Human 'mini-brains' give evolutionary insights

Human brain development occurs as a slower pace compared to other primates, according to a new study using 'mini-brains' from stem cells.

'It seems that we take more time to develop our brains but the end state that we reach is more complex,' co-author Professor Barbara Treutlein, ETH Zurich, Switzerland told the BBC. 'Maybe it takes this additional time to get the greater number of connections between neurons and reach the higher cognitive functions we have. But we don't really know yet why this might be the case.' 

In a study published in Nature, the researchers used iPS cells to create human, chimpanzee and macaque brain organoids to map the substantial genetic and developmental changes that set humans apart from other non-human primates.

'We have complex language and are capable of abstract reasoning and chimps don't. Work with (mini-brains) won't model those differences because they are not functioning brains. But they will help us understand the very important differences early on in development that set the stage for our cognitive abilities,' said Dr Madeline Lancaster of the UK's Medical Research Council, who was not involved in the study.

The researchers analysed gene expression and regulation and measured neuron maturation over the entire course of organoid development. They detected 98 genes that were differently expressed and gene-regulatory features that were unique to humans. They also discovered that although all three brains initially developed at the same speed, once the cells began to specialise into different types of neurons, the macaque organoids developed the fastest and the human organoids the slowest.

They concluded that this work will provide 'an extensive resource' to guide future exploration into the genetic changes that distinguish the developing human and chimpanzee brains, and said this will help them to answer the basic question of what makes us human.

Professor Treutlein and Dr Lancaster are working together and with others to develop an ethical framework for their research. 'It is always good to think ahead. We don't want to run into a situation where someone has created something truly unethical and we try and deal with the consequences after the event,' Lancaster said.