Ashby Denoon Assistant Professor of Neuroscience Sarah Petersen was all laughs as she casually displayed her expertise on the workings of the brain. From the perception of harmony in music to the differences in neural development of people in tonal languages, Petersen addressed the various topics of neuroscience with an air of wonder and an appetite for more. But as we started to talk about her research, Petersen’s tone changed, and her excitement became palpable. As our discussion made clear, the world of neuroscience is dominated by the neuron, a frustration for Petersen because we understand quite a lot about how they work on a molecular level. But what mediates these neurons? What determines their development, the way they take shape in our larger systems of cognition? The answer belongs to a category of cells largely ignored to this day, but which, according to Petersen, makes up “most of your brain.” Glial cells, a group of cells including astrocytes, oligodendrocytes and the focus of Petersen’s research, Schwann cells, could open the door to a new frontier of neuroscience.
Petersen’s path towards glial cells was a long one. The daughter of a college music professor in rural Tennessee, she grew up playing music, and developed an affinity for the creative which would follow her throughout the rest of her life. While enjoying a brief flirtation with journalism, Petersen was caught off guard in her high school health class, when her teacher projected onto the board pictures of a developing fetus. This was the turning point for Petersen, and she remembers her reaction vividly: “This is the coolest thing ever,” she remembered thinking. Soon this interest kindled into a passion for developmental biology, a field which satisfied Petersen’s taste for the visual as well as her passion for creative thinking and problem solving.
But it was a twist which led her to her current research, which looks at how context affects glial cell activity and neural development. Working in a lab of zebrafish, one day she came upon a fish with a mutated muscle gene, causing major issues with its development. After deciding that the fish wouldn’t do for the purposes of her research, the principal investigator announced, “Sarah can have that one,” and with that, Petersen’s exciting dive into the contextual development of glial cells began.
The debilitating mutation of Petersen’s zebrafish, which affects muscle growth, also caused major changes in neural development. As the muscles in her zebrafish failed to grow properly, the neurons and glial cells also failed to find their proper places in the fish’s body. Petersen compares the development of these cells to a group of people trying to form a line. “It may take some shuffling around before they figure out what to do,” Petersen said, “and they have brains! How do cells figure this out by themselves?” The answer, she explained, comes from cues given by their overall environment. The glial cells, neurons, muscle cells and whatever else is around the developing nervous system all interact with each other to determine how things line up. That the environment around neurons affects their eventual patterning — which in turn affects all of our higher-level conscious processes — and how this effect happens is a significant discovery, and something Petersen says we’re only beginning to understand.
The most exciting new possibility, however, Petersen said, may be found in a completely different type of glial cell, studied at Kenyon by Associate Provost and Professor of Chemistry Sheryl Hemkin and her students. Astrocytes, found in the central nervous system and known primarily for providing biochemical and nutritional support for neurons, may be the key to unlocking a treasure trove of medical applications and understanding of the brain. Though they don’t have the characteristic action potentials of neurons, these astrocytes seem to conduct ions in the same way that neurons do, Petersen said, likening them to the “brain within the brain.” And this inner brain, early research suggests, may be responsible for humanity’s noteworthy intelligence. With an air of excitement, Petersen relayed a recent study which saw human astrocytes grafted onto the brains of mice, resulting in significant improvements in their performance on cognitive tests. The processes behind this change are still shrouded in mystery, but the change itself is an exciting example of what further research on glial cells might yield.
For one, discoveries might help explain how humans became so intelligent — not only do astrocytes seem to have some link to intellect, but evolution as a whole seems to favor glial cells. More evolved animals, and animals which express greater intelligence, tend to have higher ratios of glial cells to neurons than their predecessors. Further research might also have significant medical applications, from disorders directly affected by glial cells such as multiple sclerosis — which is caused by depletion of myelin around axons — to diseases like dementia and Alzheimer’s which are marked by general cognitive decline (and which in recent studies have been linked to problems with astrocytes and microglia). Even the transhumanist goal of increasing human intelligence may be realized by glial cells.
As our interview came to an end, I joked that maybe I should be injecting Einstein’s astrocytes — his brain is still floating around somewhere, preserved for science — into my head. Petersen looks at me like I’m crazy. “No no,” she says shaking her head, “those are old astrocytes. You’ll be wanting new astrocytes.” It’s hard to predict what will come out of extensive research of glial cells; this is part of what makes the field such an exciting area of possibility. But something is there, and likely a lot more than something, so much rather that it’s not unlikely that Petersen has struck gold. Now it’s up to her and her fellows in the field to lead the rush.