A lesion is a damage to the brain (or more generally, to the nervous system). Such damage may be large or small, localised or widespread. It can be caused by an accident, such as a traffic accident that results in a head injury. It can also be the result of a brain haemorrhage or stroke.
Often, brain damage is tragic and very upsetting for patients, but researchers can learn something from it in some cases. A relatively small lesion in a specific brain area can lead to very specific symptoms, allowing researchers to deduce the role of the damaged brain area. For example, some patients with a localised lesion in visual area 'V4' can still see the world around them, but without colour! Similarly, certain lesions can cause specific problems with processing movement, faces, or certain object categories.
Some neuroscientists use very exact lesions that they themselves make in the brains of laboratory animals to address important questions about how the brain works. Other neuroscientists induce temporary but harmless lesions in laboratory animals or even in humans.
Much of what we now understand about the brain has been learned from research into and with lesions in the brain.
Author: Tom de Graaf (translated by Thomas von Rein)