View Full Version : Comorbidity and Brain Activity

11-12-14, 05:31 PM
I am interested in Dyslexia and ADHD. If Dyslexia is typically related to right brain activity with corresponding under usage of language parts pf the left brain, whereas ADHD is related to neurotransmitters , why is comorbidity so high?

11-12-14, 08:39 PM
That's a really excellent question, and one that researchers are still busy trying to figure out.

I think a big part of it is that descriptions of dyslexia that reduce it to left-brain language processing problems alone, and descriptions of ADHD that pin ADHD on neurotransmitters alone, are over-simplifications.

There are structural differences, on average, in the brains of people with ADHD as well. Conversely, poor working memory and related processes (which are implicated in ADHD) can also affect language development, reading comprehension, and other areas.

There are undoubtedly some shared genetic (--> neurobiological) pathways that influence both learning disabilities and ADHD. In addition, in those cases where environmental factors like lead poisoning cause or worsen behavioral problems, academic / cognitive skills are also often affected.

Finally, there may be some "surveillance bias" at work. It may be that kids who come to clinical attention for one reason are more likely to be assessed for other conditions as well. But having ADHD + LD together also often exacerbates both conditions -- learning and communication problems tend to be detrimental to kids' behavior for many reasons, and difficulty with self-control and attention (and associated things like being kicked out of class or singled out and embarrassed) can interfere with the development of academic skills.

I might be able to dig up some references for you. Off the top of my head, I vaguely think that Thomas Brown wrote a book on diagnosing ADHD and comorbid conditions, and that book may provide some useful information on the underlying reasons for the comorbidity.

P.S. I just noticed you are in the UK. Just to clarify, I think "learning disability" in the UK is roughly equivalent to what in the U.S. might be called "intellectual impairment" or (formerly) "mental retardation". However, when I say "learning disability" or "LD" in this post, I'm using it to refer to conditions like dyslexia, dysgraphia, dyscalculia, and other relatively specific learning deficits in people who otherwise have average or even very high intellectual capacity.

11-13-14, 03:08 PM
I should have realised that the left/right brain analogy with dyslexia was an over simplification. Yes poor working memory does seem to be common to both dyslexia and adhd. But that is frontal lobe? My thoughts are that dyslexia and adhd may not be "different" but rather part of a continuim. Some people with dyslexia can read well but have difficulties around spelling and writing. But also may exhibit ADHD type symptoms.

I wonder if we turn it on its head and look at the advantages rather than deficits, the similarities become stronger. Though I am.not.sure whether that is more.coincidental than anything else.

Interested that you seem to.suggest that some aspects of behaviour are a learnt reponse rather than endemic. For example would you suggest that overexcitability / impulsiveness is a pyscho -social reaction rather than endemic?

Terminology always changes :-) we use "specific" learning disabilitiy to.cover Dyslexia, ADHD etc., As you may possibly gather, I am beggining to come round to a neurodiversety perspective....