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A reduction in the activity of neurons in the brain's prefrontal cortex is probably a cause, rather than a consequence, of depressive behaviours.

Eric Nestler at Mount Sinai School of Medicine in New York and his colleagues found, at post-mortem, unusually low expression of key genes in parts of the prefrontal cortex of people with depression. Mice displaying depressive behaviours after being repeatedly defeated by aggressive mice showed similar gene-expression changes in the same brain region. However, some resilient animals showed neither these behaviours nor reduced gene activity.

The researchers then used light to directly activate cortical neurons in the mice, which had been engineered to overexpress a light-sensitive protein in these cells. The depressive behaviour of susceptible mice was reversed — without affecting other behaviours such as movement or social memory.

J. Neurosci. 30, 16082–16090 (2010)