I’m going to explain why I think this question is worth considering.
I have recently been reading a most interesting book that has been descibed as a “medical memoir”. I have read that the fiction writer Siri Hustvedt has mirror-touch synaesthesia, and I was rather interested in reading about that, but the main topic of Hustvedt’s book The Shaking Woman is her search for an explanation for her seizure-like shaking episodes that are triggered by public speaking.
One thing that I’ve noted is that both Siri and her late father have experienced PTSD-type flashbacks of traumatic memories (warfare, car accident). Like myself, Siri Hustvedt has also experienced the Tetris effect, which is like PTSD flashbacks in that it is an involuntary experience of a visual memory. I don’t experience the Tetris effect much these days, but when I do it is typically in response to a full day of weeding or some other outdoor repetitive work. I don’t think scientists know how common the Tetris effect is, and if it is a thing that everyone experiences then it wouldn’t mean a thing that the novelist and I both experience it. I have at least one other close blood relative who has also experienced the Tetris effect quite a few times. The Tetris effect operates through an unknown memory system, possibly related to procedural memory, according to the Wikipedia. I would think that the Tetris effect would have some type of visual memory system as its basis. It is interesting that Hustvedt’s mysterious shaking episodes were dampened-down but not completely cured by the drug propranolol, which (according to the book) is also used to treat high blood pressure, migraine, performance anxiety and PTSD. Hustvedt seems to have a lot of whatever mechanism is the basis of PTSD, which I guess might be a very strong or hyperconnected visual memory system in her brain. I would think this system is also probably responsible for the Tetris effect. Another reason to believe that the Tetris effect and PTSD operate in the same brain system is that a study described in the Wikipedia found that playing a Tetris-like video game soon after a traumatic event “….reduces the number of flashbacks that are experienced afterwards”. I guess a specific memory system becomes overloaded with memories if the game is used as preventative treatment, so less of the traumatic memories can be encoded properly for long-term storage.
Hustvedt and I have quite a few things in common. We are both synaesthetes, we have both experienced the Tetris effect, we have also both experienced and migraine headaches, and we have both apparently had brain-based experiences of involuntarily-retrieved visual memories. In her book Hustvedt did not spell out explicitly that her flashbacks included visual content, and she did mention the memory of sound, but I’m happy to assume that anything labelled as a “flashback” included visual content. My involuntarily-retrieved visual memories are two different types of synaesthesia which I’ve experienced which trigger visual memories of scenes or a face. Hustvedt’s shaking episodes are like synaesthesia in that they have a very specific trigger (public speaking) and a very specific manifestation (violent body tremors without apparent anxiety, or under the influence of propranolol, an “electric buzz” quiver throughout the body).
There seem to be a lot of things here that are inter-connected. My experiences of my fine-motor->visual memories of scenes synaesthesia and The Strange Phenomenon, which is I believe a hybrid of face recognition and synaesthesia in which seeing one face under very specific conditions triggers an involuntary experience of a very old memory of the face of another person, show that synaesthesia concurrents or triggered additional sensory experiences can be in some ways similar to PTSD flashbacks, but without any accompanying psychological distress. My fine-motor-triggered visual memories are very subtle and hardly noticeable, while the face memory evoked in The Strange Phenomenon is more of an intrusion into ordinary consciousness. I’d like to put forward the theory that the flashbacks of PTSD (and not any of the other distressing features of PTSD) are synaesthesia concurrents that just happen to be distressing visual or sensory memories. I guess they must have some type of trigger, and I guess could be something purely sensory, very subtle or ordinary. I have never experienced PTSD myself, probably because I have fortunately never been in the type of extremely traumatic situation that causes this psychological syndrome, so I can only guess at what PTSD flashbacks are really like from what I’ve read. Are PTSD flashbacks the result of a type of synaesthesia that can manifest as quite a subtle experience, but are only troublesome or exceptional because of the very unpleasant nature of the memories evoked? Are synaesthetes more likely to develop PTSD if exposed to trauma than non-synaesthetes exposed to equivalent situations? It’s just a theory!
Wikipedia contributors Tetris effect. Wikipedia, The Free Encyclopedia. http://en.wikipedia.org/w/index.php?title=Tetris_effect&oldid=448999724
The Shaking Woman. The Book Show. Radio National. April 22 2010. http://www.abc.net.au/rn/bookshow/stories/2010/2878610.htm