Month: September 2022

MORE NUMBERS. “Likewise, the capuchin monkey brain has more than twice the number of neurons of the larger-brained capybara (3.7 billion against 1.6 billion), and also about four times more neurons in the cerebral cortex (1.1 billion against 0.3).” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

AMPLIFYING THE LINE. “The significance of the difference in scaling rules for building brains with large numbers of neurons becomes even more obvious if one considers the expected number of neurons for a generic rodent brain of human-sized proportions.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

AMPLIFIED SCALING FAILS. “A generic rodent brain of human-sized proportions, weighing 1.5 kg: such a brain would have only 12 billion neurons, and a much larger number of 46 billion non-neuronal cells. This number of neurons is smaller than the number of neurons estimated to exist in the human cerebral cortex alone, and about seven times smaller than the number of neurons predicted for a 1.5-kg brain built with the scaling rules that apply to primates.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

RED HERRING. “Although not observed in the comparatively small rodent species analyzed, the enlargement of the cerebral cortex is not, in principle, an exclusive feature of the human brain: a similar expansion of the mass of the cerebral cortex, relative to the whole brain, is predicted by both the rodent and primate cellular scaling rules, irrespective of the number of neurons contained in the cortex.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

A LEVELING FACT. “Remarkably, the human cerebral cortex, which represents 82% of brain mass, holds only 19% of all neurons in the human brain – a fraction that is similar to the fraction that we observed in several other primates, rodents, and even insectivores.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

DISTRIBUTION CURVE. “The relatively large human cerebral cortex, therefore, is not different from the cerebral cortex of other animals in its relative number of neurons.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

FOOTNOTE. “It should be noted that the unchanging proportional number of neurons in the cerebral cortex relative to the whole brain does not contradict an expansion in volume, function and number of neurons of the cerebral cortex in evolution.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

NON-LINEAR. “The absolute number of neurons in the rodent and primate cerebral cortex does increase much faster in larger brains compared to the number of neurons in the combined brainstem, diencephalon and basal ganglia, and is accompanied by a similarly fast increase in the number of neurons in the cerebellum.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

DIVERGING LINES. “Because of the diverging power laws that relate brain size and number of neurons across rodents and primates, the latter can hold more neurons in the same brain volume, with larger neuronal densities than found in rodents.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn

DIVERGING CONSEQUENCES. “Since neuronal density does not scale with brain size in primates, but decreases with increasing brain size in rodents, the larger the brain size, the larger is the difference in number of neurons across similar-sized rodent and primate brains.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/ View in LinkedIn