Anterograde amnesia is the inability to form new declarative memories after the onset of brain damage or disease. Patients can remember events from their past (remote memories) but cannot create lasting new memories of experiences occurring after the injury. The condition was brought to the forefront of cognitive neuroscience by the famous case of patient H.M. (Henry Molaison), whose bilateral medial temporal lobe resection in 1953 provided critical evidence that the hippocampus is essential for forming new declarative memories but not for retrieving old ones or for many other cognitive functions.
Patient H.M.
Henry Molaison underwent surgical removal of the medial temporal lobes (including the hippocampus, amygdala, and surrounding cortex) bilaterally to treat severe epilepsy. The surgery controlled his seizures but produced profound anterograde amnesia. H.M. could not remember people he met, events he experienced, or information he learned after the surgery. He had near-normal intelligence, language, and perception, demonstrating that the hippocampus is specifically required for new memory formation rather than for cognition generally. He was studied extensively for over 50 years until his death in 2008.
Preserved Abilities
Despite dense anterograde amnesia for declarative information, H.M. and other amnesic patients show preserved learning on several types of tasks. Motor skill learning (mirror tracing), perceptual learning, classical conditioning, and priming are all intact, demonstrating that these forms of memory depend on brain systems outside the medial temporal lobe. This dissociation was critical evidence for the multiple memory systems framework — the idea that declarative memory (facts and events) and nondeclarative memory (skills, habits, conditioning) depend on different neural substrates.
British musician Clive Wearing developed one of the most severe cases of anterograde amnesia ever documented after herpes simplex encephalitis destroyed his hippocampus and surrounding structures in 1985. Wearing lives in a perpetual present, with a memory span of only seconds. He repeatedly writes in his diary "I am now conscious for the first time" — only to cross it out moments later and write the same thing again. Yet he retains his musical abilities: he can still play the piano and conduct a choir, providing a vivid demonstration that procedural memory survives even devastating amnesia.
Causes and Neural Basis
Anterograde amnesia results from damage to the medial temporal lobe memory system, particularly the hippocampus and entorhinal cortex. Common causes include surgical resection, herpes simplex encephalitis (which selectively attacks the temporal lobes), hypoxic/anoxic brain injury, stroke, and Korsakoff's syndrome (thiamine deficiency from chronic alcoholism). The severity of anterograde amnesia correlates with the extent of hippocampal damage, with bilateral damage producing the most severe impairments.
Disorder Of
Memory Consolidation
Anterograde Amnesia can affect memory consolidation, the process by which newly acquired information is stabilized into lasting memory traces. New experiences and learned information may fail to transfer from temporary to permanent storage.