Labs worldwide report converging evidence that undermines the low-sugar theory of depleted willpower

One of the main findings in willpower research is that it's a limited resource. Use self-control up in one situation and you have less left over afterwards - an effect known as "ego-depletion". This discovery led to a search for the underlying physiological mechanism. In 2007, Roy Baumeister, a pioneer in the field, and his colleagues reported that the physiological correlate of ego-depletion is low glucose. Self-control leads the brain to metabolise more glucose, so the theory goes, and when glucose gets too low, we're left with less willpower.

The breakthrough 2007 study showed that ego-depleted participants had low blood glucose levels, but those who subsequently consumed a glucose drink were able to sustain their self-control on a second task. In the intervening years the finding has been replicated and the glucose-willpower link has come to be stated as fact.

"No glucose, no willpower," wrote Baumeister and his journalist co-author John Tierney in their best-selling popular psychology book Willpower: Rediscovering Our Greatest Strength (Allen Lane, 2012). The claim was also endorsed in a guide to willpower published by the American Psychological Association earlier this year. "Maintaining steady blood-glucose levels, such as by eating regular healthy meals and snacks, may help prevent the effects of willpower depletion," the report claims.

But now two studies have come along at once (following another published earlier in the year) that together cast doubt on the idea that depleted willpower is caused by a lack of glucose availability in the brain. In the first, Matthew Sanders and his colleagues in the US report what they call the "Gargle effect". They had dozens of students look through a stats book and cross out just the Es, a tiresome task designed to tax their self-control levels. Next, they completed the famous Stroop task - naming the ink colour of words while ignoring their meaning. Crucially, half the participants completed the Stroop challenge while gargling sugary lemonade, the others while gargling lemonade sweetened artificially with Splenda. The participants who gargled, but did not swallow, the sugary (i.e. glucose-containing) lemonade performed much better on the Stroop task.

The participants in the glucose condition didn't consume the glucose and even if they had, there was no time for it to be metabolised. So this effect can't be about restoring low glucose levels. Rather, Sanders' team think glucose binds to receptors in the mouth, which has the effect of activating brain regions involved in reward and self-control - the anterior cingulate cortex and striatum.

The other study that's just come out was conducted by Martin Hagger and Nikos Chatzisarantis based in Australia and the UK. Their approach was similar to Sanders' except that participants gargled and spat out a glucose or artificially sweetened solution prior to performing a second taxing task, rather than during. Also, this research involved a series of 5 experiments involving many different ways of testing people's self-control, including: resisting delicious cookies; reading boring text in an expressive style; unsolvable puzzles; and squeezing hand-grips. But the take-home finding was the same - participants who gargled, but did not swallow, a glucose drink performed better on a subsequent test of their willpower; participants who gargled an artificially sweetened drink did not. So again, willpower was restored without topping up glucose levels. Moreover, the benefit of gargling glucose was displayed only by participants who'd had their self-control taxed in an initial task. It made no difference to participants who were already in an untaxed state.

Hagger and Chatzisarantis agree with the interpretation of the Sanders' group, except they make a distinction. The effect of glucose binding to receptors in the mouth could either stimulate activity in brain regions like the anterior cingulate that tend to show fatigue after a taxing task. Or they say that glucose in the mouth could trigger reward-related activity that prompts participants to interpret a task as more rewarding, thus boosting their motivation. The explanations are complementary and need not be mutually exclusive.

The key point is the new results suggest depleted willpower is about motivation and the allocation of glucose resources, not about a lack of glucose. These findings don't prove that consuming glucose has no benefit for restoring willpower, but they suggest strongly that it's not the principle mechanism. It's notable that the new findings complement previous research in the sports science literature showing that gargling (without ingesting) glucose can boost cycling performance.

"While our findings are consistent with the predictions of the resource-depletion account, they also contribute to an increasing literature that glucose may not be a candidate physiological analog for self-control resources," write Hagger and Chatzisarantis. "Instead ego-depletion may be due to problems of self-control resource allocation rather than availability." An important next step is to conduct brain-imaging and related studies to observe the physiological effects of gargling glucose on the brain, and on motivational beliefs. There are also tantalising applications from the new research - for example, could the gargle effect (perhaps in the form of glucose-infused chewing gum) be used as a willpower aid for dieters and people trying to give up smoking?

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Hagger, M., and Chatzisarantis, N. (2012). The Sweet Taste of Success: The Presence of Glucose in the Oral Cavity Moderates the Depletion of Self-Control Resources. Personality and Social Psychology Bulletin DOI: 10.1177/0146167212459912

Sanders, M., Shirk, S., Burgin, C., and Martin, L. (2012). The Gargle Effect: Rinsing the Mouth With Glucose Enhances Self-Control. Psychological Science DOI: 10.1177/0956797612450034

--Further reading--
From The Psychologist: Roy F. Baumeister outlines intriguing and important research into willpower and ego depletion.

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Are 3D films more psychologically powerful than 2D?

The revival of 3D movies in recent years has prompted much debate among fans and critics. Some say it's gimmicky and too expensive. Others have heralded the return of the technology as the industry's saviour. A key claim in favour of 3D technology is that it makes for a more realistic, immersive experience. But does it really?

Brendan Rooney and his colleagues at University College Dublin showed 8 different movie clips (ranging from 13 to 68 seconds in length) to 27 participants (13 males; average age 27). The gory clips were chosen deliberately for their disgusting content and were taken from Bugs 3D, Friday 13th, Jaws 3-D and Frankenstein.

Each participant watched the clips alone in a mini-cinema on campus featuring a 2.5m x 2.5m screen. Crucially, half the participants viewed the clips in 3D, the others in 2D. To ensure any effects of the 3D format were not due to novelty, all the participants watched an abridged version of Journey to the Centre of the Earth in 3D, at least 24 hours prior to the study proper.

Participants in the 3D condition reported finding the film clips more realistic. They also had a higher heart rate whilst watching the clips compared with participants in the 2D condition. However, there was no difference in amount of skin conductance (another measure of arousal) between the two groups, and no difference in how much they said they enjoyed the clips.

Rooney and his colleagues explain that skin conductance - that is, the skin's sweatiness - is influenced only by the sympathetic nervous system (which triggers the fight or flight response) and not by the parasympathetic nervous system (which calms us down). By contrast, heart rate is influenced by both. This suggests to them that the calming parasympathetic nervous system is less active in viewers of 3D. Why? Well, one theory for how we calm our emotions during films is by reminding ourselves that they're not real. The 3D viewers said they found the viewing experience more realistic and it's possible that this made it more difficult for them to step outside of the experience, leaving their emotional response relatively unchecked. The researchers concede that the causal direction could also run the other way - the 3D viewers raised heart rate could cause them to perceive the experience as more realistic. Most likely the influences are bi-directional.

Is it a good thing that the 3D clips were rated as more realistic and triggered more physiological arousal? The 3D viewers didn't rate the clips as any more enjoyable, but then they only gave these ratings afterwards, which means they were relying on their memory of the experience. Also, they had no baseline to measure their ratings against. Finally, perhaps "enjoyment" is the wrong word when it comes to disgusting movie clips. If the study were repeated with a different genre, perhaps 3D viewers would give higher enjoyment ratings.

Rooney's team stressed that this was an exploratory study and that more research is clearly needed. For now they concluded the "suspension of disbelief is ... assisted by stereoscopic depth, with associated increases in reported perceived apparent reality and in heart-rate ... ".

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Rooney, B., Benson, C., and Hennessy, E. (2012). The apparent reality of movies and emotional arousal: A study using physiological and self-report measures Poetics, 40 (5), 405-422 DOI: 10.1016/j.poetic.2012.07.004

--Further reading--
Right-handers sit to the right of the movie screen to optimise neural processing of the film.

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People make more moral decisions when they think their heart is racing

Why did the proverbial Good Samaritan cross the road to help the injured stranger? Perhaps he listened to his heart. Not in the poetic sense, but literally. A new study by Jun Gu and his colleagues has highlighted the way cardiac feedback influences people's moral decisions. When students were fed false feedback, leading them to think their heart was racing, they were more likely to volunteer for a good cause and less likely to lie to gain more money.

Eighty-six undergrads arrived at a psychology lab and were asked if they could quickly test out some heart-recording equipment that was needed for a separate study. A wrist monitor was attached to a headset though which false normal (60 beats per minute) or fast (96 beats per minute) heartbeat sounds were played. While the students test-drove the equipment, they were asked to read a recruitment letter, seeking their time for another study into the negative consequences of homophobic discrimination. Forty per cent of students who heard their heart beating fast agreed to volunteer their time, as compared with 17 per cent of students who heard their heart beating at a normal speed.

A second study with 65 more students was similar, but this time as the students tested the heart-monitoring equipment, they played a quick money-sharing game. They simply had to decide whether to instruct their partner, located in another room, to pick option A (which was actually more lucrative for the participant him or herself) or option B (more lucrative for the partner). Participants who heard their heart beating fast were less likely to lie and tell their partner that he or she would be better off choosing option A (31 per cent of them did so, compared with 58 per cent of participants who heard their heart beat at normal speed). A handful of participants were suspicious about the false heart feedback so they were excluded from the analysis, though the general pattern of results was the same with their data included or omitted.

Gu and his colleagues think that a fast heart beat is interpreted by people as a sign they are stressed and that they should adhere to moral conventions as a way to escape that stress. The new finding is consistent with Antonio Damasio's influential Somatic Marker hypothesis, which is based on the idea that bodily feedback guides our decisions, often at a non-conscious level. For example, people playing a card game sweat more when picking from the wrong, costly pile, even before they've realised at a conscious level that it's the wrong choice. The new research also complements recent research showing how bodily perceptions can influence the moral conscience. In one study, participants were less likely to volunteer their time after being given the chance to wash their hands - as if the process of physical cleansing left them feeling less need to compensate for past transgressions.

Cardiac feedback doesn't affect everyone in the same way. In further experiments, Gu and his colleagues demonstrated that the moral decision-making of people who are more mindful (for example, they agreed with statements like: "I perceive my feelings and emotions without having to react to them") was unaffected by the false cardiac feedback. The researchers also found that telling participants that the financial game was a "decision-making" task led to immunity from the false heart feedback, relative to being told the game was an "intuitive task".

This last result is particularly intriguing since we usually assume that thinking more deliberatively helps rein in the wild horses of our emotions, allowing us to behave more morally. The finding of Gu's team suggests that in some circumstances at least, thinking more deliberately can undermine the influence of the heart, actually making it less likely that we'll make a more moral decision.

"The current research reveals that perceived physiological experiences play an important role in influencing moral behaviours," the researchers said. "Listening to your heart may indeed shape ethical behaviours."

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Gu J, Zhong CB, and Page-Gould E (2012). Listen to Your Heart: When False Somatic Feedback Shapes Moral Behavior. Journal of experimental psychology. General PMID: 22889162

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Judges are more lenient toward a psychopath when given a neuro explanation for his condition

Last month, a prescient editorial in the New York Times warned that a greater understanding of the neural correlates of behaviour risks having a distorting effect on the criminal justice system. John Monterosso and Barry Schwartz highlighted their own research showing that people are far more forgiving of crimes with ostensibly neurobiological causes, compared with psychological causes - a worrying demonstration of what they called "naive dualism" given that "all psychological states are also biological ones."

Now a multi-disciplinary team of psychologist Lisa Aspinwall, legal scholar Teneille Brown and philosopher James Tabery, has surveyed nearly 200 state trial court judges in the U.S., showing how their decision making is swayed by a neurobiological explanation for psychopathy.

The judges read about a case, based loosely on real events, in which a robber brutally attacked a restaurant manager who refused to hand over any money. All judges were given evidence from the prosecution or defence that said the perpetrator had been diagnosed with psychopathy - an untreatable condition. Additionally, half of them were also presented with expert evidence from a neurobiologist about the causes of psychopathy, including genetic factors. The perpetrator had been tested and had low MAOA activity - a profile, the judges were told, previously associated with increased propensity for anti-social behaviour. The neurobiologist also explained how this genetic profile leads to brain abnormalities that impair the psychopath's ability to tell right from wrong.

Compared with what they estimated to be their usual sentencing for aggravated battery (9 years), overall the judges said they would give a higher sentence to the psychopathic perpetrator in the current case - 12.93 years. This shows the criminal's psychopathy was overall treated as an "aggravating factor", a sign of utilitarian thinking on the part of the judges, in the sense that he was highly likely to be violent in the future.

However, among the judges exposed to a neurobiological account of psychopathy, the diagnosis also had a "mitigating" effect on their decision-making. Judges in this condition sentenced the attacker to an average of 12.83 years compared with the 13.93 years given by judges who didn't receive the neurobiological information. Although the judges in receipt of the neurobiology didn't agree with the explicit suggestion that the attacker had compromised free will or moral responsibility, their open-ended explanations for their sentencing suggested otherwise. The neural evidence "makes possible an argument that psychopaths are, in a sense, morally 'disabled'," said one.

Aspinwall and her team described as a "double-edged sword" the way that psychopathy, accompanied by neurobiological explanation, can have both an aggravating and mitigating effect at once. Supporting this, judges who received the neurobiological testimony, and heard the psychopathic diagnosis from the defence counsel, tended to mention "weighing" or "balancing" factors over twice as often as judges in the other conditions. "Psychopathy may make the defendant less morally culpable, but it increases his future dangerousness to society," said one. "In my mind, these factors balance out ...".

This new research adds to a growing literature showing how people seem to be particularly beguiled by neuroscientific evidence. Last year, for example, a study reported that people were more persuaded by brain-scan-based lie-detection evidence compared with more traditional lie-detection approaches. This study also isn't the first to examine the factors affecting the decision making of judges. For instance, it was shown last year that hungry judges are less forgiving.

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Lisa G. Aspinwall, Teneille R. Brown, & James Tabery (2012). The Double-Edged Sword: Does Biomechanism Increase or Decrease Judges' Sentencing of Psychopaths? Science : 10.1126/science.1219569

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Does your heart rate hold the secret to getting in “the zone”?

An awkward, incomprehensible problem has you ripping your hair out. Too easy a task, on the other hand, and you’re drawing dust-patterns on the desk out of boredom. To work long, hard and well on a project, what’s needed is a level of challenge that pushes you to the edge of your abilities, but not too far beyond. Such a test provokes a mental state that positive psychologist Mihály Csíkszentmihályi calls “flow”, known more colloquially as being in the zone.

An intriguing area of study that’s only emerged over the last few years concerns the physiological correlates of flow. If we could find out what’s going on in the body during mental flow, it would make it easier and less intrusive to measure when people are in such a state (at the moment, researchers have to nudge someone absorbed in an activity to ask them how it feels, with the risk of spoiling their flow, or they have to ask them about the experience afterwards). Even more exciting, discovering the physiological correlates of flow could lead to new bodily means by which to help ourselves achieve the zen-like state.

A promising candidate is heart rate coherence - when the rhythm of the heart attains a smooth, sine-like waveform over time. Like flow, it too has been linked with positive emotions and superior performance, including more focused attention and speeded reaction times.

Brenda Mansfield and Roger Couture at Laurentian University in Canada and their co-workers have looked directly for the first time at the relationship between coherence and flow. They invited dozens of undergrads to undertake three different tasks: answering a batch of learning style and happiness questionnaires; playing a bio-feedback game in which a hot-air balloon on a screen rises and falls in line with heart-rate coherence; and completing a Playstation 3 game, inspired by Csíkszentmihályi’s theory, which is designed to trigger a flow state in players as they guide an aquatic creature through an underwater world.

The researchers monitored the participants’ heart-rate coherence through all three tasks via a device attached to the earlobe, and the participants also completed a measure of their state of flow after each task (example items included “Things just seemed to be happening automatically”). The study’s key question was whether coherence and flow would fluctuate in tandem, indicating that the former is the physiological marker of the latter.

Unfortunately, and to put it bluntly, the results were a mass of contradictions. On the questionnaire task (which triggered a surprising amount of flow), heart-rate coherence tended to be lower in students who reported more flow – a negative correlation. During the coherence-inducing hot-air balloon task, flow and coherence did correlate with each other positively, but overall flow was low, perhaps because the students found the task too frustrating. Finally, the Playstation flow game succeeded in inducing flow as you’d expect, but there was no correlation between flow and coherence.

The researchers admitted their results were “puzzling” and they said more research was needed. “We discovered that coherence and flow, however mutually beneficial to optimal experience, can occur and/or be induced independently of one another,” they wrote. “Our results provide evidence of a dissociation between the concepts, as we can turn them on separately.”

Perhaps it was overly optimistic to hope that the psychological construct of flow would map neatly onto the physiological state known as coherence. Life is often more complicated than this. Assuming that flow itself is a unitary concept, which is far from established, it’s more likely that it is associated with a number of different kinds of physiological state. But this is a new field of study, and Mansfield’s team carried out an important first test.

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Brenda E. Mansfield, Bruce E. Oddson, Josee Turcotte, and Roger T. Couture (2012). A possible physiological correlate for mental flow. The Journal of Positive Psychology DOI: 10.1080/17439760.2012.691982

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Body-sensitive people are tuned into their heart and their stomach

We know from past research that some people are better than others at being able to detect their own heartbeat. There's lots of research on that topic, partly because it's so easy to compare people's estimates of their heartbeats against the true reading. But is this a characteristic that generalises? Are people who are accurate at detecting their cardiac activity also in-tune with their other internal bodily functions?

Before now, just one study from the early 80s had looked for and found an association between cardiac awareness and gastric awareness. But that study relied on an uncomfortable sounding procedure in which participants had to swallow a balloon. That necessarily ruled out a lot of potential participants who wouldn't have wanted to do such a thing, and the internal gastric sensations that the remaining participants detected were artificially induced.

Now Beate Herbert and her colleagues have used a more natural test of gastric awareness. Forty-nine healthy women fasted for four hours before arriving at the lab where they were instructed to drink water until they felt full. The container they drank from was opaque and re-filled after each swig, so that there was no way for the women to judge visually how much they'd drunk. The participants also completed a test of their heartbeat awareness. For both tasks, medical equipment in the form of electrocardiogram (ECG) and electrogastrogram (EGG) provided objective measures of heart and stomach activity.

The key finding is that women who were more accurate in detecting their own heartbeats also tended to stop drinking earlier, as if they were more sensitive to internal feelings of fullness. The EGG provided objective confirmation that they experienced less gastric activity than the other participants before stopping drinking, so it wasn't the case that their stomachs were actually more full or issuing more powerful signals. Rather the heartbeat sensitive women seemed to be particularly sensitive to signals arising from their stomachs. There were no links between either cardio or gastric awareness and anxiety.

Herbert and her team concluded: "'Interoceptive awareness' as assessed by heartbeat perception seems to represent a better ability to focus, to perceive and to process internal bodily information across visceral modalities, such as gastric signals, with cardiac and gastric signals both representing bodily cues that show perceivable activity changes during situations of everyday life."
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Herbert, B., Muth, E., Pollatos, O., and Herbert, C. (2012). Interoception across Modalities: On the Relationship between Cardiac Awareness and the Sensitivity for Gastric Functions. PLoS ONE, 7 (5) DOI: 10.1371/journal.pone.0036646

Previously on the Digest: People who are more aware of their own heart-beat have superior time perception skills.

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Introducing "therapy genetics" - genes can predict whether therapy will help

Psychotherapy, like other forms of treatment, doesn't work for everyone and there would be huge advantages to knowing in advance who's likely to benefit. In the case of drugs, there's a thriving research field - pharmacogenetics - looking at whether a person's genetic profile can predict their chances of responding to treatment. Can the same approach be applied to therapy? A team of researchers at the Institute of Psychiatry in London believes so.

In one of the first papers published on "therapy genetics", Kathryn Lester and her colleagues, including Thalia Eley, took swabs from hundreds of white children with anxiety, aged 6 to 13. The researchers were specifically interested in the genes the children had that code for Nerve Growth Factor (NGF) and Brain Derived-Neurotrophic Factor (BDNF) - proteins involved in the survival and development of neurons. The children, some based in the UK and some in Australia, then underwent a CBT programme designed for helping anxious children. The key question was whether the children's genetic profile would be associated with how well they responded to the treatment.

There were no genetic associations with the children's immediate response to the treatment. However, at follow up (assessed at 3, 6 or 12 months), the children's particular NGF genotype was related to their therapeutic responsiveness. We each have two copies of the NGF gene, rs6330, which can come in two versions, known as the T allele or the C allele. Lester and her team found that among children with two copies of the T allele version, 76.7 per cent were free of their primary anxiety diagnosis at follow up, compared with 63.5 per cent of children with one C version and one T version, and just 53.2 per cent of children with two copies of the C allele. These associations held, even after controlling for other clinically relevant factors such as age, gender and geographical location.

Why should the children's particular form of NGF gene affect the way they respond to CBT? Definite answers will only come from more research, but Lester and her colleagues argued that the finding makes sense based on what we already know about NGF being involved in the growth of new neurons and in changing connections between existing neurones - known as "neuroplastic changes" in the scientific jargon. "Significant learning experiences of the kind undertaken during CBT may very well be underpinned by neuroplastic modifications in brain activity and function," they said.

This new result complements another recent paper published by the same research group, in which anxious children responded more successfully to CBT if they had a particular version of a gene involved in the activity of the neurotransmitter serotonin. Again, the association was found at follow-up rather than immediately after therapy.

Lester and her team said they believed the association they documented in this new research is "clinically meaningful", but that "clinically significant prediction by genetic markers is likely to be best achieved by combining multiple genetic markers (perhaps in combination with clinical predictors) into predictive indices or algorithms."

The research has some shortcomings. For example, without a no-treatment control group of anxious children, it's not possible to say for sure that NGF genotype is specifically associated with therapeutic responsiveness rather than an advantageous tendency to recover regardless of treatment. "These findings should be considered preliminary," the researchers said.

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Lester, K., Hudson, J., Tropeano, M., Creswell, C., Collier, D., Farmer, A., Lyneham, H., Rapee, R., and Eley, T. (2012). Neurotrophic gene polymorphisms and response to psychological therapy. Translational Psychiatry, 2 (5) DOI: 10.1038/tp.2012.33

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Young male drivers are more vulnerable than older men to sleepiness

One might imagine the vigour of youth would allow young men to shrug off the effects of a lack of sleep. In fact, a new study on driving performance documents that young men are particularly vulnerable to the effects of sleepiness, far more than older men.

Ashleigh Filtness and his colleagues recruited 20 healthy young men (average age 23) and 20 healthy older men (average age 67) to complete two early afternoon driving challenges in a full-size simulator. One of the monotonous two-hour drives was completed after a normal night's sleep, as confirmed by a wrist actimeter that records nocturnal movement. The other two-hour drive was performed after a previous night's sleep of just five hours. The participants weren't allowed to consume alcohol for 36 hours before either test.

The researchers were mainly interested in lane drifts, in which all four wheels of the car left the lane the driver was supposed to be in. As you'd expect, these increased in the later stages of both the drives. Both groups of men also drifted more on the drive that followed less sleep. But the key finding was that the young men were affected far more drastically by a lack of sleep. For instance, in the last 30 minutes of the drive that followed a five-hour sleep, the young men averaged just over six lane drifts compared with fewer than two by the older men. This difference was also reflected in other measures - the younger men reported feeling more sleepy after a lack of sleep than the older men and this was confirmed by their brainwave recordings.

The new findings are consistent with previous night time studies in simulators and on the road that showed young male and female participants struggled more than older participants to maintain safe driving performance. They also help make sense of road accident data that show sleep-related incidents predominantly involve young male drivers.

However there are some complications in interpreting the new research. For example, it's likely the older drivers had more driving experience. Are they less vulnerable to sleepiness or simply better drivers? The researchers state only that both groups were experienced, with all participants having driven for over two years, more than three hours per week. Another complication acknowledged by the researchers is that young men typically sleep for longer than older men. This means the five-hour sleep limit condition was a greater departure from routine for the younger men.

A problem not mentioned in the paper is the potential influence of "stereotype threat" - whereby a fear of fulfilling stereotypes can undermine the performance of stereotyped groups. A researcher was present in the driving simulator room and it's possible the young men were aware of the negative attitudes commonly felt towards young male drivers and were affected as a result. A final weakness is the use of a simulator - the participants would have known any errors were inconsequential.

"The greater vulnerability of [young men] ... to sleep restriction potentially puts them at a greater driving risk under these circumstances, and may help further explain the relatively high proportion of young men being responsible for serious sleep related road collisions," the researchers said.
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Filtness, A., Reyner, L., and Horne, J. (2012). Driver sleepiness—Comparisons between young and older men during a monotonous afternoon simulated drive. Biological Psychology, 89 (3), 580-583 DOI: 10.1016/j.biopsycho.2012.01.002

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