Our science news are hopelessly biased towards propagating prevailing beliefs about the mind and brain. It seems that whenever there are published scientific studies that seem to support prevailing dogmas about the brain, we will see many press stories talking about such studies, no matter how insufficient their sample sizes may or no matter how dubious their methodology may be, and even if the stories were only done with mice rather than humans. But if we have a study providing results conflicting with prevailing dogmas about the brain, it will usually not be covered by the science news sites even if the study had a good sample size and used humans. And so despite reading several science news websites every day, I read no mention in them of a recent study finding the important result that there is no correlation betwen the number of brain cells and intelligence.
The study published in the January 2021 volume of the journal Cerebral Cortex was entitled "Is There a Correlation Between the Number of Brain Cells and IQ?" The authors (Nicharatch Songthawornpong, Thomas W Teasdale, Mikkel V Olesen, and Bente Pakkenberg) examined 50 brains of Danish males who had died for reasons other than brain disease. It was possible to reliably estimate the IQ of these Danish males because they all had taken a military mental performance test that very highly correlates with IQ, and is essentially an intelligence test.
The paper very clearly states its results:
"In our sample of 50 male brains, IQ scores did not correlate significantly with the total number of neurons (Fig. 1A), oligodendrocytes (Fig. 1B), astrocytes (Fig. 1C) or microglia (Fig. 1D) in the neocortex, nor with the cortical volume (Fig. 2A), surface area (Fig. 2B) and thickness (Fig. 2C). This also applied to estimates of the four separate lobes (frontal-, temporal-, parietal-, and occipital cortices; see ). Neither did IQ score correlate significantly with the volumes of white matter (Fig. 2D), central gray matter (Fig. 2E) or lateral ventricles (Fig. 2F), nor with the brain weight (Fig. 3A), or body height (Fig. 3B). All of these correlation coefficients were less than 0.2."
What this means is that the authors found:
- It is not at all true that the more brain cells you have, the more likely you are to be smart.
- It is not at all true that the more gray matter in your brain, the more likely you are to be smart.
- It is not at all true that the more white matter in your brain, the more likely you are to be smart.
- It is not all true that the heavier your brain, the more likely you are to be smart.
Although such results do not by themselves show that your brain is not the source of your mind, such results are quite compatible with the hypothesis that your brain is not the source of your mind. In Figure 1A of the paper, we see that 3 of the 7 or 8 subjects with the lowest number of neuron cells had above average intelligence. The correlation between the number of neuron cells and intelligence was actually a very slight negative correlation, although not statistically significant.
The results of this study should come as no surprise to anyone who has studied the posts on this site, such as my post here discussing how removal of half of the brain (to stop very epileptic seizures) has little effect on intellect or memory. The results of this study should also come as no surprise to anyone familiar two items mentioned by the study's authors: that "the rather large difference in neocortical neuron number between men and women (16% higher in men, Pakkenberg and Gundersen 1997) does not match with the minor gender difference in IQ (Halpern and LaMay 2000) and that highly demented female Alzheimer’s disease patients have normal neocortical neuron numbers (Regeur et al. 1994, Pelvig et al. 2003)."
The 2019 study discussed here studied the brains of 324 people by brain scanning, and found no good evidence for any relation between brain parameters or knowledge and intelligence.