Openness versus conservatism - its cultural evolution

Acerbi et al. ask what might make different groups of people more liberal or conservative (or open minded versus having inflexible views), and develop a model which shows that cultural evolution can maintain openness to new information as well as effectiveness at cultural transmission. They consider how rules of cultural transmission can be modified by social learning. For example, individuals might learn from others whether or not to rely on social information. Their model predicts smaller societies to be more conservative, which agrees with the observation that traditional societies (whose very name implies conservatism) tend to be small. It is consistent with archaeological evidence showing that large cultural repertoires can be maintained only by large groups.

We present a model of cultural evolution in which an individual's propensity to engage in social learning is affected by social learning itself. We assume that individuals observe cultural traits displayed by others and decide whether to copy them based on their overall preference for the displayed traits. Preferences, too, can be transmitted between individuals. Our results show that such cultural dynamics tends to produce conservative individuals, i.e., individuals who are reluctant to copy new traits. Openness to new information, however, can be maintained when individuals need significant time to acquire the cultural traits that make them effective cultural models. We show that a gradual enculturation of young individuals by many models and a larger cultural repertoire to be acquired are favorable circumstances for the long-term maintenance of openness in individuals and groups. Our results agree with data about lifetime personality change, showing that openness to new information decreases with age. Our results show that cultural remodeling of cultural transmission is a powerful force in cultural evolution, i.e., that cultural evolution can change its own dynamics.

Deconstructing the Placebo

I want to point you to this great post at Neuroskeptic. Here is its ending text:

"The placebo effect" has become a vague catch-all term for anything that seems to happen to people when you give them a sugar pill. Of course, lots of things could happen. They could feel better just because of the passage of time. Or they could realize that they're supposed to feel better and say they feel better, even if they don't.

The "true" placebo effect refers to improvement (or worsening) of symptoms driven purely by the psychological expectation of such. But even this is something of a catch-all term. Many things could drive this improvement. Suppose you give someone a placebo pill that you claim will make them more intelligent, and they believe it.

Believing themselves to be smarter, they start doing smart things like crosswords, math puzzles, reading hard books (or even reading Neuroskeptic), etc. But the placebo itself was just a nudge in the right direction. Anything which provided that nudge would also have worked - and the nudge itself can't take all the credit.

The strongest meaning of the "placebo effect" is a direct effect of belief upon symptoms. You give someone a sugar pill or injection, and they immediately feel less pain, or whatever. But even this effect encompasses two kinds of things. It's one thing if the original symptoms have a "real" medical cause, like a broken leg. But it's another thing if the original symptoms are themselves partially or wholly driven by psychological factors, i.e. if they are "psychosomatic".

If a placebo treats a "psychosomatic" disease, then that's not because the placebo has some mysterious, mind-over-matter "placebo effect". All the mystery, rather, lies with the psychosomatic disease. But this is a crucial distinction.

People seem more willing to accept the mind-over-matter powers of "the placebo" than they are to accept the existence of psychosomatic illness. As if only doctors with sugar pills possess the power of suggestion. If a simple pill can convince someone that they are cured, surely the modern world in all its complexity could convince people that they're ill.

Watching our brains judge gain versus pain

Yet another lucidly presented bit of work from a collaboration involving Dolan's group at University College London:

The maxim "no pain, no gain" summarizes scenarios in which an action leading to reward also entails a cost. Although we know a substantial amount about how the brain represents pain and reward separately, we know little about how they are integrated during goal-directed behavior. Two theoretical models might account for the integration of reward and pain. An additive model specifies that the disutility of costs is summed linearly with the utility of benefits, whereas an interactive model suggests that cost and benefit utilities interact so that the sensitivity to benefits is attenuated as costs become increasingly aversive. Using a novel task that required integration of physical pain and monetary reward, we examined the mechanism underlying cost–benefit integration in humans. We provide evidence in support of an interactive model in behavioral choice. Using functional neuroimaging, we identify a neural signature for this interaction such that, when the consequences of actions embody a mixture of reward and pain, there is an attenuation of a predictive reward signal in both ventral anterior cingulate cortex and ventral striatum. We conclude that these regions subserve integration of action costs and benefits in humans, a finding that suggests a cross-species similarity in neural substrates that implement this function and illuminates mechanisms that underlie altered decision making under aversive conditions.

Curing musicians' dystonia.

Here is another bit on music or musicians. (I seem to be doing a fair number of postings in this area, maybe because I'm back into more hard core piano playing since returning to Fort Lauderdale...my hands are fatigued after 3 hours of Dvorak and Dohnanyi piano quintets yesterday.) Rosenkranz et al. show that an overly expanded spatial integration of proprioceptive input into the hand motor cortex that can cause deficiencies in hand motor controls (dystonia) can be reversed by proprioceptive training in pianists with musician's dystonia to the pattern seen in healthy pianists. (The training intervention requires the subject's attention to be focused for 15 min on random vibrations delivered to three hand muscles.):

Professional musicians are an excellent model of long-term motor learning effects on structure and function of the sensorimotor system. However, intensive motor skill training has been associated with task-specific deficiency in hand motor control, which has a higher prevalence among musicians (musician's dystonia) than in the general population. Using a transcranial magnetic stimulation paradigm, we previously found an expanded spatial integration of proprioceptive input into the hand motor cortex [sensorimotor organization (SMO)] in healthy musicians. In musician's dystonia, however, this expansion was even larger. Whereas motor skills of musicians are likely to be supported by a spatially expanded SMO, we hypothesized that in musician's dystonia this might have developed too far and now disrupts rather than assists task-specific motor control. If so, motor control should be regained by reversing the excessive reorganization in musician's dystonia. Here, we test this hypothesis and show that a 15 min intervention with proprioceptive input (proprioceptive training) restored SMO in pianists with musician's dystonia to the pattern seen in healthy pianists. Crucially, task-specific motor control improved significantly and objectively as measured with a MIDI (musical instrument digital interface) piano, and the amount of behavioral improvement was significantly correlated to the degree of sensorimotor reorganization. In healthy pianists and nonmusicians, the SMO and motor performance remained essentially unchanged. These findings suggest that the differentiation of SMO in the hand motor cortex and the degree of motor control of intensively practiced tasks are significantly linked and finely balanced. Proprioceptive training restored this balance in musician's dystonia to the behaviorally beneficial level of healthy musicians.

More on the trust and empathy hormone...

Natalie Angier does a summary of some recent studies on oxytocin, several of which I've already mentioned in MindBlog posts (enter oxytocin in the search box to list them). Of particular interest is recent work from Keltner's group showing that genetic differences in people’s responsiveness to the effects of oxytocin are linked to their ability to read faces, infer the emotions of others, feel distress at others’ hardship and even to identify with characters in a novel. Here is the abstract from the Keltner group:

Oxytocin, a peptide that functions as both a hormone and neurotransmitter, has broad influences on social and emotional processing throughout the body and the brain. In this study, we tested how a polymorphism (rs53576) of the oxytocin receptor relates to two key social processes related to oxytocin: empathy and stress reactivity. Compared with individuals homozygous for the G allele of rs53576 (GG), individuals with one or two copies of the A allele (AG/AA) exhibited lower behavioral and dispositional empathy, as measured by the “Reading the Mind in the Eyes” Test and an other-oriented empathy scale. Furthermore, AA/AG individuals displayed higher physiological and dispositional stress reactivity than GG individuals, as determined by heart rate response during a startle anticipation task and an affective reactivity scale. Our results provide evidence of how a naturally occurring genetic variation of the oxytocin receptor relates to both empathy and stress profiles.

Origins of empathetic yawning?

Interesting observations by Palagi et al:

Yawn contagion in humans has been proposed to be related to our capacity for empathy. It is presently unclear whether this capacity is uniquely human or shared with other primates, especially monkeys. Here, we show that in gelada baboons (Theropithecus gelada) yawning is contagious between individuals, especially those that are socially close, i.e., the contagiousness of yawning correlated with the level of grooming contact between individuals. This correlation persisted after controlling for the effect of spatial association. Thus, emotional proximity rather than spatial proximity best predicts yawn contagion. Adult females showed precise matching of different yawning types, which suggests a mirroring mechanism that activates shared representations. The present study also suggests that females have an enhanced sensitivity and emotional tuning toward companions. These findings are consistent with the view that contagious yawning reveals an emotional connection between individuals. This phenomenon, here demonstrated in monkeys, could be a building block for full-blown empathy.

Three different yawning displays performed by gelada baboons. Covered teeth yawning (left) uncovered teeth yawning (middle). and uncovered gums yawning (right).

Sounds during sleep aid memory

Rudoy et al. (PDF here) find that if, while asleep, people hear sounds that had earlier been associated with objects at specific spatial locations, upon waking they recalled these locations more accurately than other locations for which no reminder cues were provided. Consolidation thus operates during sleep with high specificity and is subject to systematic influences through simple auditory stimulation.

The Music Instinct

Steven Mithen (author of The Singing Neanderthals) does a summary of his ideas on the evolutionary basis of musicality in this open access article in the Annals of the New York Academy of Sciences.

Why does music pervade our lives and those of all known human beings living today and in the recent past? Why do we feel compelled to engage in musical activity, or at least simply enjoy listening to music even if we choose not to actively participate? I argue that this is because musicality—communication using variations in pitch, rhythm, dynamics and timbre, by a combination of the voice, body (as in dance), and material culture—was essential to the lives of our pre-linguistic hominin ancestors. As a consequence we have inherited a desire to engage with music, even if this has no adaptive benefit for us today as a species whose communication system is dominated by spoken language. In this article I provide a summary of the arguments to support this view.

Musicians are not as bothered by background noise.

From Parbery-Clark et al.:

Musicians have lifelong experience parsing melodies from background harmonies, which can be considered a process analogous to speech perception in noise. To investigate the effect of musical experience on the neural representation of speech-in-noise, we compared subcortical neurophysiological responses to speech in quiet and noise in a group of highly trained musicians and nonmusician controls. Musicians were found to have a more robust subcortical representation of the acoustic stimulus in the presence of noise. Specifically, musicians demonstrated faster neural timing, enhanced representation of speech harmonics, and less degraded response morphology in noise. Neural measures were associated with better behavioral performance on the Hearing in Noise Test (HINT) for which musicians outperformed the nonmusician controls. These findings suggest that musical experience limits the negative effects of competing background noise, thereby providing the first biological evidence for musicians' perceptual advantage for speech-in-noise.

Imagination and bad governance

I liked this column by Thomas Friedman. Some clips:

...I’m not ready to cede the 21st century to China just yet...there are still two really important things that can’t be commoditized. Fortunately, America still has one of them: imagination...Who would cede a century in which imagination will have such a high value to an authoritarian society that controls its Internet and jails political prisoners?

But while our culture of imagination is still vibrant, the other critical factor that still differentiates countries today — and is not a commodity — is good governance, which can harness creativity. And that we may be losing. Why? Because at least six things have come together to fracture our public space and paralyze our ability to forge optimal solutions:

1) Money in politics has become so pervasive that lawmakers have to spend most of their time raising it, selling their souls to those who have it or defending themselves from the smallest interest groups with deep pockets that can trump the national interest.

2) The gerrymandering of political districts means politicians of each party can now choose their own voters and never have to appeal to the center.

3) The cable TV culture encourages shouting and segregating people into their own political echo chambers.

4) A permanent presidential campaign leaves little time for governing.

5) The Internet, which, at its best, provides a check on elites and establishments and opens the way for new voices and, which, at its worst provides a home for every extreme view and spawns digital lynch mobs from across the political spectrum that attack anyone who departs from their specific orthodoxy.

6) A U.S. business community that has become so globalized that it only comes to Washington to lobby for its own narrow interests; it rarely speaks out anymore in defense of national issues like health care, education and open markets.

And, while I'm passing on interesting New York Times pieces, this one on economic recovery viewed as self fulfilling prophecy.

Neural predictors of attitude changes.

Some work from van Veen et al. on attitude changes induced by cognitive dissonance:

When our actions conflict with our prior attitudes, we often change our attitudes to be more consistent with our actions. This phenomenon, known as cognitive dissonance, is considered to be one of the most influential theories in psychology. However, the neural basis of this phenomenon is unknown. Using a Solomon four-group design, we scanned participants with functional MRI while they argued that the uncomfortable scanner environment was nevertheless a pleasant experience. We found that cognitive dissonance engaged the dorsal anterior cingulate cortex and anterior insula; furthermore, we found that the activation of these regions tightly predicted participants' subsequent attitude change. These effects were not observed in a control group. Our findings elucidate the neural representation of cognitive dissonance, and support the role of the anterior cingulate cortex in detecting cognitive conflict and the neural prediction of attitude change.

Why sex matters - more on brain differences between men and women

Luders et al. examine brain differences not dependent on size in gray matter distributions between men and women. They find a number of regions where matched women had significantly larger gray matter (GM) volumes than in matched men, suggesting that anatomical differences between male and female brains exist independently of brain size effects. While they did not detect any regions of larger GM volume in men than in women, there were a number of regions indicating larger GM volumes in women than in men. Comparing men and women with identical brain sizes, they detected the largest clusters in the right and left caudate extending into adjacent regions of the basal ganglia, as well as into the left orbitofrontal region. These findings appear to disagree with previous findings indicating that brain volume (rather than sex) is the main variable accounting for differences in gray matter proportion. Their abstract:

The different brain anatomy of men and women is both a classic and continuing topic of major interest. Among the most replicated and robust sex differences are larger overall brain dimensions in men, and relative increases of global and regional gray matter (GM) in women. However, the question remains whether sex-typical differences in brain size (i.e., larger male and smaller female brains) or biological sex itself account for the observed sex effects on tissue amount and distribution. Exploring cerebral structures in men and women with similar brain size may clarify the true contribution of biological sex. We thus examined a sample of 24 male and 24 female subjects with brains identical in size, in addition to 24 male and 24 female subjects with considerable brain size differences. Using this large set of brains (n = 96), we applied a well validated and automated voxel-based approach to examine regional volumes of GM. While we revealed significant main effects of sex, there were no significant effects of brain size (and no significant interactions between sex and brain size). When conducting post hoc tests, we revealed a number of regions where women had larger GM volumes than men. Importantly, these sex effects remained evident when comparing men and women with the same brain size. Altogether, our findings suggest that the observed increased regional GM volumes in female brains constitute sex-dependent redistributions of tissue volume, rather than individual adjustments attributable to brain size.

The weirdest people in the world?

Many broad claims about human behavior are based on experiments done samples drawn from western, educated, industrialized, rich, and democratic societies (i.e. WEIRD - the subjects of psychological experiments are mainly U.S. college undergraduates!). Henrich et al. argue in a Brain and Behavioral Sciences preprint (PDF here) that WEIRD subjects are particularly unusual compared with the rest of our species - frequent outliers. Here is their abstract:

Behavioral scientists routinely publish broad claims about human psychology and behavior in the world’s top journals based on samples drawn entirely from Western, Educated, Industrialized, Rich and Democratic (WEIRD) societies. Researchers—often implicitly—assume that either there is little variation across human populations, or that these “standard subjects” are as representative of the species as any other population. Are these assumptions justified? Here, our review of the comparative database from across the behavioral sciences suggests both that there is substantial variability in experimental results across populations and that WEIRD subjects are particularly unusual compared with the rest of the species—frequent outliers. The domains reviewed include visual perception, fairness, cooperation, spatial reasoning, categorization and inferential induction, moral reasoning, reasoning styles, self-concepts and related motivations, and the heritability of IQ. The findings suggest that members of WEIRD societies, including young children, are among the least representative populations one could find for generalizing about humans. Many of these findings involve domains that are associated with fundamental aspects of psychology, motivation, and behavior—hence, there are no obvious a priori grounds for claiming that a particular behavioral phenomenon is universal based on sampling from a single subpopulation. Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions of human nature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity. We close by proposing ways to structurally re-organize the behavioral sciences to best tackle these challenges.

Cyclic variations in our vigilance

I had been unaware that our vigilance during a sustained attention task varies in a systematic way. Aue et al. have examined suggested rhythmic oscillations in the vigilance with which we maintain sustained attention by developing some continuous performance tasks:

...The current series of investigations sought to manipulate suggested periodicities of 1.5 and 5.2 min by altering task difficulty: tracking a white dot moving in a random pattern across an otherwise black computer display , administering caffeine, and testing on an ecologically valid task (simulated driving). Strong evidence of a 1.5 min periodicity was found across studies. Most participants did not demonstrate a 5.2 min periodicity. Moreover, the 1.5 min periodicity was resistant to task manipulations and appeared in similar levels across conditions in all experiments. These rhythms may be indicative of an endogenous system that modulates sustained attention in humans.

Low fat makes you happier?

Here is a curious fragment... Brinkworth et al. studied 106 obese people put on either a low fat or low carbohydrate diet for a year, doing psychological assessment tests during this period. Initially, shedding pounds put both groups in a better mood. But, in the low carbohydrate group this effect began to wear off after the first few weeks. Over 1 year, there was a favorable effect of an energy-restricted low fat diet compared with an isocaloric low carbohydrate diet on mood state and affect in overweight individuals, but both diets had similar effects on working memory and speed of information processing.

The sooner you can sleep, the better you learn.

Van Der Werf et al. investigate whether motor skill enhancement through prior observation requires sleep to follow the observation to consolidate the procedural memory:

Numerous studies have shown that sleep enhances memory for motor skills learned through practice. Motor skills can, however, also be learned through observation, a process possibly involving the mirror neuron system. We investigated whether motor skill enhancement through prior observation requires sleep to follow the observation, either immediately or after a delay, to consolidate the procedural memory. Sequence-specific fingertapping performance was tested in 64 healthy subjects in a balanced design. Electromyography verified absence of overt or subliminal hand muscle activations during observation. The results show that immediate sleep is necessary for the enhancement of a motor skill through prior observation. Immediate sleep improved the speed of subsequent performance by 22 ± 11% (mean ± SEM) (P = 0.04) and reduced the error rate by 42 ± 19% (P = 0.02). In contrast, no performance gains occurred if sleep was initiated more than 12 h after observation. A second study on 64 subjects ruled out explicit familiarity with the sequence or the spatiotemporal rhythm of the sequence to underlie performance improvements. The sleep-dependent observational motor learning enhancement is at least similar to that previously reported for implicit and declarative memory. The apparent prerequisite of observing real movements indicates that subjects transfer experience obtained through observation of movements to subsequent self-initiated movements, in the absence of practice. Moreover, the consolidation of this transfer requires an early sleep window. These findings could improve learning new motor skills in athletes and children, but also in patients having to remaster skills following stroke or injury.

Neurogenetics of remembering emotions past

It turns out that genetic makeup would determine how vididly Proust's narrator, on biting into a madeleine cake dipped in tea, would experience his emotional memories. Work by Rasch et al. suggests that individual differences in the ADRA2B gene that codes the α2B adrenoreceptor, which plays an important role in vasoconstriction and blood pressure regulation, is also related to brain activation patterns underlying heightened emotional recall:

Emotionally arousing events are typically well remembered, but there is a large interindividual variability for this phenomenon. We have recently shown that a functional deletion variant of ADRA2B, the gene encoding the α2b-adrenergic receptor, is related to enhanced emotional memory in healthy humans and enhanced traumatic memory in war victims. Here, we investigated the neural mechanisms of this effect in healthy participants by using fMRI. Carriers of the ADRA2B deletion variant exhibited increased activation of the amygdala during encoding of photographs with negative emotional valence compared with noncarriers of the deletion. Additionally, functional connectivity between amygdala and insula was significantly stronger in deletion carriers. The present findings indicate that the ADRA2B deletion variant is related to increased responsivity and connectivity of brain regions implicated in emotional memory.

Evolution of "the God gene"

Articles on a particular topic seem to come out in clusters. Shortly after doing yesterday's post on the origin of religions I see this article by Nicholas Wade in the NYTimes. He makes some further interesting points.

For atheists, it is not a particularly welcome thought that religion evolved because it conferred essential benefits on early human societies and their successors. If religion is a lifebelt, it is hard to portray it as useless...For believers, it may seem threatening to think that the mind has been shaped to believe in gods, since the actual existence of the divine may then seem less likely.

It is easier to see from hunter-gatherer societies how religion may have conferred compelling advantages in the struggle for survival. Their rituals emphasize not theology but intense communal dancing that may last through the night. The sustained rhythmic movement induces strong feelings of exaltation and emotional commitment to the group. Rituals also resolve quarrels and patch up the social fabric.

The ancestral human population of 50,000 years ago, to judge from living hunter-gatherers, would have lived in small, egalitarian groups without chiefs or headmen. Religion served them as an invisible government. It bound people together, committing them to put their community’s needs ahead of their own self-interest. For fear of divine punishment, people followed rules of self-restraint toward members of the community. Religion also emboldened them to give their lives in battle against outsiders. Groups fortified by religious belief would have prevailed over those that lacked it, and genes that prompted the mind toward ritual would eventually have become universal.

Could the evolutionary perspective on religion become the basis for some kind of detente between religion and science? Biologists and many atheists have a lot of respect for evolution and its workings, and if they regarded religious behavior as an evolved instinct they might see religion more favorably, or at least recognize its constructive roles. Religion is often blamed for its spectacular excesses, whether in promoting persecution or warfare, but gets less credit for its staple function of patching up the moral fabric of society. But perhaps it doesn’t deserve either blame or credit. If religion is seen as a means of generating social cohesion, it is a society and its leaders that put that cohesion to good or bad ends.

Cognitive science and the origin of religions

Elizabeth Culotta writes the 11th essay in Science's series in honor of the Year of Darwin, which explores the human propensity to believe in unseen deities. She describes a new field:'the cognitive science of religion', which draws on psychology, anthropology, and neuroscience to understand the mental building blocks of religious thought. Here are a few slightly edited clips from the essay:

...there remains a yawning gap between the material evidence of the archaeological record and the theoretical models of psychologists. Archaeological objects fall short of revealing our ancestors' minds while on the psychological side more evidence is needed.
...Many researchers take the use of symbols as a clue to budding spirituality. As far back as 100,000 years ago, people at the South African site of Blombos Cave incised pieces of ochre with geometric designs, creating the first widely recognized signs of symbolic behavior.

...While archaeologists trace the outward expressions of religious and symbolic behavior, another group of researchers is trying to trace more subtle building blocks of religious belief, seeking religion's roots in our minds.
...According to the emerging cognitive model of religion, we are so keenly attuned to the designs and desires of other people that we are hypersensitive to signs of "agents": thinking minds like our own... a "hypertrophy of social cognition" leads us to attribute random events or natural phenomena to the agency of another being.
...young children prefer "teleological," or purpose-driven, explanations rather than mechanical ones for natural phenomena...in several studies British and American children in first, second, and fourth grades were asked whether rocks are pointy because they are composed of small bits of material or in order to keep animals from sitting on them. The children preferred the teleological explanation. They give an animistic quality to the rock; it's protecting itself...we all from childhood have a bias to see the natural world as purposefully designed. It's a small step to suppose that the design has a designer.
...a hair-trigger agency detector could work with another sophisticated element of the human mind to make us prone to believe in gods: what's called theory of mind, or the understanding that another being has a mind with intentions, desires, and beliefs of its own.
...If you suspect that an agent was responsible for some mysterious event, it's a short step to thinking that the agent has a mind like your own. Higher order theory of mind enables you to represent mental states of beings not immediately or visibly present, and who could have a very different perspective than your own. That's what you need to have a rich representation of what it might be like to be a god. (It's also what is needed to have a functional religion, because people need to know that others share their beliefs.) As Darwin put it, humans developing religion "would naturally attribute to spirits the same passions, the same love of vengeance, or simplest form of justice, and the same affections which they themselves feel."
...Some fMRI studies lend support to this idea. When subjects in an fMRI scanner are asked to evaluate statements about God's emotions and relationships to humans, such as, "God is removed from the world" and "God is forgiving," the areas that light up, such as the inferior frontal gyrus on both sides of the brain, are also involved in theory of mind. This and other results argue against any special "god region" of the brain as some have suggested; rather, religious belief might co-opt widely distributed brain sectors, including many concerned with so-called theory of mind.

Many favor an additional class of explanations for why religion is so prominent in every culture: It promotes cooperative behavior among strangers and so creates stable groups. The hypothesis is that religion is actually adaptive: By encouraging helpful behavior, religious groups boost the biological survival and reproduction of their members. Adhering to strict behavioral rules may signal that a religion's members are strongly committed to the group and so will not seek a free ride, a perennial problem in cooperative groups

When the boss feels inadequate - power, incompetence, and aggression

Fast and Chen note that a startling 37% of American workers—roughly 54 million people—have been bullied at work, primarily having been sabotaged, yelled at, or belittled by their bosses . This statistic resonates with research showing a link between social power and aggression (i.e., acts aimed at harming other individuals, physically or otherwise). However, it also indicates that the link between power and aggression is not universal—after all, 63% of American workers have not been bullied at work. These observations raise an intriguing pair of questions: When are power holders most likely to behave aggressively, and why do they do so? Their abstract (PDF here):

When and why do power holders seek to harm other people? The present research examined the idea that aggression among the powerful is often the result of a threatened ego. Four studies demonstrated that individuals with power become aggressive when they feel incompetent in the domain of power. Regardless of whether power was measured in the workplace, manipulated via role recall, or assigned in the laboratory, it was associated with heightened aggression when paired with a lack of self-perceived competence. As hypothesized, this aggression appeared to be driven by ego threat: Aggressiveness was eliminated among participants whose sense of self-worth was boosted. Taken together, these findings suggest that (a) power paired with self-perceived incompetence leads to aggression, and (b) this aggressive response is driven by feelings of ego defensiveness. Implications for research on power, competence, and aggression are discussed.