Diffusion models can be validated by observing their functional dependencies, exemplified by the b-1/2 power-law scaling recently used to validate the “stick” compartment in white matter. In contrast, such behavior has not been observed in grey matter (GM), potentially due to a) water exchange between dendrites and extra-neurite space and/or b) a distinct signal contribution from somas. We report the first observation of the stick power-law in GM at very large b-values consistent with b). Nevertheless, the dependence on diffusion time indicates significant water exchange affecting the scaling range. The combined observations thus offer a window into more complicated microstructure.
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