"Take off your clothes, step into the pod and shut the top. And be really careful not to get any of the salt in your eyes." Those were the instructions I was given recently just before I entered a sensory isolation tank in Seattle. Finally, I would have my chance to see what it would be like to be a brain in a jar.
Lying in a supersaturated solution of magnesium sulphate - better known as Epsom salts - cranked up to body temperature, I pulled the top down over me.
Cut off from the world of sensory stimuli, my brain had free rein to invent any experience it had up its sleeve. So I floated in pitch blackness and waited for a profound experience to wash over me. This is what adherents paid US$89 (S$128) a pop to feel. I'd heard it was better than meditation, yoga and drugs - perhaps because it promised nirvana without any effort or side effects.
But I felt nothing. After some time, I became acutely aware that I could not feel my body, which I suppose was the whole point of depriving the brain of any connection to the physical world. I started to slowly move my hands and legs to reassure myself they were still there. Check. I had a vivid image of my phantom body; I knew intellectually that it was present, but couldn't detect it in the normal sense.
Just then, I made the error of letting my head drop too low in the salt broth and got some into my eyes. The sting was immediate and distinctly unpleasant. The brief period of nothingness had ended, and over the next few minutes, my mental state moved from curiosity to boredom to annoyance. I blinked and rubbed my eyes. My stomach rumbled. My brain was bombarded with all kinds of physical sensations. I was beginning to feel sympathy for pickled fish. Instead of a transcendent excursion into an altered consciousness, sensory deprivation had hilariously underscored the primacy of my body; it was almost a purely physical experience from start to finish. My brain was simply incapable of escaping the signals my body was sending it.
When the hour was up, I showered and came down to the receptionist to pay. There were three women there who were first-timers like me, and they all looked blissful. "How was it?" one of them dreamily asked me. Not wanting to be a downer, I replied that it was lovely and interesting. At least it was half true.
The experience made me wonder about a question that has never let go of me: Are you more than your brain? Hardly a week goes by, it seems, without an enthusiastic report in the popular media about intriguing neuroscience research linking some human behaviour to the function of a particular brain circuit. So you might hear that the insula lights up when you're sad, another region when you're happy and still another when you're enjoying a drink or an orgasm.
For some reason, we love to hear our mental experiences described in the language of neuroscience, yet what does it actually add to our understanding of ourselves to learn that our brain shows activity when we think and feel one thing or another? By itself, not a lot, except to encourage the erroneous and simplistic idea that the brain is an independent sovereign, calling all the shots.
Of course, the brain gives rise to our mind, which then tries to understand and manipulate the very neural apparatus that brought it about. It gives me a headache just thinking about it. Some very smart neuroscientists and philosophers like to say that the very notion of mind is an illusion, a trick of the brain - something they have been carrying on about for rather a long time.
Don't get me wrong. I'm a neuroscience junkie. But we are not just a brain in a jar; we are also bodies, and what we do with those bodies can influence the brain. You can alter your thinking and mood by manipulating your body: by, for example, injecting your forehead with Botox, shining light into your eye, exercising - or floating in an isolation tank.
In the end, whether or not we are more than our brain is less important and less interesting than the fact that our brain does not just give orders; it takes them, too. An isolation tank can turn the body weightless and invisible, but your brain knows better.
- The writer is a professor of clinical psychiatry and the director of the psychopharmacology clinic at the Weill Cornell Medical College.