A clear-eyed look at the neuroscience of mental health

The Balanced Brain: The Science of Mental Health. By Camilla Nord. Princeton University Press; 304 pages; $29.95. Allen Lane; £25

In some areas of medicine, certainty is possible. Tests and scans reveal the cause of an ache or pain. Treatments usually work, whether they are deployed to fight an infection or restore the balance of a hormone. One exception is mental illness.

Take depression, one of the most common mental disorders. There are 227 symptom combinations that can lead someone to be diagnosed with depression. The drugs prescribed for it work better than placebos for only 15% of sufferers. That has led some scientists to dismiss the idea that depression is caused by a malfunction in the brain, such as a shortage of serotonin (a neurotransmitter chemical which is the target of most antidepressants). The cause of depression, they think, is adversity, better treated by psychological therapy that teaches people how to deal with their circumstances.

“The Balanced Brain” brings some much-needed clarity to the debate. Camilla Nord leads a neuroscience lab dedicated to mental health at Cambridge University. Her book is an enlightening round-up of what scientists know about the workings of the brain, and how they know it. Beware “neurobollocks”, she warns: catchy stories that pin a mental disorder on one chemical or brain region. Moods, thoughts and sleep all involve a large number of neurotransmitters and several parts of the brain.

Mental disorders are caused by malfunctions, she shows, and shaped by environment. Scans show that some patients with depression share distinct patterns in certain brain circuits and in the processes related to those circuits. One process involves learning from experience and forming expectations: people with depression have a bias towards emotionally negative memories and perceptions. Antidepressants target the system that deals with expectations and tip the negative emotional bias in a positive direction.

All treatments for depression—including psychological therapies, electric brain stimulation, diet, sleep and exercise—change some brain systems, but not all of them. They work, but not for everyone. The problem is that there is no easy way to tell which brain system is impaired in any given case of depression. That means one approach has to be tried, then another, to see what works. Finding effective drugs for mental illness is also stymied by the fact that each brain chemical has multiple roles. The hormone dopamine, for instance, is involved in addiction, attention and movement.

Many neuroscientists, including Dr Nord, think that the current diagnostic categories for mental disorders are problematic. Some of the neurological and cognitive patterns that cause depression also cause other problems, such as anxiety and anorexia: that explains why patients with mental disorders often have more than one. Finding new ways to pinpoint the brain pattern in each case will not only help patients by offering treatment that is personalised, argues Dr Nord, it will also improve the search for treatments. For sufferers, that is cause for optimism.

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