Cryonics is the cryopreservation of a brain in liquid nitrogen. It is used by companies like Alcor and the Cryonics Institute.

 

Aldehyde preservation, also known as chemical preservation, is the technique used here at Oregon Brain Preservation. The brain is stored in a liquid chemical at refrigerator temperature. While we do use liquid nitrogen sometimes, it is not our primary or preferred preservation technique.

 

Here is some information about the two different techniques:

 

The quality is similar

Aldehyde is heavily used by scientists and is very well respected as a high quality preservation technique. Nearly all microscopic images of brain tissue ever taken have used aldehyde. Cryopreservation is also heavily used and well respected. There is no reason to believe that one style of preservation is fundamentally superior to the other.

 

Aldehyde preservation can later be converted to cryopreservation

This can be an advantage in some situations and provides more options.

 

Aldehyde is a lot less expensive

This allows us to save many more lives and it also reduces the risk and complexity. When large amounts of money are not involved, everyone is safer. It means less overall risk of organizational failure.

 

Alcor images don't look great

Alcor has posted electron micrographs of brain tissue that has been preserved with their protocol:

https://www.cryonicsarchive.org/library/alcor-new-york-academy-of-sciences-paper/

https://www.cryonicsarchive.org/library/new-cryopreservation-technology/

The images demonstrate significant dehydration and they don't even look like normal brain tissue. They claim that this mechanical damage is reversible, but this is debatable and lacks strong evidence. By using aldehyde instead of cryopreservation, this damage is avoided.

 

Aldehyde and cryopreservation can be used together

In 2016, Robert McIntyre and Greg Fahy published a paper describing Aldehyde Stabilized Cryopreservation, which combined both techniques into a single protocol and demonstrated excellent quality of preservation of brain tissue. But while they can be used together, there's really no advantage over just using aldehyde.

 

Cooling slows reaction rates

The Q10 rule of thumb applies between 0 C and 40 C. The rule states that biochemical reaction rates are cut in half for every reduction of 10 degrees. For this reason, ice baths are frequently used in cryonics to slow reaction rates to buy more time to perform the perfusion. In constrast, if aldehyde can be quickly introduced, then most reactions stop and the Q10 rule no longer applies. Aldehyde is an alternative to cooling in this temperature range.

 

Cryopreservation works by conversion to solid

Conversion from liquid to solid happens at -123 C in cryopreservation. This is what finally locks the molecules in place. When aldehyde is used, the molecules are locked in place much sooner and the temperature doesn't matter.

 

Cryopreservation causes a delay of many hours

When cryopreservation is used alone, it takes hours to perfuse the cryoprotectant chemicals through the circulatory system. During that entire time, there's nothing locking the molecules in place, which could result in significant damage. Locking the molecules in place many hours earlier with aldehyde should preserve more information.

 

Refrigeration keeps lipids solid

The reason we refrigerate after using aldehyde is to keep the lipids solid. Aldehyde does a great job of quickly locking the proteins in place, but the lipids are only immobilized because they are trapped in a web of proteins. If we allow the lipids to remain liquid at room temperature, some of them might gradually leach out.

 

Cryopreservation provides no additional benefit

Nobody has ever been able to provide an example of any potential benefit of cryopreservation compared to aldehyde fixation. Without any clear benefit, we cannot recommend cryopreservation.

 

Cryonics is claimed to be a path to suspended animation

Some scientists who are involved in cryonics defend its use because they see it as a path to Suspended Animation. They envision being able to cryopreserve organs and then revive them, and then eventually moving to full suspended animation. Unfortunately, there is broad consensus among mainstream scientists that we are at least 100 years away from such technology. That means the two technologies are completely unrelated and making compromises for that reason is a terrible idea that's bad for patients.

 

Cold might penetrate more thoroughly than aldehyde

This is an argument for why cryonics might be better than aldehyde. But the argument quickly falls apart. Whether you use chemical fixative or cryoprotectant, you must get the chemicals to a given area of the brain or there will be poor preservation. In the case of cryopreservation, the poorly perfused areas would be subjected to a straight freeze. That’s probably not compatible with preservation of memories as explained here: Straight Freeze 

 

Alcor and CI seem to have social inertia

One explanation for why Alcor and CI continue to only pursue cryonics is that it might just be social inertia. If everyone around you is telling you cryonics is better than aldehyde, maybe you just believe it without questioning it too much.