Does phase of the moon influence our sleep? Three contradictory studies.

This is an update on a previous MindBlog posting. Vyazovskiy and Foster review three recent studies that give contradictory results on how or whether the phase of the moon influences our sleep. They note that the three studies compared data obtained from different subjects at different lunar phases and were biased and imbalanced in terms of age, gender, and many other factors. They suggest that in future research it should be mandatory to design within-subject experiments, rather than perform further retrospective studies. Here is their statement of the situation:

Whether the moon affects our sleep has intrigued our species since ancient times, but in the last decades only relatively few attempts have been made to address this issue with scientific rigor, and solid conclusions have been elusive [1]. A new cycle of research on the lunar effects on sleep was triggered by a retrospective study which carefully re-analyzed the sleep data collected under laboratory conditions in 33 subjects (age range 20–74 years) and showed clear cut effects of the lunar phase on several subjective and objective sleep parameters [2]. Specifically, EEG slow-wave activity (SWA), total sleep time and subjective sleep quality were reduced around the time of the full moon, while sleep latency and latency to REM sleep were prolonged. This study corroborated an earlier report [5], which found a significant decrease in the amount of subjective sleep around the full moon in 31 subjects (mean age of 50 years). This report triggered two further studies, published in the current issue, which either contradict or report novel effects of lunar phase 3 and 4.

One of these studies, a re-analysis of existing large data sets, could not confirm any of the findings made by Cajochen et al. [3]. By contrast, a second retrospective study [4], in which 47 young volunteers were analyzed, confirmed a decreased total sleep time around the full moon, but REM sleep latency was longer around the new moon. This contradicts the Cajochen et al. study as they found that the latency to REM was longest around the full moon [2].

References: 1. R.G. Foster, T. Roenneberg. Human responses to the geophysical daily, annual and lunar cycles. Curr. Biol., 18 (2008), pp. R784–R794 2. C. Cajochen, S. Altanay-Ekici, M. Munch, S. Frey, V. Knoblauch, A. Wirz-Justice. Evidence that the lunar cycle influences human sleep. Curr. Biol., 23 (2013), pp. 1485–1488 3. M. Cordi, S. Ackermann, F.W. Bes, F. Hartmann, B.N. Konrad, L. Genzel, M. Pawlowski, A. Steiger, H. Schulz, B. Rasch, M. Dresler. Lunar cycle effects on sleep and the file drawer problem. Curr. Biol., 24 (2014), pp. R549–R550 4. M. Smith, I. Croy, K.P. Waye. Human sleep and cortical reactivity are influenced by lunar phase. Curr. Biol., 24 (2014), pp. R551–R552 5. M. Roosli, P. Juni, C. Braun-Fahrlander, M.W. Brinkhof, N. Low, M. Egger. Sleepless night, the moon is bright: longitudinal study of lunar phase and sleep J. Sleep Res., 15 (2006), pp. 149–153

The untutored mind does not like to be alone with itself.

Our mammalian brains evolved to physically engage the world in the interest of our survival and passing on genes. Humans are distinctive among animals in being able to disengage, and some meditation techniques train just such disengagement. A recent collaboration including Daniel Gilbert (see "A wandering mind is an unhappy mind.") makes the interesting observation that not only is disengagement difficult for most people, some, if asked to just sit in a room and do nothing (with a nine volt battery the only entertainment provided), prefer to electrically shock themselves rather than be deprived of external sensory stimuli!

In 11 studies, we found that participants typically did not enjoy spending 6 to 15 minutes in a room by themselves with nothing to do but think, that they enjoyed doing mundane external activities much more, and that many preferred to administer electric shocks to themselves instead of being left alone with their thoughts. Most people seem to prefer to be doing something rather than nothing, even if that something is negative.

Caring for the future

In a fascinating behavioral economics experiment Hauser et al examine willingness of people in a group to sacrifice personal gains for future generations, and show that whether majorities that will sacrifice for the future are adequate for the task depends on whether choices are made individually or by group decision. Nature magazine does a nice presentation of this work with an instructive video and a news and views commentary. Here is the abstract of the article:

Overexploitation of renewable resources today has a high cost on the welfare of future generations. Unlike in other public goods games however, future generations cannot reciprocate actions made today. What mechanisms can maintain cooperation with the future? To answer this question, we devise a new experimental paradigm, the ‘Intergenerational Goods Game’. A line-up of successive groups (generations) can each either extract a resource to exhaustion or leave something for the next group. Exhausting the resource maximizes the payoff for the present generation, but leaves all future generations empty-handed. Here we show that the resource is almost always destroyed if extraction decisions are made individually. This failure to cooperate with the future is driven primarily by a minority of individuals who extract far more than what is sustainable. In contrast, when extractions are democratically decided by vote, the resource is consistently sustained. Voting is effective for two reasons. First, it allows a majority of cooperators to restrain defectors. Second, it reassures conditional cooperators that their efforts are not futile. Voting, however, only promotes sustainability if it is binding for all involved. Our results have implications for policy interventions designed to sustain intergenerational public goods.

And, by the way, here is a nice piece on "Caring for the present", how peer presence and pressure can help preserve electric grids.

Information integration without awareness.

I want to point to an excellent review by Christof Koch and colleagues. It contains some useful summary graphics.

•Empirical data suggest that consciousness is not necessary for integration.

•Unconscious integration is nevertheless limited.

•Consciousness enables integrations over extended spatiotemporal windows.

•Consciousness may be needed for novel and high-level semantic integrations.

Information integration and consciousness are closely related, if not interdependent. But, what exactly is the nature of their relation? Which forms of integration require consciousness? Here, we examine the recent experimental literature with respect to perceptual and cognitive integration of spatiotemporal, multisensory, semantic, and novel information. We suggest that, whereas some integrative processes can occur without awareness, their scope is limited to smaller integration windows, to simpler associations, or to ones that were previously acquired consciously. This challenges previous claims that consciousness of some content is necessary for its integration; yet it also suggests that consciousness holds an enabling role in establishing integrative mechanisms that can later operate unconsciously, and in allowing wider-range integration, over bigger semantic, spatiotemporal, and sensory integration windows.

Couch potato? You should be taking omega-3!

I pass on the abstract from Leckie et al. (DHA refers to docosahexaenoic acid, an omega-3 polyunsaturated fatty acid that is highly concentrated in the brain, and has been associated with better performance on measures of executive function.) I guess the idea is that if you don't want to exercise, you should at least take an omega-3 supplement!

Greater amounts of physical activity (PA) and omega-3 fatty acids have both been independently associated with better cognitive performance. Because of the overlapping biological effects of omega-3 fatty acids and PA, fatty acid intake may modify the effects of PA on neurocognitive function. The present study tested this hypothesis by examining whether the ratio of serum omega-6 to omega-3 fatty acid levels would moderate the association between PA and executive and memory functions in 344 participants (Mean age=44.42 years, SD=6.72). The Paffenbarger Physical Activity Questionnaire (PPAQ), serum fatty acid levels, and performance on a standard neuropsychological battery were acquired on all subjects. A principal component analysis reduced the number of cognitive outcomes to three factors: n-back working memory, Trail Making test, and Logical Memory. We found a significant interaction between PA and the ratio of omega-6 to omega-3 fatty acid serum levels on Trail Making performance and n-back performance, such that higher amounts of omega-3 levels offset the deleterious effects of lower amounts of PA. These effects remained significant in a subsample (n=299) controlling for overall dietary fat consumption. There were no significant additive or multiplicative benefits of higher amounts of both omega-3 and PA on cognitive performance. Our results demonstrate that a diet high in omega-3 fatty acids might mitigate the effect of lower levels of PA on cognitive performance. This study illuminates the importance of understanding dietary and PA factors in tandem when exploring their effects on neurocognitive health.

Moral judgements depend on what language we’re speaking.

Costa et al. use the famous trolley problem to offer another example of the incredible power of the tribal or "us versus them" nature of our psychology. Studies have shown that this mentality (fundamental, for example, to the current chaos in the Middle East) emerges spontaneously in previously homogenous groups of young children as well as adults. In the trolley problem, the following scenario is presented to subjects: An approaching trolley is about to kill five people farther down the tracks. The only way to stop it is to push a large man off the footbridge and onto the tracks below. This will save the five people but kill the man. (It will not help if you jump; you are not large enough.) Do you push him? Costa et al. find that when people are presented with the trolley problem in a foreign language, they are more willing to sacrifice one person to save five than when they are presented with the dilemma in their native tongue. Their abstract:

Should you sacrifice one man to save five? Whatever your answer, it should not depend on whether you were asked the question in your native language or a foreign tongue so long as you understood the problem. And yet here we report evidence that people using a foreign language make substantially more utilitarian decisions when faced with such moral dilemmas. We argue that this stems from the reduced emotional response elicited by the foreign language, consequently reducing the impact of intuitive emotional concerns. In general, we suggest that the increased psychological distance of using a foreign language induces utilitarianism. This shows that moral judgments can be heavily affected by an orthogonal property to moral principles, and importantly, one that is relevant to hundreds of millions of individuals on a daily basis.

Consciousness is constructed through a discrete set of activity spaces.

This fascinating work by Hudson et al. shows that as the brain recovers consciousness from a perturbation such as anesthesia, it does not follows a steady and monotonic path towards consciousness, but rather passes through several discrete activity states. They performed a principal component analysis on local field potentials recorded with electrodes inserted into rat anterior cingulate and retrosplenial cortices and the intralaminar thalamus:

It is not clear how, after a large perturbation, the brain explores the vast space of potential neuronal activity states to recover those compatible with consciousness. Here, we analyze recovery from pharmacologically induced coma to show that neuronal activity en route to consciousness is confined to a low-dimensional subspace. In this subspace, neuronal activity forms discrete metastable states persistent on the scale of minutes. The network of transitions that links these metastable states is structured such that some states form hubs that connect groups of otherwise disconnected states. Although many paths through the network are possible, to ultimately enter the activity state compatible with consciousness, the brain must first pass through these hubs in an orderly fashion. This organization of metastable states, along with dramatic dimensionality reduction, significantly simplifies the task of sampling the parameter space to recover the state consistent with wakefulness on a physiologically relevant timescale.

Parenting rewires men's brains.

From Abraham et al., interesting material on a global "parental caregiving" neural network in our brains:

Although contemporary socio-cultural changes dramatically increased fathers' involvement in childrearing, little is known about the brain basis of human fatherhood, its comparability with the maternal brain, and its sensitivity to caregiving experiences. We measured parental brain response to infant stimuli using functional MRI, oxytocin, and parenting behavior in three groups of parents (n = 89) raising their firstborn infant: heterosexual primary-caregiving mothers (PC-Mothers), heterosexual secondary-caregiving fathers (SC-Fathers), and primary-caregiving homosexual fathers (PC-Fathers) rearing infants without maternal involvement. Results revealed that parenting implemented a global “parental caregiving” neural network, mainly consistent across parents, which integrated functioning of two systems: the emotional processing network including subcortical and paralimbic structures associated with vigilance, salience, reward, and motivation, and mentalizing network involving frontopolar-medial-prefrontal and temporo-parietal circuits implicated in social understanding and cognitive empathy. These networks work in concert to imbue infant care with emotional salience, attune with the infant state, and plan adequate parenting. PC-Mothers showed greater activation in emotion processing structures, correlated with oxytocin and parent-infant synchrony, whereas SC-Fathers displayed greater activation in cortical circuits, associated with oxytocin and parenting. PC-Fathers exhibited high amygdala activation similar to PC-Mothers, alongside high activation of superior temporal sulcus (STS) comparable to SC-Fathers, and functional connectivity between amygdala and STS. Among all fathers, time spent in direct childcare was linked with the degree of amygdala-STS connectivity. Findings underscore the common neural basis of maternal and paternal care, chart brain–hormone–behavior pathways that support parenthood, and specify mechanisms of brain malleability with caregiving experiences in human fathers.

Emotional contagion through social networks

I have frequently noticed that simply reading the barrage of negative news in the daily New York Times about the myriad things in our world that aren't working can unconsciously tilt me into a more negative or depressed mood that requires active countermeasures. Kramer et al. now use the newsfeed of a social network to demonstrate and quantify such a phenomenon. (The collaboration of Facebook with researchers that used a random selection of 500,000 Facebook users as lab rats has drawn a storm of comment.. I'm posting this earlier than I planned, because now I'm watching the NBC evening news do a segment on the issue. And, here is Jaron Lanier weighing in on the debate.) The article's abstract:

Emotional states can be transferred to others via emotional contagion, leading people to experience the same emotions without their awareness. Emotional contagion is well established in laboratory experiments, with people transferring positive and negative emotions to others. Data from a large real-world social network, collected over a 20-y period suggests that longer-lasting moods (e.g., depression, happiness) can be transferred through networks [Fowler JH, Christakis NA (2008) BMJ 337:a2338], although the results are controversial. In an experiment with people who use Facebook, we test whether emotional contagion occurs outside of in-person interaction between individuals by reducing the amount of emotional content in the News Feed. When positive expressions were reduced, people produced fewer positive posts and more negative posts; when negative expressions were reduced, the opposite pattern occurred. These results indicate that emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks. This work also suggests that, in contrast to prevailing assumptions, in-person interaction and nonverbal cues are not strictly necessary for emotional contagion, and that the observation of others’ positive experiences constitutes a positive experience for people.

Mind reading has to be taught.

A review by Heyes and Frith notes how our learning to read minds is like learning to read print, except that it occurs much earlier in our development. It is a slow effortful process in which a novice adds to innate neurocognitive mechanisms by developing culture-specific skill through expert tuition .

It is not just a manner of speaking: “Mind reading,” or working out what others are thinking and feeling, is markedly similar to print reading. Both of these distinctly human skills recover meaning from signs, depend on dedicated cortical areas, are subject to genetically heritable disorders, show cultural variation around a universal core, and regulate how people behave. But when it comes to development, the evidence is conflicting. Some studies show that, like learning to read print, learning to read minds is a long, hard process that depends on tuition. Others indicate that even very young, nonliterate infants are already capable of mind reading. Here, we propose a resolution to this conflict. We suggest that infants are equipped with neurocognitive mechanisms that yield accurate expectations about behavior (“automatic” or “implicit” mind reading), whereas “explicit” mind reading, like literacy, is a culturally inherited skill; it is passed from one generation to the next by verbal instruction.

Stress chemistry predicts age-related cognitive decline.

Anderson et al. show, in studies on rats, that elevated hypothalamo-pituitary-adrenal (HPA) activity impairs not only hippocampal function during aging but may underlie deterioration of other cognitive functions. In aging (but not younger) animals spatial working memory deficits were exacerbated by increased HPA activity. They note changes in nerve synapse structure that correlate with these deficits. The abstract offers details:

Cognitive decline in aging is marked by considerable variability, with some individuals experiencing significant impairments and others retaining intact functioning. Whereas previous studies have linked elevated hypothalamo-pituitary-adrenal (HPA) axis activity with impaired hippocampal function during aging, the idea has languished regarding whether such differences may underlie the deterioration of other cognitive functions. Here we investigate whether endogenous differences in HPA activity are predictive of age-related impairments in prefrontal structural and behavioral plasticity. Young and aged rats (4 and 21 months, respectively) were partitioned into low or high HPA activity, based upon averaged values of corticosterone release from each animal obtained from repeated sampling across a 24 h period. Pyramidal neurons in the prelimbic area of medial prefrontal cortex were selected for intracellular dye filling, followed by 3D imaging and analysis of dendritic spine morphometry. Aged animals displayed dendritic spine loss and altered geometric characteristics; however, these decrements were largely accounted for by the subgroup bearing elevated corticosterone. Moreover, high adrenocortical activity in aging was associated with downward shifts in frequency distributions for spine head diameter and length, whereas aged animals with low corticosterone showed an upward shift in these indices. Follow-up behavioral experiments revealed that age-related spatial working memory deficits were exacerbated by increased HPA activity. By contrast, variations in HPA activity in young animals failed to impact structural or behavioral plasticity. These data implicate the cumulative exposure to glucocorticoids as a central underlying process in age-related prefrontal impairment and define synaptic features accounting for different trajectories in age-related cognitive function.

Megascience efforts and the brain.

Grillner offers a commentary on the current megascience efforts (costing gazillions of dollars) to develop infrastructure for tools, modeling, or neuroinformatics. It seems a bit surprising that they are not instead focused directly on gaining fundamental new insights into brain function. We're putting the cart before the horse...the macro-efforts are not going to get us there if we haven't painstakingly worked out the steps of what goes on between ion channels, nerve cells, simple systems of nerve cells, and increasingly higher levels of integration.  He makes his simple point in a summary graphic which I pass on:

The Interface between the Cellular Level and Global Brain Function Is the Major Challenge for Current Neuroscience.

The two extreme levels of neuroscience that have evolved rapidly, cellular (left) and brain imaging (right). The challenge is to bridge these levels in order to be able to explain behavior in terms of cells and synapses. It emphasizes the fact that in order to have a solid underpinning of the circuits underlying a specific function, one needs to be able to bridge from gene through the different steps indicated below in the figure to, for instance, a cognitive or behavioral function.

Executive control training reduces rumination.

Rumination (thinking repetitively and passively about negative emotions, focusing on symptoms of distress) is a maladaptive form of self-focus that is a core factor in depression and other disorders of emotion dysregulation. Cohen et al. show that training individuals to exert executive control when processing negative stimuli (to attenuate the effects of emotional content) can alleviate subsequent ruminative thinking and rumination-related sad mood. The training used an arrow version of the flanker task:

In this task, participants indicate the direction of a middle arrow while ignoring two distracting arrows on either side. The distractors are either congruent or incongruent with the direction of the target arrow. Responding to incongruent trials is slower than responding to congruent trials because they present a cognitive conflict and executive control is recruited to resolve this conflict. In each trial, the flanker stimulus is followed by a negative or a neutral picture. The effect of the flanker stimulus type (congruent vs. incongruent) on emotional interference is assessed using a simple discrimination task in which participants are required to indicate whether a square is blue or green. The discrimination task is performed immediately after the presentation of the picture. Our prior work has shown that prolonged RT on the discrimination task following negative compared with neutral pictures was found following congruent but not incongruent stimuli...Participants were assigned either to an experimental group, in which 90% of the negative pictures were preceded by incongruent stimuli, or to a control group, in which only 10% of the negative pictures were preceded by incongruent stimuli. For both groups, the emotional flanker task contained 50% congruent and 50% incongruent stimuli, which were followed by 50% negative and 50% neutral pictures. Thus, the only difference between the groups was the pairing of congruent and incongruent flanker stimuli with negative or neutral pictures. We predicted that compared with participants in the control group, participants in the experimental group (i.e., where 90% of the negative pictures were preceded by incongruent stimuli) would show reduced ruminative thinking and rumination-related negative mood following the training.

Their data show that processing incongruent flanker stimuli prior to the presentation of emotional stimuli (i.e., exercising executive control) can promote inhibition of irrelevant emotional information and reduce its interference. Here is the abstract:

Rumination, a maladaptive self-reflection, is a risk factor for depression, thought to be maintained by executive control deficits that impair ruminators’ ability to ignore emotional information. The current research examined whether training individuals to exert executive control when exposed to negative stimuli can ease rumination. A total of 85 participants were randomly assigned to one of two training conditions. In the experimental condition activation of executive control was followed predominantly by the presentation of negative pictures, whereas in the control condition it was followed predominantly by neutral pictures. As predicted, participants in the experimental group showed reduced state rumination compared with those in the control group. Furthermore, trait rumination, and particularly its maladaptive subtype brooding, was associated with increased sadness only among participants in the control group, and not in the experimental group. We argue that training individuals to exert executive control when processing negative stimuli can alleviate ruminative thinking and rumination-related sad mood.

Distinguishing the 50 united states with a tightness-looseness measure.

Harrington and Gelfand offer a parsimonious mechanism for the striking cultural and political differences between the 50 United States by suggesting that the states differ in tightness (many strongly enforced rules and little tolerance for deviance) versus looseness (few strongly enforced rules and greater tolerance for deviance), with this being a logical outcome of their different circumstances (ecological threats, human threats, etc.). They find that tightness–looseness and collectivism–individualism are distinct constructs. Data from their index and state-level indices of collectivism–individualism demonstrate that there are tight states that are collectivistic (e.g., Alabama, Mississippi, Texas, South Carolina), loose states that are collectivistic (e.g., Hawaii, New Jersey, Maryland, California), loose states that are individualistic (e.g., Oregon, Washington, New Hampshire, Vermont), and tight states that are individualistic (e.g., Wyoming, Kansas, Oklahoma, Ohio). In this tightness-looseness figure, the states are organized into quintiles, with the top ten loosest being the lightest color. The map (click to enlarge) was constructed at www.diymaps.net.

Here is their abstract:

This research demonstrates wide variation in tightness–looseness (the strength of punishment and degree of latitude/permissiveness) at the state level in the United States, as well as its association with a variety of ecological and historical factors, psychological characteristics, and state-level outcomes. Consistent with theory and past research, ecological and man-made threats—such as a higher incidence of natural disasters, greater disease prevalence, fewer natural resources, and greater degree of external threat—predicted increased tightness at the state level. Tightness is also associated with higher trait conscientiousness and lower trait openness, as well as a wide array of outcomes at the state level. Compared with loose states, tight states have higher levels of social stability, including lowered drug and alcohol use, lower rates of homelessness, and lower social disorganization. However, tight states also have higher incarceration rates, greater discrimination and inequality, lower creativity, and lower happiness relative to loose states. In all, tightness–looseness provides a parsimonious explanation of the wide variation we see across the 50 states of the United States of America.

Early music training enhances cognitive capacities in adults.

Further experiments on the profound effect that early musical training has on executive functioning in adults. The article has a useful introduction that references previous related work. (As a lifelong performing pianist, I enjoy articles like this!)

Executive functions (EF) are cognitive capacities that allow for planned, controlled behavior and strongly correlate with academic abilities. Several extracurricular activities have been shown to improve EF, however, the relationship between musical training and EF remains unclear due to methodological limitations in previous studies. To explore this further, two experiments were performed; one with 30 adults with and without musical training and one with 27 musically trained and untrained children (matched for general cognitive abilities and socioeconomic variables) with a standardized EF battery. Furthermore, the neural correlates of EF skills in musically trained and untrained children were investigated using fMRI. Adult musicians compared to non-musicians showed enhanced performance on measures of cognitive flexibility, working memory, and verbal fluency. Musically trained children showed enhanced performance on measures of verbal fluency and processing speed, and significantly greater activation in pre-SMA/SMA and right VLPFC during rule representation and task-switching compared to musically untrained children. Overall, musicians show enhanced performance on several constructs of EF, and musically trained children further show heightened brain activation in traditional EF regions during task-switching. These results support the working hypothesis that musical training may promote the development and maintenance of certain EF skills, which could mediate the previously reported links between musical training and enhanced cognitive skills and academic achievement.

Functional MRI imaging during mental task switching: Panels A and B shows brain activation in musically trained and untrained children, respectively. Panel C shows brain areas that are more active in musically trained than musically untrained children

Monday music - Debussy Nocturne

I pass on this Debussy Nocturne I recorded at my Twin Valley Middleton home last week, after playing it for a local music group on Tuesday evening.

On the precipice - a "Majority-Minority" America.

Sigh.... another chilling vision of America's future from Craig and Richeson. Increasing polarization of groups:

The U.S. Census Bureau projects that racial minority groups will make up a majority of the U.S. national population in 2042, effectively creating a so-called majority-minority nation. In four experiments, we explored how salience of such racial demographic shifts affects White Americans’ political-party leanings and expressed political ideology. Study 1 revealed that making California’s majority-minority shift salient led politically unaffiliated White Americans to lean more toward the Republican Party and express greater political conservatism. Studies 2, 3a, and 3b revealed that making the changing national racial demographics salient led White Americans (regardless of political affiliation) to endorse conservative policy positions more strongly. Moreover, the results implicate group-status threat as the mechanism underlying these effects. Taken together, this work suggests that the increasing diversity of the nation may engender a widening partisan divide.

Dopamine receptor genes and independent versus interdependent social orientation.

Kitayama et al. make yet another stab at finding correlates of the often cited distinction of European American (more independent) and Asians (more interdependent). Their suggested genetic correlate can be compared with the environmental correlate I just noted in a recent post. Here, with the usual 'correlations are not causes' disclaimer, is their abstract:

Prior research suggests that cultural groups vary on an overarching dimension of independent versus interdependent social orientation, with European Americans being more independent, or less interdependent, than Asians. Drawing on recent evidence suggesting that the dopamine D4 receptor gene (DRD4) plays a role in modulating cultural learning, we predicted that carriers of DRD4 polymorphisms linked to increased dopamine signaling (7- or 2-repeat alleles) would show higher levels of culturally dominant social orientations, compared with noncarriers. European Americans and Asian-born Asians (total N = 398) reported their social orientation on multiple scales. They were also genotyped for DRD4. As in earlier work, European Americans were more independent, and Asian-born Asians more interdependent. This cultural difference was significantly more pronounced for carriers of the 7- or 2-repeat alleles than for noncarriers. Indeed, no cultural difference was apparent among the noncarriers. Implications for potential coevolution of genes and culture are discussed.

Given that the independent/interdependent ratio is a consequence of gene-cultural environment interaction, it is possible that some cultural effects might be moderated by specific dopamine receptor genetic variants. (Other work has suggested different alleles of the serotonin transporter gene correlate with susceptibility to stress and depression, and that serotonin 1A receptor gene polymorphism correlates with cultural difference in holistic attention.)

Speed reading apps blow away comprehension.

Schotter et al. make a demonstration that being able to glance back during reading (not allowed under speed reading conditions) significantly enhances comprehension...readers' control over their eye movements is important.

Recent Web apps have spurred excitement around the prospect of achieving speed reading by eliminating eye movements (i.e., with rapid serial visual presentation, or RSVP, in which words are presented briefly one at a time and sequentially). Our experiment using a novel trailing-mask paradigm contradicts these claims. Subjects read normally or while the display of text was manipulated such that each word was masked once the reader’s eyes moved past it. This manipulation created a scenario similar to RSVP: The reader could read each word only once; regressions (i.e., rereadings of words), which are a natural part of the reading process, were functionally eliminated. Crucially, the inability to regress affected comprehension negatively. Furthermore, this effect was not confined to ambiguous sentences. These data suggest that regressions contribute to the ability to understand what one has read and call into question the viability of speed-reading apps that eliminate eye movements (e.g., those that use RSVP).

Watching the physical correlate of memory improvement during sleep.

Euston and Steenland do a perspective on nice work by Yang et al. that probes the role of sleep in altering mouse brain structures. I pass on their summary figure (click to enlarge) and some context comments.:

Figure Legend. Three phenomena that occur during sleep have been linked to memory enhancement—slow-wave oscillations in brain electrical activity, reactivation of recent experiences, and changes in synaptic connectivity but the strength of the evidence (indicated by arrow thickness) varies. As shown in red, Yang et al. link both reactivation and slow-wave sleep to changes in synaptic connectivity that enhance learning.

To address whether synaptic strength increases or decreases during sleep, Yang et al. used a powerful technique to visualize dendritic spines in the motor cortex of live mice. The mice were genetically engineered to express a fluorescent protein in a subset of cortical cells. A small window was created in the skull, allowing microscopic imaging of dendritic spines repeatedly over the course of hours or even days. This technique was previously used to show that training mice to stay atop a rotating rod—an acquired skill—induced the formation of new dendritic spines in the motor cortex. Further, the rate of new spine formation was correlated with the degree of task improvement. These findings provided direct evidence that synaptic change in the mammalian cortex underlies learning. Yang et al. extend these findings, showing that learning-induced spine changes are segregated on specific dendritic branches. After learning, when two branches on the same dendritic arbor were examined, one typically showed many more new spines than the other. If mice were subsequently trained on a different skill (i.e., running backward on the spinning rod), the new spines induced by the second task grew selectively on the previously underproductive branch. Hence, different skills seem to be localized on different dendritic branches.

To test the role of sleep in spine formation, Yang et al. repeated their experiment with and without an 8-hour period of sleep deprivation immediately after training. Sleep deprivation markedly decreased the number of new spines. This effect also was branch-specific in that sleep deprivation reduced spine formation primarily on the dendritic branch with the higher number of new spines. Importantly, sleep had no effect on the rate of spine elimination. The authors also observed that sleep made newly formed spines much more likely to still be present 1 day later, consistent with the idea that consolidated memories are less sensitive to decay. In other words, sleep gives spines staying power.