Memories, light the corners of my mind

Dealing with an elderly (and ageing) population, the importance of memory in our functioning is made abundantly clear. It is one of those functions you may take for granted, until you are no longer able to remember whether you have already had your breakfast, taken your medication or have had a wash today.

I often doubt my memories - I blame being busy - and adopted the 'write important stuff down' approach when newly qualified. I once went through all the case notes of an antenatal clinic, convinced that I had seen a woman over 35 years without discussing screening with her. I was wrong - probably the emotion of desperately wanting to be seen as effective and competent had made me seem precisely the opposite. Memory is complex and what we know has largely been gleaned from studying memory-deficit problems such as dementia and amnesia with newer technology such as functional MRI. We do know that in addition to ageing, emotion and stress can also influence our encoding and retrieval of memories. As the song says, "Can it be that it was all so simple then, or has time re-written every line?"

Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events. The part of the brain that is critical in creating the feeling of emotion is the amygdala, which allows for stress hormones to strengthen neuron communication. People with amygdala damage tend to lack these emotional memories.

However, memories can be manipulated. A 1974 study (Elizabeth Loftus and John Palmer) showed people a film of a traffic accident and then asked them about what they saw. The researchers found that the people who were asked, "How fast were the cars going when they smashed into each other?" gave higher estimates than those who were asked, "How fast were the cars going when they hit each other?" Furthermore, when asked a week later whether they have seen broken glass in the film, those who had been asked the question with smashed were twice as likely to report that they had seen broken glass than those who had been asked the question with hit. There was no broken glass depicted in the film. The wording of the questions distorted viewers' memories of the event. Importantly, the wording of the question led people to construct different memories of the event - those who were asked the question with smashed recalled a more serious car accident than they had actually seen. The findings of this experiment have been reproduced around the world and they consistently show that when people are provided with misleading information, they tend to misremember. Julian Barnes (The Sense of an Ending) and Ian McEwan (Atonement) have both written powerful novels dealing with an individual's ability to misremember and chilling warnings about putting your trust in memories.

So it was with some trepidation (but also faint glimmers of hope) that I read that researchers at the San Diego School of Medicine have erased and successfully reactivated memories in rats. The study is the first to show the ability to selectively remove a memory and then reactivate it. Robert Malinow, professor of neuroscience, said: "We can form a memory, erase that memory and we can reactivate it, at will, by applying a stimulus that selectively strengthens or weakens synaptic connections. Since our work shows we can reverse the processes that weaken synapses, we could potentially counteract some of the beta amyloid's effects in Alzheimer's patients." In the experiment, the researchers stimulated a group of nerves in a rat's brain that had been genetically modified to make it sensitive to light, while simultaneously delivering an electrical shock to the animal's foot. Rats in the experiment soon learned to associate the optical nerve stimulation with pain and displayed fear behaviours when these nerves were stimulated. In the next stage of the experiment, the research team stimulated the same nerves with a memory-erasing, low-frequency train of optical pulses.

These rats subsequently no longer responded to the original nerve stimulation with fear, suggesting the pain-association memory had been erased. The scientists found they could then re-activate the lost memory by re-stimulating the same nerves with a memory-forming, high-frequency train of optical pulses. These re-conditioned rats once again responded to the original stimulation with fear, even though they had not had their feet re-shocked. When memories are so fragile and the capacity to manipulate them so large, I wonder what we may be creating in our quest to help.

This month we have reviewed and improved our resources concerning memory loss, including Alzheimer's, dementia and supporting the family of people with dementia. We have also added links to the new campaign encouraging people to become Dementia Friends. For a full list of this month's content updates see here.