The final flight of Atlantis will be STS-135. (The STS stands for “Space Transportation System.” The more you know.) I’ve been skimming through previous missions, especially the earliest missions and the Hubble-centric ones, looking for things to write & think about while I wait patiently to board a plane to Florida next month.
These 26 experiments made up Neurolab. I was surprised I had never heard of it, and glad to find a wealth of scientific literature about the experiments, some of which looked incomprehensible at first glance.
I love science that looks incomprehensible at first glance.
This one, for instance, sounded promising: “Spaceflight Induces Changes in the Synaptic Circuitry of the Postnatal Developing Neocortex.”
Note: I’m used to teaching neuroscience concepts to 7-year-olds (which is amazing and fun and wonderful, by the way), so forgive me and skip ahead if I over-explain obvious things.
The title is easy enough to pick apart: spaceflight leads to some unusual development of the neocortex (that’s essentially the outside of the brain, the most newly-evolved part) in the period of growth shortly after birth.
The neocortex is unique to mammals, and tends to be used for more advanced functions, like sensory perception, and language in humans. Synapses are the gaps between neurons, across which the chemical or electric “message” must travel. It can be argued (convincingly, I think) that the synapse, not the neuron, is the functional unit of the brain.
At birth, infants have more neurons than they will have as adults; as their brains develop, to put it simply, the synaptic connections that are not used are “pruned” away. This is just fine–not every cell in the brain needs to be connected to every other cell. The process may sound wasteful (why create so many cells, just to destroy them?), but ultimately works out for the best. The remaining cells and connections are necessary, and unnecessary connections have been removed.
With the terminology out of the way, this paper really raises the questions of how and why this should be. What is it about spaceflight that would affect the brain, especially in its developmental stage? (I’m kind of a sucker for developmental neuroscience, because, well, babies.)
(Before we go any further, you should know that the experiments in this paper were performed on rats. Significantly less cute, but also much easier to cart up to space.)
Developmental neuroscience is important because it can tell us a lot about learning and memory, as well as offer clues to problems that may arise later in life due to disruptions of the normal course of development (either biological or environmental).
It stands to reason that spaceflight introduces some pretty major disruptions to normal development. The authors of the paper (abstract and PDF can be found here) discuss the impact of microgravity (the gravity, or lack thereof, on the ISS) on the development of the brain.
The authors of this study concluded that Earth-level gravity is necessary for the normal development of the brain, specifically the creation of synaptic pathways in the neocortex. In rats, the section of the neocortex that was studied was involved in motor movements that atrophy due to microgravity–because they are no longer needed, they fall into disuse.
As stated above, the neocortex plays a large part in many of the functions that define us as human beings. Presumably, human motor pathways would be affected by microgravity, but what about the more abstract neocortex functions?
Obviously, the brain evolved on Earth, and so would develop best here. But what is it, ultimately, about gravity that affects the development of the brain? Is it simply the effect of gravity on muscles and their connection to the brain, or does gravity affect the brain tissue itself? Could the tug of this rock beneath our feet be necessary both to keep us grounded and to create the bit of tissue that lets us daydream of flying, talk about the stars, and finally build machines to escape Earth’s gravity?
I will repeat the scientists’ chorus: Further study is needed. And I will add my own verse: If more study is needed in space neuroscience, sign me up.