This is NOT medical advice. Lithium can be lethal very easily. I'm not asking you to ingest lithium without first properly educating yourselves in basic biochemistry of Lithium. Use this information at your own peril.

Lithium microdosing just might be the key to cure depression/mania/ and even prion disease, I shouldn't say cure but rather prevent prion disease. What is common between prion disease(CJD), alzheimer's, huntington's, parkinson's and several other disorders? Accumulation of proteinaceous compounds leading to cell death. The worse thing about these diseases is the very long incubation periods which explains why older people are effected more by it.
There are two primary ways the body deals with these kinds of rampant proteins, that is through aptosis and autophagy. Lithium is of interest because of it's effects on autophagy. It has been shown in studies that prion disease is spread through exosomes and autophagy can arrest the spread of this through lysosomal action. Autophagy induced by the drug rapamycin and also salts of lithium function in different ways, rapamycin activates the mTOR (mammalian target of rapamycin) pathway while lithium works independent of this pathway to reduce exosomal release of infectious prions. Combined they maybe a therapeutic prophylaxis for the incurable diseases.
links for reading:
[1] https://onlinelibrary.wiley.com/doi/full/10.1111/j.1471-4159.2009.05906.x
[2] http://www.jbc.org/content/293/23/8956.long
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3972801/
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6380616/