Aired on BBC World Service Radio, November 6, 2001
THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.
ROGER HEARING, BBC: Now are you a big head? Traditionally, if you have a large brain you are supposed to be cleverer than average. Then scientists said it wasn't the amount but the quality of gray matter that mattered. But now it seems that those with bigger brains may in fact be more brainy. Professor Paul Thompson is the leader of the research team at the University of California that's come up with this result. I asked him if it really was the case that more brains means more intelligence.
PAUL THOMPSON: I think so, but only to a comparative degree. We know that people with big heads are not necessarily more intelligent. One of the results of this study was that the proportion of gray matter in the frontal lobe - those are the parts of the brain just behind the eyes - was actually a moderate predictor of our performance on IQ tests. When I say moderate, it explains about 10-15% of the variation in your score. So depending on your perspective, it's either a reasonably strong linkage between the structure and the function of the brain, or it leaves about 80-85% of the variation unexplained.
ROGER HEARING, BBC: So if you looked at the brain -- Is there are particular area, you say these bits just behind the eyes – you say between 10 and 15% of the variance in the intelligence score, Is there are particular area that explains this most?
PAUL THOMPSON: We were particularly interested in asking: 'Which parts of the brain do we inherit most from our parents?'. That's relevant to understanding the heritability of intelligence, and also the heritability of diseases that run in families. The frontal cortex - and also the language cortex - are very genetically determined. That means that members of the same family will have structurally the same, or very similar, parts of the brain that control language. We think that's interesting because not only do reading skills and language skills run to a degree in families, but also disorders of language such as dyslexia and also autism - which has profound difficulties in speaking and language function. These disorders are also known to be genetically mediated. And part of why may be that there is just a tremendous affinity in brain structure among family members in these regions.
ROGER HEARING, BBC: Now how did you determine all this? Did you just look at a scan of the brain to look at where the larger parts were?
PAUL THOMPSON: I wish we could do that, that would be very fast! The way it's actually done is that we looked at 20 pairs of twins. Twins provide a very interesting way of getting into genetic effects on brain structure. Identical twins share the same genes, whereas fraternal twins on average only share half their genes. So what you do is you compare brain scans of twins, and you say, how much more similar are the brains of identical twins than fraternal twins, and if they are more similar, you really can quantify how much those extra genetic affinities are participating in the resemblances.
ROGER HEARING, BBC: Well you've hinted there at one of the great debates of course, which is between experience, or learning if you like, forming intelligence, and heritability. What you're saying I think, is that you're tending to come down to a certain extent, or to a certain percentage, on the side of inherited intelligence.
PAUL THOMPSON: I think so but it's all a question of degree. These gray matter differences explain only a very small proportion of intelligence. So that rather comes down on the other side. We know that the brain is tremendously flexible. Even listening to this programme, people are forming new brain connections - the brain is responding to learning. If anything, the nature-nurture debate should come down a little more on the nurture side.
ROGER HEARING, BBC: Now much of your research, I gather, was to look at issues like Alzheimer's and look at inherited tendencies towards those. Is what you've discovered, then, useful in this area?
PAUL THOMPSON: Yes, I think to a very strong degree. So, if you have a disease that runs in families, the first question is: is it because of a similar environment in that family? So, something like a virus can affect a lot of members of the same family but that is not genetic. In something like Alzheimer's disease, we know that the frontal cortex - the same part that was very strongly inherited - degenerates very severely in Alzheimer's, and also members of the same family are at very high risk. So this really provides a way of not only understanding the mechanism of the disease, and its genetic basis, but also perhaps screening relatives for early problems. And then they can really try to, if they elect to, have some form of therapy or therapeutic intervention, before the severity of the disease has set in.
ROGER HEARING, BBC: That was Professor Paul Thompson on the latest study of brains, and whether more brains equals better brains. In your case Ollie, you are man of a substantial cranium - you have a huge hat, so you must have a huge brain. You've been listening to the brainy people on 'The World Today'.