Article Archive for ‘October, 2012’

Causes of ADHD

October 01st, 2012

ADHD is a controversial disorder despite being recognised as a valid clinical entity for many decades. A recent study (Thapar et al., 2012) has examined the evidence on the causes of ADHD in a review in the Journal of Child Psychology & Psychiatry. The paper is open to all, not just subscribers if you want to read it. At the time of this post it was available in the Early View part of the JCPP homepage. I expect it will move into the next volume of the journal proper at some point in the next 3-months. Here are some highlights for those who don’t want to read the paper.

  1. 1st degree relatives of those with ADHD are 2-8 x more likely to also have ADHD than the relatives of people without ADHD.
  2. Many twin studies have reported heritability rates of 71-90%. Note that heritability rates include not only pure genetic influences but gene-environmental interactions. Therefore high heritability rates don’t rule out environmental factors at all.
  3. Five adoption studies in which the similarities of children with ADHD to related and unrelated caregivers have shown high heritability rates. In other words, take a kid with risk of ADHD and place them in an adopted family with little risk and they are still likely to display ADHD.
  4. It’s very important to recognise that you can’t really separate genes and environment and it’s likely that the interaction between both is vital in how all neurodevelopment disorders manifest. For example, genetic risks might lead to ADHD in the presence of environmental factors such as maternal smoking or peer rejection. Or genetically coded risks via child/parent temperament might increase the risk of environmental factors such as maternal smoking or peer rejection.
  5. There are some genetic risks shared between ADHD, dyslexia, autism, conduct disorder, substance mis/use, and mood problems.
  6. There is no single gene involved and the effect sizes for single genes are typically small. What is known about genetic factors in ADHD cannot be used in clinical practice to assess risk or help diagnose.
  7. Thapar et al. remind us that the significance of environmental factors, such as maternal smoking, may have been overrated because it is possible that they have their effects via a gene-environment interaction rather than operating as  a stand-alone environmental variable. They reported that pre- and peri-natal factors like maternal smoking, alcohol and substance misuse were risk factors but not proven causes.  Same goes for lead, pesticides, low birth weight, prematurity and maternal stress. Nutritional deficiencies (e.g., zinc, magnesium) were considered correlates (i.e., they exist together) but have not been proven causal. Same with family adversity and low income and nutritional factors (e.g., high sugar and artificial colourings). Severe early deprivation was considered a likely causal risk factor.




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Cogmed improves working memory scores but not attention or academic skills

October 01st, 2012

ADHD and learning disabilities (LD) co-exist in many children. Many of these students have problems with working memory. Although a little crude, the best description I have for working memory is that it is a set of cognitive functions that help you keep your s@#* together while performing a complex task.

Working memory predicts parent ratings of inattentive behaviours and has been found to be below average in LD and ADHD samples in a large number of studies. It has also been shown to be a predictor of academic success. Previously it had been thought that working memory was a fixed trait. However, recent evidence (see for e.g., Klingberg, 2010; Klingberg et al., 2005) is suggesting that it can be modified via a computerised memory training program called Cogmed. Note that the claim has been that Cogmed improves working memory when all we can really conclude is that a period of training using the program leads to improved scores on tests of working memory. There is an important difference between these two claims.

While there may be evidence for improved working memory scores there is limited evidence of transfer to important functional skills. The sort of transfer one would want to see includes reductions in symptoms of ADHD and improved academic performance in students who have ADHD/LD.

A recent study (Gray et al., 2012) in Journal of Child Psychology & Psychiatry performed a randomised controlled trial on the Cogmed program. 60 adolescents (age 12-17) were recruited from a residential school for students with severe LD and ADHD. Inclusion criteria were (a) full time attendance, (b) diagnosis of LD and ADHD made in the community before entering the school, (c) IQ >80, and (d) English as primary language.  Data from standardised achievement tests indicated that 82% of the sample scored <25th percentile in reading, spelling and maths. 72% of the sample were <25th percentile on the WISC-IV Working Memory Index. Almost all were receiving psychostimulant medication.

Participants were allocated randomly to a Cogmed or maths training group. Working memory tests included digits forward and backward and spatial span, the D2 Test of Attention and the Working Memory Rating Scale. Transfer tests were the WRAT-4 Progress Monitoring Version tests, which includes tests of reading, spelling, maths, and sentence comprehension. Parent and teacher ratings of attention and other symptoms of ADHD were also obtained.

Results showed that the Cogmed group performed better at post-test on the measures of backwards digit span and spatial span. No group differences were found for forwards digit span. Cogmed had no effect on teacher ratings of attention and behaviour. No effects were found for any of the academic measures.

Taken together, the data showed two important things. First, they added to the evidence that working memory is trainable. Second, and this is the most important point, improving working memory via Cogmed did not lead to any improvements in teacher- and parent-rated behaviour or to improvements in any academic skill relative to a group who received maths intervention.

These conclusions are fairly consistent with the whole “brain training” (or as I call it, “neurobabble”) literature. Great claims are made by program developers about improvements in “brain function” but few gains are seen on real-life skills.

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