Henry Molaison, American memory disorder patient (born 1926)

Henry Gustav Molaison, known widely as H.M., was an American epileptic man who in 1953 received a bilateral medial temporal lobectomy to surgically resect parts of his brain—the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae—in an attempt to cure his epilepsy. Although the surgery was partially successful in controlling his epilepsy, a severe side effect was that he became unable to form new memories. His unique case also helped define ethical standards in neurological research, emphasizing the need for patient consent and the consideration of long-term impacts of medical interventions. Furthermore, Molaison's life after his surgery highlighted the challenges and adaptations required for living with significant memory impairments, serving as an important case study for healthcare professionals and caregivers dealing with similar conditions.

Memory disorders are the result of damage to neuroanatomical structures that hinders the storage, retention and recollection of memories. Memory disorders can be progressive, including Alzheimer's disease, or they can be immediate including disorders resulting from head injury.