Retrograde amnesia often results from trauma to the brain, such as concussions, traumatic brain injuries, or conditions like Alzheimer's disease. Damage to the hippocampus, a crucial brain region involved in memory formation, and the cerebral cortex, which stores long-term memories, is commonly implicated. Histological examination can reveal structural abnormalities in these areas, such as neuronal loss, synaptic dysfunction, or gliosis.