New dimensions for brain mapping

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Science  30 Nov 2018:
Vol. 362, Issue 6418, pp. 994-995
DOI: 10.1126/science.aav7357

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The representation of memory in the brain is one of the unresolved questions in neuroscience. A key feature of learning and memory is the process of neuroplasticity—the ability of the brain to remodel structurally and functionally as a result of cognitive experience. Although the neurobiological basis of this process (that is, synaptic plasticity) is well established, the system level dynamics of neuroplasticity are still unclear. Recently, diffusion-weighted magnetic resonance imaging (DW-MRI), which can be carried out noninvasively in humans, provided a new approach to explore neuroplasticity. One of the parameters extracted from DW-MRI is mean diffusivity (MD) of water molecules, which is a biomarker of tissue microstructure (1). By probing changes in MD across the brain, areas of microstructural plasticity can be detected within hours of learning. On page 1045 of this issue, Brodt et al. (2) used DW-MRI after an object-location memory task and found that brain plasticity occurs in the posterior parietal cortex (PPC) rather than in the hippocampus. Furthermore, they demonstrated that localized DW-MRI changes follow the basic definition of a memory engram (the physical manifestation of memories stored in the brain). These observations go beyond the understanding of memory representation in the brain. Probing MD with DW-MRI appears to provide a detailed and comprehensive monitoring of brain microanatomy, revealing uncharted relations between brain structure and function.