How does the memory work during different stages in life?

Memory is all about electricity and chemistry. Neuronal oscillations and the structure of your brain change as you age. What happens to the memory during that time?

Memory is the most mundane thing in the world. Everyone, from schoolchildren to pensioners, is using it the whole time. Stored somewhere deep in our memory are our knowledge, skills, interpersonal relationships and sense of self.

Memory is also an extremely complex business, involving electrical impulses, chemistry, and biology.

“Memory activates all parts of the brain in one way or another,” says Laura Hokkanen, professor of clinical neuropsychology at the University of Helsinki.

Even something as simple as going shopping requires seamless co-operation between the different memory systems. You need prospective memory so that you don’t just walk past the store on your way home from work, and retrospective memory in order to recall what you were supposed to buy there.

As you go over your shopping in your mind, thousands of neurons fire off rapidly between different areas in the brain. The senses transmit information and the working memory processes it and compares it to prior knowledge. Was there any bread in the cupboard?

Stress is bad for the memory

Short-term memory is divided into sensory memory and working memory, and long-term memory into explicit memory and implicit memory, for instance.

Working memory is important for both memorisation and recollection. Thoughts stay in the working memory for a few minutes at most while they are being processed, i.e. taken to and searched from storage. In order to retrieve a memory trace, you need to catch hold of the right thread.

“The retrieval of memories is greatly affected by mood and motivation. Some people freeze up for example in an exam situation. Stress and a bad night’s sleep are detrimental to the memory,” Hokkanen states. 

Not everything needs to be remembered

How well you are able to utilize your memory strategies matters, too. Learning things by rote does not work, but connecting new and old information, together with mnemonic devices, helps.

Why do we forget things? Things get buried underneath everything else. We cannot get to our memories and searching for them doesn’t work, in which case environmental cues can be of help. Visiting places from your childhood can trigger the return of long-forgotten memories.

Remembering everything is not even good for you. The brain chooses which memories to boost and which to dispose of while you’re sleeping.

Happy things are easier to recall

Recollections aren’t stored in any specific part of the brain. Rather, they are spread out over a large area in the cerebral cortex. Storing those memories requires collaboration between neural networks.

“When we are trying to remember something, we piece together the memory from different parts of the brain. Some other memories, dreams and thoughts are also stored in those areas. As we attempt to catch hold of a certain memory from the collection of memories, some other information may come to mind, like things we have been told or something we have seen in our dreams. A memory is not like a static photograph,” Hokkanen explains.

In general, memories initially get connected with the episodic memory, but later on they get crystallized as facts. A wedding day, for example, is first remembered as a sequence of events with all the details coloured in, but as the years pass it becomes little more than a date in the calendar.

It’s often said that you never forget how to ride a bicycle. Skills may remain stored slightly better than information, but learning new ones becomes more difficult with age.

Feelings also affect what gets remembered. Memories that bring happiness are the most likely to be preserved in the mind, whereas anxiety-inducing ones may even be repelled.

Memory is impaired by stress and depression. Digital devices, constant interruptions and a flood of information have also been shown to worsen memory problems. On the other hand, digital devices have their benefits: we no longer need to remember phone numbers or many kinds of trivia.

Neural connections

The human brain consists of a hundred billion neurons, or nerve cells, all of which have thousands of connections. Neurons in different parts of the brain form networks with each other, and all the cognitive activity, such as remembering, is created in their interaction.

In these connections, called synapses, there are channels on the neuronal membrane, which are being opened or closed. The amount and type of channels regulate how neurons affect each other. Neurotransmitter binding to the channel opens it to let ions flow through. This will change the membrane potential and initiates many biochemical reactions.

“Opening the channel is a way to take the signal forward,” says cellular biologist, Adjunct Professor Pirta Hotulainen at the Minerva Foundation Institute for Medical Research.

The neuron’s membrane potential, or electrical signal, is transmitted on the membrane through the neuron’s dendrite into the centre of the neuron. The cell adds up the signals and decides whether to send the signal forward to the next neurons in the network. Memory is affected by brain structure, by what type of neural circuits and connections there are between neurons and by how plastic these connections are. The balance of neurotransmitters is also important.

Revision really is worth it

Some people clearly have a better memory than others. Why is it that one student remembers the answers in an exam better than another who studied just as much?

”In order to remember something, one must be able to memorize, maintain and retrieve the memory trace. These are all separate processes, any of which can fail,” says senior researcher Satu Palva from the Neuroscience Center at the University of Helsinki.

Remembering is linked to attentiveness. When studying, without focusing well enough there will be no strong memory trace. Things that are carefully processed make their way into long-term memory. All the while the memory trace is active it is prone to altercations and disruption.

However, the brain does improve with use, as the connections between neurons get stronger. So, when studying for an exam, it is useful to revise previous material.

A young brain has greater plasticity

Satu Palva researches the dynamics of brain functions and the significance of neuronal oscillations. The activity of neural networks is often rhythmic. Simultaneous function, or synchronicity, between different brain areas enables communication across these areas, and is one of the basic functions of working memory.

The synchronic action of neurons in different areas of the brain enables the active maintenance of memory traces. The sync between the hippocampus and cerebral cortex, in turn, makes it possible to store information in long-term memory and recall the memory traces.

Palva has conducted a study where the participants carry out different memory tasks while their brain activity is measured to the nearest millisecond by magnetoencephalography (MEG). With the help of the data, the researcher analysed the role of neuronal oscillations and their synchrony for cognitive functions. “There are surprisingly many individual traits that predict test performance."

As we get older, our working memory deteriorates. In recent years, this has been linked to the changes in neuronal oscillations and their synchrony, and the weakening of the coordination in cognitive activity. The reason for these changes is unknown. The young brain is nevertheless more malleable, which makes it easier to learn new things.

Learn things little by little

Working memory has its limits. You can only keep one to four things, or seven at the very most, in your working memory at a time. In other words, we can only learn things bit by bit.

”Learning is inevitably a slow process,” Palva says.

In her working memory study, subjects are shown, for example, configurations of different shapes and colours. After a couple of seconds, they are shown a new configuration and asked if it matches the previous one. The task seems easy, but if there are several things that need to be remembered, as many as half of the answers might be incorrect.

“That’s how poor memory is. We think we remember but, in fact, we don’t.”

Research has shown that working memory is linked to learning results. Training it does not, however, necessarily improve academic performance. Last autumn in her doctoral research in psychology, Kaisa Kanerva compared children who trained their working memory with children who trained their numeracy. The results showed that doing working memory tasks did not improve their arithmetic skills but doing calculation exercises, on the other hand, did.

Similar results have been found among the elderly, Laura Hokkanen says. Working memory exercises can help you do better in the same exercises, but not more generally in other aspects of life.

Dementia should be detected early

Training your memory, however, is not a waste of time. Effective use of the brain prevents later decline in cognitive performance. Neuropsychologists talk about cognitive reserve.

For example, symptoms of Alzheimer’s disease on average begin to show at a later stage of the disease among more highly-educated patients. 

“Although there are many changes in the structure of the brain, memory stays in better shape for a long time, and symptoms are milder if the brain has been used a lot,” says Hokkanen.

This has its downsides, as well. It would be good to diagnose Alzheimer’s disease at an early stage and start medication in good time. If everything seems fine with the patient, the doctor will not necessarily detect the nascent disease.

For no specific reason, old memories seem to be the clearest for pensioners. Perhaps those memories have been recalled so many times that recalling them is easier than it is with more recent memories.

On the other hand, it is known that brain damage, especially injuries that damage the hippocampus, impede the imprinting of new memories. It is possible that your hippocampus works less efficiently and new memory traces become weaker as you get older. Older memories are already strong and can still be found in the cerebral cortex.

You can activate your brain

Structural changes in the brain are normal with ageing. These changes start at the age of 50 and increase from age 70 and up.

Changes in brain structure are reflected in changes in performance. Making and processing observations slows down. In the large-scale Finnish Geriatric Intervention Study (Finger) conducted by the Finnish Institute for Health and Welfare, it was noted that nutrition as well as physical and cognitive exercises affected old people’s memories. They were not helpful for patients suffering from dementia, whilst their healthy peers clearly benefited from them.

“Cognitively stimulating hobbies are recommended in retirement,” Hokkanen says, “for instance, crossword puzzles, singing in a choir and learning a new language are all beneficial for the memory.”

The article was published in Finnish in the 2/2020 issue of the Yliopisto magazine. It was translated by the following English philology undergraduates: Jonna Alahautala, Julia Anttila, Oona Anttila, Anna Gustafsson, Anna Hakala, Olli Halonen, Heta Hara, Mikael Hautanen, Noora Hettula, Reetta Hukka, Sandra Ijäs, Alina Isaeva, Erica Lankinen, Kaisa Niemi, Onerva Oja, Jonna Rinne, Eemeli Tassi, Juho Visuri, Robi Vuokko, Vilma Väliketo and Sandra Westerlund, under the supervision of John Calton, lecturer in English, Department of Languages.

Pirta Hotulainen

Adjunct Professor