Quantifying patterns of endocranial heat distribution: brain geometry and thermoregulation

The mechanisms involved in brain thermoregulation are still poorly known, and many disagreements still exist concerning the selective cooling capacity of the brain volume. This issue has also been discussed in human evolution and paleoneurology, speculating on possible changes associated with hominid encephalization. Although the vascular system is supposed to be the main component responsible for thermoregulation, brain geometry also plays an important role in the pattern of heat distribution.

In fossils, the only neuroanatomical evidence available for quantitative analyses is the endocranial form, molded by the brain morphology. Here, we present a quantitative method based on numerical simulations to quantify and localize variation in heat dissipation patterns associated with endocranial morphological changes, presenting a case-study on modern humans and chimpanzees.

Thermic maps provide a graphic tool to visualize heat loading on the endocranial surface. The distribution of the values (thermic spectrum) supplies a quantification which can help describe and compare the patterns of heat distribution within and between groups. Absolute values are largely influenced by size differences. Normalized values suggest further differences associated with brain shape.

Simulation and numerical modeling are useful to provide a descriptive and quantitative approach to endocranial thermoregulation, supplying a quantitative tool to investigate ontogenic and phylogenetic changes. This is particularly relevant in paleoneurology, considering the large shape and size differences described for fossil hominid brains.