Quantifying patterns of endocranial heat distribution: Brain geometry and thermoregulation

Abstract

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.

Functional craniology and brain evolution: from paleontology to biomedicine

“…Correlation between form and function can be used to investigate physiological processes from morphological evidences. In this sense, brain metabolism and thermoregulation are good examples of biological functions that may be modeled based on simple mechanistic and geometric principles (Nelson and Nunneley, 1998; Van Leeuwen et al, 2000; Sukstanskii and Yablonskiy, 2006; Zhu et al, 2006; Bruner et al, 2011a, 2012). Brains are well known for being among the most energy-demanding organs of the body, burning large quantities of glucose for the development and maintenance of their structural and functional integrity (Mink et al, 1981; Aiello and Wheeler, 1995; Leonard et al, 2007).…”

“…Moreover, cerebral tissues are very sensitive to temperature changes, in that a slight increase of about 0.5–1.0°C may induce structural and functional changes at the cellular, histological and systemic levels, while severe and irreversible neural damage, coma, or even death of the individual may happen under hyperthermic conditions with brain temperatures above 40°C (Kiyatkin, 2010; Bertolizio et al, 2011; Rango et al, 2012). Therefore, it seems straightforward that brain thermoregulation processes are relevant at an evolutionary level, as brain temperature homeostasis may impose pervasive selective pressures and constraints on the evolution of species, and particularly on species-specific encephalization processes (Falk, 1990; Hofman, 2001, 2012; Caputa, 2004; Bruner et al, 2011a, 2012; Manger et al, 2013). Additionally, thermal management of neural mass is relevant in a biomedical context, as higher cerebral temperatures have been found in patients suffering from traumatic brain injuries or cerebral ischemia and stroke, as well as in other neurological disorders like schizophrenia, Parkinson’s disease, epilepsy, and multiple sclerosis (Kiyatkin, 2010; Bertolizio et al, 2011; Rango et al, 2012).…”

“…In this context, brain temperature depends on the interplay between metabolic heat production and heat dissipation processes, with both factors being somewhat influenced by the gross geometry of the brain. While heat production and active removal of heat by cerebral blood flow are correlated with overall cerebral dimensions (Karbowski, 2007, 2009; Herculano-Houzel, 2011), passive heat diffusion (i.e., conduction) within the brain mostly depends on cerebral shape (Bruner et al, 2011a, 2012). Consequently, despite the fact that brain size is the main factor involved in overall thermal balance, local morphological changes may influence local cortical values associated with tissue warming/cooling.…”

“… Endocranial geometry can be useful to simulate metabolic heat production and dissipation in fossil species (Bruner et al, 2011a, 2012). In this figure endocranial heat dissipation patterns in 10 living humans (five males and five females) and eight Neanderthals (Abri Suard 51, Gibraltar 1, Guattari 1, La Chapelle aux Saints, Saccopastore 1, Spy 1, Spy 2, Tabun) have been compared after numerical simulation, by applying the heat equation to their endocasts.…”

Human Paleoneurology and the Evolution of the Parietal Cortex

“…If we consider only the parietal landmarks (below), PC1 (67%) separates again humans from apes because of the enlargement of the dorsal and anterior regions of the parietal lobe. In this example, endocasts from 1 representative individual of each species (adult males) were used, averaging 10 replicas and the 2 hemispheres, so as to limit uncertainty due to landmark localization (data after Pereira-Pedro and Bruner [2018] cranial heat exchange, and the bulging of the parietal region characteristic of modern humans can hence contribute to increase the heat load of the corresponding deeper cerebral areas [Bruner et al, 2012[Bruner et al, , 2014a. Ontogenetic analysis of the endocranial form suggested that modern human brain globularity is achieved early postnatally [Neubauer et al, 2009] et al, 2016].…”