The anxious brain
Anxiety is very common - in fact about one person in 5 at any one time reports feeling anxious. And although we know about some of the brain's "fear centres", what lies upstream of them and actually triggers sensations of anxiety in the first place, is less clear. But, by making volunteers fearful they were about to receive electric shocks, Nicholas Balderston, from the NIH in Bethesda, Maryland, has identified a brain region that may be responsible. Chris Smith hears how...
Nicholas - What we wanted to do is study the experience of being in an elevated state of anxiety and study what happens in the brain during that experience to identify what was the most prominent patterns of activity or connectivity. And it’s a very simple paradigm. You bring people in and you tell them that they're going to get shocked and periodically, you actually do give them shocks. And you can use periods when they're at risk for shock and compare them to periods where they're not at risk for shock and can very reliably evoke increases in physiological responses and then also changes in brain activity.
Chris - While that’s going on, what measurements are you making from the brain and how?
Nicholas - We used two different techniques to measure brain activity. The first technique was functional Magnetic Resonance Imaging. So we bring people in, we put them in an MRI scanner. We have different short blocks of time where they're at risk for receiving a shock and they know that they're going to receive a shock at some point. And then we also have periods of time where they know that they're not at risk for receiving shocks. We extract the data from those individual blocks and compare the safe blocks to the threat blocks. So what we did is we looked at how the pattern of communication between different brain regions changed over those periods of time. We also used a technique known as magnetoencephalography. This technique measures the changes in the magnetic field around the person’s scalp and you can figure out where in the brain is generating those magnetic fields. And, during this session, we were also able to present bursts of white noise so that we could measure their acoustic startle reflex. So, when you’re anxious, you're going to startle more than when you’re not anxious. So, we were able to show that our threat of shock manipulation is actually making them anxious and they were startling more.
Chris - And when you look at the outcome from both the MRI, the imaging study, but also the MEG, the magnetoencephalography recordings, were they the same, and which brain areas appear to be showing a change in their activity consistent with them - in some way - interpreting the threat and the heightened state of anxiety that that person finds themselves in?
Nicholas - Yes. So, with both measures, what we found is that there was one particular part of the brain - the intraparietal sulcus - that showed both increases in connectivity with the rest of the brain and also a pattern of neural oscillations consistent with increased excitability. What I think is happening is threat of shock is increasing the excitability in this region, in a manner that’s consistent with, say, an increase in stimulus-driven attention or bottom-up attention. So it’s potentially making people more aware of their surroundings.
Chris - Do you have any insights into how this region – the intraparietal sulcus – is doing this, how it’s changing the way that the brain processes and attends to stimuli?
Nicholas - One possibility is that this increase in excitability and connectivity may be lowering the threshold for detection of external events. It may make it easier to pick out stimuli that pop up in the environment – something that you otherwise wouldn’t be able to detect. This increases the salience of new stimuli through like bottom-up attentional mechanisms.
Chris - Now, obviously, if this region of the brain – the intraparietal sulcus – lies upstream of a lot of the changes and effects - manifestations - of anxiety, if you turned it off, that should abolish or reduce a person’s anxiety response. Have you tried doing that, because you could do that, for example, with transcranial magnetic stimulation? You could deactivate that brain area...
Nicholas - We haven’t tried that but that’s something that we’re very interested in doing. We’re very interested in trying to develop new techniques for treating anxiety. One potential way as you mention is to use transcranial magnetic stimulation to reduce activity in this region perhaps that would reduce some of the aspects of anxiety in these individuals.