Proposal 3 (Fig. 7c) The third proposal, the glymphatic hypothesis [25, 109, 135–137], asserts.There is an inward flow of CSF along periarterial spaces;
The flow is driven across the layer of astrocyte endfeet into the parenchyma aided by the presence of Aqp4 in the endfeet;
The flow propels the waste products of metabolism into the perivenous space again crossing the layer of endfeet, presumably again aided by the presence of Aqp4;
The flow exits the parenchyma by the perivenous route and reaches lymphatic vessels in the neck.