Ketogenic diet enhances brain network stability, a biomarker of aging

Mujica-Parodi et al. make observations suggesting that diets that changes the predominant dietary fuel from glucose (from carbohydrates) to ketones (from fats) increase available energy and enhance functional communication between brain regions, thus showing potential in protecting the aging brain. 

Significance

To better understand how diet influences brain aging, we focus here on the presymptomatic period during which prevention may be most effective. Large-scale life span neuroimaging datasets show functional communication between brain regions destabilizes with age, typically starting in the late 40s, and that destabilization correlates with poorer cognition and accelerates with insulin resistance. Targeted experiments show that this biomarker for brain aging is reliably modulated with consumption of different fuel sources: Glucose decreases, and ketones increase the stability of brain networks. This effect replicated across both changes to total diet as well as fuel-specific calorie-matched bolus, producing changes in overall brain activity that suggest that network “switching” may reflect the brain’s adaptive response to conserve energy under resource constraint.

Abstract

Epidemiological studies suggest that insulin resistance accelerates progression of age-based cognitive impairment, which neuroimaging has linked to brain glucose hypometabolism. As cellular inputs, ketones increase Gibbs free energy change for ATP by 27% compared to glucose. Here we test whether dietary changes are capable of modulating sustained functional communication between brain regions (network stability) by changing their predominant dietary fuel from glucose to ketones. We first established network stability as a biomarker for brain aging using two large-scale (n = 292, ages 20 to 85 y; n = 636, ages 18 to 88 y) 3 T functional MRI (fMRI) datasets. To determine whether diet can influence brain network stability, we additionally scanned 42 adults, age < 50 y, using ultrahigh-field (7 T) ultrafast (802 ms) fMRI optimized for single-participant-level detection sensitivity. One cohort was scanned under standard diet, overnight fasting, and ketogenic diet conditions. To isolate the impact of fuel type, an independent overnight fasted cohort was scanned before and after administration of a calorie-matched glucose and exogenous ketone ester (d-β-hydroxybutyrate) bolus. Across the life span, brain network destabilization correlated with decreased brain activity and cognitive acuity. Effects emerged at 47 y, with the most rapid degeneration occurring at 60 y. Networks were destabilized by glucose and stabilized by ketones, irrespective of whether ketosis was achieved with a ketogenic diet or exogenous ketone ester. Together, our results suggest that brain network destabilization may reflect early signs of hypometabolism, associated with dementia. Dietary interventions resulting in ketone utilization increase available energy and thus may show potential in protecting the aging brain.

How Social Networks are destroying democracy.

In the December 2019 issue of The Atlantic Haidt and Rose-Stockwell offer a must-read article titled "The Dark Psychology of Social Networks." It begins with a thought experiment asks us to imagine what chaos would result if God became bored and decided to double the gravitational constant. Birds would falls from the sky, buildings would collapse, etc.

Let’s rerun this thought experiment in the social and political world, rather than the physical one. The U.S. Constitution was an exercise in intelligent design. The Founding Fathers knew that most previous democracies had been unstable and short-lived. But they were excellent psychologists, and they strove to create institutions and procedures that would work with human nature to resist the forces that had torn apart so many other attempts at self-governance...James Madison wrote about his fear of the power of “faction,” by which he meant strong partisanship or group interest that “inflamed [men] with mutual animosity” and made them forget about the common good...The Constitution included mechanisms to slow things down, let passions cool, and encourage reflection and deliberation.

Madison’s design has proved durable. But what would happen to American democracy if, one day in the early 21st century, a technology appeared that—over the course of a decade—changed several fundamental parameters of social and political life? What if this technology greatly increased the amount of “mutual animosity” and the speed at which outrage spread? Might we witness the political equivalent of buildings collapsing, birds falling from the sky, and the Earth moving closer to the sun?

What Social Media Changed....The problem may not be connectivity itself but rather the way social media turns so much communication into a public performance...social psychologist Mark Leary coined the term sociometer to describe the inner mental gauge that tells us, moment by moment, how we’re doing in the eyes of others...Social media, with its displays of likes, friends, followers, and retweets, has pulled our sociometers out of our private thoughts and posted them for all to see...Human beings evolved to gossip, preen, manipulate, and ostracize. We are easily lured into this new gladiatorial circus, even when we know that it can make us cruel and shallow...In other words, social media turns many of our most politically engaged citizens into Madison’s nightmare: arsonists who compete to create the most inflammatory posts and images, which they can distribute across the country in an instant while their public sociometer displays how far their creations have traveled...Citizens are now more connected to one another, on platforms that have been designed to make outrage contagious.

Is There Any Way Back?...Social media has changed the lives of millions of Americans with a suddenness and force that few expected...citizens are now more connected to one another, in ways that increase public performance and foster moral grandstanding, on platforms that have been designed to make outrage contagious, all while focusing people’s minds on immediate conflicts and untested ideas, untethered from traditions, knowledge, and values that previously exerted a stabilizing effect. This, we believe, is why many Americans—and citizens of many other countries, too—experience democracy as a place where everything is going haywire...It doesn’t have to be this way...Many researchers, legislators, charitable foundations, and tech-industry insiders are now working together in search of ... improvements. We suggest three types of reform that might help:

(1) Reduce the frequency and intensity of public performance. If social media creates incentives for moral grandstanding rather than authentic communication, then we should look for ways to reduce those incentives. One such approach already being evaluated by some platforms is “demetrication,” the process of obscuring like and share counts so that individual pieces of content can be evaluated on their own merit, and so that social-media users are not subject to continual, public popularity contests.

(2) Reduce the reach of unverified accounts. Bad actors—trolls, foreign agents, and domestic provocateurs—benefit the most from the current system, where anyone can create hundreds of fake accounts and use them to manipulate millions of people. Social media would immediately become far less toxic, and democracies less hackable, if the major platforms required basic identity verification before anyone could open an account—or at least an account type that allowed the owner to reach large audiences. (Posting itself could remain anonymous, and registration would need to be done in a way that protected the information of users who live in countries where the government might punish dissent. For example, verification could be done in collaboration with an independent nonprofit organization.)

(3) Reduce the contagiousness of low-quality information. Social media has become more toxic as friction has been removed. Adding some friction back in has been shown to improve the quality of content. For example, just after a user submits a comment, AI can identify text that’s similar to comments previously flagged as toxic and ask, “Are you sure you want to post this?” This extra step has been shown to help Instagram users rethink hurtful messages. The quality of information that is spread by recommendation algorithms could likewise be improved by giving groups of experts the ability to audit the algorithms for harms and biases.

If we want our democracy to succeed—indeed, if we want the idea of democracy to regain respect in an age when dissatisfaction with democracies is rising—we’ll need to understand the many ways in which today’s social-media platforms create conditions that may be hostile to democracy’s success. And then we’ll have to take decisive action to improve social media.

Closing the gap between mind and brain - The dynamic connectome and psilocybin

Quiroga summaries elegant work by Kringelbach et al.,

...who provide a framework for incorporating into the connectome the dynamic variations caused by neuromodulatory systems...The main tenet of [their work] is that neurotransmitters’ systems can modulate the connectome over time, thus enabling a plethora of behaviors with the same underlying structural connectivity. To this end, a modeling approach is presented, in which the structural connectivity is estimated through diffusion MRI, and is coupled to the neurotransmitter system, estimated from positron electron tomography data. Both systems are portrayed by a set of mutually coupled dynamic equations, which are used to fit the functional connectivity, obtained from functional MRI. This approach was tested by exploring the effects that a psychedelic drug (psilocybin) had on neuronal activity, showing that the dynamically coupled neuronal and neuromodulatory systems give a significantly better fit to the measured data, compared to alternative models in which both systems were uncoupled, or in which the neuromodulatory system, rather than being dynamically updated, was frozen in time.

I pass on the Kringelbach et al. significance statement (not distinguished by its modesty) and abstract. The article is open source,and has excellent graphics and figures.  

Significance

In a technical tour de force, we have created a framework demonstrating the underlying fundamental principles of bidirectional coupling of neuronal and neurotransmitter dynamical systems. Specifically, in the present study, we combined multimodal neuroimaging data to causally explain the functional effects of specific serotoninergic receptor (5-HT2AR) stimulation with psilocybin in healthy humans. Longer term, this could provide a better understanding of why psilocybin is showing considerable promise as a therapeutic intervention for neuropsychiatric disorders including depression, anxiety, and addiction.

Abstract

Remarkable progress has come from whole-brain models linking anatomy and function. Paradoxically, it is not clear how a neuronal dynamical system running in the fixed human anatomical connectome can give rise to the rich changes in the functional repertoire associated with human brain function, which is impossible to explain through long-term plasticity. Neuromodulation evolved to allow for such flexibility by dynamically updating the effectivity of the fixed anatomical connectivity. Here, we introduce a theoretical framework modeling the dynamical mutual coupling between the neuronal and neurotransmitter systems. We demonstrate that this framework is crucial to advance our understanding of whole-brain dynamics by bidirectional coupling of the two systems through combining multimodal neuroimaging data (diffusion magnetic resonance imaging [dMRI], functional magnetic resonance imaging [fMRI], and positron electron tomography [PET]) to explain the functional effects of specific serotoninergic receptor (5-HT2AR) stimulation with psilocybin in healthy humans. This advance provides an understanding of why psilocybin is showing considerable promise as a therapeutic intervention for neuropsychiatric disorders including depression, anxiety, and addiction. Overall, these insights demonstrate that the whole-brain mutual coupling between the neuronal and the neurotransmission systems is essential for understanding the remarkable flexibility of human brain function despite having to rely on fixed anatomical connectivity.

Anti-Intellectualism, Populism, and Motivated Resistance to Expert Consensus

I want to pass on the abstract from Eric Merkley's article in Public Opinion Quarterly. I fervently hope that the anti-intellectuals he describes do not form a majority of those voting in the November election.

Scholars have maintained that public attitudes often diverge from expert consensus due to ideology-driven motivated reasoning. However, this is not a sufficient explanation for less salient and politically charged questions. More attention needs to be given to anti-intellectualism—the generalized mistrust of intellectuals and experts. Using data from the General Social Survey and a survey of 3,600 Americans on Amazon Mechanical Turk, I provide evidence of a strong association between anti-intellectualism and opposition to scientific positions on climate change, nuclear power, GMOs, and water fluoridation, particularly for respondents with higher levels of political interest. Second, a survey experiment shows that anti-intellectualism moderates the acceptance of expert consensus cues such that respondents with high levels of anti-intellectualism actually increase their opposition to these positions in response. Third, evidence shows anti-intellectualism is connected to populism, a worldview that sees political conflict as primarily between ordinary citizens and a privileged societal elite. Exposure to randomly assigned populist rhetoric, even that which does not pertain to experts directly, primes anti-intellectual predispositions among respondents in the processing of expert consensus cues. These findings suggest that rising anti-elite rhetoric may make anti-intellectual sentiment more salient in information processing.

Meet the psychobiome

Elizabeth Pennisi does a piece on the search for new brain drugs in human poop, generated by the ~ 2 kilograms of bacteria, fungi, viruses, and archaea that live in our gut.

..with as many as 20 million genes among them, those microbes pack a genomic punch that our measly 20,000 genes can't match. Gut bacteria can make and use nutrients and other molecules in ways the human body can't — a tantalizing source of new therapies.

Holobiome, a small startup company,...plans to capitalize on growing evidence from epidemiological and animal studies that link gut bacteria to conditions as diverse as autism, anxiety, and Alzheimer's disease. Since its founding a mere 5 years ago, Holobiome has created one of the world's largest collections of human gut microbes...A growing number of researchers see a promising alternative in microbe-based treatments, or “psychobiotics,”... the targeted ailments include depression and insomnia, as well as constipation, and visceral pain like that typical of irritable bowel syndrome—conditions that may have neurological as well as intestinal components.

One interesting approach involves finding bacteria that secrete the inhibitory neurotransmitter GABA.

One growth factor Strandwitz identified turned out to be the key to launching his entrepreneurial dreams. He and colleagues isolated a bacterium that couldn't survive on typical culture media and required an amino acid called gamma-aminobutyric acid (GABA) to thrive. GABA is a neurotransmitter that inhibits neural activity in the brain, and its misregulation has been linked to depression and other mental health problems.

The researchers reasoned that if this gut microbe had to have GABA, some other microbe must be making it. Such GABA producers might be a psychobiotic gold mine. Strandwitz and colleagues began to add gut microbes one at a time to petri dishes containing the GABA eater. If the GABA eater thrived, the scientists would know they'd found a GABA producer. They discovered such producers among three groups of bacteria, including Bactereroides. They quickly filed a patent for packaging those bacteria—or their products—to treat people with depression or other mental disorders.

Before publishing those findings, the group teamed up with researchers at Weill Cornell Medicine who were doing a brain scan study of 23 people diagnosed with depression. They found that people with fewer Bacteroides bacteria had a stronger pattern of hyperactivity in the prefrontal cortex, which some researchers have associated with severe depression. The collaboration reported its findings on 10 December 2018 in Nature Microbiology, along with the discovery of GABA-producing bacteria.

GABA is too big to reach the brain by slipping across the blood-brain barrier, a cellular defense wall that limits the size and types of molecules that can get into the brain from blood vessels. Instead, the molecule may act through the vagus nerve or the enteroendocrine cells. Some researchers might question why bacteria would be any more beneficial than GABA-boosting drugs. But Strandwitz says the bacteria may do more than simply boost GABA. He notes that they produce molecules that may have other effects on the brain and body, thereby addressing other symptoms of depression.

Arthur Brooks on "The Hero's Journey" and retirement

In the most recent installment of Arthur Brooks’ biweekly column in The Atlantic, which I suggest that you read, he talks about the classical hero's journey in literature, described by Carl Jung and Joseph Campbell as a lens through which many people see their lives:

It’s a nice narrative, especially if you’ve worked hard and done pretty well in life. The problem is the real-life ending, after the triumphant return...The hero’s journey is great when you’re in the middle of it. The trouble comes when your strengths start to wane, because now you’re off script...Joseph Campbell...notes that...“The first problem of the returning hero is to accept as real, after an experience of the soul-satisfying vision of fulfillment, the passing joys and sorrows, banalities and noisy obscenities of life.” In other words, the end of the true hero’s journey is coming home and finding a battle to be waged not with an external enemy, but with one’s own demons...your skills will decline, and life’s problems will intrude. If you try to hang on to glory, or lash out when it fades, it will squander your victories and mark an unhappy end to your journey.

Plan to spend the last part of your life serving others, loving your family and friends, and being a good example to those still in the first three stages of their own hero’s journey. Happiness in retirement depends on your choice of narrative.

Young blood plasma reverses the epigenetic aging clock.

Perhaps the best molecular biomarker of aging at present is the epigenetic clock, developed by Horvath and others, based on measurements of DNA methylation. Josh Mitteldorf points to experiments by Horvath et al. recently posted in a preprint (not yet reviewed) in bioRxiv. noting how methylation patterns characteristic of aging can be reversed.

...plasma treatment of the old rats [109 weeks] reduced the epigenetic ages of blood, liver and heart by a very large and significant margin, to levels that are comparable with the young rats [30 weeks]….According to the final version of the epigenetic clocks, the average rejuvenation across four tissues was 54.2%. In other words, the treatment more than halved the epigenetic age.

Their abstract:

Young blood plasma is known to confer beneficial effects on various organs in mice. However, it was not known whether young plasma rejuvenates cells and tissues at the epigenetic level; whether it alters the epigenetic clock, which is a highly-accurate molecular biomarker of aging. To address this question, we developed and validated six different epigenetic clocks for rat tissues that are based on DNA methylation values derived from n=593 tissue samples. As indicated by their respective names, the rat pan-tissue clock can be applied to DNA methylation profiles from all rat tissues, while the rat brain-, liver-, and blood clocks apply to the corresponding tissue types. We also developed two epigenetic clocks that apply to both human and rat tissues by adding n=850 human tissue samples to the training data. We employed these six clocks to investigate the rejuvenation effects of a plasma fraction treatment in different rat tissues. The treatment more than halved the epigenetic ages of blood, heart, and liver tissue. A less pronounced, but statistically significant, rejuvenation effect could be observed in the hypothalamus. The treatment was accompanied by progressive improvement in the function of these organs as ascertained through numerous biochemical/physiological biomarkers and behavioral responses to assess cognitive functions. Cellular senescence, which is not associated with epigenetic aging, was also considerably reduced in vital organs. Overall, this study demonstrates that a plasma-derived treatment markedly reverses aging according to epigenetic clocks and benchmark biomarkers of aging.

Take the shutdown skeptics seriously.

I have been holding back from doing posts on the current pandemic, since it completely dominates the popular press. However, I want to pass on this link to one sane piece done by Conor Friedersdorf, a staff writer at The Atlantic. I will just paste in one key paragraph here, and urge you to read the whole piece.

If we knew that a broadly effective COVID-19 treatment was imminent, or that a working vaccine was months away, minimizing infections through social distancing until that moment would be the right course. At the other extreme, if we will never have an effective treatment or vaccine and most everyone will get infected eventually, then the costs of social distancing are untenable. We don’t know where we sit on that spectrum. So we cannot know what the best way forward is even if we place the highest possible value on preserving life and protecting the vulnerable.

That uncertainty means, at the very least, that Americans should carefully consider the potential costs of prolonged shutdowns lest they cause more deaths or harm to the vulnerable than they spare.

Self, purpose, and tribal mentality as Darwinian adaptations (or…Why why aren’t we all enlightened?)

This is a post like the one I offered on March 13 that passes on a bit of writing that I think might develop into a longer piece of work. I hope the following ideas and assertions make some sense to readers:

One ultimate cause of human behaviors is the endless cycling of a “Darwin machine,” operating at the level of cells, individuals, and groups of humans. As entities - from the most simple virus particles to complex human cultures - reproduce or renew themselves to persist through time, small errors or variations that end up enhancing reproductive fitness become dominant in the population. The grand master is multilevel selection, and there is a conflict between individual-level selection (individuals competing with other individuals in the same group) and group-level selection (competition between groups). Within groups selfish individuals beat altruistic individuals, but groups of altruists beat groups of selfish individuals. E.O. Wilson risks the oversimplification of suggesting that individual selection promoted sin, while group selection promoted virtue.

The array of social emotions supporting tribal cultures that have occupied most of human history, as well as the more recent emergence of language, thought, and material culture, can be rationalized with this model. Taken together, they have enabled formation of large complex societies bonded together by laws, religions, and assumptions about purpose, meaning, and self that are unique to modern humans.

Nations and religions link language and meaning to more ancient evolved instinctive social emotional behaviors that bond groups of humans and other primates. This link is revealed when logic and language are turned inward (by both ancient meditative traditions as well as modern neuroscience) in a way that reveals that our common experiences of self or purpose are confabulations, or illusions - illusions nevertheless that have been necessary for forming complex human linguistic cultures, illusions which our emotional hormones and nerve circuitry have evolved to support.

Given the clear scientific evidence, why don’t we transcend these evolved linkages between our biology and our illusions? Why have those regarded as spiritually ‘enlightened’ throughout history remained a small minority of the population? Perhaps it is because those who become enlightened or awakened to the illusory nature of the self are granted a perspective on basic emotional drives that can divests them of much of their power. Enlightenment is subtle, not noisy, it doesn't engage the passions as well as blind devotion to nations and gods. This is why secular humanism, with its more muted versions of spirituality (‘I’m spiritual but not religious’) finds it difficult to compete with the ego-rich passions of nationalism and theism.

Because our evolved social brains incline us to cling to a complex array of nations, religions, and tribal identities that parse the world into ‘us’ and ‘them,’ we find it difficult to accept that we are a common humanity that would most effectively face our current pandemic and environmental crises by joining together.

Infant behavioral inhibition predicts personality and social outcomes three decades later

From Tang et al.:

Significance

Children show different temperamental styles early in development. Whether temperament predicts who children become as adults and how early we can predict these outcomes have been long-standing questions of interest to the scientific and public community. The current study used rigorous methods to characterize an inhibited temperament by 14 mo of age in a cohort of infants and followed them for three decades. We provide the strongest and earliest evidence showing that infants with an inhibited temperament at 14 mo became introverted adults, with poorer functioning in some social and mental health domains. Also, brain activity underlying cognitive control in adolescence was associated with adult mental health. These findings highlight the lasting influence of early temperament on social-emotional development.

Abstract

Does infant temperament predict adult personality and life-course patterns? To date, there is scant evidence examining relations between child temperament and adult outcomes, and extant research has relied on limited methods for measuring temperament such as maternal report. This prospective longitudinal study followed a cohort of infants (n = 165) for three decades to examine whether infant behavioral inhibition, a temperament characterized by cautious and fearful behaviors to unfamiliar situations, shapes long-term personality, social relationships, vocational/education, and mental health outcomes in adulthood. At age 14 mo, behavioral inhibition was assessed using an observation paradigm. In adolescence (15 y; n = 115), error monitoring event-related potentials were measured in a flanker task. In adulthood (26 y; n = 109), personality, psychopathology, and sociodemographics were self-reported using questionnaires. We found that infants with higher levels of behavioral inhibition at 14 mo grew up to become more reserved and introverted adults (β = 0.34) with lower social functioning with friends and family (β = −0.23) at age 26. Infant behavioral inhibition was also a specific risk factor for adult internalizing (i.e., anxiety and depression, β = 0.20) psychopathology, rather than a transdiagnostic risk for general and externalizing psychopathology. We identified a neurophysiologic mechanism underlying risk and resilience for later psychopathology. Heightened error monitoring in adolescence moderated higher levels of adult internalizing psychopathology among behaviorally inhibited individuals. These findings suggest meaningful continuity between infant temperament and the development of adult personality. They provide the earliest evidence suggesting that the foundation of long-term well-being is rooted in individual differences in temperament observed in infancy.

Future of the Human climate niche

Sobering analysis from Xu et al. :

Significance

We show that for thousands of years, humans have concentrated in a surprisingly narrow subset of Earth’s available climates, characterized by mean annual temperatures around ∼13 °C. This distribution likely reflects a human temperature niche related to fundamental constraints. We demonstrate that depending on scenarios of population growth and warming, over the coming 50 y, 1 to 3 billion people are projected to be left outside the climate conditions that have served humanity well over the past 6,000 y. Absent climate mitigation or migration, a substantial part of humanity will be exposed to mean annual temperatures warmer than nearly anywhere today.

Abstract

All species have an environmental niche, and despite technological advances, humans are unlikely to be an exception. Here, we demonstrate that for millennia, human populations have resided in the same narrow part of the climatic envelope available on the globe, characterized by a major mode around ∼11 °C to 15 °C mean annual temperature (MAT). Supporting the fundamental nature of this temperature niche, current production of crops and livestock is largely limited to the same conditions, and the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation. We show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 y than it has moved since 6000 BP. Populations will not simply track the shifting climate, as adaptation in situ may address some of the challenges, and many other factors affect decisions to migrate. Nevertheless, in the absence of migration, one third of the global population is projected to experience a MAT >29 °C currently found in only 0.8% of the Earth’s land surface, mostly concentrated in the Sahara. As the potentially most affected regions are among the poorest in the world, where adaptive capacity is low, enhancing human development in those areas should be a priority alongside climate mitigation.

The Diversity–Innovation Paradox in Science

From Hofstra et al:  

Significance

By analyzing data from nearly all US PhD recipients and their dissertations across three decades, this paper finds demographically underrepresented students innovate at higher rates than majority students, but their novel contributions are discounted and less likely to earn them academic positions. The discounting of minorities’ innovations may partly explain their underrepresentation in influential positions of academia.

Abstract

Prior work finds a diversity paradox: Diversity breeds innovation, yet underrepresented groups that diversify organizations have less successful careers within them. Does the diversity paradox hold for scientists as well? We study this by utilizing a near-complete population of ∼1.2 million US doctoral recipients from 1977 to 2015 and following their careers into publishing and faculty positions. We use text analysis and machine learning to answer a series of questions: How do we detect scientific innovations? Are underrepresented groups more likely to generate scientific innovations? And are the innovations of underrepresented groups adopted and rewarded? Our analyses show that underrepresented groups produce higher rates of scientific novelty. However, their novel contributions are devalued and discounted: For example, novel contributions by gender and racial minorities are taken up by other scholars at lower rates than novel contributions by gender and racial majorities, and equally impactful contributions of gender and racial minorities are less likely to result in successful scientific careers than for majority groups. These results suggest there may be unwarranted reproduction of stratification in academic careers that discounts diversity’s role in innovation and partly explains the underrepresentation of some groups in academia.

The cultural origins of metacognition.

I want to pass on this open source article in Trends in Cognitive Science by Heyes et al. Their summary:

Highlights

Human metacognition involves discrimination, interpretation, and broadcasting of subtle cues indicating the rightness of ongoing thought and behaviour.

We propose that human metacognition is made fit for purpose by cultural evolution rather than genetic evolution.

In particular, we present evidence that the effective discrimination, interpretation, and broadcasting of metacognitive cues depends on cultural learning.

The cultural origins hypothesis advances a programme of research on the development of metacognition, cultural variation, individual differences, and cross-species comparisons.

Metacognition – the ability to represent, monitor and control ongoing cognitive processes – helps us perform many tasks, both when acting alone and when working with others. While metacognition is adaptive, and found in other animals, we should not assume that all human forms of metacognition are gene-based adaptations. Instead, some forms may have a social origin, including the discrimination, interpretation, and broadcasting of metacognitive representations. There is evidence that each of these abilities depends on cultural learning and therefore that cultural selection might shape human metacognition. The cultural origins hypothesis is a plausible and testable alternative that directs us towards a substantial new programme of research.

Rising workplace inequalities in high-income countries.

From Tomaskovic-Devey et al.:

Significance

Understanding the causes of rising inequality is of concern in many countries. Using administrative data, we find that the share of inequality that is between workplaces is growing in 12 of 14 countries examined, and in no country has it fallen. Countries with declining employment protections see growth in both between- and within-workplace inequalities, but this impact is stronger for between-workplace inequalities. These results suggest that to reduce market income inequality requires policies that raise the bargaining power of lower-skilled workers. The widespread rise in between-workplace inequality additionally suggests policy responses that target the increasing market power of firms in concentrated markets as well as curb the ability of powerful firms to outsource low skill employment.

Abstract

It is well documented that earnings inequalities have risen in many high-income countries. Less clear are the linkages between rising income inequality and workplace dynamics, how within- and between-workplace inequality varies across countries, and to what extent these inequalities are moderated by national labor market institutions. In order to describe changes in the initial between- and within-firm market income distribution we analyze administrative records for 2,000,000,000+ job years nested within 50,000,000+ workplace years for 14 high-income countries in North America, Scandinavia, Continental and Eastern Europe, the Middle East, and East Asia. We find that countries vary a great deal in their levels and trends in earnings inequality but that the between-workplace share of wage inequality is growing in almost all countries examined and is in no country declining. We also find that earnings inequalities and the share of between-workplace inequalities are lower and grew less strongly in countries with stronger institutional employment protections and rose faster when these labor market protections weakened. Our findings suggest that firm-level restructuring and increasing wage inequalities between workplaces are more central contributors to rising income inequality than previously recognized.

How do cognition-enhancing drugs work?

Westbrook et al. do experiments with drugs influencing dopamine levels that suggest that cognition-enhancing drugs may act at the motivational level rather than directly boosting cognition per se.

Stimulants such as methylphenidate are increasingly used for cognitive enhancement but precise mechanisms are unknown. We found that methylphenidate boosts willingness to expend cognitive effort by altering the benefit-to-cost ratio of cognitive work. Willingness to expend effort was greater for participants with higher striatal dopamine synthesis capacity, whereas methylphenidate and sulpiride, a selective D2 receptor antagonist, increased cognitive motivation more for participants with lower synthesis capacity. A sequential sampling model informed by momentary gaze revealed that decisions to expend effort are related to amplification of benefit-versus-cost information attended early in the decision process, whereas the effect of benefits is strengthened with higher synthesis capacity and by methylphenidate. These findings demonstrate that methylphenidate boosts the perceived benefits versus costs of cognitive effort by modulating striatal dopamine signaling.

Why does awe have prosocial effects?

An interesting perspective from Perlin and Li:

Awe is an emotional response to stimuli that are perceived to be vast (e.g., tall trees, sunsets) and that defy accommodation by existing mental structures. Curiously, awe has prosocial effects despite often being elicited by nonsocial stimuli. The prevailing explanation for why awe has prosocial effects is that awe reduces attention to self-oriented concerns (i.e., awe makes the self small), thereby making more attention available for other-oriented concerns. However, several questions remain unaddressed by the current formulation of this small-self hypothesis. How are awe researchers defining the self, and what implications might their theory of selfhood have for understanding the “smallness” of the self? Building on theories regarding psychological selfhood, we propose that awe may interact with the self not just in terms of attentional focus but rather at multiple layers of selfhood. We further reinterpret the small self using the notion of the quiet ego from personality psychology. Linking awe to an enriched model of the self provided by personality psychology may be fruitful for explaining a range of phenomena and motivating future research.

Evidence that aerobic exercise reverses aging.

Brett et al. show (in mice) that aerobic exercise rejuvenates quiescent skeletal muscle stem cells in old mice and accelerates muscle tissue repair:

Ageing impairs tissue repair. This defect is pronounced in skeletal muscle, whose regeneration by muscle stem cells (MuSCs) is robust in young-adult animals, but inefficient in older organisms. Despite this functional decline, old MuSCs are amenable to rejuvenation through strategies that improve the systemic milieu, such as heterochronic parabiosis [i.e. connecting the circulatory systems of young and old mice). One such strategy, exercise, has long been appreciated for its benefits on healthspan, but its effects on aged stem-cell function in the context of tissue regeneration are incompletely understood. Here, we show that exercise in the form of voluntary wheel running accelerates muscle repair in old mice and improves old MuSC function. Through transcriptional profiling and genetic studies, we discovered that the restoration of old MuSC activation ability hinges on restoration of Cyclin D1, whose expression declines with age in MuSCs. Pharmacologic studies revealed that Cyclin D1 maintains MuSC activation capacity by repressing TGF-β signalling. Taken together, these studies demonstrate that voluntary exercise is a practicable intervention for old MuSC rejuvenation. Furthermore, this work highlights the distinct role of Cyclin D1 in stem-cell quiescence.

Non-invasive DIY brain stimulators are a bad idea.

I must admit that I've been sorely tempted to have a try with one of the transcranial magnetic or direct current stimulators, easily ordered from web vendors, whose use is claimed to enhance your smarts or chill you out. A meta-analysis by Smits et al. casts cold water on the prospects of these working as advertised.

Excessive emotional responses to stressful events can detrimentally affect psychological functioning and mental health. Recent studies have provided evidence that non-invasive brain stimulation (NBS) targeting the prefrontal cortex (PFC) can affect the regulation of stress-related emotional responses. However, the reliability and effect sizes have not been systematically analyzed. In the present study, we reviewed and meta-analyzed the effects of repetitive transcranial magnetic (rTMS) and transcranial direct current stimulation (tDCS) over the PFC on acute emotional stress reactivity in healthy individuals. Forty sham-controlled single-session rTMS and tDCS studies were included. Separate random effects models were performed to estimate the mean effect sizes of emotional reactivity. Twelve rTMS studies together showed no evidence that rTMS over the PFC influenced emotional reactivity. Twenty-six anodal tDCS studies yielded a weak beneficial effect on stress-related emotional reactivity (Hedges’ g = −0.16, CI95% = [−0.33, 0.00]). These findings suggest that a single session of NBS is insufficient to induce reliable, clinically significant effects but also provide preliminary evidence that specific NBS methods can affect emotional reactivity. This may motivate further research into augmenting the efficacy of NBS protocols on stress-related processes.

The deep historical roots of global economic inequality

Nathan Nunn does an article which describes how a substantial part of the world’s current income differences can be explained by the divergent effects of European contact globally, beginning in the late 15th century with Christopher Columbus’ arrival to the Americas in 1492, which resulted in a massive transfer of disease, food, ideas, and people between the Old World and the New World. The colonization of people of color by white Europeans and particularly the enslavement of black people starting ~500 year ago has left an enduring legacy that is hard to overcome.

I pass on Figure 1 from the paper and its discussion. It shows the evolution of economic prosperity, measured using the natural logarithm of real per capita gross domestic product, for different regions of the world from 1000 to 2000 CE.

1) The best predictor of a region’s relative income in a period is its income in the years prior. A perfect predictor of the relative ranking of regional prosperity in 2000 is the ranking in 1800. If one considers income further back in time (e.g., 1500), one finds that it is still a very good indicator, although not a perfect one.

2) The sizable differences in relative incomes that we observe today have not always been present. (Today, the richest countries in the world are about 42 times as rich as the poorest.) These differences appear to have first emerged in 1500 and to have increased starting in the 18th century, a process that has been called the “Great Divergence” (2).

3) Although there is a remarkable amount of historical persistence in comparative development, there are some important exceptions. In particular, the region “Western European offshoots,” which comprises land that today is Canada, United States, Australia, and New Zealand, moves from being the poorest region of the world in 1600 (and before) to the richest in 1800 (and after).

Changes in cerebral cortex functional organization in healthy elderly.

Sigh.... Chong et al. offer a picture of how my 78 year old brain is more muddled than that of a ~23 year old male.

SIGNIFICANCE STATEMENT

Cross-sectional studies have demonstrated age-related reductions in the functional segregation and distinctiveness of brain networks. However, longitudinal aging-related changes in brain functional modular architecture and their links to cognitive decline remain relatively understudied. Using graph theoretical and community detection approaches to study task-free functional network changes in a cross-sectional young and longitudinal healthy elderly cohort, we showed that aging was associated with global declines in network segregation, integration, and module distinctiveness, and specific declines in distinctiveness of higher-order cognitive networks. Further, such functional network deterioration was associated with poorer cognitive performance cross-sectionally. Our findings suggest that healthy aging is associated with system-level changes in brain functional modular organization, accompanied by functional segregation loss particularly in higher-order networks specialized for cognition.

Abstract

Healthy aging is accompanied by disruptions in the functional modular organization of the human brain. Cross-sectional studies have shown age-related reductions in the functional segregation and distinctiveness of brain networks. However, less is known about the longitudinal changes in brain functional modular organization and their associations with aging-related cognitive decline. We examined age- and aging-related changes in functional architecture of the cerebral cortex using a dataset comprising a cross-sectional healthy young cohort of 57 individuals (mean ± SD age, 23.71 ± 3.61 years, 22 males) and a longitudinal healthy elderly cohort of 72 individuals (mean ± baseline age, 68.22 ± 5.80 years, 39 males) with 2–3 time points (18–24 months apart) of task-free fMRI data. We found both cross-sectional (elderly vs young) and longitudinal (in elderly) global decreases in network segregation (decreased local efficiency), integration (decreased global efficiency), and module distinctiveness (increased participation coefficient and decreased system segregation). At the modular level, whereas cross-sectional analyses revealed higher participation coefficient across all modules in the elderly compared with young participants, longitudinal analyses revealed focal longitudinal participation coefficient increases in three higher-order cognitive modules: control network, default mode network, and salience/ventral attention network. Cross-sectionally, elderly participants also showed worse attention performance with lower local efficiency and higher mean participation coefficient, and worse global cognitive performance with higher participation coefficient in the dorsal attention/control network. These findings suggest that healthy aging is associated with whole-brain connectome-wide changes in the functional modular organization of the brain, accompanied by loss of functional segregation, particularly in higher-order cognitive networks.