Scientists from Yale University have been dissecting dead people's brains in an attempt to find out more about depression. They analysed brain-tissue samples from 21 people who had been diagnosed with depression and compared them to 18 depression-free individuals. They found that a gene called MKP-1 was twice as active in the people who were depressed. The gene blocks a molecular pathway crucial to the survival and function of neurons.
You can find out more about this research here.