We are far from fathoming the mystery of human memory, but we do now recognise a few basic facts.
The first is that different types of memory exist. We talk about explicit and implicit memories.
The former category relates to things we consciously think about and can be further broken down into episodic memory, what we can remember of the episodes (events) that we have experienced in our lives; and semantic memory, that related to learned facts about the world.
Implicit memory on the other hand is something we don’t pay attention to.
The classic example of this is driving a car: once practised, we no longer have to think about what we’re doing. There is a certain elegance in our brain’s ability to generate implicit memory – it is a more efficient and automated and allows our brain to use its precious energy supplies for more novel requirements.
Explicit and implicit memories are stored separately in the brain, explaining the not uncommon scenario where individuals with early dementia may struggle remembering but have no major problems with, for instance, driving.
Neither type of memory is stored in one particular place, however; rather they are underpinned by a network of nerve cells. For implicit memory, these tend to be deep in the brain in an area known as the subcortex.
The formation and storage of explicit memories is quite involved, with multiple stages. The acronym ARR-R may help you remember these steps. The first three letters stand for Attention, Retention and Retrieval – all core components of long-term memory. The final ‘R’ stands for Remember.
First, let’s consider attention. If you don’t pay attention, you don’t notice something in the first place. This is often the problem when misplacing things – for instance not noticing where you’ve put the keys when you’ve come home. Without adequate attention, there will be nothing to later remember.
Attention seems to be heavily reliant on the front part of the brain (the frontal lobe) and can be strengthened by mindfulness and active practice – deliberately paying attention when you are doing things.
Meditation also seems to strengthen attention. Conversely, stress, tiredness and alcohol (and social media!) all potentially diminish it.
Once something has grabbed your attention, you then have the chance to “hold it in mind” for a brief time while you use the information. This again relies on the front part of the brain and is often termed working memory. An example is mentally reciting and using a phone number just given to you.
At some stage, whatever you have experienced will leave your awareness as you become distracted and think about other things. It will then either be forgotten or sent through to another brain structure called the hippocampus, situated deep in the temporal lobe.
This structure is critical for the next step of memory formation – retention.
The hippocampus encodes the experience, bringing all its parts (visual, auditory, tactile etc) together and binding them into a composite memory that is then distributed to various parts of your cortex (the wrinkly outer layer of the brain).
It is the hippocampus that is often an early site of damage in Alzheimer’s disease.
Finally, to bring this embedded information back to mind, you need to retrieve it.
This again relies on the front part of the brain and seems to be quite susceptible to the ageing process – meaning that things take longer to remember than they once did. Even in middle age, I can attest to this!
So, to remember how you remember, think like a pirate: ‘ARR-R’!
Kailas Roberts is a psychogeriatrician and author of Mind your brain The Essential Australian Guide to Dementia now available at all good bookstores and online. Visit yourbraininmind.com
Dr Roberts also has created BrainScan, an iPhone app to help identify and respond to modifiable risk factors for dementia. Find it at the App Store.