization.
Let’s look at some brains.
Crow brains, octopus arms
In the human brain, the wrinkly outer layer, the neocortex, is the home of our more advanced cognitive skills.
Birds don’t have a cortex. For example, this is the brain of a New Caledonian crow, one of the feathered Einsteins. That’s much smoother than the wrinkly walnuts in our skulls.
Where are the birds hiding their smarts if not in an analog for the brain’s whirls (sulci and gyri) that house human cognition? Here’s the thing: there are different ways to biologically build advanced cognition.
Once upon a time, about 310-330 million years ago, lived the common ancestor of birds and humans. The surface of its brain was called the dorsal pallium. In mammals, hundreds of millions of years of evolution expanded this pallium into the cerebral cortex with its wrinkled appearance. In birds, this pallium became the much cooler-sounding hyperpallium. Similar outcome (smarts), different approach.
For example, bird brains contain twice as many neurons as a similar volume of primate brain. Keeping in mind that the number of (cortical or pallial) neurons appears to correlate with cognitive capability, birds suddenly sound pretty smart. Bird brains have another trick: a higher proportion of their neurons are pallial neurons. Translation: about ~20% of all primate brain cells are found in the cortex, where complex cognition happens. In birds, up to 75%(!) of brain cells are found in the hyperpallium, where bird cognition happens. Smart birds have another cognitive booster thanks to the high number of associative neurons in their hyperpallium. This type of brain cell is especially relevant for flexible thinking. Crows have about as many of these neurons as chimps. New work also suggests that bird brains, unlike what we thought for a long time, have a cortex-like organization. Their brains are not that different from ours, they just look different and are assembled more (space) efficiently.
What about a clever brain that is very unlike ours? Say, a donut2 brain that spends a lot of time in eight arms3? Octopuses are notoriously clever and, at times, mischievous. Their brains look like this:
They are very visual and very touchy creatures. Neuroscience-interested readers will rightfully point out that the peripheral arms system isn’t really part of the brain. True. Yet, functionally and structurally, some researchers argue that the ‘arm nerve cords’ of octopuses are part of the central nervous system (like the vertebrate spinal cord) rather than part of the peripheral nervous system. And only a little over a year ago, scientists discovered that the arms are connected through ‘intramuscular nerve cords’, which run through the nerve ring you see in the image above. That nerve ring enables,
… rich interarm signaling that supports arm control and coordination occurring outside of the brain.
That doesn’t mean the central brain isn’t keeping a metaphorical eye on things, but it suggests that relatively complex cognition can find a home in different brain organizations.
As we all know, it’s not about size; it’s about how you use what you have. At least, let’s hope so, because human brains are shrinking.
Einstein's brain
The extent and timing of human brain shrinkage remain topics of debate, but there are indications that human brain size peaked in early Homo sapiens and Homo neanderthalensis. Every researcher in the field has her/his pet theory — perhaps it was the transition to agriculture, perhaps it was cognitive offloading through the use of writing, perhaps our brains simply got more efficient, etc.
Should we start to panic? If it’s not about size, we might be okay. However, in the first section, we saw that brain size matters for cognitive capacity in non-human primates. But the crow and the octopus show it’s not just about size. Wait, what does intelligence actually look like in (adult) human brains?
Size matters (a little bit). If you look at correlations between IQ4 and brain size, researchers tend to find weak to moderate5 correlations. But how much does this tell us? This strength of the brain size-intelligence link differs when we measure different aspects of intelligence, and the largest human brain on record is from a 19th-century prematurely deceased young man suffering from epilepsy and neurodevelopmental problems. The second largest brain ever measured belonged to a 19th-century teacher/serial killer. And if size is such a big deal, where on the list do we find Einstein? Well, the size of the whiskered genius’s brain is… slightly below average.
But Einstein’s brain was unusual in other aspects. It possibly6 had more connections between the two brain hemispheres, an extra ‘wrinkle’ in the frontal lobe (which would increase the surface area), an expanded area for left-hand control (which may be correlated to his violin playing), and his parietal lobes were unusually large and showed an exceptionally complex pattern of ‘wrinkles’ (which may have contributed to his propensity to think in images and impressions).
What about us non-Einsteins? If we look at the brain in a very general way, the importance of size for intelligence seems evenly distributed between gray and white matter. A thicker and more wrinkly cortex also correlates with complex cognition, as does a thicker corpus callosum (linking the brain hemispheres).
Two notes:
We’ve been very anatomical in this post, but these large-scale, structural features tell us little about the effects of brain activity. For example, a brain that flexibly transitions between network states is probably a clever one. Similarly, well-networked fronto-parietal areas are helpful (both for intelligence and creativity, which show substantial overlap in the brain). How efficient your brain is might matter too, but that effect might be affected by learning — so learning is not only good for acquiring specific skills; it makes you better at learning in general too.
The brain is not static. It’s plastic7. Living, loving, and learning all change your brain, like the London cab drivers that grow chonkier posterior hippocampi through navigating the complex city.
I want a science fiction conclusion. Oh, how about this?
Maybe soon we’ll print better brains, as in this study in which the researchers used 3D bio-printing to build neural tissues (containing both neurons and astrocytes) with functional connectivity. Just upload the Einstein template and…
Thank you for reading; I hope it tickled your brain. Also good for the brain: clicking things!
Corvids and primates tend to have a similar EQ, but since this is based on a formula that used mammal species as a reference, we could wonder how fair this is to the birds…
In octopuses, the esophagus passes through the central brain.
I simply have to recommend Adrian Tchaikovsky’s brilliant Children of Ruin (sequel to the equally brilliant Children of Time), a space opera novel with, by far, the most intriguing depiction of octopus intelligence I’ve ever read.
What IQ is and is not deserves a whole post, or book, in itself. On one end we find people who state that all IQ tests measure is how good you are at taking IQ tests. On the other, some people think high IQ is the measure of all things. Several studies find correlations between overall IQ score (but know that any good IQ test has several subscores) and life outcomes. However, those correlations may be skewed by test motivation, not to mention social environment (including education opportunities).
Fun fact: assortative mating is greater for intelligence than for any other trait (personality, height, etc.) — you’re more likely to choose a partner with a similar intelligence level.
A lot of this is based on the analysis of photographs, so add a teaspoon of salt.
Another book recommendation? I thought you’d never ask. Check out Livewired by neuroscientist David Eagleman, one of the best books about our brains I’ve read in a while.
So fun! True story, I got WAY into dolphin and orca brains for like a year. This post reconnected me with that old version of me—which I’m sure is what you were going for.
Hey Gunnar! Love the post and specifically the highlight on human brains shrinking. I've wanted to build on this idea too, of writing a sci-fi take. With the capability to offload cognition to our collective intelligence (internet?), we've realized biologically that smaller brains have lower metabolic needs and excess energy can be directed towards anabolism. Then class-warfare erupts between the digitally/neuro-implanted giants versus the indigent, regular humans. Maybe a little too dystopian for my taste. What could go wrong? Thanks for the jolt of inspo!