A comprehensive cell census and atlas of the mammalian primary motor cortex, the region of the brain responsible for movement, that extends our knowledge and understanding of how the brain is organized is presented in Nature this week, as part of a collection of 17 research papers published in this week’s issue. The atlas integrates information from mouse, marmoset and human cell types. This collaboration between scientists in the BRAIN Initiative Cell Census Network (BICCN), defines distinct brain cell types and provides insights into how their identities contribute to neuronal function. Comparisons of cell types across the three different species studied may facilitate future research into treatments for human brain disorders.
The human brain is made up of billions of neurons that form trillions of connections (called synapses) with one another. Neurons come in a diverse range of types with properties that shape how neuronal connections are made and affect brain activity and behaviour. However, rigorous and quantitative definitions of neuron types have remained elusive, and efforts to map the organization and assign function to these cells on a large scale have been limited.
The generation of a cell inventory and map of the mammalian primary motor cortex is reported by the BICCN in a flagship paper published in Nature. The atlas integrates information from 16 companion papers (including earlier work published by the consortium) on molecular, spatial, morphological, connectional and functional features of the different cell types in mice, marmosets and humans. They find that cells are organized into distinct broad subclasses, with higher levels of the hierarchy made up of around 25 subclasses. Subtypes may be determined by their genetic profile and other characteristics, or by their location in the brain. The hierarchical organization is found to be conserved across the three species, and the conservation of cell types suggests that they have important roles in cortical circuitry and function in mammals as a whole. This cross-species information could inform decisions about selecting the best animal models and therapeutic targets when investigating human diseases.
Efforts are underway to extend the collaborative, multidisciplinary approaches used to map the motor cortex to generate a brain-wide cell census in the mouse, as well as extending our understanding of the brains of humans and non-human primates. “The BICCN papers represent a real treasure trove for future discovery — of particular note are explorations leading to a granular understanding of how the motor cortex helps to control and modulate many forms of movement”, writes Silvia Arber in an accompanying News & Views.
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