Child Development: Your guide to the first five years: part 6 - Memory

Memory is a complex and fascinating process binding the threads that form the tapestry of our lives, providing the links with the near and distant past which help to make up the consistent 'story' of our experiences.

Such memories colour the way we live in the present and how we think about the future, influencing our attitude to life, our decision-making, and our capacity to learn as we remember facts as well as events. We also 'remember' how to walk and run or to dance, drive, swim or knit. As we delve more into the role and function of memory we realise that, without it, we simply could not function in our day-to-day lives.

Paradoxically, memory is not only about remembering - it is also about forgetting. This suggests that there may be processes at work influencing what we are able to remember, but also what we may forget. We can also ask, when do we begin to remember? Some people think that very young children under two years have little or no capacity for memory but, of course, they do - otherwise, how would they know what is familiar? It is evident that memory does have many facets, so in this article, which can only give the broadest outline, I will talk about the types of memory(1) and links with the brain and emotions.

Types of memory

There is a song from the musical 'Gigi' called 'I remember it well', about memories of a couple's last meeting many years before. The great charm of the song is that his factual memories of the occasion such as the colour of her dress are different to hers. However, what does remain clear and bright is the joy that the memory brings to both of them.

This song provides lovely examples of some features of our memory system. Emotional content is profound and individual recall of memories of the same event can be different. It also provides an example of 'long-term memory', and in particular the memories we have that relate specifically to us and the facts surrounding them.

So, what makes up our memory 'system'? Most researchers agree that we seem to have two main types of memory - long- term, and short-term or 'working' memory. Long-term memory is further divided into explicit or declarative memory (unfortunately, different texts and articles can use different names for the same things!). This part of our memory includes autobiographical memory and implicit or 'unconscious' memory which includes procedural memory. The diagram below shows how.

Working memory

Working memory is how we remember information from one moment to the next. When we add up a column of figures, it is our working memory that allows us to 'carry over' a number from one column to the next. Without it we would be unable to read this sentence, as the words we had just read would fade away from our awareness. It enables us to remember a phone number just long enough for us to dial it. Interestingly, it is the amount of information that can be held in working memory, which in adults is about seven items, that influences how long we make our phone numbers.

In other words, without working memory we would be unable to link current experience with the immediate and long-term past. If we also consider that working memory is something that is developing over time (see below), we can also see that, for example, asking very young children to examine two things at once puts a strain on their working memory. A very broad 'rule of thumb' is that the memory span of two-year-olds is about two items, of five-year-olds about four items and nine-year-olds about six items. However, context, interest, processing speed and what is being remembered influences the capacity of this 'store' of information.

Long-term memory

Explicit (declarative) memory describes what we usually think of when we speak of 'memory', because this covers all the experiences, facts and names we recall. It is also composed of two main types, but there may be others, as memory is a topic which, because of its complexity, is constantly being revised and reviewed.

Autobiographical (episodic) memory represents our 'story', because it is associated with the events that happen directly to us and is influenced by our own interpretation of what occurred. We usually can also recall some of the factual details of the event, which may or may not be accurate! 'Flashbulb' memories of highly emotional events are included in this category. For example, many of us will remember what we were doing on 9/11.

Semantic memory is the part that allows us to name and categorise everything around us. It is where we store our knowledge of the world, such as Paris is the capital of France or Max is a dog who lives next door. People with Alzheimer's disease may gradually lose this skill, so that on seeing a banana they simply describe it as a fruit and then as something to be eaten and finally, perhaps not being able to distinguish it from other categories such as pets or furniture. If we turn this around and think of babies and young children, we can see how their understanding of the world is built up from broad categories to more specific knowledge.

Implicit memory

Explicit memory is the conscious recall of events or facts, while implicit memory can often be expressed in behaviour rather than a 'thinking recall'. It refers to experiences that we seem to process 'unconsciously'. The most common example of implicit memory is termed 'procedural memory'.

This is the memory associated with motor skills and movement. Blakemore & Frith (2005) see procedural memory as emerging from very early learning mechanisms, such as a 'conditioned response' - for example, a baby 'rooting' to their cheek being stroked. From three months, they say that babies begin 'conditional learning', when they learn early cause and effect, such as kicking a mobile makes it move. Procedural memory is involved when we learn a skill and once we have acquired it, we can do it without thinking. For example if you are able to knit, you carry out the actions without real awareness, focusing instead on following a pattern or counting stitches. How you knit has simply become part of your repertoire of motor skills.

The brain and memory

Different types of memory involve different brain systems (Blakemore & Frith, 2005). For example, in great old age or after trauma or disease, when working memory may be much poorer or even completely lost, long-term autobiographical memories can still exist. However, these can become confused both in context and timing because links with the present are disrupted.

Perhaps this is why in dementia, knowledge of people in the present can become confused with memories of people from the past. Interestingly, too, studies have found that some people with profound dementia could not recognise themselves in a mirror (Postal, 2005). However, people with dementia can retain both very early procedural skills such as walking, as well as more complex skills such as playing a musical instrument, even though they cannot remember where, when or how they were taught.

A structure in the brain called the 'basal ganglia', buried deep inside the cortex, is involved in the development of motor skills. Another crucial structure for memory storage is the 'hippocampus', which lies within the innermost fold of the temporal cortex and is fully developed by around a year(2). The hippocampus is particularly involved in making new memories and also in making links such as a name with a face or between objects in the environment.

During the second year of life, children have a growing capacity to point to parts of their bodies. They also begin to recognise themselves in a mirror, and there are links in the timing of the emergence of language. It is possible that the knowledge of a physical body that 'belongs to me' also begins to be linked to a 'me to whom things happen which I can talk about'.

The development of different types of memory also links closely with how the brain matures over time, because the various structures in the brain develop at slightly different rates. An example of memory development over time is illustrated by the way very young babies cannot yet hold the information about a fallen object long enough to realise that it is still there and they can look for it.

As the infant brain matures, so the capacity to remember the 'out of sight' increases. The baby has this new knowledge and they apply and deepen it in a variety of ways. For example, babies in this phase (usually from around eight months) frequently follow their parents around. It could be that they want to find the 'out of sight' parent so that their realisation that people are the same in different contexts increases.

'Peek-a-boo' games at this age are very popular and parents/carers seem to play them instinctively. From about ten months, babies are able to find a toy that might be hidden from them, while from about a year they love to put things in and out of containers so that the permanence of the existence of objects is practised over and over again. As children get older, their love of games such as hide and seek extends their understanding of permanence and their abilities to remember people and place.

Understanding the steady maturation of structures such as the hippocampus and its involvement with making links between different bits of information helps to make sense of children's growing understanding of both themselves and their environment. The hippocampus and a structure called the amygdala have strong connections with the pre-frontal cortex. This is the area which is involved in planning, updating information and decision-making. Without such connections, the world would seem like a series of unconnected events. This could be how very young children see the world - which is why caring and loving consistency, routine and repetition all help develop their memory circuits.

Memory and emotions

It is important to remember that emotions help us choose what to remember from the amount of sensory information that surrounds us. It is also important to remind ourselves that sensory information is a mix of information from all the senses. Our initial feeling responses will help attract and maintain or lose our attention, and so will influence what we remember.

Another aspect of emotions that influences both memory and learning is that stress impacts on both our ability to remember and, therefore, to learn, and that long-term or chronic stress actually impacts on the brain itself, especially the hippocampus. This is probably because the hippocampus forms part of our 'limbic' or emotional system and has very strong connections with the amygdala mentioned above. These early emotional memories are deep-seated and long-lasting, reverberating throughout the person's life span.

In babies and pre-verbal children, feelings and the senses combine from birth to 'lay down' memories of their early experiences. Without this sensory mapping of their daily lives, they would not be able to make any sense of their experiences, nor would there be a foundation for later, more sophisticated memory processes as the child's horizons broaden in tandem with their maturing brains.

FURTHER READING AND REFERENCES

Blakemore S-J, Frith, U (2005), The Learning Brain. Oxford: Blackwell Publishing

Bauer, PJ (2002), 'Early Memory Development' in Goswami, U, Handbook of Childhood Cognitive Development. Oxford: Blackwell Publishing

Gerhardt, S (2005) Why Love Matters. Brunner Routledge

Postal, KS (2005), 'The Mirror Sign Delusional Misidentification Sympton', in Feinberg, TE, Keenan, JP (eds), The Lost Self: Pathologies in brain and identity. Oxford: Oxford University Press

Robinson, M (2008) Child Development from Birth to Eight: A journey through the early years. Maidenhead: Open University Press

Saks, O (2007) Musicophilia. London: Picador www.bbc.co.uk/radio4/memory/understand/semantic_memories.shtml

FOOTNOTES

1. The division of memory into these different types is based on adult studies. However, research on infants and young children does suggest that these differences exist.

2. Some texts say two years before full development, but in general the 'circuits' involved in memory appear to come together by the end of the first year (Bauer, 2002), although all agree that the structures continue to develop in efficiency and complexity over time.

- Maria Robinson is an early years consultant and author of From Birth to One and Child Development from Birth to Eight: A Journey Through the Early Years (Open University Press).

Photographs at Nelly's Nursery, London, by Teri Pengilley.