For ages now I’ve been itching to try a sensory deprivation tanל. This Easter I finally got the chance and it was an experience very hard to put into word. That doesn’t mean I won’t try, read on for more.
Sensory deprivation tanks have been around since the 50’s, a body temperature salt water bath that is enclosed in a totally dark booth with sound isolation. Why would someone want to try such a thing? Well these tanks were first used in experimentation trying to test the hypothesis that if all senses were cut off the brain would go to sleep. Long story short, people do not fall asleep in isolation tanks but their brain does have stronger slow theta waves seen normally right before sleeping, in meditation states and in children. People also reported many different altered states of consciousness, hallucinations and claim that after the tank their senses were hyper strong and clear.
Getting into a laying down position in the tank wasn’t as easy as I imagined, every little movement would cause me body to rotate and move. It felt like I was in space. When I found a good position and turned off the lights it felt like slowly falling into an endless abyss. Everywhere around me there was nothing.
After a few minutes I began ‘seeing’ some purple color and shapes but that too went away and I had to remind myself to blink because I forgot if my eyes were open or closed. The most phantom feeling was in my feet. Occasionally I ‘felt’ my feet were touching the ground and had to wiggle my toes to make sure that they weren’t. After a few more minutes I began hearing the hum of electric machinery and at some point I was wondering about a ruckus someone with high heels was making, stomping around, but then realised it was my own heart beat. Usually when I meditate a thousand thoughts will pop up, mostly worrying about the future, school, finances and relationships. This time there were almost no verbal thoughts. My brain was very much awake and mostly silent. When I sent a query looking for the usual ‘stream’ the only thing that came back was: “All is good now, the future will come when it does”
My whole life I’ve experienced some oversensitivity to sensory stimulus, mainly in the soma sensory (touch) system. I hated wearing socks as a kid, everything would constantly itch me and drive me crazy. In kindergarten I was obsessed with sifting the sand in the sand box so I could run my hands through it without feeling all of these annoying bits and pieces. Whenever I would try to meditate in my martial arts training my senses would start ‘screaming’ and become overly irritated. I was hoping that this deprivation tank will help answer which part of my brain is causing the trouble.
Sensory deprivation tanks do not cut off your sensory input but they ‘feed’ the sensory receptors with information that has very little variance. In general, variance and change is exactly what your brain models. For those of you who have been following my posts, you should know by now that the brain is a hierarchical system with each layer explaining away and turning off the information from lower layers. Only the information that hasn’t been predicted progresses up the brain hierarchy in the form of ‘prediction errors’. So, once a stimulus stops changing our predictive mechanism easily explains it away and there is no information to communicate to higher brain areas. This will happen even with eyesight. Your eyes constantly make tiny micro movements to change the inputs of information. Without these movements, if you keep your eyes still you will go blind after a few moments, you can try this yourself.
My theory was the if the over sensitivity in my brain was due to increases top down prediction versus bottom up information, putting me in an isolation tank wouldn’t help and these prediction would enforce themselves on my perception anyway, perhaps even more so. But if my over sensitivity was due to increased precision of bottom up prediction errors steaming from my lower sensory areas than an isolation tank will decrease my symptoms. My top down predictions in these lower brain areas would finally be able to catch up and predict the over simplified sensory stimulus.
After a marvelous peaceful hour in the tank I have very little doubt that the second theory is much more likely. I would postulate that ‘normally’ these overly precise prediction errors drive sensory input to higher areas in my brain than most people leading to a bunch of interesting symptoms and compensatory mechanisms.
Back to the real world
The lights faded in slowly yet still caught me by surprise. I climbed out of the tank and gravity immediately hit me. I wobbled around trying to get my ‘land’ legs back. In the shower, rinsing off the salt, the stream felt like a thousand little needles hitting my skin and I jumped up startled. I took my time in the waiting room, drinking some tea and trying to prepare myself for the outside world. The ‘noise’ came back again once I hit the streets.There was a sense of ‘self pity’, but instead of giving in to that I tried to top down ‘instruct’ this brain: “Try to get to those previous quiet states now that you know they exist. I don’t know how plastic this brain is but I do believe that exposing it to this quiet state might allow it learn how to reach this state even in noisier environments.
When people ask me why I do all the strange things that I do I usually answer “because I can’t just sit down and stare at the wall in peace”. This experience has taught me that maybe I can. The wall just has to be total darkness and I have to be floating in a bath of salt water.
Finally, this has made me realize the possible benefits both in research and in therapeutic mechanisms floating can have and I will definitely be back for more. Next time I just have to remember to take out all the salt out of my ears because that’s driving me crazy now.