A Trip down Memory Lane: The Case of H.M.
Henry Molaison, known famously as H.M., was only 27-years old when he underwent a partial (but nearly complete) bilateral medial temporal lobectomy to alleviate his progressively worsening intractable epilepsy. The procedure, performed in 1953, left Henry suffering from lifelong anterograde amnesia, unable to formulate new long-term memories.
Interestingly, Henry’s deficits appeared limited to the consolidation of explicit (declarative) long-term memories, but not implicit (non-declarative) long-term memories. Henry showed improved performance comparable to “healthy” individuals, in the star-drawing mirror task, priming stem completion, and reading of backward mirror texts despite not being able to recall ever performing the task before. Henry was also able to “add” new memories by modifying existing pre-1953 memories but showed some temporally graded retrograde amnesia as he aged.
Henry’s condition, studied by Brenda Milner throughout his life, provided formidable insights into the compartmentalization of memory encoding and consolidation, and established the medial temporal lobe as the main route for explicit long-term memory consolidation.
Brenda Milner, Neuropsychologist. McGill University, 2010. 12:13 minutes.