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Big brains

The brain is the most complicated organ of any animal, formed and sculpted over 500 million years of evolution.  The cerebral cortex is a critical component of this and is the seat of higher cognitive functions such as language, episodic memory and voluntary movement.

Whilst a human’s brain is vastly superior to that of a mouse’s in terms of its complexity (a human cortex accommodates 16 billion neurons as opposed to a mouse’s mere 14 million), it may surprise you to realise that their starting points may not be too different.

This surprising result was discovered by a multidisciplinary team of mathematicians from the University of Oxford (Dr Noemi Picco, Prof. Philip Maini) and Cardiff University (Dr Thomas Woolley), and neurobiologists from the University of Oxford (Prof. Zoltán Molnár) and the Achucarro Basque Center for Neuroscience (Dr Fernando García-Moreno), supported by a grant from the St John’s College Research Centre.

The team developed an experimentally realistic mathematical model of brain development and applied it across multiple species (mouse, monkey, human). From this they were able to extract different brain development strategies that shed light on what separates us from other animals.

Critically, by accounting for differences in cell growth, changes in cell identity and the time at which these occur, the team found that their model, when comparing a monkey to a mouse, predicted that the monkey has more initial cells, leading to the creation of a larger brain. However, the surprise came when the model was extended to humans. Assuming that human and monkey progenitors progress through the cell cycle at similar speed, the model showed that humans could develop a bigger brain even though they can start with fewer initial cells than a monkey and approximately the same amount as a mouse.

The team are currently working on exploiting their results to further understand the multitude of brain creation strategies developed during evolution. Understanding such strategies can help us understand what happens in cases where the development follows alternative strategies, e.g. cases of Zika virus-induced microcephaly, schizophrenia and epilepsy.