For the neocortex and its vertebrate and invertebrate homologue to be functional for consciousness, the neurons must exhibit a high and protracted metabolic rate as maintained by dopamine and as established by a particular level of glucose uptake in μmoles per minute (Herculano 2011; Plaçias et al. 2017; Sacks 1976, 2012; Sokoloff 1977). Bilateral sensory deprivation lowers the metabolic rate of neocortical neurons, such that blockade of the auditory canals, for example, reduces the metabolic activity by 35 to 60% in the auditory cortex of awake behaving rats (Sokoloff 1977). This indicates that consciousness as it pertains to the senses is dependent on a metabolically functional neocortex, which explains why blindsight is so debilitating to visual consciousness (Tehovnik et al. 2021). Furthermore, disabling the dopaminergic inputs to the neocortex reduces the metabolic rate of rodent neocortex by 75% (Sokoloff 1977). This concurs with the observations of Oliver Sachs (1976, 2012) that dopamine depletion of 98% puts Parkinson’s patients in a perpetual slow-wave state (which has been associated with a low neocortical metabolic rate) such that both movement and consciousness are abolished. Furthermore, augmenting dopamine levels with amphetamine in awake behaving rodents increases the metabolic rate of the neocortex.

As illustrated previously, an increase in the number of neocortical neurons is associated with an increased metabolic rate per neuron (Figure 1, top curve). This is because with an increased number of neurons more synaptic connections are supported. Synapses are energy-expensive (Attwell and Laughlin 2001; Richards 2002; Sibson et al. 1998; Sokoloff 1977). Furthermore, as the number of neurons increases the amount of information stored in neocortex or its homologue also increases (Tehovnik and Chen 2015). The human neocortex contains 16 billion neurons (Herculano-Houzel 2009) to make explicit associations between the senses, and we estimate that this structure can store up to 1.6 x 10^14 bits of information, a value based on the number of neocortical synapses (Tehovnik, Hasanbegović, and Chen 2025). By comparison, the mushroom body of the fruit fly (see Footnote 1), a homologue of the mammalian neocortex, contains 2,000 neurons with each neuron, on average, having 350 synapses for learning explicit associations between the senses (Dorkenwald et al. 2024; Lin 2023; Schlegel et al. 2024). This yields an overall storage capacity of 700,000 bits of information by the mushroom body. The mushroom body is a common organ in many species including social ants which are known to have a pheromone alphabet of twenty letters (Hölldobler and Wilson 1990). Entomologists have yet to work out the universal grammar of this language, however. We are now only at the beginning of working out the biology of Chomsky’s (1965) universal grammar for all animals including the amoeba (Nakagaki et al. 2000; Saigusa et al. 2008), which should provide us with ground-zero for consciousness (Tehovnik and Chen 2015).

Footnote 1: Dopamine is believed to maintain memory consolidation in the fruit fly by modulating the energy level of the mushroom body (figure 7 of Plaçais et al. 2017). The molecular learning mechanism proposed per neuron for the mushroom body is based on the discoveries of Eric Kandel (2006).

Figure 1: Total glucose utilization (per neuron) is plotted as the number of neurons for several species from rodents to primates. Separate curves are included for the neocortex and cerebellum. The illustration is modified from figure 1b of Herculano-Houzel (2011). (file: auto_079.gif)