Higher IQ associated with bigger brain cells

27 February 2019

Interview with

Huib Mansvelder, Vrije University, Netherlands

HUMAN-BRAIN-NEURONE

A pyramidal neurone in the human cerebral cortex

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Famously, since Einstein died, researchers have studied his brain to try understand the basis of his genius. But they’ve largely drawn a blank, with no clear consensus. But, as he tells Chris Smith, Huib Mansvelder at Amsterdam’s Free University has been doing a more modern and better controlled version of this sort of experiment to try to understand why some people are more intelligent than others, and in the process answering a very important outstanding question...

Huib - Nobody has ever checked or looked at whether properties of brain cells are associated with mental abilities. So we really wanted to study whether we could find a link between properties of brain cells of the human brain and their mental abilities - IQ. So we consider the size of the brain cells - and that's not just the size of the cell body but also of the of the processes that have come out of the cell body where the cells receive information make contact with other cells - and we also consider their electrical behaviour.

Chris - And what are you relating those neuronal parameters to, in terms of an assessment of brain function? How are you measuring how good someone is at thinking?

Huib - Right. So we use IQ score. We've measured that with IQ tests. And, of course, that's a gross simplification - you cannot of course get somebody's intelligence into a single number, but at least it gives a good approximation of a general intelligence of a person.

Chris - So in a nutshell then what you're saying is let's relate how someone performs on an IQ test - notwithstanding there are limitations of an IQ test - with physically what the nerve cells are like in their brain in terms of the numbers of those nerve cells and how well those nerve cells work, and how fast they work? 

Huib - Right. And the point was others have shown certain parts of the brain - when you look at the brain on an MRI scan - the thickness of the cortex associates or correlates with IQ scores over the very same person. So people with higher IQs tend to have thicker cortical regions in temporal cortex and frontal cortex. So that's why we thought that maybe people with thicker cortex have room for bigger brain cells.

Chris - So how did you then bring the two together and access or gain access to brain cells so that you could make those sorts of measurements and relate them to IQ? 

Huib - Human brain tissue is very hard to come by. So there's very few people where actually brain tissue is taken out. One of them is epilepsy and other one is a brain tumour. So with the epilepsy patients, about 20 to 30 percent are resistant to a pharmacological treatment. And when the epileptic focus is localised well enough then the surgeon can remove the epileptic focus in the tissue that he cuts out on the way to get access to those deeper structures - that this is a cortical tissue that we take to the lab - and there we can study the shape of the cells but also the electrical activity of the cells, because we take every care that the brain cells in the tissue are alive. 

Chris - So you're able to electrically interrogate the tissue while it's still viable but then also go in and physically measure what the cells look like in the same specimen. So you know that you're comparing apples with apples?

Huib - Exactly. During our electrical recordings we fill the cells with a chemical that gives the cells a colour and that we can then later on analyse.

Chris - And what relationship emerges, because presumably you then marry up all of those measurements with the IQ tests that the patients have filled in before they underwent surgery. So what's the relationship? What do you see? 

Huib - Right. What we see is that patients that had higher scores on the IQ tests tend to have larger brain cells with larger processes that are more complex and more bifurcations. Also that these cells are larger, generate electrical signals faster and can maintain faster signals much better than patients with a lower IQ scores that have smaller cells

Chris - And do you think the cells are bigger, because they've always been bigger, or do you think they're - in the same way that the taxi drivers in London who did the knowledge of the streets got a bigger hippocampus - that these cells are responding to more use and more stimulation and they're becoming more metabolically active and that's why they're bigger? Is it cause and effect, or were they big to start with?

Huib - There are important genetic factors that associate with IQ scores, but then again training of the brain definitely affects the structure of the brain, so we think that will affect also the shape of neurons.

Chris - And you don't think the fact that you were forced to study tissue that it come from people with an underlying neuropathology might have skewed the results in some way?

Huib - So that's a good question. All the people used this study were epilepsy patients. So we compared similar patients with their similar disease backgrounds with each other. We never take tissue from the epileptic focus; so the tissue that we take to the lab was only removed for the surgeon to gain access and also for the properties that we studied, like the size of brain cells and the electrical properties, we compare these between different patient groups. We also have tissue from tumour patients: they have a different medical history than the epilepsy patients. We compare the properties of these cells between the patient groups and then check whether there is a bias in one of those groups or not or whether it generalises across the disease background. We can never get around the fact that we have to work with tissue from patients but at least we can quantify whether there are some influence of the background or not...

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