Yaniv Assaf, Ph.D.
Department of Neurobiology
The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel http://neuroimaging.tau.ac.il/ya
Neuro-plasticity is one of the key processes in our brain's physiology. This process allows our brain to change itself, functionally and structurally, following the acquisition of a
new skill or experience (1-8). While functional aspects of neuro-plasticity can be studied
using non-invasive techniques such as fMRI, EEF and MEG, investigation of the structural tissue characteristics of neuro-plasticity requires invasive histological or invasive approaches.
Structural MRI studies of long-term brain plasticity reveal significant volumetric/regional
changes (9-12). Yet, the micro-structure correlates of these changes are not well
understood. An open question is what happens at shorter term learning and memory processes?
In a short term spatial navigation study performed both in humans and rodents (13), we
found that diffusion MRI can detect structural changes in cell morphology induced by plasticity within few hours. Both in humans and rodents, the micro-structural changes, as observed by MRI, were localized to the anticipated brain regions: hippocampus, parahippocampus, visual cortex, cingulate cortex and insular cortex.
Our results indicate that significant structural occur in the tissue within mere hours - an interesting result by itself from the neurophysiological point of view. However, by investigating the induced structural changes both by histology and MRI it is possible to elucidate the relations between tissue micro-structure and the diffusion MRI signal.
Preliminary results of such comparison indicate that one of most significant cellular component that is in correlation with the diffusion MRI indices is the density and shape
of astrocytes (13-15).
The ability of MRI to follow such subtle and rapid cellular changes is striking and opens a new window into brain physiology and plasticity localization. In addition, investigation of underlying tissue changes may lead to better understanding of the diffusion MRI signal.
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