October 17, 2021

I, Science

The science magazine of Imperial College

Eleanor Magson investigates whether memories make us who we are.

Henry Molaison_1024wIn 1953, Henry Molaison left an operating theatre in Connecticut and became one of neurology’s most renowned case studies: H.M. In August of 1953, at the time of H.M.’s surgery, President Eisenhower was in the White House. But in Molaison’s mind, he never left.

Molaison’s operation was an attempt to cure intractable epilepsy which he had suffered from since childhood. His doctor believed the brain regions responsible for the seizures were the medial temporal lobes – and suggested a surgical removal. This is a practice that continues today, although a great deal more attention is given to the possible implications of removing areas of brain tissue. When Molaison had his surgery, little was known about functional specialisation of the brain – or the idea that different functions of the brain were localised in different brain regions.

Unfortunately, although the surgery was successful in its primary aim of curing Henry’s epilepsy, it left him with severe memory damage. Molaison had anterograde amnesia – he was unable to form new memories. Molaison could still remember events and information learned prior to his surgery, such as childhood memories. Learning new information, however, became impossible. Molaison still believed he was living in 1953 up until his death in 2008. He could neither retain new information, nor remember his own experiences from after the surgery.

Alzheimers_entorhinal_cortexIt became clear that the removal of the temporal lobes (see animation) was responsible. Molaison’s case helped to prove that temporal lobe structures, including the hippocampus and entorhinal cortex, play a key part in forming and retaining memories.

After Molaison’s surgery, he became the focus of scientific study and fascination. Studies performed on him from the late 50s until his death showed that Molaison had functional working (short-term) memory. His procedural memory was also intact – he could learn new motor skills with ease, despite not remembering learning to do them. This suggested that these types of memory are controlled by areas of the brain not affected by his surgery, leading the way for a more nuanced understanding of the many functions of what we term ‘memory’.

Unable to convert short-term memories into long-term ones, Molaison lived his life completely in the present. Suzanne Corkin, a researcher who spent years of her career working with Molaison, described him as an ‘engaging, docile man, with a keen sense of humour’. Although his lack of self-knowledge, and moment-to-moment existence makes it difficult to comprehend, Molaison retained his personality. He had the same manner, the same likes and dislikes, and the same sense of humour. This is perhaps much down to the type of memory loss Molaison suffered. While he remained ‘frozen in time’ at the age of 27 in a never-ending 1953, his retention of memories helped him to stay, in the minds of others as much as his own, the same person.

The same, sadly, cannot be said for those suffering from diseases such as Alzheimer’s. Memory loss is an early and major symptom of this kind of dementia, and modern histological techniques have shown that the brain regions first affected by the disease are the very same which H.M. had removed. As well as memory loss, Alzheimer’s is a degenerative disease which later affects the whole brain, leading to personality changes, which are thought to be localised in the frontal areas of

the brain. Although symptoms and experiences of Alzheimer’s are varied, many patients lose memories of their life which render them, to family and friends, as no longer the same person. One daughter of a parent with Alzheimer’s says ‘I feel as though I lost my mum a long time ago… she became a different person.’

Today, we know broadly which functions are performed by different areas of the brain (partly thanks to patients like H.M.), but trends in neuroscience have changed, with many researchers now looking at the interconnectedness of brain regions. Whether memories are localised in one brain region or across many, memories, contained within neurons, hold our experiences of life. Perhaps it is these intricacies of a fully lived existence which accumulate to make us who we are.

Eleanor Magson is studying for an MSc in Science Communication

Images: Henry Molaison by Sadhira Wagiswara (Copyright); Alzheimers entorhinal cortex by 7mike5000  (CC BY-SA 3.0  via Wikimedia Commons)