Do you remember the first time you heard about cryopreservation? What was your reaction? Maybe you were shocked that such a thing existed, or maybe excited? It probably took you some time to get a good grasp of what cryonics does and form an educated opinion on it. All of this is possible only because you do a practical thing called “remembering”. You were able to form your own opinion and learn about it because a previous encounter with the topic was anchored in your memories. Be it years, months, weeks or only hours ago, your memories are what enabled you to build upon your knowledge.
Because everything we’ve ever learned or experienced is primarily linked to our ability to memorize, losing one's memories coincides with losing one's identity.
Therefore, the concern of suddenly waking up with amnesia (memory loss) is a valid one. But is there any reason to be concerned when it comes to cryonics, or in other words: can cryopreservation store your memories?
This article will look at how memories work, where they are stored and how, if at all, cryopreservation affects all that.
Memories are stored in our brain, this shouldn’t come as much of a surprise. Their exact location inside the brain however, is a bit of a weird biological mess.
The physical trace of a memory is called an “engram”. In the early 20th century, scientists first tried to track the exact location of such engrams to no avail. Pioneering psychologist Karl Lashley wrote in 1950, after 34 years of researching memories:
“I sometimes feel, in reviewing the evidence on the localization of the memory trace, that the necessary conclusion is that learning is just not possible.”
Despite his failure to provide conclusive evidence, his research was not in vain. Modern technology has allowed us to use his research as a foundation, and get a deeper look into the brains’ activities. Eventually, scientists were able to provide an explanation to Lashley’s findings at the time: no ONE specific part of the brain is in charge of memories. Instead, they are spread over many different areas.
The areas in question include, but aren’t limited to: the hippocampus, the neocortex and the amygdala. A 2016 study by American neuroscientist Janice Chen has shown that recollecting a memory we share with others, will always trigger neurons to fire in similar brain areas. Therefore, memory allocation seems to be largely unaffected by people’s subjective perception of a moment. Recalling a face for example, will always trigger the “face-recognition” part of our brain, no matter what person we are picturing inside our head.
This lets us conclude that, while memories are widely spread out across our brain, they can still be categorised and attributed to individual areas. So, let’s look at some categories.
Have you ever studied for a test and felt like everything you’ve learned immediately left your brain again the day after? Or wrote a note to yourself because you didn’t trust the future-you to remember on their own? Then you’re certainly acquainted with what we call “short-term memory”. Short-term memories commonly last between 200ms and 30 seconds, but no longer than 1 minute, and form the base of every recollection in our head.
They can further be split into two groups:
Iconic and Echoic memories are stored in the lower part of the temporal lobe. The former stores visual information (images) for about one second at a time, while the latter holds auditory information (sound) for one to two seconds. Most of the time we don’t react to these impressions consciously, but that doesn’t mean we don’t need them. These processes are what enables us to live in the moment. Without them, we would constantly feel disoriented. This effect can be observed in people after excessive amounts of alcohol consumption. It slows down communication between nerves, which reduces the brain's ability to form these types of memories, leading to confusion and unresponsiveness.
If a memory grabs our conscious attention, it can be held for longer than the initial 1-2 second duration. All this happens within a group of neurons called “cell assemblies”. These arise from repeated and persistent stimulation of individual cells, which in turn strengthens the connection, in this case the memory. A particularly strong impression can be remembered as a short-term memory for multiple days without recall. When you heard of cryonics for the first time, we bet it didn’t leave your mind five seconds later. It possibly even turned into our next category.
If a memory is recalled continuously, thereby stimulating the neurons over and over again, a new type of cell assembly can be formed: a long-term memory. These can once again be split into two main categories:
Declarative refers to facts and events such as ones’ birthday or the corresponding birthday party. As a rule of thumb if a memory can be declared true or false, it is declarative.
Non-declarative are the memories that directly affect your behaviour or skills. Such as a habit to touch your nose when you’re nervous or the ability to be good at a sport.
Long-term memories are hard or even impossible to forget and play a big part in building our identity. If you were to lose one, it would likely have a bigger impact on you than forgetting a minor detail that happened a few seconds ago.
A memory only becomes long-term if it is strong enough to frequently stimulate the corresponding cell assembly. Neurologists call this effect “long term potentiation”. That means that these kinds of recollections once were, or still are, of significant importance to you.
The question remains: which part of the brain has to be addressed for which kind of memory? Declarative memories usually emit a response in the medial temporal lobe, thalamus and hypothalamus. The variety of possible impressions make it the furthest spread across the brain.
On the non-declarative side, emotional response is mainly handled by the amygdala. This area shows a very high neuron activity in trauma patients or people recalling past moments with loved ones.
Motor memory is recorded in the cerebellum and allows us to make use of reflexes and general movement. People with a severely damaged cerebellum might find day to day tasks like picking up objects or sitting down slowly very challenging.
It is known that many neurodegenerative diseases can lead to forgetfulness or even amnesia. On top of that, didn’t we just say short-term memories only last for a finite amount of time? You might think “of course we can forget.'. However, we can’t be fully certain of that. It’s possible that the brain never actually “forgets” anything.
A 2009 study suggests that neuron connections made through memories are still stored in your brain after they seem to have “vanished.” They might simply be too weak to be accessed directly.
One argument for this would be that at any given time you might remember something that you had completely forgotten about up to this point. You have gone years without remembering a person's name, and one day out of nowhere *pop* it’s there again. Scientific evidence for this phenomenon is limited at this point, yet if it holds true, it might even be possible to restore memories after they have been previously “lost.” This would have amazing implications for the treatment of neurodegenerative diseases.
With all this explained, what happens to our memory during cryopreservation?
A goal of cryonics is to preserve the brain as intact as possible until future revival. This, of course, includes all the areas of the brain responsible for storing memories.
To test this, a 2015 memory retention study on C.elegans was performed. Scientists used a method of sensory imprinting on them to test long-term memory of the smell in the worms. They cryopreserved the young creatures, which are a well known model organism for biological research. After revival, the animals’ were able to recall the induced scent memory, proving that their neuron-structure has not been modified by the process of vitrification or slow freezing.
Therefore, a high quality cryopreservation could have the capability to successfully retain memory.
A 2020 study that we analysed in a previous article tested the effects of cryopreservation on the brain of a female body donor. Results have again shown that cryopreservation had no adverse impact on hippocampal or cortical thickness, both regions important for memory storage.
Still, a temporary state called “brain fog” might be a possible side-effect. This would mean that your memories are a little hazy initially, as your brain slowly resumes all of its functions after revival. Short-term memory loss and brain fog are common side-effects for heart attack survivors. This is due to a temporary lack of oxygen in the hippocampus region which is located inside the temporal lobe where short-term memories are stored. Luckily, scientists are already working on a way to restore neurons in that area, opening up the possibility of this not being a problem in the future anymore.
In fact, with this treatment in addition to the complete biological pause biostasis enables shortly after legal death, you are likely to still be in possession of all your memories after revival.
If some memory loss still occurs, there is the possibility of future technology being able to help you recall it by stimulating specific regions of the brain and reactivating cell assemblies.
Our memories are an important part of who we are. We might not fully understand how they work yet, like many other things happening in our brain, but we do have an idea of where they are stored. This means we can assess what the corresponding regions look like after cryopreservation. Current data suggests they can be well preserved for cryonics patients.
Hopefully, this article was interesting enough to upgrade into a long-term memory for you. If it does, feel free to tell us about it after your potential revival in the future.
Are there any more questions you have? Feel free to read more about cryonics in one of our newly published ebooks by filling out the form below, or join our Discord server and talk to other community members.