There are people with capacity cognitive extraordinary, then there are people whose life is made extraordinary by cognitive deficits which are difficult even to imagine. Remember ReminderIn Nolan’s film the protagonist wrote important information on his skin, since he was unable to remember nothing that didn’t already belong to a distant past. Nolan’s is a fictional story, written by his brother Jonathan, but what we are about to tell you is the true story of a boy with the same type of deficit: theanterograde amnesia. Henry Molaisonknown in scientific literature as HMwas one of the most studied patients in the history of neuroscience. Following surgery to relieve his epileptic seizures, Henry suffered from severe anterograde amnesia, losing the ability to form new memories.
HM operation and its effects on memory
Henry Molaison suffered from an aggressive form of epilepsy which had worsened considerably over time, and which manifested itself with crisis which severely compromised his quality of life. At 20 years old his crises were unmanageableand they occurred in the order of ten a day. In 1953, at the age of 27 years olddevastated by his living conditions, HM decides to undergo a surgical intervention experimental conducted by neurosurgeon William Beecher ScovilleThe operation consisted of the removal of large portions of the medial temporal lobesincluding key structures such as thehippocampuswhich we now know to be essential for the formation of new memories, but also theamygdala and the entorhinal cortex (or entorhinal).
Although the surgery reduced seizures, it had a devastating side effect: Henry was no longer able to form new memories, developing a condition known as anterograde amnesia. He found himself perfectly able to remember events from his past life, but he couldn’t memorize new experiences from the two years before the day of the surgery onwards. Every day was a continuous discovery for him, as he had no memory of what he had done the previous day, or even a few minutes before.
Discovering the Complexity of Memory
Henry’s case had a huge impact on neuroscience research. Before then, little was known about the specificity of brain functions related to memory. Studies on Henry revealed that thehippocampus It is not the place where memories are stored, but it plays a crucial role in ride from the short term memory at the long term memory. Its removal did not prevent Henry from recalling old memories, but it did prevent him from transforming new experiences into long-term memories.
Memory is a more complex mechanism than it may seem intuitively, and it is divided into many subsections. The main division (to simplify a lot) is the one that distinguishes the long term memory from the short-term one. The short term memory It stores events that occurred within a few seconds to a few minutes, and sends only the particularly significant events into long-term memory. intensethat yes they often repeat or that they have some importance.
This leads us to divide the memorization process into different phases: acquisition, consolidation And recovery. The hippocampus is essential in the first two, facilitating the transition of new information into long-term memory that is stored widely in the cortex, particularly in the prefrontal cortexright behind our forehead. A process that in Henry had been interrupted precisely because of the removal of the hippocampus and the entorhinal cortex.
Remembering how to ride a bike is different from remembering summer vacations
Henry’s case has led to the understanding that there are different types of memory, each involving different areas of the brain. Resigned to not being able to create new episodic memories (memories of specific events that happen to us personally), his ability to learn new motor skills remained intact, even though not conscious. For example, even though he could not remember ever performing a certain exercise, he could improve on tasks such as tracing a star by looking at his hand only in a mirror.
This distinction between declarative memory And non-declarative memory is another fundamental subdivision. Declarative memory concerns facts and events that we can consciously recallwhile non-declarative memory refers to skills and habits learned that do not require a conscious recall. In Harry short-term memory had not been destroyed, but the ability to convert the episodic declarative contents of short-term memory into long-term memories had been interrupted.
The scientific contribution of Henry Molaison
Henry Molaison was an exceptional patient not only for his rare conditionbut also for his availability to participate in countless studies until his deathwhich occurred in 2008, at the age of 82 years old. His brain was preserved and dissected posthumously for further research, continuing to provide valuable information to the scientific community. Studies on HM have truly revolutionized neuroscience, helping to outline a more precise map of brain functions related to memory.
His personal tragedy has been made invaluable by neuroscientists like Scoville, Penfield and Brenda Milner, who have redesigned the memory mapthat is, how they come created, preserved and recalled memories. Thanks to HM, we now know much more about how these brain functions can be separate And alteredpaving the way for new discoveries and therapies, and above all with respect to the greater caution that is being put in place today in surgical interventions cerebral.
