Exercise Hormone Helps Memory
Studies connect cardio exercise with improved memory and brain function–but how? We’re just starting to see the molecular clues. Exercised muscles releas a hormone called irisin, which influences the brain’s memory center. Original report is here.
Where does irisin come from? The exercising muscles express a particular gene (that is, make messenter RNA and protein specified by the gene). The gene is called FNDC5 or Fibronectin Type III Domain Containing 5. The gene is found in humans and mice–but not invertebrates, which lack the vertebrate central nervous system. It is expressed strongly during embryonic formation of the heart. A particular peptide (short part of a protein) is cut off the FNDC5 protein; this peptide is called irision. In adults, FNDC5 expression from myocytes (muscle cells) releases irisin, whose signal is associated with converting “white fat” cells to “brown fat” with expenditure of energy.
But now, exercise is also shown to cause irisin expression and release in the hippocampus. Is this unusual, for a very particular signal molecule to have different roles in different tissues? Actually, it is very common in eukaryotic organisms (plants and animals, including us humans). Most of our proteins are multitaskers. In particular, much of brain function depends upon multitasking proteins. That is why so many single-gene birth defects have multiple effects on the body, including cognitive problems.
The hippocampus is the brain’s memory center. In the hippocampus, FNDC5 expression induces expression of BDNF (brain-derived neurotrophic factor). BDNF protects the neurons that encode memories.
So the moral is, now that spring is here (ignore the dusting of snow this morning) let’s get out and start running.
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Ultraphyte 
The question is why this effect happens. We could speculate that this aids memorization of space in vertebrates, i.e. mapping of the environment is enhanced when the animal is moving. It might also explain why I learn to navigate better when I drive rather than when I am driven.
Alex, that’s a very insightful point. I have a post somewhere on spatial learning–supposedly the foundation of all memory, for humans.
I wonder if they’ve tested whether there’s a difference in the effect of running cross country versus running in place?
I suspect that the mechanism is just movement, and not functionally related to specific movements. But intriguingly, if all memory is spatial (or spatio-temporal) then would any exercise improve memory-retention from studying? Should students study on a treadmill or exercise cycle? That might well be testable. I do like the idea that the brain saves energy by reducing memorization while inactive, but increases it once activity is restored.
One further thought. It is now believed that memories are not permanent, but are rebuilt on recall. Does exercise impact this memory rebuilding/remodeling and could it have useful therapeutic uses?
I never got the good feeling that running always gave me, when I would run on a treadmill. I would think the eyes expect a running stream of movement but don’t get it on a treadmill. Irrespective of memory proteins.
Also the eyes expect a distant view. I try to look way out the windows of our exercise facility.
Interesting observation. So running in the woods would theoretically give you a better feeling than running on a flat plain. Does watching a tv screen make a difference – either watching some show or a projection of the running course.
With respect to memory, your experiences may not be relevant. Those good feelings could be due to different sensory inputs, rather than anything related to remembering anything.
Very interesting, indeed. A question: By what route and steps through the body does the message propagate from muscle to brain?
– Love, Dad
I’m trying to get this straight from the reports. I think actually the diagram above is misleading; it’s actually the gene in the neurons that make the same irisin peptide that is also made in the muscle.