Hey, I hope you’ve enjoyed my last few posts about developmental psychology, here is the last one in this mini-series: Attention-Deficit Hyperactivity Disorder (ADHD).

ADHD is an umbrella term for a developmental disorder which can be split into 3 different subtypes: inattention, hyperactivity, or combined (this is the most common form). In total, around 2-5% of school children in the UK are thought to suffer (NHS choices). Different levels of explanation have been hypothesised to account for these symptoms, including brain structure and cognitive function, but I’ll explain these later on. First, lets look at the rigorous diagnostic criteria – there has been a lot in the press about ADHD being over-diagnosed as an excuse for bad behaviour, and some don’t believe it is mental health condition at all!  See what you think about this after reading the DSM-IV criteria for yourselves.

A: child must exhibit 6 or more of the symptoms in each category (inattention & hyperactivity) and symptoms must have persisted for at least 6 months, at a level inconsistent for developmental level.

B: these symptoms must occur before the age of 7.

C: the symptoms must occur in 2 or more settings.

D: there must be clear evidence of clinically significant impairment in social functioning or academic performance.

E: symptoms cannot be explained by another disorder.

The figure below outlines the symptoms of the different subtypes of ADHD:


Now you know the symptoms, and how ADHD is diagnosed, lets move on to possible causes:

1: Brain Function

Durstan et al (2003) carried out an experiment using the Go/NoGo task using children with and without ADHD. In this task, participants have to respond when they see a certain cue, e.g. press a button when they see a green square, but refrain from responding when they see a different cue e.g. red square. The researchers found that children with ADHD were more likely to respond on NoGo trials – they failed to inhibit their response. This corresponded with lower levels of activity in control-related circuits in the brain, such as the caudate nucleus and the frontal lobe.

2. Cognitive Deficit

This problem with inhibition has also been explained in terms of a cognitive deficit, for example, Barkley (1997) hypothesised that impairments in executive function cause deficits when sufferers have to inhibit a response.

3. Genetics

Franke et al (2009) carried out a review of studies which has estimated the heritability of ADHD, and found the average was 76%, suggesting a genetic cause. Although this research is still in its infancy, they suggested that some abnormality of neurotransmitters could contribute to the symptoms.

Thank you for reading, I’m doing my best to upload every Thursday so check back next week for another post!


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