Synchronising brain waves
When we perform demanding mental tasks the brain often has to engage multiple different regions that are specialised at performing specific functions at the same time and then exchange information between them. The theory goes that these disparate brain areas link up by synchronising the pattern of nerve firing in both; so what would happen, Ines Violante wondered, if she artificially enhanced the degree of synchronisation - would a person’s intellect be boosted? Chris Smith found out what she learnt...
Ines - I'm interested in how different regions of the brain talk to each other. So, if you have any sort of cognitive process, if you have to hold information in memory for a couple of seconds, you need different regions of the brain to communicate, to pass the information between each other. People have associated brain waves to those processes.
Chris - Are you saying then that you’ve got a pattern of brainwaves in one place and a pattern of brainwaves in the other, and the brain matches them up, like syncs them up so they're two drums beating at the same time, and that’s how you achieve the sort of coherence between these two brain areas?
Ines - Exactly. So the idea is that you have millions of neurones in one region of the brain firing up and another region and they reach their sync. If they do that in a certain beat, you'll be able to pass information.
Chris - Now was that just fanciful thinking that it was a nice model that would explain possibly how things worked or was there actually objective data supporting that idea?
Ines - There's actually both empirical data and using invasive recordings, and also other electrophysiology techniques like EEG. And there's also models supporting the same idea.
Chris - So if there's already a reasonable body of evidence supporting this idea, what was it you were seeking to find out about it?
Ines - So, we wanted to find out whether we can use stimulation techniques to manipulate the way that this information flow if we can affect behaviour, and will be even more powerful if we can use imaging at the same time. So, if we can use brain scans at the same time and we can understand what we’re doing to the brain when we manipulate how this information is flowing in the brain.
Chris - So, how did you do it?
Ines - We used a technique called transcranial alternating current stimulation which is a form of non-invasive brain stimulation. We combined this with functional magnetic resonance imaging.
Chris - Does this mean then that you're literally putting electrical current into people’s heads?
Ines - That’s right. So, we did that while people are in the scanner and we measured their brain activities.
Chris - By using alternating current, does that mean that you can then drive the rate at which neurons are firing so you'll get that beat synchronisation? That’s what you're going for between diverse regions of the brain.
Ines - Precisely. So we hope that we are able to manipulate those neurons to oscillate at the frequency that we are imposing.
Chris - So what did you ask the subjects to do in the brain scanner then while you did this to them?
Ines - We asked participants to perform two tasks in the scanner with different levels of difficulty. One of the tasks was quite simple. They just had to press a button that matches the direction of an arrow they saw on the screen. The other task was a bit more difficult. We show them numbers and we asked them to press a button when the number they saw in the screen match a specific sequence.
Chris - So, that latter task, that’s a sort of working memory task. They’ve got to hold something in mind whereas the first task is literally to interpret and react to a task. You don’t have to hold information and share information between different brain areas.
Ines - Precisely, yes.
Chris - One would therefore predict that if having synchronous activity in the brain is boosted then they should improve on a more difficult task when you do that.
Ines - Exactly, yeah. So, that was the prediction that we will be able to manipulate this process when you actually need to engage different areas of the brain. When the process that you need to execute to perform is hard enough, they need different parts of the brain to talk to each other.
Chris - Is that what you saw?
Ines - Yes, that’s what we saw. The stimulation would only influence performance in the difficult task.
Chris - Now obviously, if there is a reinforcing effect, a beneficial effect of stimulating these different brain regions so they synchronise... logically, if you were to throw a spanner in the works and these synchronised different brain areas that should impair performance or at least not help it. Did you try doing that?
Ines - Yes, we did. Behaviourally, we didn’t see a significant effect of this synchronous condition.
Chris - But is that just because the brain is pretty good at doing what it’s doing and had you stressed the system more, you might have seen an effect?
Ines - That might be the case. It might be that if we got to an even harder condition, we will see bigger spread of the effects.
Chris - You had these subjects in the brain scanner while this is going on. You’re either stimulating the brain disparate regions at the same time synchronously or asynchronously so they're offbeat. What do the brain scan show when you do this?
Ines - The synchronous stimulation shows an increase in brain activity in the regions that are involved in working memory. The asynchronous stimulation shows increasing brain activity in regions that are not involved with working memory.
Chris - So that’s sort of logical. You'd expect if you're just recruiting some brain areas, you're going to get a bit of nonspecific brain recruitment which is not related to the task in hand.
Ines - Yes, indeed. But it was quite interesting to actually be able to see those effects and to be able to see that even functional connectivity – a measure of how different areas of the brain are talking to each other – they're also changed.