The decision by the US National Institute of Mental Health (NIMH) to fund only research into the neurobiological roots of mental disorders (Nature 507, 288; 2014) presumes that these all result from brain abnormalities. But this is not the case for many people with mental-health issues and we fear that this policy could stall clinical insight into mental illness for years to come.

There is no consistent biological evidence to support the idea that all mental disorders are due to brain dysfunction. Mood and anxiety, for example, are multifactorial and depend on biological, psychological and environmental factors.

The NIMH's assumption of underlying neural mechanisms presupposes that symptoms of specific disorders cluster because they have the same biological cause. However, psychopathological symptoms of disorders such as depression differ dramatically in their causes and genetic context and do not have a common biological background (E. I. Fried et al. Psychol. Med.; 2013). Symptoms are more likely to cluster because of causal connections — for example, insomnia and its side effects are widespread features of various psychiatric conditions.