With continued debate over the functional significance of adult neurogenesis, identifying an in vivo correlate of neurogenesis has become an important goal. Here we rely on the coupling between neurogenesis and angiogenesis and test whether MRI measurements of cerebral blood volume (CBV) provide an imaging correlate of neurogenesis. First, we used an MRI approach to generate CBV maps over time in the hippocampal formation of exercising mice. Among all hippocampal subregions, exercise was found to have a primary effect on dentate gyrus CBV, the only subregion that supports adult neurogenesis. Moreover, exercise-induced increases in dentate gyrus CBV were found to correlate with postmortem measurements of neurogenesis. Second, using similar MRI technologies, we generated CBV maps over time in the hippocampal formation of exercising humans. As in mice, exercise was found to have a primary effect on dentate gyrus CBV, and the CBV changes were found to selectively correlate with cardiopulmonary and cognitive function. Taken together, these findings show that dentate gyrus CBV provides an imaging correlate of exercise-induced neurogenesis and that exercise differentially targets the dentate gyrus, a hippocampal subregion important for memory and implicated in cognitive aging.
Legend - (click on figure to enlarge) Exercise selectively increases dentate gyrus CBV in humans. (a) Exercise had a selective effect on dentate gyrus CBV. Bar graph shows the mean relative CBV (rCBV) values for each hippocampal subregion before exercise (open bars) and after exercise (filled bars). As in mice, the dentate gyrus was the only hippocampal subregion that showed a significant exercise effect, whereas the entorhinal cortex showed a nonsignificant increase in CBV. (b) An individual example. (Left) High-resolution MRI slice that visualizes the external morphology and internal architecture of the hippocampal formation. (Center) Parcellation of the hippocampal subregions (green, entorhinal cortex; red, dentate gyrus; blue, CA1 subfield; yellow, subiculum). (Right) Hippocampal CBV map (warmer colors reflect higher CBV).
Tuesday, April 03, 2007
Exercise increases nerve cell growth in brain area crucial to cognitive aging.
Pereira et al. have used an interesting approach to demonstrate that exercise causes the growth of new nerve cells in the dentate gyrus (part of the hippocampus) of mice and humans. Because new nerve cell formation usually is accompanied by synthesis of new blood vessels and increased blood flow, they used MRI measurement of cerebral blood volume as an assay of new nerve cell formation in the living brain. Here is their abstract, and a figure from the paper. The PDF of the paper can be downloaded HERE.