You don't really have a 'lizard brain', evolutionary study reveals

You don’t really have a ‘lizard brain’, evolutionary study reveals

A new study has shown that the concept of the mammalian “lizard brain” can well and truly be put to bed.

Based on a study that examined the brains of bearded dragons (Pogona vitticeps), large lizards from the Australian desert, scientists have shown that the brains of mammals and reptiles evolved separately from a common ancestor. This is another nail in the coffin of the notion of the so-called trinitarian brain.

The lizard brain idea emerged and became popular in the 1960s and 1970s, based on comparative anatomical studies. Parts of the mammalian brain, neuroscientist Paul MacLean noted, were very similar to parts of the reptilian brain. This led him to the conclusion that the brain evolved in stages, after life moved to earth.

First, according to MacLean’s model, came the reptilian brain, defined as the basal ganglia. Then came the limbic system – the hippocampus, amygdala and hypothalamus. Finally, the neocortex appeared in primates.

Within the framework of the triune brain model, each of these sections is responsible for different functions; the most basal parts of the brain, for example, were thought to be more concerned with primary responses – like basic instincts for survival.

However, neuroscientists have been decrying the model for decades. The brain just doesn’t work like that, in discrete sections that each play a distinct role. Brain regions, as distinct as they are anatomically, are highly interconnected, a network of buzzing neural networks. And with the advent of new techniques, we can begin to better understand how brains evolved.

In a new study, a team of researchers from the Max Planck Institute for Brain Research turned to real lizard brains to investigate, publishing their findings in a paper led by graduate neuroscience students David Hain and Tatiana Gallego-Flores.

By comparing the molecular characteristics of neurons in modern lizards and mice, the researchers hoped to decipher the evolutionary stories written in the brains of reptiles and mammals.

“Neurons are the most diverse cell types in the body. Their evolutionary diversification reflects alterations in the developmental processes that produce them and can lead to changes in the neural circuits to which they belong,” says neuroscientist Gilles Laurent of the Institute. Max Planck for brain research.

About 320 million years ago was a very important period for the evolution of vertebrates and their brains. It was then that the first four-limbed animals (tetrapods) emerged from the water onto land and began to branch out into parental families that would eventually produce birds and reptiles, of a hand, and mammals, on the other hand.

There are structures in the brain established during the embryonic development of all tetrapods: an ancestral architecture shared in the subcortical regions.

But, because traditional anatomical comparisons of developmental regions might not be sufficient to fully detail all of the differences and similarities between reptile and mammalian brains, the researchers took a different approach.

They sequenced RNA – a messenger molecule used as a template to form proteins – in individual bearded dragon brain cells to determine the transcriptomes – the full range of RNA molecules in the cell – present, and thus generate a cell type atlas. of the lizard’s brain. This atlas was then compared to existing mouse brain datasets.

“We profiled more than 280,000 cells from Pogona’s brain and identified 233 distinct types of neurons,” says Hain.

“Computational integration of our data with mouse data revealed that these neurons can be grouped transcriptomically into common families, which likely represent ancestral neuron types.”

In other words, there was a core of neuron types with similar transcriptomes that mammals and reptiles have in common, even though they have been evolving separately for over 320 million years.

But these neurons are not limited to a specific “reptilian” region of the brain. The analysis revealed that most brain regions contain a mix of ancestral and newer neuron types, challenging the idea that some brain regions are older than others.

In fact, researchers have found that neurons in the thalamus can be separated into two groups based on their connectivity to other brain regions. And these connected regions are quite different in mammals and reptiles.

The team found that the transcriptomes diverged in a way that matched regions of connection, suggesting that a neuron’s transcriptomic identity – the full genetic readout of proteins it might need – originated or reflects its connectivity.

“Since we don’t have the brains of ancient vertebrates, reconstructing the evolution of the brain over the last half-billion years will require connecting very complex molecular, developmental, anatomical and functional data,” explains Laurent.

“We live in very exciting times, because it becomes possible.”

The research has been published in Science.

#dont #lizard #brain #evolutionary #study #reveals

Leave a Comment

Your email address will not be published.