Cerebral blood flow rates in recent great apes are greater than in Australopithecus species that had equal or larger brains

Abstract

Brain metabolic rate (MR) is linked mainly to the cost of synaptic activity, so may be a better correlate of cognitive ability than brain size alone. Among primates, the sizes of arterial foramina in recent and fossil skulls can be used to evaluate brain blood flow rate, which is proportional to brain MR. We use this approach to calculate flow rate in the internal carotid arteries ( Q ˙ ICA ) , which supply most of the primate cerebrum. Q ˙ ICA is up to two times higher in recent gorillas, chimpanzees and orangutans compared with 3-million-year-old australopithecine human relatives, which had equal or larger brains. The scaling relationships between Q ˙ ICA and brain volume ( V br ) show exponents of 1.03 across 44 species of living haplorhine primates and 1.41 across 12 species of fossil hominins. Thus, the evolutionary trajectory for brain perfusion is much steeper among ancestral hominins than would be predicted from living primates. Between 4.4-million-year-old Ardipithecus and Homo sapiens , V br increased 4.7-fold, but Q ˙ ICA increased 9.3-fold, indicating an approximate doubling of metabolic intensity of brain tissue. By contrast, Q ˙ ICA is proportional to V br among haplorhine primates, suggesting a constant volume-specific brain MR.

Regional femoral bone blood flow rates in laying and non-laying chickens estimated with fluorescent microspheres

“…Femoral bone blood flow index (Q i ) was calculated using an equation derived from Poiseuille's Law: Q i = r 4 /L, where r (mm) is the foramen radius and L (mm) is an arbitrary length, measured as femur length (Allan et al, 2014;Hu et al, 2018;Seymour et al, 2012). It was assumed that the arbitrary units of Q i (mm 3 ) are proportional to absolute blood flow rate.…”

“…Interspecifically, terrestrial vertebrates with higher maximum metabolic rates and higher activity levels tend to have relatively larger femoral nutrient foramen sizes (Allan et al, 2014;Seymour et al, 2012). The femoral bone perfusion rates between the non-laying hens and roosters are not significantly different.…”

“…This ‘foramen technique’ relies on a theory that foramen size is proportional to the size of the occupying vessels. This technique has been developed to evaluate the blood supply to femora through nutrient foramina ( Allan et al, 2014 ; Hu et al, 2018 ; Schwartz et al, 2018 ; Seymour et al, 2012 ) and to brains through carotid foramina ( Boyer and Harrington, 2018 , 2019 ; Seymour et al, 2015 , 2016 , 2019 ). Blood flow rates estimated from human, rat and mouse carotid foramina match direct blood flow measurements ( Seymour et al, 2015 ), suggesting this technique can provide accurate regional perfusion values in some cases by simply measuring the size of foramina.…”

The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism

“…Given that the vertebral arteries are bigger in species with bigger brains and the cranial capacity in StW 573 is similar to the extant chimpanzee values 24,47 , these results may be expected. It is interesting to consider that brain perfusion in extant great apes is suggested to be higher than in Australopithecus 48 . Thus, future analyses would have to investigate selective pressures that could explain the increase of brain perfusion over the last three million years of hominin evolution and if similar evolution could be detected in other primate lineages.…”

Morphology of the nutrient artery and its foramen in relation to femoral bone perfusion rates of laying and non‐laying hens

“…If the size relationship between the foramen and the occupying artery is known, then quantitative blood flow rate can be estimated from theoretical or empirical equations. For example, blood flow rates in the marsupial and primate internal carotid arteries have been estimated from foramen sizes, because the artery occupies the carotid foramen almost entirely (Boyer & Harrington, 2018, 2019; Seymour et al, 2015, 2016, 2019a). However, the relationship between foramen and artery lumen size becomes much more complex when a foramen, such as the femoral nutrient foramen, also passes substantial veins.…”