How does memory work?

Assembling my memoirs has led me to reflect on the nature of memory, and how the process of storing and retrieving memories actually works.

I started in medical school aged 17 in February 1944 - 70 years ago - so the little bit of knowledge I picked up all those years ago is buried deep and isn’t much help.  When I was a medical student I learnt a smattering of neurology and read a few books on neuropsychology and psychiatry. Reflecting on the rather haphazard recollections that comprise my memoirs I am aware that my reading over the years since I graduated in 1949 hasn’t added enough current knowledge of brain function to know where to begin. I understand in a vague sort of way how the brain is structured. How the brain functions, however, is unknown territory to me. Nerve cells are connected to each other at synapses where information is exchanged. The number of synapses, connections of one nerve cell to other nerve cells, is prodigious, estimated to be in the billions. These interconnections are involved in all forms of intellectual function, including memory, There are specialized centres to process and arrange particular kinds of information, for example about what we see, hear, smell, taste, and feel.  Stimulation of any of these senses can evoke memories.

I’m intrigued by the fact that sensory input can sometimes instantly evoke a particular memory; but at other times, for instance connecting a name to a face, an author to a recently read book, or the name of a former politician whose decisions come up in conversation, retrieval of particular personal names the specific parts of the memory may take days. What does this tell us about the nature of the process, the extent to which it is electrical (which ought to be instantaneous) and chemical (which if complex chemicals are involved, might well take hours or even days)?  

Here are some of my observations that touch on how my memory works.

Sensory input – things I see, hear, smell, taste, feel – can trigger memories. Snatches of music sometimes remind me of episodes from the past. The strongest trigger may be the sense of smell, which is a reminder that this sense is mediated through the most primitive part of the brain. Strong smells don’t necessarily evoke memories but occasionally a subtle smell can induce an overwhelming flood of recollection of an episode from the past, something that hasn’t entered conscious memory for years, or even decades. For instance when I had my car serviced recently I caught a distant whiff of hot engine oil. It triggered a recollection of the diesel engines on the Adelaide Star, the cargo ship that in 1954 carried me from Tilbury Docks in East End London to Tenerife in the Canary Islands then on around the Cape of Good Hope and across the Southern Ocean to Adelaide. Not just a general memory of that splendid journey but a particular occasion when I climbed down the companion way to the engine room where one of the engineers had crushed his fingers in the moving machinery.  I administered first aid on the spot, then took him to the ship’s surgery, which was in the stern just above the propeller shaft, where I cleaned up his fingers and put in a few stitches to hold the split skin in place until it healed.

Throughout the1980s and early 1990s I coordinated and taught in a delightful course called Human Dimensions of Health and Illness. I had about 72 hours of contact time with the class of 84 first year medical students and saw many of them frequently in small groups, some of them one-on-one for counseling or in the role of mentor. I got to know many students very well, was on first-name terms with almost all of them. As they walked towards me on the path leading to the entrance to the health sciences building I could greet each of them by name. In the early 1980s when the synapses engaged promptly, I could greet them as they approached me; by the late 1980s, my synapse time had increased and I could greet them by name as we were passing each other; and by the 1990s, I retrieved their names only after we had passed each other. The memory function that links names to faces took longer as I grew older. The process of retrieving stored memories takes longer with advancing age. I think many people observe this. Does this reveal whether neural synapse connections are chemical or electrical? Or does it indicate other characteristics of neural synapse connections? It reveals something about the memory function of linking names to faces but I’m not sure what this is.

At the international scientific meeting of the International Epidemiological Association in Los Angeles in 1990, I convened and ran a workshop on ethical problems in epidemiological practice, research and teaching. About 100 people attended this workshop. They came from many countries, and I had met about two thirds of them before; about a dozen were old friends. The workshop took place in an auditorium with gently sloping rows of seats.  I chaired two lengthy discussion sessions in which I stood at the front and was able to call upon almost everyone by name – impressing myself as much as everyone else. Reflecting on this now, I think it indicates that this kind of memory function worked most efficiently when I was on an adrenalin ‘high’ that made my juices flow better than usual.

So I have – or formerly had – the ability to connect names to faces, which is a rather specialized memory function.  I could remember places too and their relationship to each other, in cities that I visited again after a long interval. When I returned after several years to London, Edinburgh, Paris, Geneva, New York, San Francisco, Boston, Sydney I could unerringly find my way back to a favourite book shop, a favourite restaurant (or where it had been) even when in the interim there had been drastic changes – newly imposed one-way streets, demolition and rebuilding that obliterated familiar landmarks. 

Like almost everybody, I find now in my late 80s that when names of politicians or authors of books come up in conversation, these names usually escape me, at least for a time, only to bubble back into consciousness hours or days later when the moment to drop them into conversation has long passed.  This suggests that a slow chemical reaction rather than electrical impulses which are virtually instantaneous, must be involved in memory storage and retrieval. Yet we know that electrical impulses are involved in brain function, because we can record and measure them by attaching electrodes to the skull and observing and measuring the discharge of tiny electrical currents that take place when people are thinking, using their brain to perform various types of intellectual activity, or experience various emotions.

Going back to the distant past, when I was a school boy and when I was a medical student, I had to learn innumerable facts but always, always, I tried not to adopt rote learning – that is, learning by memorizing without necessarily understanding. Very early in grade school, in Grade 1 or Grade 2, I can remember 80 years later, that I tried consciously as we learnt the multiplication tables, to understand why 2 x 2 = 4 and 12 x 12 = 144, not just to memorize as we recited them in unison in class in a sing-song way I can recall as clearly as if it were yesterday. I’m told we use a different part of the brain to reason things out, rather than memorizing them. Does the part of the brain involved affect ability to remember?

In the six years of the medical course, we had to learn the vocabulary of medical practice, about 14,000 new technical terms, the equivalent of three modern languages. Knowledge of Latin and Greek used to be a mandatory requirement for admission to medical school until well after my father’s time in the 1920s, because anatomical and pathological terminology are derived from these 2 classical languages. It was no longer essential by my student days in 1944-49, but it helped that I’d taken Latin to Intermediate level: I understood words like anterior, posterior, ventral, dorsal, and why the mitral and tricuspid valves are so named. But daily use that led to familiarity was how I learnt the languages of biochemistry, physiology, pathology, and the clinical names for many diseases and the symptoms they cause. Many of my classmates swotted for exams by memorizing vast arrays of facts – by using mnemonics or rote learning – but I never did that. I studied by trying to reason things out. Many of my classmates learnt by rote that some conditions, such as chronic lung infections and congenital heart disease that deprives the extremities of oxygenated blood, cause the ends of fingers to swell like drumsticks.  I tried to learn by reasoning out why this happened (the explanation is far from straightforward). Nevertheless, whether memorizing vast numbers of facts or trying to use reason and logic, successful passage through medical school demands prodigious feats of memory. And that’s just the beginning: staying abreast of the rapidly advancing frontiers of medical science requires never-ending surveillance of medical journals, regular and frequent attendance at formal courses of continuing medical education, and, of course, remembering this newly acquired knowledge.     

More than this I can’t say with any confidence. I know if I consulted Google or Wikipedia I would learn more about how memory works. But I’m not writing a scholarly monograph, merely my memoirs. These memoirs are all about things I remember from a long, most enjoyable, and very interesting life. It’s not for me to say more than I have said here, about how or why I remember the assortment of facts and episodes I’ve reported here.