Blood flow

Carotid canalsThe fossil record offers several possible approaches to study the evolution of the human brain. Besides cerebral size and shape, we can make inferences about cognitive functions and metabolic processes. Analyses of the craniovascular system are required to better understand both aspects. A recent article in the Royal Society Open Science journal adds new evidence into this issue comparing cerebral blood flow rate and endocranial volume in fossil hominids. The metabolic rate of the human brain is tightly related to the cerebral blood flow, which is mainly supplied by internal carotid arteries (ICAs). The authors measured the dimensions of the carotid foramen, the external opening of the carotid canal, in 35 fossil skulls, and calculate the size of the internal carotid arteries lumen. Then, they calculated the blood flow based on the shear stress, arterial lumen radius and blood viscosity (using supporting data from human and rats models). Their results show that the ICAs blood flow rate increases disproportionately in hominids, when scaled against brain volume. The authors then speculate about metabolic rate and its association with greater synaptic activity, cognitive functions, and life-history evolution. The paleoneurological information considered in the article is not much updated, and the sample includes many casts, which reliability is not comparable with original specimens. Also, inferences on cognition or life-history sound probably too much speculative when dealing with a simple carotid canal. Nonetheless, this paper supplies a good perspective in vascular biology, with a clear application in paleoanthropology. The possibility of calculating the cerebral blood flow in fossil specimens is interesting and opens new research opportunities.

Stáňa Eisová

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