Neuro-hormonal Regulation Is a Better Indicator of Human Cognitive Abilities Than Brain Anatomy: The Need for a New Paradigm

Abstract

Human intelligence has been theorized since the ancient Greeks. Plato and Aristotle incorporated theories of human intelligence into their metaphysical and cosmological theories which informed the social and medical sciences for centuries. With the advent of the 20th century, human intelligence became increasingly standardized based on Intelligence Quotients (IQ). Moreover, multiple theories of human intelligence were posited on morphological features of the human brain, focusing on cranial volume and size of the pre-frontal cortex which was suggestive of superior human cognitive abilities. This article argues that fixation with anatomical features of the brain was tended to ignore the importance of neuro-hormonal regulation which is a more appropriate indicator of human cognitive abilities. The article challenges the correlation between brain size and human cognitive abilities while offering an alternate theory of human cognitive abilities which emphasizes the roles of neurotransmitters, neurotrophins, and enteric gut microbiome (EGM) regulation.

Comparative Study of Brain Size Ontogeny: Marsupials and Placental Mammals

“…The volume of the hominin braincase has tripled in the last 3 million years (from about 450 mL to currently 1350 mL) [ 56 ]. However, evolutionary hominin brain size increase matches the increase in hominin body size [ 57 , 58 , 59 , 60 ]. Interestingly, human brain volume during the Holocene period has decreased by approximately 10% (100–150 mL or one standard deviation) following a reduction in the human body’s robusticity [ 61 , 62 ].…”

“…It has been suggested that the quality of human brain functions depends more on neurohormonal and neurotransmitter regulation than on its size [ 63 ]. Behavioural differences between mammals may also result more from neurohormonal regulation than brain size [ 60 ]. The nature of the increase in adult brain size requires further investigation, especially in the areas of neuronal connectivity and structure which reveal differences between mammalian species.…”

Emerging epigenetic dynamics in gut-microglia brain axis: experimental and clinical implications for accelerated brain aging in schizophrenia

“…In terms of pharmacodynamic effects, the gut microbiome is an important site for the synthesis of different neurohormone transmitters including dopamine, serotonin, noradrenaline, acetylcholine, while microbiota diversity may strongly affect these neurochemical levels ( Roshchina, 2010 ; González-Arancibia et al, 2019 ; Saniotis et al, 2020 ; Szõke et al, 2020 ). Given that the primary mechanism of action for antipsychotic drugs is neurochemical modulation ( Ben-Azu et al, 2018c , 2023 ; González-Arancibia et al, 2019 ; Szõke et al, 2020 ), it is unsurprising that the gut microbiome could significantly impact the action of antipsychotic drugs in the brain, either by reducing or enhancing their effectiveness ( Seeman, 2021a ).…”

A brief sketch across multiscale and comparative neuroanatomical features

“…A greater number of neurons has often been posited as correlating with human cognitive abilities; but a less neuron-centric view assigns a prominent role to biochemical variations and interactions of neurotransmitters, neurotrophins, and other substances facilitating communication (cf. Saniotis et al, 2020;Chin et al, 2022).…”