Let’s Discuss: Is Bigger Better?

Oh boy, sometimes I come in really HOT to a course discussion, and that’s the case this week. I’m taking Duke’s Medical Neuroscience on Coursera — a truly wonderful course which must have taken hundreds of man-hours to put together, and involves tons of helpful videos with real-brain dissections, just beautiful and fascinating for all of us who don’t have our own backyard brain lab.

AND YET I can’t help but be difficult. I really chafed at our first discussion question:

Let’s Discuss: Is Bigger Better?
What do you think? Is brain like muscle? Is a bigger brain better than a smaller brain? What about for subregions, such as a particular area within the cerebral cortex; do you think that size scales with performance?

Please share your thoughts, reflections, insights, research, etc., that you may be inspired to consider by this long-standing question in the brain sciences.

Participation is optional

Woof. So much to unpack here. I understand to some extent the pedagogical goal: get us thinking about the difference between muscle tissue and nervous tissue. Get us to appreciate the complexity of the brain versus a muscle. And still note that there can be some anatomical features on the brain surface (like the dominant hand bump in the pre-central gyrus) that seem to be related to use.

But oh my HEAVENS I am not ready to deal with all the connotations of this question. I appreciate that they tried to juke around the implications of BIG = SMART ( = WHITE) here a bit by saying “performance” but guys: you did not succeed. The reason why this question is long-standing is because racial bias is long-standing.

Here was my imperfect attempt at a response, which was WAY too long for a discussion board. Maybe by virtue of its very longness it’ll catch a MOOC TA’s attention though, and invite the course managers to reconsider this as a discussion point. Maybe in a very carefully guided anti-racist classroom discussion, you could talk about this and its scientific value — but not in a wild and free MOOC where most people are just gonna surface interact and drop their unedited thoughts into comments!! Lord.

In general: no, the brain is not like a muscle — we cannot easily examine the gross anatomy of a brain and make meaningful observations about the performance or capacities of the person. (Unlike muscle, where we can observe fairly direct physical results of training. Note that even in muscle, though, actual performance in a sport or skill can hardly be perfectly characterized from mere analysis of someone’s tissues.) My more detailed response, however, is: should we, as scientifically-minded people, ask or think about this question? I propose: no.

The question of brain size & performance has roots intertwined with racial violence, segregation, and slavery. On its surface, there is a plausible question here: regular use of some tissues causes their hypertrophy — is the brain such a tissue? To some extent, this is settled fact: no. The brain doesn’t undergo neurogenesis in the adult, even with training, and although glial cells do regenerate in the CNS to some degree, particularly in response to tissue damage, this does not seem to be causally connected to how skills and knowledge are acquired in the adult–instead, the key player here is synaptic connection and neural pathways. We have done enough science to know that mass or volume of neurons is one of their least interesting features.

Outside of the analogy to muscle, there may be interesting research questions to ask. Brain atrophy seems to play a role in some conditions (dementia, traumatic brain injury, cerebral palsy, schizophrenia) that affect capacity and behavior. Developmental differences in brain growth occur that are worthy of detailed study (hydrocephaly, childhood cannabis use, malnutrition) with careful statistical methodologies. (A collection of papers here: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C30&q=cerebral+atrophy&btnG= ) I certainly support these various research avenues.

But we’re not asking the question “how does cerebral atrophy relate to cognitive impairments in Parkinson disease?” or “is cerebral atrophy ‘normal’ in aging or a result of pathological processes such as TIAs, smoking, alcohol consumption, hyperlipidemia?”

We’re asking, for good or ill, “are bigger brains better?”

This question is ill-framed along several dimensions: first, what does bigger mean? 19th and 20th century anthropologists used craniometry (measurement of the skull), cephalometry (measurement of the head) and phrenology (measurement of the bumps on the skull). Many neuroscience texts allude humorously to their clumsy attempts to estimate brain capacity by filling skulls with seeds or palpating the brow ridge — but is it so much more absurd than our techniques today? What should we measure: cranial capacity? volume of soft tissues in the skull? mass of cortical tissue? surface area of grey matter? mass of white matter including myelin? number of neurons? How could we get such measurements — and how can we validate them as fair approximations of some kind of meaningful metric? I could ask the question are heavier computers faster? and even do research along those lines, but no matter how precise my measurements I am going to find little of use because the question just isn’t precise enough or based on a strong enough model of computer function. Weight is not the most salient feature of computers, based on how we know computers work. Research on computer weight will not advance computer science. (Although it may advance my sales of extra-heavy computers!)

A similar but even more scathing critique could be written for what does “better” mean? — usually, we understand this to mean intelligence or intellectual capacity, whether general or in specific performance of a task. Choosing what to measure and how to measure it and why are hardly settled questions. (A collection of quite varied articles here: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C30&q=validating+intelligence+tests&btnG=)

So, if “are bigger brains better” isn’t really precise enough to be a scientific research question, what kind of question is it? Based on its historical and modern use, I suggest that it is a racist one. (And, to some extent, a sexist one.) It was formulated by “race scientists” of the 19th and 20th centuries looking consciously or unconsciously for ways to justify segregation and racial violence (see: Samuel Morton’s anthropology research: https://www.penn.museum/sites/expedition/the-samuel-george-morton-cranial-collection/ ) and is perpetuated in the modern day by racists trying to use race and brain size as an explanatory factor for IQ differences (see: John Rushton’s many research papers https://www.sciencedirect.com/science/article/abs/pii/S016028960200137X).

To be clear, although the racist motivations and racist policies that derive from the work of these authors are detestable, that’s not why the science is bad. The science is bad because the question is poorly-framed, more out of the political and personal agendas of the researchers than the best scientific models of brain function we have. Matching up race, brain size, and IQ is completely scientifically useless without clear and relevant genetic or biological definitions of race (not widely agreed-upon), validation of the relevance and consistency of the specific size measurement technique, and validation of the performance-measurement (IQ test, etc) in a cross-cultural milieu. We can choose to gloss over these details and look for a “big-picture” answer — but if we do, we are following not scientific inquiry, but the motivations and biases of the people who ask this question. Looking for big-picture answers here is an irresponsible and invalid way to approach such an important topic — important not because of its scientific worth, but because of its historical impact on the real people whose brains were harmed because of their supposed inferiority and the modern danger of racism and white supremacy in our society.