Fig. 2

Scaling of the diffusive and advective flux rates in the interstitial space, \(\mathcal {F_{\mathrm{D}}}\) and \(\mathcal {F_{\mathrm{A}}}\), with changes in porosity \(\alpha\). In each case, the flux is normalized by its (unknown) value in the awake state. The values of the porosity for wake (\(\alpha = 0.141\)) and sleep (\(\alpha = 0.234\)) are those determined by Xie at al. for the mouse brain. In going from wake to sleep, the diffusive flux decreases slightly while the advective flux increases by a factor of nearly 2.5