A fissure is like a sulcus but deeper and longer.
Brain fissures are convolutions in the structure of the brain that form valleys between folds. The valleys are called fissures or sulci (plural of sulcus), and lie between the raised folds called...
the purpose is to create larger surface area.. refer to medical dictionary/encyclopedia for a certain answwer.
The lateral fissure, also known as sylvian fissure, of the brain divides the frontal and parietal lobes.
obviously since its a medical deficiency