The neuroscientist's brain


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Some have more neurons, others, less... Where does one draw the line?

I just received an email from somebody who was concerned about how my research on numbers of neurons in cats and dogs (and so many other species...) has been portrayed in the media. Her points: so many reports of "sorry, cats, you're dumb" might encourage people who mistreat and abuse their pets; along the same lines, claims that humans "stand out" cognitively in having the most neurons in the cerebral cortex might encourage, and perhaps even justify, thoughts of human abuse over all other creatures.

I had received messages expressing a similar concern before: where does one draw the line below which "cruelty is acceptable"? If cortical neurons are those that endow brains with flexible and complex cognition, and the more the better (in terms of flexibility and complexity of information processing), how many are enough for self-awareness, for suffering, for caring? When is the number of cortical neurons "large enough" to warrant personhood and legal rights? To warrant not being eaten? Some ask this in search of legitimacy, comforted by the knowledge that no other species has as many neurons in the cerebral cortex as we do* (apparently). Some have political motivations, and want to have this or that species granted personhood status, too; others are just looking for an easy way out of the animal condition of not doing photosynthesis: we, animals, have to eat other life forms.

The main message I always try to get across from my work is that we humans are just another animal. We are a scaled-up primate, the animal with the biggest primate brain and thus the largest number of cortical neurons, which I believe is the simplest basis for all our cognitive feats (once we educate those neurons by feeding them knowledge through education) - but a primate, nonetheless. Differences between humans and other animals are a matter of quantity, not quality; in keeping with this continuum, I think there is neuroanatomical reason to work with the hypothesis that ALL vertebrates have some level of consciousness. We're not the only ones.

So no, I don't set a bar anywhere. In terms of who is deserving of respect, I don't even set a bar at who has ANY neurons.

With the awareness that we are animals, and therefore belong in the same Nature as all others, comes the realization that, as animals, we need to eat. We don't have the genes for photosynthesis, for grabbing matter our of thin air. That means that we have to ingest other forms of life. Yes, LIFE; not just animals. A raw carrot is chewed alive. Fruits are alive and breathing as we pop them into our mouths (something that I love to remind vegans who start proselithising). I say this in all seriousness: my point is that we should be aware of our place in nature, and be respectful of ALL others, even as we kill them in order to sustain ourselves or chew them still alive, as we do with plants.

What people choose to do with the knowledge we can offer them is something that, as much as we disagree with them, they alone can decide (the alternative turns very rapidly into a totalitarian state, which some would argue is what you get with ANY type of law, but that is a whole other discussion). We can always keep offering more information, of course, in the hope that they will someday choose to act differently. This applies to journalists and pet owners alike - and to parents, voters and so many other people we will disagree with during one's life.

So here is my answer to those who ask what can possibly be gained from examining how many neurons different species have, human or not, and what difference does that make in terms of cognition: I believe it helps humans to know that we are JUST ANOTHER ANIMAL. Some animals may be more cognitively capable, others less (cats vs dogs, gorillas vs humans), but NONE is less deserving of respect because of that. I do noy believe, or argue, that "intelligence" or "number of neurons", or anything that can be put a number on,  could/should be used as criterion for "what creature is it ok to NOT be respectful to".

I don't and won't draw a line anywhere. I'm respectful of the bugs that I would gladly move back outdoors rather than kill. I'm respectful of the fish that I eat. I'm respectful of the beautiful cows and pigs that some day end up on my plate (again, because of my animal nature), and of the gorgeous vegetables that I roast alive so that I can live another day.

Yes, the continuum seems to put humans at the top in terms of cognitive capability. Yes, some people will choose to state that that position warrants/justifies whatever-we-want. I don't subscribe to that. Unfortunately, I can't make every journalist or reader understand that. But then again, it is the fact that some disagree, and some disagree enough to write to me, that brings people together and fosters respectful discussion and exchanges of opinions and ideas. As long as that is the case, I'm happy.


A raccoon school in my backyard

I wish I had raccoons in my backyard. So far it's only been dumb squirrels (I speak from experience, I know how few neurons they have in their cortex) that dug up my succulents so fastidiously that I gave up and took them indoors to my office.

I was happy to see the raccoon portrayed in the first Guardians of the Galaxy movie: back then, we had just found out that these critters had very respectable, primate-like numbers of neurons in their cat-sized cerebral cortex, which is perfectly in line with all the lore that accompanies them (and that, having moved recently to the US from the tropics of Brazil, I have yet to witness on my own).

A reader of our new report on numbers of neurons in cat & dog & raccoon brains was kind enough to share with me the hilarious story below. If I had raccoons in my backyard, I might start leaving them puzzles to solve - a different one every night, tasty treat inside. Maybe they would soon advertise the new Raccoon School in the neighrborhood...


Generations of Barrys have been raccoon bait

Q. HOW MUCH FOOD SHOULD I TAKE? [when I go camping with my family]

A. A lot. You'll be providing food not only for your family, but also for the entire raccoon community. And please do not be so stupid as to think you can keep your food away from the raccoons. Raccoons are the most intelligent life form on earth, as was proven in the October 2000 world chess championship match in London, where a raccoon not only defeated reigning champion Garry Kasparov in six moves, but also took his sandwich. 

I know what raccoons are capable of. When I was a boy in rural Armonk, our garbage cans were regularly terrorized by a gang of brilliant criminal raccoons. I recall being awakened at 3 a.m. by loud noises, and looking out the window to see, by moonlight, my father, a peace-loving Presbyterian minister, charging around in the bushes in his pajamas, wildly swinging a baseball bat and saying non-Presbyterian words. Of course he did not get the raccoons; you NEVER get the raccoons. The raccoons were safe in their secret headquarters, recording my father via high-resolution night-vision videotape technology that humans would not develop for another 25 years. That particular video is still hugely popular on Raccoon Entertainment TV ("Tonight we present the classic episode, 'Crazed Minister in Pajamas' "). 

Ten years later, I was a counselor at Camp Sharparoon, which meant that I had to go camping in the woods with a group of boys and a nutritionally balanced food supply consisting of 75,000 small boxes of Kellogg's Frosted Flakes. I tried to protect our food at night via the Boy Scout-handbook technique of suspending it from a rope strung between two trees; the raccoons, who were monitoring me via tiny cameras hidden in pine cones, thought this was hilarious. When darkness fell, they got the food down in seconds, using lasers. It would not surprise me to learn that they had paid the Boy Scouts to put that technique in the handbook.


Dogs (and raccoons) have the most neurons


Cat lovers are going to hate this: our new research shows that cat brains have only about half as many neurons in the cerebral cortex as dogs. Because this is the part of the brain that allows for complex and flexible cognition, the expectation is that dogs have better cognitive capabilities than cats. 

While animal trainers and owners often agree that dogs do seem to have a richer behavioral repertoire and to be better than cats at problem solving, evidence of that is far from systematic, much less definitive. The reason is that counting neurons in brains (by turning them into soup, a method that we developed) has proved far simpler than putting a number on behavior and cognition so that they can be compared across species.

Still, numbers of neurons in the cerebral cortex have been telling a coherent story. Humans have by far the most of those, even though their cerebral cortex is nowhere near the largest: the African elephant cortex, for instance, has only one third as many neurons (5.6 billion) as the twice smaller human cerebral cortex (which has on average 16 billion neurons). Second place currently goes to gorillas and orangutans, tied at 8-9 billion neurons; chimpanzees, at 6-7 billion neurons, occupy third place in the ranking of Most Neurons in Cerebral Cortex.

The discrepancy between Most Neurons in Cortex and Largest Cortex is due to an evolutionary divergence of primates (ourselves included) from all other non-primate mammals examined so far. Whereas early mammals seem to have added neurons to their cortices that also became progressively larger, primates appeared on the planet with a number of distinctions that included flat fingernails (not claws), binocular vision, and neurons that no longer got larger as they became more numerous. As a result, over evolutionary time, non-primate brains increase in size much faster than primate brains as their cortices gain neurons.

Our latest work, about to be published in Frontiers in Neuroanatomy, added eight carnivoran species to the still-growing list of animal species whose brains the group has been turning into soup to count their neurons. The simplest expectation was that this new set of species – ferret, banded mongoose, cat, raccoon, dog, hyena, lion and brown bear – should have brains that scaled like any other non-primate brain. On the other hand, large carnivorans such as lions rely on hunting large game, which might impose a heftier cognitive requirement to outsmart prey whose longer legs can outrun them. In turn, others, like cats and dogs, have been domesticated for thousands of years, which is often presumed to alter the relationship between brain and body size in the direction of smaller brains for a given body size (or larger bodies for a given brain size). Would their numbers of neurons also have been affected?

Drawings by Lorena Kaz

The work, led by Ms. Débora Jardim-Messeder as part of her Master’s degree, shows that most of the examined carnivorans, including domesticated cats and dogs, match other non-primate species in the numbers of brain neurons they have for a given brain structure mass. Cats, with brains that are always smaller than those of dogs, have, as expected, fewer neurons, too: in the cerebral cortex, the authors found around 250 million neurons in the cat, a meager number compared to 430 million neurons in a small dog and an even larger 620 million neurons in a golden retriever. Because both small and large dogs still fit the relationship between cortical volume and number of neurons that apply to all other non-primate mammals, it seems that even though domestication and artificial selection led to dogs of a wide variety of sizes, their brains still scale like any other non-primate species.

That is not at all the case for the raccoon, one of two marked exceptions uncovered by the study. Despite having cat-sized brains, the two wild-caught raccoons had dog-like numbers of neurons in their cerebral cortex, around 400 million. So many neurons in such a small cortex puts raccoons on par with primates. Shrewd and cunning that these masked animals are, they were indeed once classified as monkeys before being acknowledged as carnivorans. Behavioral neuroscientist Prof. Kelly Lambert, from the University of Richmond, VA, who provided the raccoons for the study, has long been amazed by the behavior of raccoons and was pleased to see that they have appropriately large numbers of cortical neurons. Lambert studies rats in her own lab, though; when I asked why she doesn’t study raccoons, since they are so clever (whatever that means or however that’s measured), her answer was “because the lab would have to be a maximal-security facility to keep those guys indoors!”.

In the opposite direction is the brain of the brown bear, with far fewer neurons than expected: although it was the largest carnivoran brain examined, at 315 grams (almost 10 times as large as a cat or raccoon brain), it only had about 250 million neurons in the cerebral cortex, like the cat, and almost 50% fewer cortical neurons than the raccoon. It seems unlikely that the particular bear brain examined was abnormal, for it showed no obvious signs of disease, and had exactly as many non-neuronal cells as expected for a mammalian brain of its size (and so did the raccoon brain, by the way).

We suspect that having an enormous body to support is incompatible with sustaining a large number of neurons in the brown bear cerebral cortex. Because these animals are omnivores, they get fewer calories per gram of food ingested compared to other large but meat-eating carnivorans – and yet bears have even bigger bodies: the brown bear examined in the study weighed 350 kg, against the 180 kg of the female lion analyzed. In line with an insufficient diet to keep body and brain going, brown bears hibernate for about six months of the year, which decreases dramatically their energy cost during the winter. We speculate that the bear cortex might grow to its full size and then lose a very large number of its cortical neurons, as their energetic cost is not met.

The lion, the second largest carnivoran studied, shows a similar tendency. Although its body was 9 times as large as a golden retriever and its brain was twice the size of the dog’s, the female lion analyzed had only around 500 million neurons in the cerebral cortex, fewer than the golden retriever (and only slightly more than one of the raccoons). I suspect that the meager number of neurons in the lion cerebral cortex, despite its respectable size, is explained by the same problem faced by other large meat-eating carnivorans: running is so energetically expensive that their brains only deem large prey as worthy of purchasing – but that also means that what they give chase to also runs very fast, on long legs, which makes hunting a costly and uncertain enterprise. They are hailed as kings and queens of the jungle, but all that majesty seems to come at a steep energetic price. It must suck to be a large carnivoran...


Jardim-Messeder et al. (2017) Dogs have the most neurons, though not the largest brain: trade-off between body mass and number of neurons in the cerebral cortex of large carnivoran species. Front Neuroanat, in press. 

See numbers of brain neurons in carnivoran species here



An evolutionary study of attending the annual meetings of the Society for Neuroscience 

"25 year membership pins", read the box behind the counter of the SfN booth where I was updating the information on the current president of the Middle Tennessee Chapter of the Society for Neuroscience (me!). I did some quick math: I should merit one of those pins next year, I believe. It's been interesting to observe how the experience of the very same meeting changes over the years.

1993: Newbie Year

I started attending the annual meetings of the Society for Neuroscience in 1993, when I first joined a neuroscience lab: Story Landis's, at Case Western Reserve University. I had graduated in Biology with emphasis in Genetics, but knew essentially zero about brains. A new friend in graduate school convinced me to do my last mandatory rotation in a neuroscience lab - and I was hooked. Story encouraged me to attend the meeting, and off I went.

I had zero plans on how to do it. Everything looked new and interesting. So I roamed around, trying to take as much in as I could. Rookie mistake: of course I could not be in so many places at the same time, attending posters and symposia and oral presentations and special lectures scheduled at the same time in different parts of a gigantic convention center. So the following years, I learned to have a plan.

1995 to 1998: the PhD years

Lesson #1: SfN meetings run impeccably on time (it was only this year, 2017, that I first saw a Special Presidential Lecture run over time, but then it was the last event of the day). It couldn't be different or attendants wouldn´t be able to jump freely from one presentation to another in different rooms. So I learned that I could plan to attend talks in not-so-adjacent rooms and thus expose myself to different themes in the same afternoon. I would choose those that were related to my work topic - development of the nervous system at first, then visual system neurophysiology once I moved to Wolf Singer's lab at the Max-Planck Institute for Brain Research in Germany.

I still walked the pre-selected poster aisles screening the presentations, printed program booklet for the day in hands, a bunch of poster titles highlighted on my copy, trying to take it all in, speaking to the presenters, enjoying the nearly private scientific presentations in 2-minute bits. I sat at as many of the special lectures as possible, soaking in the presenters´ knowledge. Exhibitors´ booths? I ignored all of them, except for Publishers´ Row, home to academic publishers offering their books at a significant discount, something always important for a graduate student. I spotted PIs whose names I recognized from papers, but never dared approach them, for I had absolutely nothing to say to them. But I appreciated the newly acquired bit of information: those names had faces that belonged to real people - and they looked pretty normal.

1999 to 2004: science communicator years

I was officially a post-doctoral fellow in Singer's lab for a few months after finishing my PhD, then moved to Brazil to work in a science museum. I soon started writing on the neuroscience of everyday life for the general public in my own website, Our Daily Brain (in Portuguese) - and attending the SfN meeting turned into my annual opportunity to catch up with the latest discoveries that would also be fun to report on.

I had a blast: with a solid education in neuroscience under my belt, I could now pick and choose. I skipped the posters - I was not that concerned with talking to the researchers as much as gathering information - and focused on sitting in as many slide sessions as possible. Decision making, drug addiction, human vs. macaque comparisons, brain development, it didn't matter: if it sounded cool, and interesting (or unusual) enough to be worth writing about for my blog and then early books in Portuguese for the lay public in Brazil, I highlighted it on the program and put it on my schedule. Exhibitors? But for the cool sponge brains that served as pin cushions, I ignored them all.

2005 to 2015: PI years

...and then I became a PI. I wasn't expecting that, for I was happily living the life of a scientific communicator and author, but I realized that neuroscientists could do a bunch of really cool stuff yet still didn't know the first things about what brains are made of (how many neurons, how many glia, of what size), and I had an idea about how to obtain that information myself. So, with the help of a colleague who lent me lab space, I got to work and started a new line of investigation.

For the first five of those years I had a budget far too small to consider buying any type of equipment (surgical tools would have been nice, but even that was way above my budget), so the SfN meeting turned into my annual opportunity to acquaint myself with my new field of comparative neuroanatomy. This time, however, I not only went to posters but started talking to the PIs themselves. I later realized that was called "networking" and was really important; all that I knew then was that I was getting to know the players in the field and learn about their thoughts and opinions, including what they thought were still open questions. I met Jon Kaas, who introduced me to a whole new world of people interested in brain evolution who used to gather around beers at the end of each day at the meeting, so they were easy to find - and by association, I became easy to find, too. Wherever Jon was, hanging out with his buddies, I was probably not far away. That took the thing called "networking" to a whole new level, as I started recognizing some of the key players over the years and being recognized by them at the meetings.

My budget was catapulted by two orders of magnitude when I received a large award from the McDonnell Foundation in 2010. All of a sudden, I was on the market for microscope systems that I never thought I would be able to consider purchasing. From then on, I started scouting the exhibitors' section of the poster floor. I started skipping the main lectures - more and more were from people whose work I was already familiar with, or were too distant from my new field to be worth the time that I would be taking away from the precious opportunity to meet my colleagues and growing number of collaborators from different countries, all gathered at the SfN meeting. Like myself, by the way, for at the time I still ran a lab at the Federal University of Rio de Janeiro in Brazil. I could still visit some posters, but more and more that was in search of my fellow PIs who would most certainly be hanging around their posters. My students ask me why I insist on having them present posters rather than talks. "Because that gives you a known GPS location for a whole four hours, not just ten minutes, when people can find you and talk to you", I explain to them. "By the way, that is the main reason to attend SfN: go learn, but also go realize that the people whose papers you read and admire are real persons with a face and a favorite brand of beer", I tell my students.

2016 onwards: Vanderbilt years

This is fun. I realize that experiencing the SfN meeting is a whole other game now, far, far away from how I used to experience it. I'm at my known GPS location during the entire four hours of our poster presentations and don't even try moving away. At best, I will cross the aisle to check out a poster and talk to its presenter (usually asking questions about the fun details that are NOT on the poster) during a lull in our own visitation, and go right back. I am glad to pose for pictures with students who come to the poster to talk to me and ask for that.

Finished the poster session, I'm on to the meetings of the committees I now serve on, or sitting down with my collaborators to go over data analysis or the pending paper revisions for resubmission. Most of the time, however, I'm on the Exhibitor floor, taking the opportunity to talk to the representatives of different businesses about their hardware or software or instruments and how they may or may not suit our needs. It helps that I am sitting on a nice, comfortable pile of start-up money; I now have a good time finally shopping for things that I WILL be able to acquire for the lab. I attend socials no longer for the free food (I'm gluten-intolerant and can hardly ever eat any of the fingerfood anyway), but accompanying my colleagues or collaborators or friends from faraway places that I run into at the meeting. I take my lab out to dinner. I don't have a chance to attend one single talk (except for that presidential one that turned out to run very late). But it doesn't matter: there is no down time in my day at the SfN meeting (ok, except for that one time when I declared that I needed a nap after a very early-morning committee meeting or I would not be able to function the rest of the day).

Are all SfN meetings the same, year in, year out? Certainly not. Even though the program structure may be quite constant, attending the annual meeting is an evolving, ever-changing experience: not better (and also not worse) over the years, just different. 




I may have found Douglas Adams´ heir...

I had read, sorry, listened to, another one of his books during the two weeks of intensive sitting at the microscope during a visit to a colleague in Hong Kong, and much enjoyed it: Lock In, a very entertaining suspense set in a near future where a virus had left some people locked inside their brains, conscious but unable to move, so they hired the services of facilitators of sorts, people who would lend them their bodies. Criminal hijink ensues, of course, and somebody gets killed by a body that was inhabited by an unidentified user. The book was smart and quick-paced and entertaining to the point that I remembered the name of the author, which I usually don't: John Scalzi.

I ran into The Dispatcher, a novella by the same author, while browsing the kindle store for something light to read in bed - and quickly devoured it, a delicious mental exercise on the use of a device that, if applied before someone's imminent death, could instantly kill and roll them back to a previous state a few hours earlier, back home. On to the next title, then, one that came with plenty of good recommendations (although recommendations at amazon are less and less to be trusted, but that's a whole other story): The Android´s Dream.

(What is the android's dream, you ask? The title of Philip K. Dick's book of Blade Runner fame plays a key role in the plot. It involves aliens living on Earth. Yes, it doesn't seem to make sense. I'll say no more.)

It took me a while to warm up to it. I typically read fiction in bed, as an invitation to slumber, and while the first two pages were preposterously hilarious ("Dirk Moeller didn't know if he could fart his way into a diplomatic incident. But he was ready to find out", is the opening line of the book), they were so dense with information that my eyes would quickly glaze from the effort to keep up, and off into sleep I went. But then I tried again during the day, with more gamma waves in my brain, and I realized that I had before me quite a pearl. Could this author finally be the long-sought heir of Douglas Adams, the king of fast-paced narratives, crazy all-over-the-place ideas and dense yet immensely witty prose?

I haven't finished the book yet, for I'm attending a five-day meeting and still fall asleep after the second page. But it's for the better: the writing is so delicious that I want to savor every bit of it, so the slow progress is welcome. 

 Douglas Adams´ fans, rejoice: there is intelligent life in the Universe again!