So this post is to summarise some of the current thinking in neuroscience around ADHD as discussed by Dr. Joel Nigg, Ph.D. in a free webinar on ADDitude which aired on 28 June 2016. My intention is to make webinars like this one a bit more accessible to the everyday person who might get a little lost in all the scientific jargon. I studied A-Level Biology and Chemistry and then Applied Genetics and the University of Liverpool before transferring to a Business Management degree so I have a reasonable basic scientific understanding, but I struggle to follow some of the webinars, I can’t be the only one!
Neuroscience Basics (How the brain works)
Very basically, the brain consists of different areas, each playing a different role in helping us to function. These areas are connected together by axons, like little wires, which are wrapped in something called white matter or myelin sheath, like insulation. This insulation helps to transmit messages from one part of the brain to the other without losing any information so any damage to this can prevent the brain from working properly.
Up until now there has been a lot of focus on the actual brain tissue, the grey matter, with a suggestion that there is a slight reduction in the amount of grey matter in ADHD brains but now there is a shift in focus to the white matter, the insulation around the wires connecting the areas of the brain.
The white matter develops over time as we grow from infant, to child, to adult but in ADHD brains there seems to be slower development of this layer, and it can be underdeveloped, or thinner, than in ‘neurotypical’ brains. This would therefore explain why the brain does not function as it should do.
What part of the brain does it affect?
Broadly it can affect all areas of the brain, there is a lot of variation between individuals with ADHD which may explain why symptoms can vary so much from person to person. As each area has a different role, it’s natural that it would cause different problems depending on where the connections are weak.
It’s a bit like a rail network map when trying to look at the brain connections, with different lines being affected and causing different disruptions. It would look a little bit like this:
The interaction between the areas or stations each controls different parts of our behaviours, thoughts and our ability to regulate or manage our responses to information coming in, and there can be delays on one line while the other lines run smoothly. There are more connections than depicted but it serves as a basic concept!
Top Down/Bottom Up Signalling
This was a bit confusing during the webinar as this concept seemed very wordy so this is a simplified version explaining how weakened connectivity between the frontal cortex, parietal cortex and basal ganglia, the red and green lines in the network, can cause impairments in our executive functions and our ability to pay attention.
In neurotypical brains this ability is fairly balanced, we notice something then dismiss it and carry on. However in ADHD brains the arrow going up to our brain is stronger than the one coming back down. The ability to control our response to an interruption is lessened by the poor connectivity in the brain and we find it difficult to ignore or move on from the event. We may be unable to look away from something interesting, something that has novelty value, or be overcome with an emotional response which takes over our thoughts.
Meta analysis/brain scans showed that there was visibly less activity in those areas of the brain on the red line whilst performing an attention based task in the brain of someone with ADHD compared to a neurotypical brain.
OTHER Consequences of Connection Issues
If the connections are weakened between the frontal cortex and the thalamus and/or supplemental motor area then there will be a delay in the ability to stop our impulses. For example you may be speaking to someone and become aware that you are actually being quite offensive but your brain will not be able to stop you as quickly as it should so you keep talking. This would explain why some people with ADHD seem to interrupt or speak over other people too. The part of your brain that should tell you to wait a moment isn’t giving the signals quickly enough. Dr. Nigg likened it to ‘always being half a step behind’.
If the connections on the blue line in our diagram, between the frontal cortex and the amygdala or nucleus accumbens, are weakened then it is more difficult to regulate our emotional responses. This circuit would normally process our ability to see the rewards in completing tasks and so what we choose to do. It can lead to over-responding to an immediate reward, for example, over-excitement or frustration at something not working immediately, and can also mean that we under-respond to rewards that are not immediate. We don’t attach the value or even remember the long-term rewards and so find it difficult to work towards them. This can cause motivation difficulties and lead to procrastination, putting off tasks until they’re urgent.
Anger and anxiety often stems from weakened connections in this area, as the brain cannot get the messages through to regulate the emotions, and therefore the behaviour that stems from them.
Not all ADHD cases are the same!
Dr. Nigg was quite clear that there is a lot of variability between individuals but that there were distinct groups of people who showed similar emotional characteristics. He talked about three ADHD subtypes citing research carried out by JAMA Psychiatry, 2014:
- ADHD Irritable: High levels of discomfort and anger, are more likely to have tantrums or meltdowns and are slow to recover from them, quite shy around other people.
- ADHD Surgent: More active and exuberant personalities, outgoing and reward seeking. Not as angry, less tantrums.
- ADHD Simple: Closer to normal emotional responses, slightly lower than normal activity levels, more inattentive symptoms.
In the Q & A session after the main lecture this was revisited and he suggested that diagnosis could move away from the current three presentations as described in the DSM-5 but to a more biologically based analysis comparing emotion, temperament and behaviour types.
He also gave his opinion that using brain scans for diagnosis is still in it’s infancy, that although the concept is sound he doesn’t feel that there is enough evidence to use brain scans as solitary means of diagnosing ADHD. I am aware that there is growing interest in paying for brain scans to confirm or assist diagnosis so I found his opinion interesting.
This webinar was very informative but a lot of information was packed into a short space. There were lots of brain imaging scans and scientific names to process as you watched so I found it quite hard work. The main point that came across was that ADHD symptoms are not caused necessarily by damage to the physical brain matter, or grey matter, but in fact was more to do with underdevelopment of the myelin sheath, or white matter, which enables the different parts of the brain to communicate with each other and therefore controls the way we think, feel and behave.
The link to the webinar again is here, it was aired by ADDitude magazine which is a great resource for all things ADHD. I hope I was able to provide a simpler version of the information, please let me know if I have made any mistakes. Any comments, please leave them below or contact me here.