Introducing the brain:during sleep waves of fluid clean it (Introduction)

by dhw, Sunday, March 10, 2024, 11:32 (256 days ago) @ David Turell

Introducing the brain: Sleep waves of fluid clean it

DAVID: although the article doesn't mention it the waste material is probably picked up by the brain's lymphatic system, delivered to circulatory blood and then to the kidneys.

Thank you for this comment. I was wondering where the waste went!

I’m always struck by the fact that while we spend a great deal of time admiring the wonders of the human brain, all this research is done on the brains of mice. In the hope of finding a definitive rundown of what distinguishes our brain from that of other mammals, I hit on an article which turned out to be enormous. Eventually I had to skip to the conclusion, but on the way I found myself bewildered by what seemed like an obvious contradiction concerning the remarkable but unremarkable, exceptional but unexceptional number of neurons. I don’t want to subject you to a long read, as the problem is encapsulated in the two quotes below. I’m just wondering if you can explain the apparent anomaly.

The Remarkable, Yet Not Extraordinary, Human Brain as a Scaled-Up Primate Brain and Its Associated Cost
National Institutes of Health (NIH) (.gov)
https://www.ncbi.nlm.nih.gov › books › NBK20718

QUOTE: Compared with other primates, the human brain is therefore not exceptional in its number of neurons, nor should it be considered an evolutionary outlier. If absolute brain size is the best predictor of cognitive abilities in a primate (Deaner et al., 2007), and absolute brain size is proportional to number of neurons across primates (Herculano-Houzel et al., 2007; Gabi et al., 2010), our superior cognitive abilities might be accounted for simply by the total number of neurons in our brain, which, based on the similar scaling of neuronal densities in rodents, elephants, and cetaceans, we predict to be the largest of any animal on Earth (Herculano-Houzel, 2009). (dhw’s bold)

CONCLUSION: REMARKABLE, YET NOT EXTRAORDINARY

Despite our ongoing efforts to understand biology under the light of evolution, we have often resorted to considering the human brain as an outlier to justify our cognitive abilities, as if evolution applied to all species except humans. Remarkably, all the characteristics that appeared to single out the human brain as extraordinary, a point off the curve, can now, in retrospect, be understood as stemming from comparisons against body size with the underlying assumptions that all brains are uniformly scaled-up or scaled-down versions of each other and that brain size (and, hence, number of neurons) is tightly coupled to body size. Our recently acquired quantitative data on the cellular composition of the human brain and its comparison to other brains, both primate and nonprimate, strongly indicate that we need to rethink the place that the human brain holds in nature and evolution, and to rewrite some basic concepts that are taught in textbooks. The human brain has just the number of neurons and nonneuronal cells that would be expected for a primate brain of its size, with the same distribution of neurons between its cerebral cortex and cerebellum as in other species, despite the relative enlargement of the former; it costs as much energy as would be expected from its number of neurons; and it may have been a change from a raw diet to a cooked diet that afforded us its remarkable number of neurons, possibly responsible for its remarkable cognitive abilities. (dhw’s bold)