A recent article in Nature celebrates the 20th birthday, more or less, of functional magnetic resonance imaging, which practioners refer to as fMRI. This technique has revolutionized brain science. As one researcher is quoted in the article as saying, it has turned psychology “into a biological science.”
That’s because fMRI lets scientists noninvasively image activity inside – even deep inside – the living brain and, thus, learn which clusters within that incredibly complex organ are involved in the various activities taking place there. That lengthy list includes thinking, remembering, experiencing emotion, interpreting the information of our senses, and commanding bodily movements both voluntary and involuntary. What did I leave out? (Oh, right. Forgetting.)
No strangers to the charms of fMRI, Stanford neuroscientists have for some years now been burning the midnight electrodes. Mike Greicius, MD, has used fMRI to differentiate among networks, composed of widely distributed brain clusters working in concert, that are active during diverse mental tasks such as singing to oneself or working on a math problem. Allan Reiss, MD, has used it to pinpoint differences in brain development of young kids with or without fragile X syndrome, the most common known cause of inherited intellectual disability and autism. These examples merely scratch the surface.
As varied and fascinating as fMRI’s uses are, how it actually works is equally intriguing. And there lies a tale. Although the Nature article never mentions them, the working-class heroes in the fMRI story belong to a class of brain cells most people have never heard of.
It’s not the transmission of electrical impulses along nerves in the brain that produces an fMRI signal but, rather, increases in oxygen-rich blood being supplied to specific active brain regions. Those increases are, in turn, carefully micromanaged by a type of brain cells far outnumbering the vaunted nerve cells that gave neuroscience its name.
Called astrocytes because of their starlike shape, these unsung superstars are a subtype of cells collectively known as glia, which is the Greek word for”glue.” That snickering monicker is a vestige of early brain scientists’ failure to notice any better purpose served by glia, which account for 90 percent of the cells in the brain. (Quite possibly, no single individual on the planet has been more effective at or, certainly, passionate about disabusing neuroscience of that misperception than Stanford’s Ben Barres, MD, PhD).
As I wrote in this tribute to glial cells that appeared in Stanford Medicine a couple of years ago:
Unlike their flashier electronic cousins, glia speak in chemical whispers. Learning their language has been tougher. As a result, glial cells were long seen as inert nerve cement: just so many packing peanuts whose raison d’être is to keep our neurons from jiggling when we jog… We now know they’re doing much more.
Take the astrocytes, for example. One thing we now know they’re doing (among the many things they’re doing that we do or do not know about) is monitoring both nerve cells and blood vessels, the better to pick up signs of furious nerve-cell signaling and, in response, to command nearby blood vessels to enlarge. If you don’t believe me, by all means click on this link to my magazine article, then click again on the video display on the right-hand side of the page (just above the caption “Spying on Glia”) and see for yourself! (I’m serious. Do it now.)
Not that that’s all astrocytes do. They also determine, to no small extent, exactly where and when the all-important connections between nerve cells known as synapses get laid down. Those synapses, taken as a whole, pretty much define who we are, mentally speaking. Does that sound to you like something glue could do? Who knew. (Answer: Ben Barres.)
Previously: Unsung brain-cell population implicated in a variety of autism, A one-minute mind-reading machine? Brain scan results distinguish mental states and Making kids laugh for science: Study shows how humor activates children’s brains
Photo by stephenhampshire