It is well known that the larger the organism, the less energy consumed per unit mass (Delong et al. 2010; Moses et al. 2016; Wells 2007). This is known as Kleiber’s Law, whereby the energy consumed by an organism increases at the power of ¾ with body mass, which explains why following a massive extinction, larger animals are added to the population over periods of evolutionary stability, a stability that guarantees that the food chain remains resilient. If there is a major collapse of life sustaining resources, however, the larger animals tend to fall first as happened to the dinosaurs 64 million years ago. For animals to survive, large portions of the brain such as the cingulate and orbital cortices and their subcortical targets in mammals are dedicated to energy regulation controlled by motivational systems (Katsumi et al. 2021). Katsumi and colleagues (2021) have suggested that emotionality/motivation as mediated by the brains of mammals evolved for an animal’s need to control its energy consumption via its external and internal body-sense innervations of the neocortex, hippocampus, and cerebellum to guarantee energy stability. Furthermore, they posit that energy regulation mediated by signals from the cardiovascular, respiratory, gastrointestinal, waste excretion, and immune systems may be central to all mental states. The mental state of ‘consciousness’ is an attribute of all vertebrates and many invertebrates, which is in line with the thinking of many neuroscientists (e.g., Hebb 1960; Koch 2013; Morgan 1900; Murray et al. 2017; Nakagaki et al. 2000; Saigusa et al. 2008; Varela 1999ab).
At least in mammals the energy consumption per neuron by the neocortex is over one order of magnitude higher than that of the subcortex (Herculano-Houzel 2011), and this consumption is relatively uniform despite the bodily activities of an animal, whether immobile or active (Shulman et al. 2009; Troubat et al. 2009). The reason for this is that consciousness is never turned off during wakefulness (Chomsky 2023) and therefore requires a continuous supply of energy. There was some suggestion in the sports world that chess players consume as much energy (because of brain activity) as do athletes (because of bodily activity, as attributed to Robert Sapolsky of Stanford on ESPN by Kumar 2020). This supposition is wrong because consciousness is a continuous affair whether one is engaged in a task or not (Troubat et al. 2009), and energy variability is determined mainly by the body, namely by the autonomic, ocular and skeletomotor systems. Reading into the night produces ocular tiredness but not neural tiredness.
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