Can you stimulate a better short term memory?

We're tackling some neuroscience news with our local experts....
20 October 2019

Interview with 

Helen Keyes, ARU; Duncan Astle, Cambridge University


Brain schematic


Can you stimulate a better short term memory? And how tapping into the patterns our brains are familiar with makes us more likely to believe something. Katie Haylor chatted through a couple of recent neuroscience papers with perceptual psychologist Helen Keyes from Anglia Ruskin University, and cognitive neuroscientist Duncan Astle from Cambridge University. First up - Helen ... 

Helen - Our brains love to search for passions and we love to be very efficient, and in that way if something falls into a pattern that our brain recognizes or likes, it believes that, it's attracted to something that fits into a normal pattern for it. So it's an efficient way of processing information, that's what I mean by being a cognitive miser.

Katie - OK. The brain likes patterns. Got it.

Helen - The brain likes patterns and there are some patterns or sequences that are so well learned that we might call them natural sequences. So things like numbers 1 2 3 4 5 or indeed the alphabet, which is what this paper focuses on.

So we're more susceptible to believing a message any sort of message if it's repeated, so that's one key way of getting people to believe you. But also if there's a perceptual fluency. If it's easy for your brain to process something, you are more likely to believe it.

So this study that wanted to know that if perceptual fluency is so important to us, will statements that conform to some sort of natural sequence be more believable? And the natural sequence this paper focused on was the alphabet. They asked 172 participants how much they believed in a particular statement and they made subtle changes based on the alphabet. So they might ask a participant how much they believed a statement such as “Androgel increases testosterone”.

So the letter A comes before the letter T in the alphabet “Androgel increases testosterone”, compared to a statement very similar which would be “Undrogel increases testosterone”. So here the letter U does not come before the letter T in the alphabet, it's not following that natural sequence.

So they found surprisingly really clear results. They they matched these words for how much these words were liked and how much they seemed like brand names, so there was a lot of things controlled for here. And they found very consistently that people preferred statements where the first word began with a letter earlier in the alphabet and the second word began with a letter from later in the alphabet.

What surprised me was they did a second experiment that showed if they primed people by playing the alphabet backwards, prior to this experiment, the effect could be reversed, so that you would demonstrate a preference for “Undrogel increases testosterone” instead of “Androgel increases testosterone”.

I found that a bit strange because the natural sequence of letters is so ingrained and so overlearned in our brain that that was quite a surprising result for a cognitive psychologist, but they do show that it has this immediate priming effect.

So really what they're saying is that the brain stores these natural sequences and when it finds a natural sequence, so A coming before B, A causes B, the brain feels at ease and it's more much more susceptible to liking that statement and believing it as true.

Katie - It sounds like rhetoric is what you're talking about. Are we talking about politicians making speeches, advertising campaigns, the idea of rhetoric and using this potentially to reinforce messages?

Helen - We absolutely are. So this paper was coming at it from a marketing perspective. So everything you're saying there, but it does equally apply -  if we're looking at politics we can use this in a positive way. If we're looking to nudge a particular population towards particular behaviour, so if we’re looking at health claims perhaps this would be a better way to get a message across, “A causes B” rather than “C causes B” or “B is caused by A”. There's clearer ways to get messages across and they say there may be implications as well for even for things like jury duty. So “A killed B” is more believable than “B killed A”, for example. So there's more to explore here around how we construct statements and how they can be used to good or nefarious effect.

Katie - I find this a bit unnerving because I like to think that I'm quite critical when it comes to statements that claim to be true or not true. Do you think perhaps we all just need to be a little bit more critical when it comes to the messages that we're receiving?

Helen - Well I couldn't agree with you more and I think this is going to be a subtle effect. I think if you read a headline that said [something outrageous] “A causes B”, it's not taking away all of your critical capacity. But when we do skim over things and when we're very distracted by things and a headline grabs our attention it is suggesting our brain just likes things that are easy, that fit with patterns, that we're very familiar with. That makes a lot of sense to us really, we tend to believe things that fit with our own patterns of thought anyway.

Katie - So how are you going to change your behaviour not to fall into this trap? Have you got any advice?

Helen - I'm just going to read the full article!


Next up, Duncan Astle told us about a paper looking at short term memory...

Duncan - Do you know what the secret to great comedy is …? Timing!

Katie - You beat me to it.

Duncan - Actually it’s really important for all types of communication is timing. And that's true of the human brain as well. And so we know that rhythmic electrical activity in the brain is a really important way in which different groups of neurons synchronize and speak to each other.

So if you have a very small network with just a few neurons that has a rhythm that's very rapid. And that's because there are fewer neurons in it and the gaps between the synapses is shorter. If you have a very large network, then the overall rhythm is much slower. And this is really important because what these larger networks with slow rhythms can do, they can act a bit like a conductor in an orchestra. So if we had two different groups of neurons that are small and far away from each other and they have a rapid rhythm, what they can do is synchronize themselves with the slower long range brain network and that rhythm can act like a coordinator or a conductor that helps them work together. And we know that's a really important feature of how brain activity is organized in the human brain.

Katie - Okay so what's this got to do with the paper that you’re going to tell us about?

Duncan - So what they did is they attached electrodes to people's heads so that they could look at this kind of rhythmic coordination and what they showed is in much older adults, so adults over 65, there was a reduction in the coupling that you get between these different frequencies in parts of the frontal lobe, towards the front of your head, and parts of the temporal lobe, towards the side of your head. And that this drop in coupling that they observed mirrored a drop in short term memory performance in these older adults.

Katie - Is the inference then that this coordination, this orchestration, is important for short term memory? Do we know that to be the case?

Duncan - Well people have made that claim before. But what this paper does next is really nice and showing the causal relationship between those two things. Because what they then did is attach different types of electrodes to people’s heads and then passed a type of electrical current through their brains which is called Transcranial Alternating Current Stimulation, and what they do is they tune the frequency of the stimulation coming from these electrodes, to the normal frequency of each person's slow kind of conductor rhythm and then they essentially stimulated them for 10 blocks of trials, where they performed the short term memory task. And what they found is that subjects’ performance improved markedly during this stimulation, relative to a control condition, and these improvements continued even once the stimulation was turned off.

And then when they looked at the brain oscillations, they saw that not only was performance improved but this kind of rhythmic coupling was also improved by the stimulation. So that implies that there is some causal relationship between the strength of this rhythmic coupling and people's short term memory abilities.

Katie - Okay, could this be used in a situation where you're trying to help somebody with their short term memory? Perhaps it's age related?

Duncan - Exactly. So we're all getting older and those of us who are over 60 plus might start to experience difficulties in areas like short term memory. And as a society we're always looking for new interventions. And people often think immediately of pharmacological interventions. But the exciting thing here, is that if we can build a proper evidence base surrounding what this kind of stimulation does, to the brain, and how it works, and what the benefits are, then in the long run we might be able to move to interventions that aren't just pharmacologically based but that are also based on things like brain stimulation.

Katie - You talked about a stimulation type technique last time actually on last episode I think. And I asked you a similar question which was, how long does this effect last?

Duncan - There are various different schools of thought so last time we talked about Transcranial Magnetic Stimulation which, depending on how you do it, has a relatively short after period.

This Transcranial Alternating Current Stimulation is a little bit different to that, but again people tend to think that it has a relatively short after period. But the idea is that regular sessions, regular treatments where it might be able to result in a sustained change.



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