Different people will tell you different ways of how you make memories. But you will hear about a man named Henry Molaison if you ask a neuroscientist about this. He lost a certain part of his brain in a surgery in 1953 which made him lose the ability to form most kinds of long-term memory changing our understanding of human brains.
Early Ideas:
We had no idea up until 1950s about the brain being able to convert an experience into a memory that could also be retrieved and relived. Scientists due to not having enough technology like fMRI scanners to let them look inside living human brains failed in this attempt. The studies based on animal brains and dead human brains made them decide that memories might get stored throughout the brain. That made sense as patients with several injuries to different parts of their brains sometimes develop amnesia. So they were clueless about Henry Molaison.
A Surgery:
As a kid, Molaison got hit in his head while riding a bike and started having severe seizures after that. In spite of all out efforts from the doctors, in 1953 at the age of 26 he was the same. Doctors thought one last procedure that could help was removing the part of the brain which was creating the seizures. So they removed two finger-sized brain tissues from the left and right temporal lobes of his brain these parts included hippocampus, amygdale, and part of the entorhinal cortex. We now know that these are really important parts of the brain. Doctors at that time though didn’t know how important they were. After waking up Molaison could remember things like his name, his childhood memories but he had anterograde amnesia. In other words he could not form any new memories. Although the doctors couldn’t give him back his memories, they tried to learn from him as much as they could. Apparently hippocampus plays a big part in the formation of certain kinds of memory. There are also multiple kinds of long term memory, controlled by different parts of the brain.
Types of Long Term Memory:
The memories we store for a long period of time are long term memories, it’s anything your brain retains after 30 seconds. There are declarative (explicit) and non-declarative (implicit) long term memories. Declarative memories require conscious processing for example the memories that are episodic and semantic which include the facts and ideas. Implicit memories are memories of habits.
Molaison’s Contribution:
Molaison could not learn new facts or remember new events after his surgery. He would forget a person as soon as they walked out the door. There was an interesting discovery that different kinds of long term memory depends on different kinds of brain structures, because as for Molaison he could still form implicit memories. So he could learn something with practice. Molaison was kept a secret while being studied by dozens of doctors and was referred to as H.M in publications. His name was published in 2008 after his death. Even after his death, he is continuously helping us learning about the brain. After his death, his brain was removed and flash frozen before being cut into 2,401 microsections, slices were super thin to be mounted on slides for experiments. Using these sections a 3D recreation of his brain was created in 2014. And surprisingly from that we discovered that Molaison had not lost his entire hippocampus. But this remaining part of hippocampus could not regain his memory for being cut from the rest of the memory system by this injury. So Molaison may not know how much contribution he put to science but he sure is still teaching us about memory and human brains.
Transcripted by Benazir Elahee Munni