Memories emerge intact from cryogenic resurrection machine

By John Hewitt

Many animals can survive prolonged periods of exposure to freezing temperatures. To do this, they run a sophisticated ‘freeze’ program on the way into the frozen state, and another ‘thaw’ program on the way out. Although there have been advances in freezing and thawing animals that lack these built-in cold survival responses, it hasn’t been made clear whether important higher-level functions, like memory, would emerge unscathed. Two researchers, Natasha Vita-More and Daniel Barranco, have now proven for the first time that cryogenically-suspended worms retain specific acquired memories after reanimation.

To do this, the researchers first trained the worms to move to specific areas when they smelled benzaldehyde (a component of almond oil). After mastering this new task, the worms were bathed in a glycerol-based cryoprotectant solution and put into to a deep freeze. When the worms were thawed, they remembered their job and moved to the right spot when benzaldehyde wafted in. The researchers compared two different methods of cooling: The first one was based on the old-fashioned way to freeze cells or organs — a low concentration of cryoprotectant and a slow cool/thaw cycle. The second way was a more aggressive procedure known as vitrification.

Vitrification requires a higher concentration of cryoprotectant, but does the freezing and thawing so fast that damaging ice crystals don’t have much chance to form. Only about a third of the worms that are frozen by the slow method actually survive, while almost all of those vitrified will survive. Surprisingly, Vita-More and Barranco found that worms frozen by either method retained the proper memory for what to do.

While all that is good news for cryonics, if we expect the fragile filaments and tender excrescences of much larger nervous systems (like ours) to survive such an ordeal intact, a little more care will be needed. To deliver cryoprotectant into all the nooks and crannies of a larger body from the outside, you generally need to drain the blood out and pump the new solution in through the circulatory system. While that might work pretty well if done properly, the problem is on the flip side — namely, getting the cryoprotectant back out.

Animals like arctic fish, frogs or insects can survive multiple freeze/thaw cycles because they do it from the bottom up rather than top down. In other words, each cell has a local copy of the freezing protocol, which has been scripted uniquely for it. The cell can therefore manufacture or import not just the cryoprotectants and associated adjuvants it needs, but also make and export the products that the cell’s host organ needs (which in turn, must be delivered to the other organs that make demands on the host organ).

If all that was required to survive freezing was for each cell to reel off a few million copies of an antifreeze protein, synthesize some ice-crystal blocking glycerol, or import glucose, then specific genetic arrangements might be readily made to accommodate that. New DNA could be spliced in, along with warm-inducible ‘promoters’ to keep the freeze proteins properly suppressed during happy times.

Unfortunately, things don’t really work like that. Santa Claus doesn’t fill an order for 10,000 sleighs if there are no trees at the North Pole. In the same way, cells probably couldn’t fulfill the requirements that massive, near-instantaneous antifreeze protein synthesis would make unless its entire genome, or at least those genes in the critical metabolic cycles that supply the building blocks (and degrade them afterwards), have been similarly adapted simultaneously through deep evolutionary time. In the case of antifreeze proteins, it seems that the original proteins evolved from digestive trypsins in the gut, presumably to deal with cold-susceptible fluids that would tend to accumulate there.

Creatures that synthesize other cryoprotectants like glycerol or glucose have their own special needs. An organism-level operating system must be engaged so that each organ supplies what is needed, and then is powered down in the right sequence, so that the most essential functions remain online until the end. For example, at low temperature, Arctic frogs produce a special form of insulin to stimulate cells to gorge on blood-supplied glucose. That glucose order must be filled by the liver, which has painstakingly packed it into the form of large glycogen molecules, which must now be broken down by running their metabolic synthesis program in reverse. When spring comes and the frog warms, the extra glucose must be rapidly removed from the cells before it compromises proteins, and then recycled through kidney excretion and ultimately stored in the bladder.

When ice crystal do form, they generally start in the extracellular regions, driving the dissolved molecules distributed there into dense congregation. The subsequent high concentration osmotically draws water out from cell interiors and jams things up there as well. In freeze-adapted creatures, the body shuttles the extra water to various ‘safe’ compartments, where it is dealt with by various mechanisms, all highly planned and routinely executed.

Showing that worm brains can handle top-down freezing by artificial means is an important step towards doing the same for larger organisms. If more researchers pick up where Vita-More and Barranco have now led, survivable cryonic suspension may eventually be mainstreamed for those that would desire it.