Diffusion imaging reveals anatomical connectivity and microstructural changes due to learning

Diffusion imaging is a method where magnetic resonance imaging is utilized to measure movement of water within the brain; in modern diffusion imaging sequences water movement is measured in several tens of directions. Since the glia cells and neurons that make up the brain tissue obstruct free diffusion of water, there are significant deviations from Brownian (i.e., random) motion in most brain structures (other than ventricles of course). What makes this phenomenon really interesting is that by measuring the directions of local diffusion, it is possible to reconstruct the white matter tracts of the brain (as water flows along the direction of the myelinated neural fibers) and thus inspect anatomical connectivity of the brain. A recent paper by Dr. Wedeen and colleagues published in Science shows how accurately the anatomical connectivity of human brain can be measured non-invasively in healthy volunteers. This paper nicely combines the vast improvements that have recently taken place in both diffusion imaging sequences as well as data analysis methods.

As another highly interesting recent publication on diffusion imaging, it was shown by Sagi et al. in Neuron that there are rapid changes in diffusion properties of focal brain structures that correlate with learning. In this study, diffusion was measured prior to and immediately after volunteers were intensely playing a car-racing game where they had to learn to navigate the racetrack. One control group was playing the same game but with changing racetracks so that their spatial learning was not to the same extent engaged during the gameplay. Compared to pre-game diffusion measures, there were microstructural changes revealed by diffusion imaging after two hours of racing in several brain structures and, furthermore, learning the racetrack correlated with microstructural changes in the right-hemisphere parahippocampus. These results are really fascinating as they suggest that structural imaging can be utilized to measure short-term plastic changes in the human brain.

References:

Sagi Y, Tavor I, Hofstetter S, Tzur-Moryosef S, Blumenfeld-Katzir T, Assaf Y. Learning in the fast lane: new insights into neuroplasticity. Neuron (2012) 73: 1195-1203. http://dx.doi.org/10.1016/j.neuron.2012.01.025

Wedeen VJ, Rosene DL, Wang R, Dai G, Mortazavi F, Hagmann P, Kaas JH, Tseng WY. The geometric structure of the brain fiber pathways. Science (2012) 335: 1628-1634. http://dx.doi.org/10.1126/science.1215280