Tuesday, December 24, 2013

A Cup of Coffee in the Bluelight District: Synergistic Effects of Caffeine + Blue Light on Psychomotor Effects. Plus: Yerkes-Dodson and U-Shaped Dose-Response Curves

This could be your new wake-up routine: Strong coffee and a bath in blue light.
"The abuse of ADHD drugs in people from all social classes is on the rise..." I guess you will have heard or read news like these several times over the past 12 months and in an article over at Forbes.com that was published on St. Nicholas' Day, Todd Essing even claimed: "Adderall use at work by the healthy to enhance cognitive performance is back in the news." Essing cites, among others, Stephen Petrow whose article over at The Atlantic is what Essing calls "a love letter to his 2-3 times per week Adderall use" - and a scary one for Petrow who is a psychologist by trade and says of himself that he "treats lots of hard-driving career-focussed 20- and 30-somethings". (Essing. 2013)

I guess Essing, whose previous article "When ‘Study Drugs’ Kill" took a reasonably critical stance towards the use of Adderal and similar drugs by healthy individuals, will be delighted by the results C. Martyn Beaven and Johan Ekström present in their latest paper in the peer-reviewed open access journal PLOS|One (Beaven. 2013). The intention of their experiment was ...
"[....] to compare and contrast the physiological responses to blue light and caffeine, administered both separately and conjointly. Measures of cognitive function, reaction time and wakefulness were assessed and it was hypothesized that similarities would be observed with the administration of 240 mg of caffeine and a 1 h dose of ~40 lx blue light." (Beaven. 2013)
Moreover, Beaven and Ekström assumed that combining the caffeine equivalent of two small or one large, strong coffees with the 'enlightening' power of a r  ~40lx  blue light LED light source (Techlight® RGB, 3W,  λmax = 470 nm) would induce alerting and psychomotor effects greater than either intervention in isolation.
What exactly did the scientists test for? The study participants had to complete a computer-based psychomotor vigilance test protocol (PVT) that consisted of 20 trials of a visual and audio Go/No-Go test, an Eriksen Flanker test, and 5 trials of a visual reaction time task (all tasks are available online at www.cognitivefun.net, so just try them out and judge for yourself how significant they are).
In view of the fact that you will probably have read the "Sunlight à la Carte" (read more) article I published as part of my Circadian Rhythm Series, you shouldn't be surprised by either, ...
  • the experimental design that involved the ingestion of a gelatine capsule containing either 240 mg of caffeine or a visually indistinguishable sugar placebo with a small glass of water (CAF), the exposure to ~40 lx of blue light from a LED light source (Techlight® RGB, 3W, λmax = 470 nm) or a white light alternative (~100 lx) for 1 h (BLU) or a combination of both, or
  • the assumption that caffeine and blue light should exert additive effects on both physical and psychological measures of alertness
... the effects of both caffeine and high frequency (=low wavelength) light have after all been discussed at length, here at the SuppVersity. What struck me (and maybe you, too) as odd, initially, though, was the assumption that "eye colour would influence the degree of the psychomotor and physiological responses to blue light" (Beaven. 2013), as well.

Figure 1: Eye color determines the extent of the melatonin suppressing effects of 2h of bright light exposure during the night. The effect is significantly stronger in "dark-eyed" Asians vs. "light-eyed" Caucasians (Higuchi. 2007)
The assumption that light-eyed participants would show a more pronounced reaction to light exposure is based on observations by Higuchi et al. (2007) who observed a direct link between eye color and the decrease in melatonin secretion in response to light, when they compared the effects of 2h of nightly light exposure in "light-eyed" Caucasians "with blue, green, or light brown irises" to Asians with "dark brown irises" (Higuchi. 2007).

Contrary to what you may have expected, the suppression was increased for the Asians (see Figure 1), not the Caucasians, of whom you'd argue that their ancestors lived at a latitude, where sun is scarce in the winter time, so that you'd have to make the most of it, when it shines.

If we now turn to the results of the study at hand, we'll see that Beaven and Ekström observed a very similar trend in their study, where he increase in visual reactions in the blue light only condition was significantly more pronounced in the blue-eyed, non-shift worker, non-smoking, low to moderate caffeine and alcohol consuming study participants (13 men, 18 women) than in their darker-eyed peers.
Figure 2: Effects of placebo (Pla), blue light (BLU), caffeine (CAF) or blue light + caffeine (BCAF) on psychomotor performance in 24 (13 male, 11 female) healthy subjects with a mean age of 26 ± 4 years; as it is common in science changes that were statistically significant are marked with letters, i.e. "a", "b", "c" (Beaven. 2013)
When they took a closer look at the caffeine (CAF), blue light (BLU) and caffeine + blue light (BCAF) treatment induced performance boosting effects you can see in Figure 1, the researchers from the Mid Sweden University observed a baseline advantage in reaction times in the visual reaction time task in male vs. female study participants (255 vs 274 ms; p = 0.0172). If you scrutinize the data in Figure 2, you will also realize that Beaven & Ekström are generally correct, when they state that their experiment is the first demonstration of distinct effects of caffeine and blue light on aspects of psychomotor function - it's after all hard to deny that (a) both worked and that (b) they did not have identical effects.

Beware of the consequences of the Yerkes-Dodson law

The researchers go on to explain that "[b]oth blue light exposure and caffeine ingestion improved accuracy in the visual Go/No-Go task", but that their combination "did not result in enhancement in the number of correct responses" (see Accuracy in incongruent task in Figure 2). For caffeine alone similar effects have been observed. These observations form the basis of the"Yerkes-Dodson law", in which it is postulated that the relationship between arousal and performance follows an inverted U-shape curve (Fredholm. 1999). Consequently, Beaven & Ekström suspect that
"[...], it is possible to rationalize that the combined treatment of blue light and caffeine dose exceeded the optimal state of arousal and consequently resulted in impaired accuracy." (Beaven. 2013)
At first sight, this hypothesis appears to conflict the improved fast reaction time the researchers observed in the visual Go/No Go task, but when you come to think about it, the stimulating effect of caffeine + blue light that is an advantage, when it comes to relatively simple tasks, may well be too pronounced for an exercise that requires a higher degree of mental focus / contentration.
Learn how to use light to modulate or realign your circadian rhythm.
So what we learn from the results? Actually there are two things you can take away from the study.
  • It may well be worth to add a blue light lamp to your list of birthday, not Christmas presents. You do after all you want to have it before Fall 2014.
  • You would be well-advised if you remembered "Yerkes-Dodson law" and the futility of a "more helps more" approach to cognitive enhancement.
Considering the fact that it's Christmas Eve this certainly isn't too bad as far as the total amount of subject matter or its quality is concerned - right? Apropos: Merry Christmas!
  • Beaven, C. M., & Ekström, J. (2013). A comparison of blue light and caffeine effects on cognitive function and alertness in humans. PloS one, 8(10), e76707.
  • Essing, T. (2013). Managing The Risks Of Taking Adderall To Enhance Work Performance. Forbes.com. Dec. 06 2013 < http://www.forbes.com/sites/toddessig/2013/12/06/managing-the-risks-of-taking-adderall-to-enhance-work-performance/ > retrieved on 12-24-2013.
  • Fredholm, B. B., Bättig, K., Holmén, J., Nehlig, A., & Zvartau, E. E. (1999). Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacological reviews, 51(1), 83-133.
  • Higuchi, S., Motohashi, Y., Ishibashi, K., & Maeda, T. (2007). Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 292(6), R2352-R2356.
  • Petrow, S. (2013). The Drugs of Work-Performance Enhancement. The Atlantic. < http://www.theatlantic.com/health/archive/2013/11/the-drugs-of-work-performance-enhancement/281055/ > retrieved on 12-24-2013.