The very first attempts to take pictures of the living brain go back to the 1930s, but it is only in the last 20 years that MRI, SPECT and PET studies of the brain have really moved the field forward. After thousands upon thousands of imaging studies, we are beginning to approach the time when we can start harvesting the data collected over these years.
We are on the cusp of an extraordinary advance in our understanding of the brain and how it can go wrong in a large number of neurological and psychiatric illnesses. But that is only a side show: being able to identify the neurological correspondences of, say a psychiatric illness, does not mean that we reduce the illness to the firing of a group of neurons. But it does mean that we are gong to be much closer to providing suitable treatment for the neurological component aspect of the illness.
One of the biggest puzzles for those of us who look at brain scans, is why there is so much variability in the structure of the brain. In the rest of the body, veins and arteries can turn up all over the place, but nerves tend to be in pretty much the same position in everybody. This is not the case in the brain. I’ve looked at many thousands of MRI scans of the brain, and I’ve never found any two alike. It’s one of the reasons that I’m a little doubtful about some of the claims of imagers who say that they can diagnose someone by looking at a brain scan. Most of the time there’s just too much normal variation.
All over the world, there have practitioners who have claimed to derive all sorts of information from brain images. Most experts remain a bit skeptical: hundreds of experts and hundreds of millions of dollars have only enabled us to speak in generalities. Some private practitioners even perform scans for diagnosis.
Some time ago I met a psychiatrist who had an unusual theory about the causes of mental illness. He wanted us to do two MRI scans on a patient to prove his theory. When I told him that we were not yet able to do that in individuals, he was indignant, “But you’ve published all those studies showing abnormal brain structure in schizophrenia.” I explained that all the brain imaging studies have told us quite a lot about groups of people with mental illness, but little about individuals. I do not know of any academic psychiatrists anywhere in the world who think that we can yet use PET, SPECT, fMRI or MRI scans for diagnosis of mental illness. Maybe we’re just being a bit slow. Or perhaps the brain scan diagnosers haven’t got all the pieces of the puzzle just yet. Research is expensive and takes a great deal of time. Busy clinicians are eager to exploit new investigative tools for the benefit of their patients, and usually do not publish their results in peer reviewed journals. With this new research we are going to be able to see if these individual practitioners are correct.
Not only are there many inter-individual differences, but also the current state of the person can have a big impact on some types of imaging. I was recently asked to review a paper for a scientific journal in which the authors had enthusiastically explained the way in which they could now diagnose a certain illness by doing a brain scan. Sad to say, they had not asked a couple of basic questions, like the person’s mood when they were scanned. Depression reduces the flow of blood in regions of the brain, the patients turned out to be depressed, and the results were invalidated. It was a real shame, but it is so important that patients don’t get misled by investigations that cannot help them.
So the moral of the story is this. If someone wants to do any kind of investigation for diagnostic purposes, ask them first whether there is any published evidence that the test actually works: what are the sensitivity and specificity of the findings generated by the test? And who else is doing it?
“If the brain were so simple we could understand it, we would be so simple we couldn't.” --Lyall Watson (South African Biologist and Writer, 1939-)