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After brain surgery in 1953 to stop severe epileptic seizures, Henry Molaison, known in research as patient H.M., could no longer form most new memories of facts and events. Yet he could still learn new physical skills.

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Surgeon William Scoville removed the inner parts of both of Molaison's temporal lobes, including about two-thirds of each hippocampus, a seahorse-shaped structure now known to be central to forming new memories. Afterwards Molaison kept his intelligence, could hold a thought for a short while and remembered much of his earlier life, but new events faded within minutes. In the early 1960s psychologist Brenda Milner asked him to trace a star while seeing his hand only in a mirror. His errors fell day by day, although each day he had no memory of doing the task before. Studies of Molaison, continued for decades by Suzanne Corkin, showed that memory is not one system: learning a skill relies on different parts of the brain from remembering facts.

Türkçe oku
Bilim dünyasında “H.M.” diye bilinen Henry Molaison, 1953'teki beyin ameliyatından sonra yeni olayları ve bilgileri kalıcı olarak aklında tutamaz oldu, ama yeni el becerileri öğrenmeyi sürdürdü. Ameliyat, ağır epilepsi nöbetlerini durdurmak için yapılmıştı.

Cerrah William Scoville, Molaison'ın iki şakak lobunun iç kısımlarını, bu arada her iki hipokampusun da yaklaşık üçte ikisini aldı. Denizatına benzeyen hipokampusun yeni anıların oluşmasında kilit rol oynadığı bugün biliniyor. Ameliyattan sonra Molaison'ın zekâsı yerindeydi; bir düşünceyi kısa süre aklında tutabiliyor, eski hayatının büyük kısmını hatırlıyordu, ama yeni yaşadıkları birkaç dakikada siliniyordu. 1960'ların başında psikolog Brenda Milner ondan, elini yalnızca aynada görerek bir yıldız çizmesini istedi. Molaison her gün daha az hata yaptı, oysa her seferinde bu işi daha önce yaptığını hiç hatırlamıyordu. Suzanne Corkin'in onlarca yıl sürdürdüğü çalışmalarla birlikte bu deneyler, belleğin tek bir sistem olmadığını gösterdi: Beceri öğrenmek, bilgi hatırlamaktan farklı beyin bölgelerine dayanır.

Sources and further reading

Background reading: Henry Molaison
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