Until I read this paper, I seriously had no idea that spontaneous eyeblink was a clinical indicator for dopaminergic function. I guess this shows you how divorced the pure research side can be from the clinic.
But before I cover this article, I must make a plea on behalf of all over-read and over-worked grad students out there: please, if you are going to publish your data (not a review article), PLEASE present your data in a pretty pretty graph. Data tables SUCK. Nobody likes them. I see a paper filled with nothing but tables and I conceive an instant dislike. Perhaps there are some statisticians out there who like them because they can look at it and go "oooh, I notice that your people had a mean cannabis use of 483.3 with an SD of 174.9?! Nifty!" But the rest of us mere mortals like graphs. They are simple, they are clear, and they get the point across. A really GOOD graph will knock your socks off. A table will always make sure your socks stay on.
In closing: Graphs = good. Tables = big pile of suck. Moving on.
"Reduced Spontaneous Eye Blink Rates in Recreational Cocaine Users: Evidence for Dopaminergic Hypoactivity" Lorenza S. Colzato*, Wery P. M. van den Wildenberg, Bernhard Hommel. PLoS ONE, October 2008.
Lately I've had a thing for dopaminergic hypoactivity. Dopaminergic hypoactivity is basically what happens when your dopamine system is not functioning as well as it should. The big examples of dopaminergic hypodunction out there are things like Parkinson's, where there is destruction of the substantia nigra, the region that produces dopamine, producing profound hypodopaminergia in the motor system. The other example is what happens after chronic HIGH levels of dopamine are induced from an outside source. This happens with any drug that blocks the dopamine transporter (which is covered in my dopamine post), and the best example of this is cocaine. When people have something blocking their dopamine transporters very often, inducing really high levels of dopamine, the dopamine cells themselves fire less, and thus you will have less dopamine being released in your brain when cocaine is not around. This phenomenon is called hypodopaminergia.
So it turns out that spontaneous eyeblinks are a sign of how your brain dopamine levels are doing. Apparently sponatanous eyeblink is high in disorders where dopamine is chronically high (this is one of the theories for schizophrenia), and low in disorders like Parkinson's where dopamine is chronically low. So the authors of this study wanted to look at spontaneous eyeblinking in people who used cocaine recreationally. The recreational use (not addicts, just bingeing on some weekends) of cocaine is linked already with reductions in cognitive flexibility (which is usually measured as how well you adapt to a new situation in a mental game).
And it turns out that recreational cocaine use is linked to reduced eyeblinking as well. One of the things I find amusing about this paper is that they COULD have just counted how much someone blinked. But no, they had to use a "brain vision analyzer". Perhaps they really just wanted to use the new toy. 🙂
Argh, I can't stand it. This paper is full of tables. Not a graph to be seen. You know WHAT? I'm gonna graph your data, people, just to show you how much cooler it could have been. Besides, if I don't I'm stuck saying "out of a total n of 24, EBR per minute was..." Yikes.
So here it is:
THERE. Isn't that BETTER?! As you all can see from me and my fast graphin' skillz, cocaine users had significantly fewer eyeblinks per minute than non-users (SEE?! I even ran your stats!). Since spontaneous eyeblink rate is linked to low function in a dopaminergic system, this means that, overall, cocaine users have lower functioning dopamine systems than non-users. Additionally, the researchers also found that people who used cocaine more often had fewer eyeblinks than those who used it less often, implying that eyeblinks are good measure for a hypofunctioning dopamine system in humans.
I happen to like this paper (despite its lack of graphs), because it's the first paper to show that dopamine hypofunction can be measured by something as simple as an eyeblink in a group of recreational users. Normally, when we do cocaine research on humans, we compare controls and people who are seriously addicted to cocaine. It's very cool to see measureable differences in a group that is not considered to be "addicted" to cocaine. And a measure like this could have implications for other studies in humans and other animals (if this works in other animals). It's non-invasive and could give a quick and dirty evaluation of the striatal dopamine system. So you stars out doing your coke on the weekends, don't let the paparazzi see you blink!
Lorenza S. Colzato, Wery P. M. van den Wildenberg, Bernhard Hommel, Antonio Verdejo García (2008). Reduced Spontaneous Eye Blink Rates in Recreational Cocaine Users: Evidence for Dopaminergic Hypoactivity PLoS ONE, 3 (10) DOI: 10.1371/journal.pone.0003461