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Tuesday, December 15, 2009

Gamma Knives Out

The Guardian covers contemporary psychosurgery - in their "Life and Style" section, believe it or not -
A radical treatment for Obsessive-compulsive disorder patients
The treatment being "gamma knife" lesions in OCD. Surgeons use a gamma knife to destroy part of the brain by aiming several beams of gamma rays at it from different angles. At the point of the target the beams overlap, and the total radiation level is intense enough to kill cells. Other parts of the brain only get hit by one beam, which is, hopefully, harmless. It's quite a clever technique, although it's not exactly brain surgery. (Sorry...)

Unlike actual surgery, the gamma knife doesn't involve cutting holes in people. This makes it safer, because any neurosurgery carries risks of infection or haemorrhage. But functionally, it's exactly the same as physically removing the tissue with a scalpel. It's hardly "non-invasive", which is what the Guardian call it (twice). Maybe technically, in the sense that it doesn't break the skin, but it does permanently destroy a substantial part of the brain. That's rather more invasive than, say, getting a tattoo, if you ask me.

Lesioning the brain to treat severe OCD has a long history. In the past couple of decades, it's been done on some dozens of patients at a few hospitals such as the Karolinska Institute in Sweden, Brown University in the US, Spain, China and South Korea.

Does it work? Some reports say that about 60% of OCD patients experience a good response others put the rate at more like 40%. So it doesn't work for everyone although given that the patients who get psychosurgery are severely ill and have not benefited from other treatments (medication and therapy), it's not so bad. But it's impossible to know how much of the improvement is a placebo effect, because there's never been a placebo controlled trial of any kind of psychosurgery for OCD, including gamma knife. This is something that the Guardian unfortunately doesn't mention.

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Newspapers at the moment are pretty keen on neurosurgery for mental illness. Deep brain stimulation (DBS) has been getting positive coverage for years, and psychosurgery is also becoming popular nowadays. The NYT recently ran a cautious, but generally positive, piece on it.

There seems to be an unwritten rule that every such article has to include a bit reassuring us that today's psychosurgery is Not Like In One Flew Over the Cuckoo's Nest. Hence The Guardian:
The technique certainly could not be further from the brutal lobotomies made famous by Ken Kesey's novel, One Flew Over the Cuckoo's Nest. While the frontal lobotomy essentially destroys part of the brain, Gamma Knife is highly accurate and non-invasive, damaging only a minute area - 100 millimeters square - of brain tissue. It is usually done as an out-patient procedure. Some might experience a mild headache afterwards, but most report no physical problems at all.
And the NYT:

In the early days of psychosurgery doctors published scores of papers detailing how lobotomy relieved symptoms of mental distress. But careful follow-up painted a darker picture: of people who lost motivation, who developed the helpless indifference dramatized by the post-op rebel McMurphy in Ken Kesey’s novel “One Flew Over the Cuckoo’s Nest”... The newer operations pinpoint targets on specific, precisely mapped circuits, whereas the frontal lobotomy amounted to a crude slash into the brain behind the eyes, blindly mangling whatever connections and circuits were in the way.
This old bad, new good message is simplistic and misleading. The old (1930s-1940s) psychosurgery didn't consist of "blindly mangling" the brain. At least at first, it was targeted as precisely as the technology and neuroanatomy at the time allowed. And although some psychosurgeons used it in a cavalier way, there is no doubt that it often seemed to produce dramatic benefits; the contemporary testimonials of patients and their families are proof of that.

Today's surgery allows more accurate (and smaller) lesion placement, thanks to advances in stereotactic techniques and now the gamma knife. But we still have no solid understanding of the brain circuits underlying mental illness. We still don't know why destroying certain frontal white matter pathways in the brain alleviates symptoms. We still don't know why it works in some people and not others.

There's not even much agreement on which parts of the brain to hit; the most popular surgical target for OCD is the anterior limb of the internal capsule (capsulotomy) although cingulotomy has also been used, and for depression there are a handful. To say that "The newer operations pinpoint targets on specific, precisely mapped circuits" is true only in the sense that if a modern surgeon tries to destroy the anterior limb of the internal capsule, they will probably do it.

None of this means that psychosurgery doesn't work. It probably does - or rather, it certainly does, and it's probably not just a placebo. (For one thing the fact that accidental brain damage to the same regions also seems to reduce emotional distress is very promising.) But it's not so different to what was going on in the 1930s. It's still, basically, a stab in the dark.

Link: The Lobotomist and Last Resort are excellent books on the history of psychosurgery.

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