Neuroscientists from The Scripps Institute have identified a specialized population of stem cells that have an impressive vocational calling: higher brain functioning. It's an important finding that holds promise for the treatments of serious cognitive disorders — including those that impact on conscious function. And it also reveals how humans and other mammals are able to have such big brains.
It seems that there's nothing that stem cells can't do — which is actually kind of the point. They're basically cells with an identity crisis, unsure of what they want to be when they grow up — at least not until they're placed in their right biological context.
But not all stem cells are equal. Biologists are learning that there's a diversity to these progenitor cells, and that different populations go on to acquire highly specialized jobs. And now, new research from a study led by Ulrich Müller has revealed that the mammalian brain is subject to this diversity, and that its growth and size can be attributed to at least two different kinds of stem cells.
Specifically, the Scripps researchers showed how neurons in the uppermost layers of the cerebral cortex form during embryonic brain development. It's in the cerebral cortex where information gets consolidated, memories form, and consciousness emerges.
Prior to Mueller's study, neuroscientists believed that all cortical neurons (including those that make up the lower and upper layers of the cerebral cortex) emerged from the same type of stem cell, what's known as the radial glial cell. But by looking deeper into the cognitive development of mice, the Scripps Institute researchers were able to identify a new and distinct population of stem cells (called Cux2-positive stem cells) responsible for the emergence of more highly specialized neurons — namely those responsible for consciousness, creativity, abstract thinking, future planning, and problem solving.
The researchers likened embryonic brain development to the gradual layering of an onion. The smaller, interior layers of the onion — what's a part of our more "reptilian" heritage — hosts neurons that connect the brainstem and spinal cord required for basic functions like breathing and movement. The larger upper layers, however, contain neurons that integrate information coming in from the senses and connect across the two halves of our brain.
It's this upper layer of the brain-onion that's a relatively recent evolutionary add-on — and one that neuroscientists now know is generated by a completely different set of neural stem cells. Moreover, the finding also shows that the mammalian embryonic brain goes through "waves" of development, spawned by the maturation of at least two different kinds of stem cells.
And because these neural stem cells are so "plastic", it's thought that scientists may be able to grow their own strains in the lab for therapeutic purposes. It's hoped that the planting of these stem cells in the upper layers of the brain will facilitate the healing of such conditions as Alzheimer's, schizophrenia, and other psychological disorders.
The study was published in the August 10, 2012 issue of the journal Science.
The above image of a precursor neural cell courtesy Su-Chun Zhang/ University of Wisconsin-Madison. Inset images via Scripps Research institute and SciencePhoto.