It’s all in your head
Depression is just feeling a little down, right? Well, no. For a start, depression has a specific clinical definition, and it’s not just about feeling a little bit down. Sufferers can experience a number of different symptoms, including low mood, lack of interest in activities they used to enjoy, sleep disturbances and recurrent thoughts about wanting to die — and that’s just a few of the options. Usually, a person has to display a number of these symptoms over a certain period of time before a doctor will diagnose them as being depressed.
That might still sound kind of woolly and hard to pin down. After all, it’s possible for someone to just say that they have those symptoms, and it’s difficult to measure them objectively. But there is one objective symptom found in people with persistent depression: a part of the brain shrinks about 10%. That part is the hippocampus.
It can be hard to pin down what exactly each part of the brain does, especially as the brain is very adaptable, but there are a lot of theories about what the hippocampus does. It’s certainly involved in memory, because when the hippocampus is destroyed, certain forms of amnesia set in without fail. Hippocampal damage also tends to reduce your ability to inhibit your own behaviour. Other theories point to involvement in spatial awareness. All of this could be true and more: our brains are enormously versatile.
The reduction in the size of the hippocampus is thought to be related to a decline in its function as well. People with depression might have trouble encoding memories, inhibiting their own behaviour and interpreting spatial cues — and hippocampal shrinkage is just one obvious way depression damages the brain. There’s almost certain to be more changes in the depressed brain which we could find with good enough scanning equipment.