We have known for decades that people are at increased risk of depression after they've had a stroke. That may at first seem obvious: After all, a stroke can lead to weakness or paralysis in parts of the body, and to difficulty with speech and memory — all conditions that anyone would find discouraging.

But that's not the half of it.

The depression that may follow a stroke is often more severe than would be expected, even after suffering a physical disability, and this unusual depth of sadness is believed to be caused partially by the physical damage the stroke has done to the brain and to changes in neurotransmitters.

In fact, the exact location in the brain that the stroke damaged can be predictive of whether depression will set in, and of how severe the mood changes will be. Strokes in the left frontal portion of the brain, for example, are especially likely to be associated with subsequent depression.

People may not survive severe strokes, and in some cases physical disabilities may be permanent; but, on the other hand, a person may recover completely with no permanent effects. In any case, one's recuperation time from a stroke — how long it takes a person to return to normal physical functioning — can often depend largely on the stroke's location, size, and type.

I'm writing about post-stroke depression right now because of a new study just published in the journal Stroke, which focused on how long it takes employed individuals who have had a stroke to return to work.

The authors first point out that about 20 percent of people who have strokes are relatively young and so are still working. The researchers then report that the depression following a stroke turns out to be almost as great an obstacle as the physical disabilities themselves, in terms of delaying the return to work.

Depression following a stroke can last a few years if untreated, but antidepressants can be very helpful in many of these cases. If you or someone you know is depressed after having a stroke, don't assume it's just a normal reaction to being suddenly saddled with a physical disability — the mental symptoms might very well be due to physical changes caused by the stroke.

So make sure the doctors involved are aware of the depression so that it can be treated — treating the depression can speed overall recovery.