The ADHD brain
With illnesses like attention deficit hyperactivity disorder - ADHD - some people may say that “it’s all in your head!” That may be the case - but that doesn’t mean it isn’t real. The brain of someone with ADHD is very different to that of someone without it, as Adam Murphy heard from King’s College London’s Katya Rubia…
Katya - ADHD is a neurodevelopmental disorder, which means there is an association with changes in the brain compared to healthy age-matched children. The differences aren't huge - they're on the order of 3%, so these are small differences - but there are differences. So it's not the case that ADHD is just naughty children who suffer from poor parenting, which is often depicted in the media. They have abnormalities in the structure and the function of the brain. The structure is like the hardware, the function is like the software of the brain. And what has been shown over the last three decades of imaging is there are differences in the volume of the brain. They have smaller volumes in areas which develop late in life, like the frontal lobes, the basal ganglia - which is very heavily innervated by dopamine, which is also a transmitter which is deficient in ADHD - which are deep in the brain, and the cerebellum, which is at the very back of the brain at the neck level. These three structures of the brain form networks. And the functions they mediate are late developing functions which you need for mature adult behaviour, like the ability to self control, your emotions, your behaviour, the ability to control your attention, timing functions like looking forward and planning ahead in the future, and the ability to shift your behaviour - so if plan A doesn't work out you have to shift and change. When ADHD children are put in an MRI scanner and they're asked to do an attention task, or a task where they have to inhibit a motor response, or where they have to do some timing tasks, then these areas are not activated in the same way as they are in healthy controls. So they're under-activated and they're smaller in structure. And there's also evidence that these areas are delayed in maturation. What this means is that ADHD children behave like younger children.
Adam - And then how do you actually test that? What do the experiments look like when you put a kid in an MRI - what do you actually ask them to do?
Katya - When you measure the structure of the brain, they do nothing. So they lie in the scanner and we show them usually a video, and they're just asked to lie really still and we just measure the structure of the brain. In functional MRI - that measures, like I said, the software, so the brain functions when they do a task - what we do is we give them a task of attention or a task of inhibition. We give them very short tasks because they get so easily bored. When we started 25 years ago, everyone said, "oh, you cannot scan ADHD children because they move too much in the scanner!" But it is actually possible if you give them very short tasks, and if they're interesting and short and fast, and then you change, you give them a little break, then you do the next task. So that's how it's done. We put them in the scanner for one hour, we give them four tasks of five minutes to do, and then we look at the brain in action, in vivo, while they're doing this task. And that's how we can measure which areas light up when you do this task, and then we compare them with healthy controls.
Adam - You mentioned dopamine there when you were talking. How do those chemicals, those neurotransmitters... what role do they play?
Katya - Neurotransmitters play a huge role in our behaviour and cognitive functions. And dopamine is very important for working memory, for planning, for timing functions. It's also important for self-control. And it's also important for motivation and emotional self control. Noradrenaline is another neurotransmitter that has been shown to be abnormal in ADHD, and this one is very important for tension.
Adam - If the brain in people with ADHD is measurably different, could that be used for diagnosis?
Katya - It could. We have tried to do that. And we have tried to use what's called pattern recognition analysis, where we're trying to find patterns which could classify ADHD children from healthy controls, and we achieved about 80% classification accuracy. But this is still in very early days, because most of the studies we've done so far - I mean, all the studies we've done so far - have been based on group statistics. It's not the case that every child has abnormalities - there are some children who are normal, others are obviously severely abnormal, and then we look at the group. So to diagnose, you need a method which can diagnose individual patients.