A new study that was just released on Sunday and published online in Nature Neuroscience has found that Ritalin, a popular medication to treat ADD/HD, helps improve learning not only by improving focus, but also by increasing plasticity of neural connections.
The player involved in this new discovery is none other than that magical little neurotransmitter, one of my good friends, dopamine. As well as giving insight into to the nature of attention deficit disorders, providing new avenues to pursue for treatment, this study brings to light a few important facts about dopamine.
First, note that the authors specify particular dopamine receptors that are acted upon by Ritalin, D1 and D2, which result in different changes depending on which receptor is activated.
From the article:
"... different dopamine receptor subtypes contribute to distinct aspects of learning performance, such that cue-reward learning depends upon dopamine D1 receptor–dependent mechanisms, and the suppression of task-irrelevant behavior depends upon D2 receptor–dependent mechanisms. Together, these findings indicate a specific synaptic mechanism whereby MPH may enhance associative learning through actions in the lateral amygdala."
Here is a little more information regarding dopamine. There are (at least) 5 types of known dopamine receptors, D1, D2, D3, D4, and D5. There is some debate as to the existence of further distinct types, but these are the ones currently agreed upon. Each of these receptors has a different function in the brain, and are activated or deactivated in varied circumstances, and under different conditions.
Dr Patricia Janak, co-senior author of the paper says,
"We found that a dopamine receptor, known as the D2 receptor, controls
the ability to stay focused on a task – the well-known benefit of Ritalin. But we also discovered that another dopamine receptor, D1, underlies learning efficiency."
So what does this mean? For one thing, it shows us that there is more than just one benefit resulting from Ritalin or similar psychostimulants used to treat ADD/HD. It also gives us more insight as the the nature of the deficits in ADD/HD, and how it can be more directly and effectively treated.
Additionally, it emphasizes the many different types of dopamine receptors and the varying functions of each. Dopamine is often in the headlines as a player in things such as addiction, reward/motivation, novelty-seeking, inattention, learning, sexual behaviors, etc, etc. The point is, dopamine is a multi-functional neurotransmitter, with a multitude of receptors in the brain, with a multitude of functions.
To say that Person X has a [psychological disorder] because of a "dopamine deficit" or "too much dopamine" is far too vague of a conclusion. You can't look at one function of dopamine under a specific condition and use it as a blanket explanation for all things/syndromes/disorders dopamine-related. Given a person's other genetic traits, a deficit of dopamine may mean vastly different things. For one person, it may mean ADD, for another, an addiction. Dopamine is but one factor that contributes to disorders; a person's other genes determine what role dopamine plays in their behavior.
The take-home point? Everyone's neurochemistry is different, and not all dopamine receptors are created equal.
***The name of the study referenced is, "Methylphenidate facilitates learning-induced amygdala plasticity" and can be found here.
