One of the Brain’s Biggest Mysteries Might Soon Be Solved
Tantalizing hints about what “the other half” of your brain is doing.
Posted January 19, 2022 | Reviewed by Gary Drevitch
- The function of half of all human brain cells—the non-neuronal cells called glia—has been cloaked in mystery.
- Glial cells do not exhibit the dramatic membrane voltage changes that make neurons so easy to study with micro-electrodes.
- New techniques are beginning to overcome these difficulties.
- The new findings reveal that Glia actually play an important role in information processing and brain disease.
Your brain has about 86 billion neurons, which, according to traditional neurobiology, underlie all the wonders of perception, learning, memory, emotion, and consciousness. In homage to all those neurons, researchers who study the brain, like me, are called neuroscientists, while doctors who treat brain disorders are called neurologists and neurosurgeons.
But all the focus on neurons, along with the prestige that goes with having “neuro” in your job description, ignores an incredibly important, but inconvenient fact: Neurons comprise only half of your brain. That’s right: The average human skull is home to over 170 billion brain cells, half of which aren’t neurons at all but cells called glia.
This graphic depicts the four types of Glial cells in the brain.
The pink ependymal cells line the ventricles of the brain, while the green astrocytes, dark red microglia, and light blue oligodendrocytes surround, encase, and connect to neurons (shown as light tan) in the brain’s interior.
You can be forgiven for not having heard much about glia, because for over a hundred years most neuroscientists viewed glia as uninteresting cells whose main functions were merely to glue neurons together (hence the Greek name glia, for glue) and to perform mundane metabolic functions in support of the true heroes of the brain: nerve cells. A few scientists were doubtful that evolution—which strives for ruthless efficiency in all things—would “waste” half of a brain on relatively unimportant functions, but even those scientists found the true value of glia mysterious because, unlike neurons, which exhibit easily measured action potentials (spikes) and graded potentials, the electrical and neuro-chemical activity of glia have been quite hard to capture with instruments like micro-electrodes.
However, despite a long history of being seen as supporting actors, glia are quickly rising to the status of brain superstars as new techniques begin to unravel the mystery of their function. Here are some of the latest findings that are propelling glia to their proper place of respect:
- Glial cells are crucially important to information processing through multiple paths of neuron-glia communication including, according to Doug Fields of NIH, “ion fluxes, neurotransmitters, cell adhesion molecules, and specialized signaling molecules released from synaptic and nonsynaptic regions of the neuron.”
- Glia play an important role in human intelligence. Human brain astrocytes transplanted into mice made the targeted mice smarter at running mazes and other learning tasks. And earlier research showed that Einstein’s brain had an unusually high number of glia in certain regions of his cerebral cortex
- One way that glial cells contribute to intelligence, memory, and learning is that they surround and encase synapses, communicating with presynaptic and postsynaptic nerve membranes in ways that increase the efficiency of synaptic transmission and the formation of new synapses during learning
- Inflammation associated with glia cell activity — some glia release pro-inflammatory compounds such as cytokines — is increasingly implicated in the development of neurodegenerative disorders such as Parkinson’s disease and Alzheimer’s disease. Although initial research suggested that glia cells were merely responding to disease processes in neurons, new findings suggest that changes in glia may actually be the main triggers of a broad range of neurodegenerative diseases.
- New evidence suggests that ependymal glia cells can transform into functioning neurons even in adult brains, helping to preserve healthy brain function as we age.
Why all this matters
Apart from being able to boast that we have over 170 billion (vs. just 85 billion) brain cells, why should we care that glia are lot more glamorous than we thought?
- Early diagnosis and treatment of neurodegenerative diseases could improve with a greater focus on pathology of glial cells
- Rehabilitation from stroke and brain injury could be improved through greater knowledge of the role that glia play in the formation of new synapses, and in some cases, harmful scar tissue.
- Pharmaceuticals that specifically target glia-neuron communication pathways could offer new hope for treating depression, anxiety, schizophrenia, and other mental illnesses.
- AI systems could be significantly improved (and become less brittle and faulty) if they modeled glia-neuron networks, instead of just neural networks, as is now the case.
With all this new data from the lab, and the exciting possibilities for the future, I hope you are as jazzed about glia as I am. In fact, I am so enamored of these unheralded brain cells that I am officially changing my job description from Neuroscientist to Gliascientist, and if I ever develop symptoms of brain disorder, I’ll seek medical help not from a neurologist or neurosurgeon, but from a Gliologist or Gliasurgeon.