On September 1st, 1953, William Scoville used a hand crank and a cheap drill saw to bore into a young man's skull, cutting away vital pieces of his brain and sucking them out through a metal tube. But this wasn't a scene from a horror film or a gruesome police report. Dr. Scoville was one of the most renowned neurosurgeons of his time, and the young man was Henry Molaison, the famous patient known as "H.M.", whose case provided amazing insights into how our brains work. As a boy, Henry had cracked his skull in an accident and soon began having seizures, blacking out and losing control of bodily functions. After enduring years of frequent episodes, and even dropping out of high school, the desperate young man had turned to Dr. Scoville, a daredevil known for risky surgeries. Partial lobotomies had been used for decades to treat mental patients based on the notion that mental functions were strictly localized to corresponding brain areas. Having successfully used them to reduce seizures in psychotics, Scoville decided to remove H.M.'s hippocampus, a part of the limbic system that was associated with emotion but whose function was unknown. At first glance, the operation had succeeded. H.M.'s seizures virtually disappeared, with no change in personality, and his IQ even improved. But there was one problem: His memory was shot. Besides losing most of his memories from the previous decade, H.M. was unable to form new ones, forgetting what day it was, repeating comments, and even eating multiple meals in a row. When Scoville informed another expert, Wilder Penfield, of the results, he sent a Ph.D student named Brenda Milner to study H.M. at his parents' home, where he now spent his days doing odd chores, and watching classic movies for the first time, over and over. What she discovered through a series of tests and interviews didn't just contribute greatly to the study of memory. It redefined what memory even meant. One of Milner's findings shed light on the obvious fact that although H.M. couldn't form new memories, he still retained information long enough from moment to moment to finish a sentence or find the bathroom. When Milner gave him a random number, he managed to remember it for fifteen minutes by repeating it to himself constantly. But only five minutes later, he forgot the test had even taken place. Neuroscientists had though of memory as monolithic, all of it essentially the same and stored throughout the brain. Milner's results were not only the first clue for the now familiar distinction between short-term and long-term memory, but show that each uses different brain regions. We now know that memory formation involves several steps. After immediate sensory data is temporarily transcribed by neurons in the cortex, it travels to the hippocampus, where special proteins work to strengthen the cortical synaptic connections. If the experience was strong enough, or we recall it periodically in the first few days, the hippocampus then transfers the memory back to the cortex for permanent storage. H.M.'s mind could form the initial impressions, but without a hippocampus to perform this memory consolidation, they eroded, like messages scrawled in sand. But this was not the only memory distinction Milner found. In a now famous experiment, she asked H.M. to trace a third star in the narrow space between the outlines of two concentric ones while he could only see his paper and pencil through a mirror. Like anyone else performing such an awkward task for the first time, he did horribly. But surprisingly, he improved over repeated trials, even though he had no memory of previous attempts. His unconscious motor centers remembered what the conscious mind had forgotten. What Milner had discovered was that the declarative memory of names, dates and facts is different from the procedural memory of riding a bicycle or signing your name. And we now know that procedural memory relies more on the basal ganglia and cerebellum, structures that were intact in H.M.'s brain. This distinction between "knowing that" and "knowing how" has underpinned all memory research since. H.M. died at the age of 82 after a mostly peaceful life in a nursing home. Over the years, he had been examined by more than 100 neuroscientists, making his the most studied mind in history. Upon his death, his brain was preserved and scanned before being cut into over 2000 individual slices and photographed to form a digital map down to the level of individual neurons, all in a live broadcast watched by 400,000 people. Though H.M. spent most of his life forgetting things, he and his contributions to our understanding of memory will be remembered for generations to come.
Prvog septembra 1953. godine, Vilijam Skovil je iskoristio polugu i jeftinu ručnu bušilicu da probuši lobanju mladića i odstrani važan deo njegovog mozga isisavajići ga kroz metalnu cev. Ovo nije scena iz horor filma ili odvratni policijski izveštaj. Dr Skovil je bio jedan od najpriznatijih neurohirurga svog vremena, a mladić je bio Henri Moleson, poznat kao pacijent "H.M.", iz čijeg slučaja su proistekli brojni zaključci o tome kako naš mozak radi. Kao dečaku, Henriju je napukla lobanja u nesreći i počeo je da dobija napade, nesvestice i gubi kontrolu nad telesnim funkcijama. Nakon što je godinama trpeo česte epizode i čak se ispisao iz srednje škole, očajan mladić se javio dr Skovilu, pustolovu poznatom po rizičnim operacijama. Parcijalna lobotomija je decenijama unazad korišćena u lečenju duševnih poremećaja, na osnovu pretpostavke da su mentalne funkcije strogo lokalizovane u određenim oblastima mozga. Pošto ju je uspešno koristio da bi redukovao napade kod psihoza, Skovil je odlučio da ukloni H.M.-ov hipokampus, deo limbičkog sistema koji je povezan sa emocijama ali čije su funkcije i dalje nepoznate. Na prvi pogled operacija je bila uspešna. H.M.-ovi napadi su praktično prestali bez promena u njegovoj ličnosti, a IQ mu se čak i povećao. Međutim javio se jedan problem. Njegovo pamćenje je bilo oštećeno. Pored toga što je izgubio većinu uspomena iz prethodne decenije, H.M. nije mogao ni da formira nove, zaboravljao je koji je dan danas, ponavljao je komentare i čak jeo više obroka za redom. Kada je Skovil o ovome obavestio drugog stručnjaka, Vajldera Penfilda, on je poslao doktorantkinju Brendu Milner da proučava H.M. u njegovoj porodičnoj kući, gde je on provodio svoje vreme obavljajući neobične radnje i gledajući klasične filmove, po prvi put, iznova i iznova. Ono što je otkrila, kroz niz testova i intervjua, nije samo doprinelo proučavanju pamćenja, već je potpuno redefinisalo značenje pamćenja. Jedno od Milnerovih otkrića osvetlilo je očiglednu činjenicu da iako H.M. ne može da stvori nove uspomene, on ipak pamti informacije dovoljno dugo da završi rečenicu ili pronađe kupatilo. Kada mu je Milnerova pokazala nasumični broj uspeo je da ga zapamti na 15 minuta tako što ga je stalno ponavljao. Ali samo pet minuta kasnije, zaboravio je da su uopšte uradili test. Neurolozi su smatrali da je pamćenje monolitno, u suštini jednako i ravnomerno raspoređeno kroz mozak. Rezultati Milnerove ne samo da su bili prvi korak ka danas poznatoj razlici između kratkoročnog i dugoročnog pamćenja, već su pokazali da su oni smešteni u različitim delovima mozga. Danas znamo da je za stvaranje uspomena potrebno nekoliko koraka. Nakon što su senzorne informacije pomoću neurona privremeno stigle u korteks, one dalje putuju do hipokampusa, gde proteini ojačavaju kortikalne sinaptičke veze. Ukoliko je iskustvo bilo dovoljno jako, ili ga se u prvih nekoliko dana redovno prisećamo, hipokampus će onda prebaciti sećanje nazad u korteks gde će biti trajno smešteno. H.M-ov mozak može da formira početni utisak, ali bez hipokampusa koji bi odradio konsolidaciju sećanja, utisak bledi, poput poruke ispisane u pesku. Ali to nije bila jedina razlika u pamćenju koju je Milnerova našla. U poznatom eksperimentu, ona je pitala H.M. da ocrta treću zvezdu u uskom prostoru između dve koncentrične zvezde pri čemu je papir i olovku mogao da vidi samo u ogledalu. Poput bilo koga ko izvršava ovako čudan zadatak prvi put, i njegov rezultat je bio jako loš. Ali se kroz više pokušaja popravio, na opšte iznenađenje, iako se nije sećao prethodnih pokušaja. Njegovi nesvesni motorni centri su zapamtili ono što je svest zaboravila. Milnerova je otkrila da je deklarativno pamćenje imena, datuma i činjenica drugačije od proceduralnog pamćenja, poput vožnje bicikla ili potpisivanja. Danas znamo da se proceduralno pamćenje oslanja više na bazalne ganglije i cerebelum, strukture koje su u mozgu H.M.-a bile neoštećene. Ova razlika, između "znati šta" i "znati kako" je uticala na sva kasnija istraživanja. H.M. je umro u 82. godini nakon uglavnom mirnog života u staračkom domu. Tokom godina ispitalo ga je preko 100 neurologa, što čini njegov mozak najviše proučavanim u istoriji. Nakon smrti, njegov mozak je očuvan i skeniran pre nego što je podeljen na preko 2000 delova i fotografisan, kako bi se napravila digitalna mapa, na nivou pojedinačnih neurona, i sve to u prenosu uživo, koji je pratilo 400,000 ljudi. Iako je H.M. proveo veći deo života zaboravljajući stvari, on i njegovi doprinosi našem razumevanju pamćenja