Brain Science Podcast discussion

2017 > Episode 133

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message 1: by Dalton (new)

Dalton Seymour | 20 comments Let me preface this post with - I admire Suzana Herculano-Houzel's enthusiasm. However, if what she has expressed in this interview is an accurate reflection of what's in her book, then a lot of it is wrong. I agree with her statement that there is a lot of dogma and myth being perpetuated via cut and paste from authoritative sources from the past - I've been complaining about that for a long time. Dogma and myth in science is primarily due to what becomes fashionable.

Let me get on with the nit-picking by presenting examples from the interview.

The Reptilian Brain and Evolution: Mother Nature has a fondness for "copy with modification" to advance proficiency through diversity. Combined with survival of the fittest and natural selection, Evolution Does Strive To Advance Lifeforms. It's not just diversity- that's an oversimplification of the process. Comparative anatomy among the phyla of species present today presents an obvious hierarchy distribute among the species. Tallying the neural population present in a brain does not take into consideration modularization or the regional specialization and integration that comes from connectivity. Environmental stress is the driver behind evolution and adaptation. It comes in the form of parasitism, be it from disease producing organisms or predator/prey relationships.

I have never seen anyone attempt to apply the Power Law directly to the size of a brain. Generally speaking, it's relationship to neuroscience has been to explain the diminishing diameter of projections with regard to branching. Each branch being a tap off the conductor reducing the amplitude of the neurons output signal. It is a mechanism that offsets the drop in signal strength as it is transmitted to a target neuron. Also, to help maintain intracellular osmotic pressure for the diffusion and distribution of nutrients within the cell.

Brain Size vs Cell Size vs Brain Weight - scowl. Brain Size without discussion and consideration of connectivity is next to meaningless. The effect of Cell Size has two implications. One is a population limiting factor and the other may be directly related to metabolic rate and stamina. Equating Brain Size to Brain weight is next to meaningless since the brain like all tissues in around 90% water. Bring mylination into the consideration (those fatty little cells) and the density of tissue goes down a lot - so the mylination of more advanced brains would make them lighter yet more integrated.

In terms of the number of neurons in the human brain (86 billion), I wish she had discussed the dissolution and extraction of nuclei more thoroughly. If there is 10 times more glial cells than neurons, how were the nuclei of neurons isolated from the nuclei of all other nucleated cells? I suspect that the detergent and maceration would be indiscriminate. Why would one use a fluorescent stain and microscopy to do the count? One would think that larger sample sizes could have been applied to a gel and analyzed with isoelectric-focusing electrophoresis (electrophoresis along a pH gradient for nucleic acids) or gas chromatography, staining, and tuned spectrometry. The larger the sample size, the more accurate the measurement.

Determinants of brain size has a lot to do with sensory bandwidth and resolution. The broader the sensory range and finer the resolution, the greater the resources needed downstream to support it. This is also true for motor output as well. The finer the movement, the more cortical resources are required to produce that level of control. Body size/surface area and musculature also impact brain size - as in the elephant. It's not surprising that much of the resources that go into making such a large cerebellum has to do with body size instead of cortex. The elephant is a herbivore and its prey doesn't evade predation, so cortical resources need not provide for planning and communications related to hunting.

The Bird Brain and Intelligence: As I understand it, birds have been around since the dinosaurs, so evolution has had a long time to tinker with regional specialization, connectivity, and integration in their cortex. Most birds are omnivores as well, therefore, survival depends on successful predation.

I did find her hypothetical explanation concerning the myth about using only 10% of the brain interesting. It would do as an explanation for how the myth came about. I also find it interesting that on very rare occasions brain injuries have lead to savant traits in survivors due to plastic re-connection during healing (implying that some resources may exist within the brain but unconnected).

message 2: by Virginia (new)

Virginia MD (gingercampbell) | 321 comments Mod
I don't have time to respond to all your comments right away, but I will remind you that using Power Laws is actually very common in Network theory such as the work of Olaf Sporns.

Also, at no time did she equate Brain Weight to Brain Size.

Also, she clearly stated that there is evidence that the ration of glial cells to neurons is more like 2-3 to 1 rather than 10:1, but I agree that the question of how they are stained separately is a good one that I should have asked.

message 3: by Dalton (new)

Dalton Seymour | 20 comments Indeed, power law is commonly employed as part of the design and engineering of networks, but that's not what she she said in the interview. In fact, as I recollect, she never mentioned networking at all, just size. Perhaps she expanded on it in her book.

Brain weight to brain size - I'll have to listen to the interview again for I thought she did mention it.

message 4: by Dalton (new)

Dalton Seymour | 20 comments Comments on the brain weight with regard to brain size can be found at 31:30 and 31:57 in the interview comparing the rodent with the primate brain size.

message 5: by Dalton (new)

Dalton Seymour | 20 comments One more nitpick with regard to cognitive prowess between species. It was highly stressed that the difference between the human brain and other primate brains was the result of cooking and breaking down food to release more energy. I think this borders on the level of a myth as well. Leastwise, it ignores the difference between the diets of a carnivore vs herbivore. The production and support of cell population would be dependent upon both the amount of ATP (energy) and the substrate types available for cell structure (proteins and aminoacids). Fats are a far more dense energy source than carbohydrates and carbohydrates provide very sparse amounts of fat and protein that can be commandeered by the cells for modification and incorporation into structure and enzymes. Carbohydrates are mostly empty calories and most of the species she drew comparisons from (pigs, elephants, whales, and primates) are herbivores. In the case of herbivores, due to poor diet it is necessary for the animal to forage and consume foliage all day to meet it's energy needs. Dependency on such a behavior leaves little time for the accumulation of diverse experiences that would stress the animal to cognitively develop and advance.

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