Making Memories: how memory works

With our next podcast focusing on memory difficulties after stroke, we thought we’d start with exploring how memory works.

The hippocampus is the key part of the brain responsible for memory. The hippocampus creates memories and then directs the brain where to file them. It’s like a gateway through which new memories must pass before being stored. Usually each side of people’s brains are specialised. In right handers the left side of the brain deals with numbers and words, and the right with visual and special perception. The right and left hippocampus are similarly specialised. However, for information to reach the hippocampus the information must first be perceived, designated as being worthy of storage or not and understood. For instance, if you are in a coma, you can’t form memories, and if your stroke affects the language understanding part of the brain, you can’t store verbal memories.

There are three stages to memory:

Registration. In this stage, you pay attention, process information and give it meaning. Most stroke-related memory problems are caused during this stage. If you can’t focus on what is happening, you won’t be able to remember it later. For stroke survivors, it’s not surprising the first few weeks after their stroke are often a bit of a blur. The impact of a sudden, life-changing event, an injured brain and a busy, noisy hospital all add up.

Storage. In this stage, a record or memory is created and stored, either working memory (short-term) or long-term.

Short-term memory is our working memory. We keep small amounts of information active and readily available for a short period of time. For instance if you are repeating a number in your head to dial it, or someone spells out a name to you and you then go and write it down, this is ‘working memory’.

If you need to remember something for a longer period, it is then moved by your hippocampus and connected areas into long-term memory. When we recollect memories we solidify their place in long-term storage. While our working memory capacity is limited, long-term memory is relatively unlimited. Long-term memories can be about events in time and place (episodic memory), our knowledge of abstract facts (semantic memory) or skills, procedures, and movement (procedural memory). Stroke survivors are often surprised and delighted to find their procedural memories are completely intact despite other deficits (you can read about David Roland discovering he could still play the harmonica, despite being unable to speak, in the Spring 2015 edition of StrokeConnections here).

Retrieval. The last stage of memory is accessing it. This can only happen if both registration and storage have taken place. Retrieval is based on cues that trigger your memory of how the information was first registered. Smells, sights and sounds are often linked to memories; this is why hearing an old song can take you straight back to the past. Again, things such as stress, fatigue, anxiety or depression can interfere with this stage.

Memory changes after a stroke are not always picked up straight away. Once you’re home you may notice them, particularly as you return to more challenging activities. The first day back at work after stroke can bring a whole host of changes into sharp focus, memory included.

Our memory helps make us who we are and it allows us to function in the world. So it’s not surprising that noticing memory changes can panic us a little (or a lot). The best advice is to speak to your doctor and to seek out testing if needed. Testing can tell you about your specific memory difficulties and the specific strategies that can help you. Consideration of your overall health and the impact of your stroke, along with a medication review, will be helpful too.

Got all that? Our next blog will cover strategies for improving memory, and for compensating for memory problems. Stay tuned for this and the upcoming memory podcast soon.

Best wishes - The StrokeLine Team

1800 787 653 (Mon-Fri 9am-5pm EST)