Depression has long been associated with darkness and grey skies, but a new study suggests there might actually be a scientific basis for these cultural motifs.

A new study published in Biological Psychiatry this month suggests that people who are clinically depressed have difficulty detecting the contrast between black and white, which means that while they’re feeling blue the world might actually look dull or grey. By attaching electrodes to the lower eyelids and ears of 40 depressed patients and 40 control subjects, lead author Dr. Ludger Tebartz van Elst and his team measured the electro-physiological response of the retina to flickering black-and-white checkerboards. The clinically depressed subjects had difficulty perceiving the contrast gain as the squares changed from white to black. The German team based at University of Freiburg believes the relationship between depression and poor black-and-white contrast perception might exist because receptive fields in the retina that are critical for perceiving contrast involve dopamine, one of the key neurotransmitters involved in depression. 

Can't smell the roses? Well, maybe you're depressed, says a new study, which has found that the part of depressed people's brain responsible for the sense of smell is smaller than normal.

The new finding could explain why many psychological disorders such as depression, schizophrenia and seasonal affective disorder seem to suppress the sense of smell, and it has implications for the treatment of depression itself, reports New Scientist. To reach the conclusion, researchers at the University Of Dresden Medical SChool in Germany exposed people – 21 with major depression and 21 who weren't depressed – to a chemical with a faint odor, gradually increasing the concentration until the volunteers could smell it. The researchers also measured the volunteers' olfactory bulbs – the part of the brain that gives us our sense of smell – using magnetic resonance imaging. Non-depressed people were able to smell the chemical at significantly lower levels than the depressed volunteers. The depressed also had much smaller olfactory bulbs, on average by 15 per cent. The researchers also found that the more severely depressed a person was, the smaller their olfactory bulb. The effects were present whether or not an individual was taking antidepressant drugs.

The researchers say that olfactory bulb volume and depression are probably linked by the process of neurogenesis, the growth of new neurons in the brain. Depression is known to inhibit neurogenesis in brain areas such as the hippocampus, and depressed people often have low blood levels of a chemical called brain-derived neurotropic factor, which promotes neurogenesis has implications for treating depression. Olfactory bulb volume could be used as an objective measure of whether a treatment is working, he says. The study appears in the Journal Neuroscience.