For a change of pace, I thought I’d cover two recent neuroscience findings in today’s post. It’s not all academic, either, since both of these studies might help improve your everyday life. Just sit back, suspend your disbelief and fire up the expectation and reward centers of your brain. You might be able to unleash your inner endurance athlete – or epicure, if so inclined – all through the power of the mind.
I’ll start with a surprising finding that I’ve tried to explain to other long-distance runners, who often take a small snack to eat in the middle of a run. I’ve seen the gamut, from orange slices to salty sports drinks and space-age energy gels. The rationale is that these foods quickly replenish the glucose available as blood sugar, the fuel for muscle contraction.
But if you are running for less than an hour, it is biologically impossible for these snacks to improve your performance. For one thing, the amount of carbohydrate that can be effectively absorbed from the stomach to muscle cells in an hour is too small to make any real difference1. And besides, our muscles can hold vast stores of energy in the form glycogen, more than we can possibly use in that span of time, anyway. Spend an hour on a stationary bike, cycling all-out, and you still won’t fully deplete the glycogen in your muscle tissue – so long as you were charged up to begin with2. And yet the snacks work, even in controlled laboratory tests of exercise performance3. No wonder athletes everywhere continue to use them.
Incredibly, this energy boost has nothing to do with caloric consumption, and everything to do with the act of eating.
This surprising fact was discovered by a group of exercise physiologists at the University of Birmingham. Lead author Ed Chambers wanted to examine the effects of different carbohydrates on athletic performance. He found that you can get the performance-enhancing effect of a snack just by rinsing and spitting – provided you use a carbohydrate solution4. His results might also explain some of my weaker moments while working in the garden at the Croskery farm. When it comes to tapping into your second wind, sneaking a green bean can be just as effective as escaping to the berry patch.
Here’s how they figured it out. Chambers, along with coauthors Matt Bridge and David Jones, had trained athletes complete a cycling time trial under three different conditions. In one, they periodically rinsed their mouths with a glucose solution. In other trials, the athletes used a rinse containing the synthetic starch maltodextrin. The key difference here is that glucose needs no further digestion – it is already in the form used by cells to produce energy.
There was also a placebo condition where the mouth rinse contained no carbohydrate, but it tasted like it did, since it contained the artificial sweetener saccharin. The time trial task involved completing a set distance on a stationary bike, the energetic equivalent of cycling for one hour at 75% of your maximum effort. This doesn’t sound so bad, until you hear that the subjects had to do it as fast as they possibly could – a torture that, as experienced cyclists, they were apparently quite familiar with.
Both the simple sugar glucose and the starch maltodextrin had a considerable effect on performance, shaving several minutes off of the athletes’ times relative to the placebo trials. The snack effect occurred, despite the fact that no energy was actually consumed by the rinse-and-spit cyclists. The results also indicate that taste has nothing to do with it, since flavourless maltodextrin had the same performance boosting effect as glucose – whereas the artificial sweetener did not.
This is groundbreaking. Somehow, we are able to detect the presence of carbohydrate in the mouth, without being aware of it. For a short-term boost in performance, the act of eating carbohydrate is enough. A green bean or two should do the trick, since energetic content and sweet taste are not required. These results also make sense of an earlier study showing that a direct shot of glucose into the bloodstream has no effect whatsoever on athletic performance5. The problem with intravenous glucose is that it bypasses the carbohydrate sensing system in the mouth.
Exactly which cells in the mouth cause this remarkable effect remain a mystery6. However, the rinse-and-spit study also included a neuroscience component that offers some hints about what might be going on further down the line. Chambers and colleagues also had regular people, none of whom were athletes, use the same mouth rinses while scanning their brains in an MRI machine4. This functional MRI technology allowed the researchers to compare the amount of oxygenated blood flowing to various parts of the brain under the influence of the carbohydrate rinses. The assumption here is that an increase in oxygenated blood means increased neural activity.
Consistent with the time trial results, the fMRI scans showed that glucose and maltodextrin had similar effects on the brain. Both carbohydrates activated reward centers of the brain that did not respond to the saccharin placebo; specifically, the anterior cingulate cortex and the striatum. Regardless of the sensory receptors involved, it seems as though the performance boost is mediated by a mental response.
Of course, there are limits to what we might be able to take from this. Most of us aren’t elite athletes, and it’s not known whether the rinse-and-spit effect works for the kind of fatigue that the rest of us are more familiar with. In addition, the cyclists (and the MRI subjects) were tested after a prolonged fast of at least six hours. This kind of motivational brain magic may not work for the well-fed.
Nevertheless, the average person might be able to harness the brain’s reward centers in other useful ways. A 2008 study at the California Institute of Technology used fMRI to look at the pleasure we derive from tasting wine – and showed that the mind plays a major role7.
The subjects here were given samples of what they thought were five different red wines, when in actual fact they were only tasting three. The catch was that they tasted two of the wines more than once, under different fictitious price scenarios. An expensive wine was tasted after the subjects were informed of its actual price of $90 a bottle; at some other point in the sequence, subjects were given the same wine with a fictitious $10 price. In addition, a cheap $5 red was tasted at cost, and at a markup to $45.
The subjects were scanned in an MRI machine while all of this tasting was going on. The scans showed that the brain regions responsible for taste responded to a given wine the same way, regardless of its price. But the price alteration had a real effect on how pleasant the subjects rated the flavours. This rating corresponded to activity in the medial orbitofrontal cortex – yet another region of the brain involved in the experience of rewards. In other words, extrinsic cues like price can have a real effect on pleasure, and can easily override our sensory perceptions.
Some caveats: the subjects here were male students in their early 20s, hardly connoisseur material. They were also sipping a minuscule amount through a straw, while holding perfectly still in the confines of narrow tube, inside a very noisy machine. I doubt this expectation effect would be anywhere near as strong for most people in realistic wine drinking situations. In fact, nearly all of the pleasure resulting from tasting wine in the MRI machine was the result of labelling. In a follow-up experiment, the same group of young men reported no difference in how much they liked the wines when the price information was removed.
There are a few salient points here. First, environment matters when we’re talking about gastronomic pleasure. Being told you are about to be treated to an expensive morsel, at no cost to you, has a real effect on the brain. Second, the wine tasting results show an interesting quantitative pattern. The markup on the cheapest $5 wine, to $45, brought it up to the level of the $90 bottle in terms of subject rating. In other words, the idea of a $45 wine felt just as good to these guys as $90 did. What this means is that, assuming you have an open mind, the best bang for your buck is to buy as low as you can while maintaining a sense of optimism about the product. Easier said than done, no doubt, but this study also proves that the expensive luxury can be a risk, since it is relatively easy for environmental cues to suck all the pleasure out.
The problem with these MRI studies is that, in hindsight, they can seem painfully obvious. Save money by purchasing the cheapest thing you know you will enjoy? Hardly news. And salesmen have known for a long time that labels have a powerful effect on consumer behaviour. Marketing researchers have validated this in a number of controlled experiments, demonstrating that expectation can influence how much we enjoy all kinds of things from movies and vacations to beer and energy drinks8,9,10.
Similarly, when it comes to athletic performance, physiologists have long known that fatigue depends on more than just metabolic balance in the muscles. We’ve all felt that extra boost of power when nearing a goal, or the end of an exercise session. Fatigue is not just energy depletion – it’s a call-and-response game between the body and the brain. As Ed Chambers explains, the brain probably keeps track of the level of stored fuel in the muscles during exercise; at some point, it intervenes with a protective response reducing how frequently motor neurons are able to fire11. It makes sense that this happens well before complete energetic exhaustion.
The real merit of these studies is not their shock value. Instead, they bring us one step closer to the mechanics of how the mind works. And even if you can’t fool yourself into epicurean delight, or drag yourself onto the race course, others might be able to apply this research in useful ways. Perhaps this could lead to new cognitive or pharmaceutical strategies for cheating the reward system. There may be many ways to get real pleasure – or performance – out of artificially enhanced expectations.
- McConell, G. K. et al. 2000. Journal of Applied Physiology 89: 1690-1698.
- Hawley, J. A. et al. 1997. European Journal of Applied Physiology and Occupational Physiology 75: 407-412.
- Jeukendrup, A. et al. 1997. International Journal of Sports Medicine 18: 125-129.
- Chambers, E. S. et al. 2009. Journal of Physiology 587: 1779-1794.
- Carter, J. M. et al. 2004. Medicine and Science in Sports and Exercise 36: 1543-1550.
- Jeukendrup, A. E. and Chambers, E. S. 2010. Current Opinion in Clinical Nutrition and Metabolic Care 13: 447-451.
- Plassmann, H. et al. 2008. PNAS 105: 1050-1054.
- Klaaren, K. J. et al. 1994. Social Cognition 12: 77-101.
- Lee, L. et al. 2006. Psychological Science 17: 1054-1058.
- Shiv, B. et al. 2005. Journal of Marketing Research 42: 383-393.
- Reynolds, G. 2009. Well, in The New York Times. 15 July 2009.