My recent foray into the world of hypnosis and the brain has been, until now, primarily focusing on what EEG has shown us. Today I am talking about PET scans and their studies, let me explain what a PET scan is.

PET = Positron Emission Tomography

Rolls off the tongue, doesn’t it? PET scans and their subsequent studies really began in the 1970s and what does a PET scan actually do? Well, a small amount of radioactive isotopes, which are often referred to as ‘tracers’ are injected into the bloodstream and the PET scan proceeds to measure and track the brain’s positron emissions following that injection.

So we get to examine how much blood flow there is in varying parts of the brain by following those tracers. When a particular part of the brain is activated, more blood flows to that part, so that activity can then be mapped by using differing colours to represent differing levels of activity in the brain (these are the things you often see on medical TV drama shows which brain surgeons hold up and they look all clever). They get done in machines like this:

This technology has since been used to study the brain when hypnotised. I thought I’d share some of the more notable studies here and their findings.

In 1998, Szechtman, Woody, Bowers and Nahmias published a study in the Proceedings of the National Academy of Sciences of the United States of America entitled Where the imaginal appears real: A positron tomography study of auditory hallucinations. The participants had been tested prior to the research and only those who had an ability to hallucinate sounds while hypnotized were chosen. With their eyes covered, the participants had their brain activity measured in four different stages: Firstly, when they were resting. Secondly, when they were listening to a voice recording that said “The man did not speak often, but when he did, it was worth hearing what he had to say” (you’ll notice the very auditory language used in that sentence). Thirdly, the brain activity was measured while they just imagined hearing the same voice recording. Finally, while hallucinating that the recording was happening after being told that the recording was being played, when in reality it was not.

The Pet study demonstrated that the right anterior cingulated cortex (I expect you to remember these very simple names) was just as active during the hallucination as during the listening to the actual recording. However, the same region of the brain was inactive while the participants in the study were just imagining the recorded voice – the brain showed that the participants’ brains responded as if the hypnotically induced hallucination was real. Which I think is pretty cool.

Probably the most well-known study of hypnosis using PET scan is that by Kosslyn, Thompson,Constantini-Ferrando, Alpert and Spiegel, published in 2000 in the American Journal of Psychiatry entitled Hypnotic visual illusion alters color processing in the brain (the title does tend to give away the findings, eh?). Again, the participants of the study were selected following tests for good levels of hypnotisability. When hypnotized and when not hypnotized, they were then shown a number of different patterns of which some where coloured and others were just black and white with shades of grey.

When looking at colours, the brain activity was in a different part of the brain to when looking at the black and white patterns. The participants were then asked imagine each image when they were shown it, but with a slight difference – they were asked to imagine the black and white images in colour and vice versa.

The findings were that the parts of the brain that responded to colour previously was now active when looking at black and white images but imagining colour. Just  as if they were looking at the coloured one for real.  However, there were also marked differences  between the activity of the brain when imagining while hypnotized and when not. There was much less activity and only in certain areas when just imagining the colours, but when hypnotised and suggestions given to imagine the colours while being shown the black and white pattern, the brain responded to the suggestions in measurable ways on the PET scan.

Similar to the UK study I mentioned on this blog previously (mentioned here at the BBC) the researchers concluded that hypnosis had neurological distinctions all of its own.

There are other PET scan studies, but all offer a similar methodological approach to those here and tend to have the same results. Though this does not necessarily mean that hypnosis is a distinct special ‘state’ just that different parts of the brain respond to it. Makes for some fascinating reading and offers up something tangible.

Have a great day.