Because the current generation of vitrification agents permit cryopreservation of the brain without ice formation, the current objective of cryonics research is maintenance of viability of the brain during cryopreservation. The most popular viability assay that has been used in cryonics and cryonics-associated cryobiology research is the potassium/sodium ratio (K+/Na+ ratio). Because the ability of a cell to regulate its ionic composition reflects and affects many other biochemical processes, the K+/Na+ ratio is a good measurement of viability in general. For example, all the brain slice experiments to validate the Cryonics Institute’s vitrification agent VM-1, were assessed using the K+/Na+ ratio as a measure of viability.
In the case of the brain, demonstrating such “basic” viability after vitrification is a necessary, but perhaps not sufficient, condition for reversible vitrification of the brain without adverse (long term) effects. Recovery of function in the brain is a more subtle concept than in other organs. In 2007, 21st Century Medicine reported maintenance of long-term potentiation (LTP) in vitrified brain slices. Chana de Wolf proposed more specific experiments to demonstrate maintenance of memory after cryopreservation. And more specific molecular assays could assist in illuminating the effects of cryoprotective perfusion, cryoprotectant toxicity, and cryogenic cooling on the brain. Such viability and functional assays can be correlated and combined with structural assays to assist in developing cryoprotective solutions, and perfusion and cooling protocols that will permit successful resuscitation of whole brains after vitrification.
Further reading: Securing Viability of the Brain in Cryonics