Attention Deficit/Hyperactivity Disorder is a terribly named disorder. The reason is simple: There is not an actual deficit of attention. We’re used to thinking of illnesses as resulting from a shortage of something – people with a thyroid disease are missing TSH, just as people with scurvy are missing Vitamin C – but ADHD doesn’t seem to work like that. Instead, recent evidence suggests that people with ADHD have plenty of attention – that’s why they can still play video games for hours, or get lost in their Legos, or devote endless attentional resources to activities that they find interesting.
What, then, is the problem in people with ADHD? The disorder is really about the allocation of attention, being able to control our mental spotlight. . . .
To understand this model of ADHD, it’s important to understand the anatomy of attention. The story begins with dopamine. While dopamine neurons are relatively rare, they are clustered in very specific areas in the center of the brain, such as the nucleus accumbens and ventral striatum. These cortical parts make up the dopamine reward pathway, the neural system that’s responsible for generating the pleasurable emotions triggered by pleasurable things. It doesn’t matter if we’re having sex or eating sugar or snorting amphetamine: These things fill us with bliss because they tickle these cells.
But the caricature of dopamine as simply the chemical of hedonism is woefully incomplete. For instance, studies have shown that the dopamine reward pathway is also extremely active when people are forced to eat something disgusting, or when a subject is gasping for air after holding their breath. . . . there’s a growing body of evidence suggesting that the real purpose of the dopamine is to help us efficiently assess the outside world. Many dopamine researchers, for instance, refer to the chemical as our “neural currency,” since it allows us to quickly assign a value to the multitudes of things and ideas we perceive. (In other words, dopamine is the price tag of sensory information, and it attaches hefty prices to things that are delicious, beautiful, or reflect some urgent homeostatic need.) When we see something we want - and it doesn’t matter if it’s a chocolate cupcake or a glass of water – the mere sight of the object triggers a wave of emotional desire, which motivates us to act. The world is full of possibilities, and it is our dopaminergic urges that help us choose between them.
And this returns us to attention and ADHD. There’s a highway of nerves connecting the dopamine reward pathway to the prefrontal cortex, a crucial fold of tissue that controls the spotlight of attention. This makes perfect sense: A sensation or idea that triggers more dopamine release – it’s deemed worthy of more neural currency – is more likely to get noticed, and enter the crowded theater of consciousness. In other words, the prefrontal cortex is now paying attention. The chemical has told us what we should notice.
The problem with ADHD is not that there’s no attention. As I mentioned before, kids with ADHD can still immerse themselves in activities that require focus – they just tend to require a higher threshold of interest, which is why they don’t pay attention to a boring arithmetic lesson but can easily spend all day on World of Warcraft. Drugs for ADHD, such as the amphetamine-derivatives Ritalin, Adderall, Concerta, etc. work by increasing the amount of dopamine in the synapse.
Saturday, September 18, 2010
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