Memory systems

Memory problems are one of the most common effects of brain injury. Many people affected by memory problems describe having issues such as forgetting people’s names, failing to remember appointments, or forgetting what they had just gotten up to do.

These examples are just some of the common issues reported by brain injury survivors, but there are countless other ways in which memory can be affected.

People may lose personal memories such as details of their wedding day, or they may forget who their close friends and family are. They may forget how to do a job or a skill they had previously done for many years such as how to drive a car. They may remember things from before their injury but forget what they did the previous day. They may forget last year’s news, or plans made for tomorrow. for tomorrow.

The reason that there is so much variation in types of memory problems is that memory is not one single skill – rather, there are multiple memory systems and types of memory, any of which can be affected by brain injury.

In this feature, we focus on some of the different ways that memory can be classified.

Stages of making a memory

There are broadly three stages involved in making a memory – these are termed encoding, storage, and retrieval.

Encoding requires taking information into our memory in the first place; it is where we are ‘registering’ information into our memory.

Storage refers to the process of keeping the information in our memory. Sometimes repeating information or thinking about it every now and then can help with storing it – for example when we revise before an exam or interview!

Retrieval means extracting the information from our memory when we need to use it. This is usually what we refer to when we say we ‘remember’ things.

Length of storage

We take information in through our senses – through our vision, our hearing, our sense of smell etc. As we do this, our sensory memory stores the information for less than a quarter of a second.

The information is then held in our working memory system for a few seconds. We use this memory system when we need to ‘hold on’ to information for a short period of time, such as remembering the sentences we have just read in a book so that we can follow the storyline.

Finally, information from longer than 10 seconds ago up to decades is held in our long-term memory system.

Types of information

There are many different types of information, and differences in the way that we remember these.

General knowledge, knowing the meaning of words, social customs and so forth, is referred to as semantic memory. Generally we cannot exactly say how or when we learned these things – for instance knowing that breakfast is the first meal of the day, knowing that elephants have trunks, etc. We gradually accumulate this information over time and can retrieve it when necessary.

Episodic memory refers to our personal memories, things that have happened in our personal life, for instance what we did yesterday. It is the type of memory that most brain injury survivors have problems with remembering.

Learning a new skill such as learning to play an instrument or learning to drive is called procedural memory. People improve with practice, but they do not necessarily remember how they actually learned the skill.

For more information on this topic, see our booklet Memory problems after brain injury available at www. headway.org.uk.

Did you know...

There is no single part of the brain that is responsible for processing memories. Rather, many different parts of the brain are responsible for the different processes that underlie the encoding, storage and retrieval of memories.

Memory is strongly linked to the skill of attention– if someone is not attending to information, they are not able to efficiently store it in order to form a memory. Sometimes when people report having problems with memory, in actual fact it may be that they have an attention problem instead.