We all have memories that we hold onto very hard. There’s also a few we’d like to shed. It might be that time you thought your dancing was way better than it actually was or a bout of food poisoning on a 16 hour plane flight. For me it’s the whole of the 18 months I thought I’d give my hair a chance to grow down to my shoulders. (Tangentially, this episode also tells me I can’t trust anyone I know to act when an intervention is required.)
Well every one of those memories isn’t even the memory you thought it was. All those memories are actually about you right now more than they reflect you back then. And that fact also has me thinking about one of the more commonly mentioned fears in anaesthesia – being aware of the operation while you’re supposed to be deeply unconscious.
Let me add some detail here because that was a bit opaque. Growing up I used to view memories as my personal museum exhibits. Curios encased in glass and placed haphazardly on dusty shelves for me to pick up and examine as required on rainy weekend afternoons. At the time the theory was that after initial establishment and consolidation your memories were filed away in spots around the brain to be drawn on at will. This knowledge had been around since the early stages of the 1900s.
Over some decades mechanisms for memory consolidation were slowly uncovered. So it has been known for decades that at the time of initial memory formation, proteins need to be produced in the memory areas. More recent rodent research has shown that this protein formation is also a feature of retrieval of that memory, and that blocking that protein formation at the right time (close to the point of memory retrieval) alters the previously established memory associations. (There’s an excellent if long article on this stuff here.)
This is profound stuff. If memory is rewritten continuously what does that mean for the way you incorporate your recollections into your current actions and thoughts? We use our memories of people and behaviour to govern our interactions with the world. What emerges is not a static history informing our progress but a constant revision and re-examination of how we relate our present and past.
Since the emergence of this concept of rewriting the whole process of memory only becomes more intriguing. In addition to further work demonstrating our constant ‘White Out’-wielding ways (with more here and here) there’s early evidence of the ability to artificially manipulate memories. A team at UC Irvine have demonstrated that they can create an enhanced response to the memory of a sound by manipulating cerebral cells (more rodent work, but interesting).
So if it’s true we both continually revise our memories and that we’re starting to see ways to manipulate them, maybe Eternal Sunshine of the Spotless Mind (the rather brilliant movie where a guy takes up the offer to erase the memories of a recent failed love and then realises he wants to keep them after all, even attempting trickery to protect and rewrite them) is not so abstract.
This new understanding also has implications for one of the common fears expressed by patients undergoing anaesthesia – that they’ll be aware of what is happening during the operation while everyone thinks they are asleep. Called awareness, it’s easy to see why this would be something that causes some concern. After all, the whole purpose of the anaesthetic is to make sure you don’t know what’s going on, right?
The thought then that you’d feel the full extent of a surgery with no ability to respond sounds pretty horrifying. The experience can be scarring. In adults there’s studies including follow-up on small numbers of patients who have experienced explicit recall (the classic story of knowing everything that is going on while apparently asleep) which suggest a reasonably high rate of post-traumatic stress disorder and anxiety symptoms. I suspect most people would assume that’s almost inevitable.
Interestingly in kids the rate of awareness appears to be higher (anywhere between 0.2-1.2% of operative cases under general anaesthesia compared to 0.1-0.2% in adults). You might assume kids would be more likely to find that incredibly scary, but there’s at least one study (see 6 in the bibliography) suggesting no difference in apprehension about future surgery or differences in the post-operative phase. There’s even been some work suggesting that a proportion of kids experiencing awareness expected to be aware of their operation (not exactly selling the skill of the anaesthetists, there).
In the anaesthetic literature awareness was once described as an issue of conscious perception. It’s actually an issue of memory formation. Being aware alone isn’t enough to have the patient retelling theatre jokes – there has to be a stage of establishing and consolidating a memory. It’s probably then true that the individual keeps remodifying that memory each time they retrieve it. The question of why some people are more likely to end up with an episode of awareness than others (and a prior history has been suggested to increase your chance of a subsequent event 5 times over) could relate to personal differences in the way individuals revise the manuscript of their operative awareness.
As we’re still trying to figure out exactly how anaesthetics work (but getting there, as discussed here) it’ll be a while before we figure out how to guarantee that patients won’t be left with the distress of experiencing awareness, or any of the surgeon’s jokes. Perhaps more achievable is finding therapeutic options to apply just after the event so that any memories are no longer scary. This would be more like convincing the friendly lab rat that grabbing the cheese won’t lead to a nasty shock and that stuff has already been done.
The appeal of being able to intervene on day one to prevent a memory turning into a trigger for long-term PTSD is immediately apparent and could prevent a lot of long-term distress. And if science could rapidly deliver a way to help me forget this ever happened (while delivering back that 3:31 thanks Hasselhoff) I’d be even more impressed.
Some reading on anaesthetic awareness for the curious:
1. Ghoneim MM, Block RI, Haffarnan M, Mathews MJ. Awareness During Anesthesia: Risk Factors, Causes and Sequelae: A Review of Reported Cases in the Literature. Anesth Analg 2009;108:527-35.
2. Pryor KO, Hemmings HC. Increased Risk of Awareness under Anesthesia: An Issue of Consciousness or of Memory? Anesthesiology 2013;119:1236-8.
3. Aranake A, Gradwohl S, Ben-Abdallah A, et al. Increased risk of intraoperative awareness in patients with a history of awareness. Anesthesiology 2013;119:1275-83.
4. Mashour GA. Post-Traumatic Stress Disorder After Intraoperative Awareness and High-Risk Surgery. Anesth Analg 2010;110:668-70.
5. Davidson AJ, Smith KR, Blussé van Oud-Alblas HJ, et al. Awareness in children: a secondary analysis of five cohort studies. Anaesthesia 2011;446-54.
6. Malviya S, Galinkin JL, Bannister CF, et al. The Incidence of Intraoperative Awareness in Children: Childhood Awareness and Recall Evaluation. Anesth Analg 2009;109:1421-7.