Illustration of Alzheimer?s disease. Alzheimer?s disease is caused by neuron and synapse (degeneration). This abnormal loss leads to atrophy of the affected areas, including the temporal and parietal lobes, part of the frontal cortex and the cingulate gyrus : the areas affecting speech and memory are affected. Neuronal degeneration is linked to a build up of tau protein between cells, as well as a build up of beta-amyloid outside cells, causing amyloid plaques.