More on stress and the brain.

There seems to be a surge recently in articles on stress in the brain. Here I point you to two pieces: work from McEwen and collaborators showing that acute stress enhances glutamatergic transmission in prefrontal cortex and facilitates working memory, and Admon et al.'s study of new recruits to the Israeli military that shows that an individual's amygdalar reactivity (i.e., predated neural sensitivity) before stress is predictive of later vulnerability to stress and stress symptoms.

Cultural and Biological evolution similar, or not?

Strimling et al. develop a simple model to test the most popular recent evolutionary hypothesis about culture, memetics, which maintains that cultural evolution is the playing field of selfish memes. Simply put, the idea is that the success of cultural traits is determined by their inherent power to spread between human minds. The analysis, based on their model which considers the diffusion and retention of cultural variants (ideas), suggests that the possibility to predict long-term cultural evolution by some success index, analogous to biological fitness, depends on whether individuals have few or many opportunities to learn. Their abstract:

Although genetic information is acquired only once, cultural information can be both abandoned and reacquired during an individual's lifetime. Therefore, cultural evolution will be determined not only by cultural traits' ability to spread but also by how good they are at sticking with an individual; however, the evolutionary consequences of this aspect of culture have not previously been explored. Here we show that repeated learning and multiple characteristics of cultural traits make cultural evolution unique, allowing dynamical phenomena we can recognize as specifically cultural, such as traits that both spread quickly and disappear quickly. Importantly, the analysis of our model also yields a theoretical objection to the popular suggestion that biological and cultural evolution can be understood in similar terms. We find that the possibility to predict long-term cultural evolution by some success index, analogous to biological fitness, depends on whether individuals have few or many opportunities to learn. If learning opportunities are few, we find that the existence of a success index may be logically impossible, rendering notions of “cultural fitness” meaningless. On the other hand, if individuals can learn many times, we find a success index that works, regardless of whether the transmission pattern is vertical, oblique, or horizontal.

Summer evenings

As summer winds down, I've decided to record a few more Grieg lyrical pieces.

Monkeys affiliate with humans who imitate them.

It is generally thought that imitation is one mechanism through which cultural learning occurs. When others mimic us, we like them more, empathize with them more, and are more helpful and generous toward them. Recent work with capuchin monkeys suggests that imitation may of general importance in enhancing prosocial social behaviors, suggesting that the social consequences of mimicry may have deeper evolutionary roots than previously thought. Paukner et al. find that these animals behave in a more affiliative manner, as assessed by direction of gaze, physical proximity, and token exchange, toward humans who imitate them as compared to humans who perform the same movements, but not at the same time.

What distinguishes our minds from those of other creatures?

The September issue of the Scientific American (the 'Origins Issue') has an article by Marc Hauser in which he makes a list of what he considers distinctive human competencies (enter 'Hauser' in the search box in the left column to see my previous posts mentioning Hauser's work). Here is a clip from the article:

Although humans share the vast majority of their genes with chimps, studies suggest that small genetic shifts that occurred in the human lineage since it split from the chimp line produced massive differences in computational power. This rearranging, deleting and copying of universal genetic elements created a brain with four special properties. Together these distinctive characteristics, which I have recently identified based on studies conducted in my lab and elsewhere, constitute what I term our humaniqueness. The first such trait is generative computation, the ability to create a virtually limitless variety of “expressions,” be they arrangements of words, sequences of notes, combinations of actions, or strings of mathematical symbols. Generative computation encompasses two types of operation, recursive and combinatorial. Recursion is the repeated use of a rule to create new expressions. Think of the fact that a short phrase can be embedded within another phrase, repeatedly, to create longer, richer descriptions of our thoughts– for example, the simple but poetic expression from Gertrude Stein: “A rose is a rose is a rose.” The combinatorial operation, meanwhile, is the mixing of discrete elements to engender new ideas, which can be expressed as novel words (“Walkman”) or musical forms, among other possibilities.

The second distinguishing characteristic of the human mind is its capacity for the promiscuous combination of ideas. We routinely connect thoughts from different domains of knowledge, allowing our understanding of art, sex, space, causality and friendship to combine. From this mingling, new laws, social relationships and technologies can result, as when we decide that it is forbidden [moral domain] to push someone [motor action domain] intentionally [folk psychology domain] in front of a train [object domain] to save the lives [moral domain] of five [number domain] others.

Third on my list of defining properties is the use of mental symbols. We can spontaneously convert any sensory experience—real or imagined— into a symbol that we can keep to ourselves or express to others through language, art, music or computer code.

Fourth, only humans engage in abstract thought. Unlike animal thoughts, which are largely anchored in sensory and perceptual experiences, many of ours have no clear connection to such events. We alone ponder the likes of unicorns and aliens, nouns and verbs, infinity and God. Although anthropologists disagree about exactly when the modern human mind took shape, it is clear from the archaeological record that a major transformation occurred during a relatively brief period of evolutionary history, starting approximately 800,000 years ago in the Paleolithic era and crescendoing around 45,000 to 50,000 years ago. It is during this period of the Paleolithic, an evolutionary eyeblink, that we see for the first time multipart tools; animal bones punctured with holes to fashion musical instruments; burials with accoutrements suggesting beliefs about aesthetics and the afterlife; richly symbolic cave paintings that capture in exquisite detail events of the past and the perceived future; and control over fire, a technology that combines our folk physics and psychology and allowed our ancestors to prevail over novel environments by creating warmth and cooking foods to make them edible.

Stressed Memories

Following this week's (accidental) emphasis on stress and its effects, I'll point out an article by Henckens et al. on the enhancement of memory by stress, apparently through hypervigilant sensory processing, even though hippocampal activation is diminished. (Chronic stress is known to damage and shrink the hippocampus):

Stressful, aversive events are extremely well remembered. Such a declarative memory enhancement is evidently beneficial for survival, but the same mechanism may become maladaptive and culminate in mental diseases such as posttraumatic stress disorder (PTSD). Stress hormones are known to enhance postlearning consolidation of aversive memories but are also thought to have immediate effects on attentional, sensory, and mnemonic processes at memory formation. Despite their significance for our understanding of the etiology of stress-related mental disorders, effects of acute stress at memory formation, and their brain correlates at the system scale, remain elusive. Using an integrated experimental approach, we probed the neural correlates of memory formation while participants underwent a controlled stress induction procedure in a crossover design. Physiological (cortisol level, heart rate, and pupil dilation) and subjective measures confirmed acute stress. Remarkably, reduced hippocampal activation during encoding predicted stress-enhanced memory performance, both within and between participants. Stress, moreover, amplified early visual and inferior temporal responses, suggesting that hypervigilant processing goes along with enhanced inferior temporal information reduction to relay a higher proportion of task-relevant information to the hippocampus. Thus, acute stress affects neural correlates of memory formation in an unexpected manner, the understanding of which may elucidate mechanisms underlying psychological trauma etiology.

Stem cells generate an entire functioning eye!

Mair describes work by Viczian et al. who show that frog cells forced to express seven transcription factor genes form functioning eyes in tadpoles. (The transcription factors are proteins that bind to DNA and turn on a panel of genes involved in building the eye).

Some neat visual illusions.

Check out this Illusion Sciences blog from Arthur Shapiro.

Chronic stress dials the brain from adaptive to habitual behaviors.

Sousa's group makes interesting observations on brain changes caused by chronic stress. There is a distinctive shift away from adaptive goal directed decision making towards habitual routines that can persist in spite of being inappropriate. Chronic stress actually causes opposing structural changes in the associative and sensorimotor corticostriatal circuits underlying these different behavioral strategies, with atrophy of medial prefrontal cortex and the associative striatum and hypertrophy of the sensorimotor striatum. The change is reversible: rats given a four week vacation from the bullying and tasers used for the stress-out reverted to normal behaviors. Angier's review points out the obvious relevance of such observation to our human behavior:

If after a few months’ exposure to our David Lynch economy, in which housing markets spontaneously combust, coworkers mysteriously disappear and the stifled moans of dying 401(k) plans can be heard through the floorboards, you have the awful sensation that your body’s stress response has taken on a self-replicating and ultimately self-defeating life of its own, congratulations. You are very perceptive. It has....Robert Sapolsky, a neurobiologist who studies stress at Stanford University School of Medicine, said, “This is a great model for understanding why we end up in a rut, and then dig ourselves deeper and deeper into that rut.”...The truth is, Dr. Sapolsky said, “we’re lousy at recognizing when our normal coping mechanisms aren’t working. Our response is usually to do it five times more, instead of thinking, maybe it’s time to try something new.”

With regard to the reversibility of the behavior:

According to Bruce S. McEwen, head of the neuroendocrinology laboratory at Rockefeller University, the new findings offer a particularly elegant demonstration of a principle that researchers have just begun to grasp. “The brain is a very resilient and plastic organ,” he said. “Dendrites and synapses retract and reform, and reversible remodeling can occur throughout life.”

The stress response is essential for maneuvering through a dynamic world — for dodging a predator or chasing down prey, swinging through the trees or fighting off disease — and it is itself dynamic. As we go about our days, Dr. McEwen said, the biochemical mediators of the stress response rise and fall, flutter and flare. “Cortisol and adrenaline go up and down,” he said. “Our inflammatory cytokines go up and down.”...The target organs of stress hormones likewise dance to the beat: blood pressure climbs and drops, the heart races and slows, the intestines constrict and relax. This system of so-called allostasis, of maintaining control through constant change, stands in contrast to the mechanisms of homeostasis that keep the pH level and oxygen concentration in the blood within a narrow and invariant range.

Unfortunately, the dynamism of our stress response makes it vulnerable to disruption, especially when the system is treated too roughly and not according to instructions. In most animals, a serious threat provokes a serious activation of the stimulatory, sympathetic, “fight or flight” side of the stress response. But when the danger has passed, the calming parasympathetic circuitry tamps everything back down to baseline flickering...In humans, though, the brain can think too much, extracting phantom threats from every staff meeting or high school dance, and over time the constant hyperactivation of the stress response can unbalance the entire feedback loop. Reactions that are desirable in limited, targeted quantities become hazardous in promiscuous excess. You need a spike in blood pressure if you’re going to run, to speedily deliver oxygen to your muscles. But chronically elevated blood pressure is a source of multiple medical miseries.

Why should the stressed brain be prone to habit formation? Perhaps to help shunt as many behaviors as possible over to automatic pilot, the better to focus on the crisis at hand. Yet habits can become ruts, and as the novelist Ellen Glasgow observed, “The only difference between a rut and a grave are the dimensions.”

The smell of stress activates our amygdala.

To continue the topic of an earlier post on the smell of emotion, I would like to point out work from Mujica-Parodi et al. Their abstract:

Alarm substances are airborne chemical signals, released by an individual into the environment, which communicate emotional stress between conspecifics. Here we tested whether humans, like other mammals, are able to detect emotional stress in others by chemosensory cues. Sweat samples collected from individuals undergoing an acute emotional stressor, with exercise as a control, were pooled and presented to a separate group of participants (blind to condition) during four experiments. In an fMRI experiment and its replication, we showed that scanned participants showed amygdala activation in response to samples obtained from donors undergoing an emotional, but not physical, stressor. An odor-discrimination experiment suggested the effect was primarily due to emotional, and not odor, differences between the two stimuli. A fourth experiment investigated behavioral effects, demonstrating that stress samples sharpened emotion-perception of ambiguous facial stimuli. Together, our findings suggest human chemosensory signaling of emotional stress, with neurobiological and behavioral effects.

Independence of our logical inference and natural language

Monti et al. examine the proposition that logic inference recruits neural structures traditionally engaged by linguistic processing, and make some very interesting points. Their abstract:

Is human thought fully embedded in language, or do some forms of thought operate independently? To directly address this issue, we focus on inference-making, a central feature of human cognition. In a 3T fMRI study we compare logical inferences relying on sentential connectives (e.g., not, or, if … then) to linguistic inferences based on syntactic transformation of sentences involving ditransitive verbs (e.g., give, say, take). When contrasted with matched grammaticality judgments, logic inference alone recruited “core” regions of deduction [Brodmann area (BA) 10p and 8m], whereas linguistic inference alone recruited perisylvian regions of linguistic competence, among others (BA 21, 22, 37, 39, 44, and 45 and caudate). In addition, the two inferences commonly recruited a set of general “support” areas in frontoparietal cortex (BA 6, 7, 8, 40, and 47). The results indicate that logical inference is not embedded in natural language and confirm the relative modularity of linguistic processes.

A sane article on life-extending drugs.

Nicholas Wade offers one of the best reviews I have seen of work with drugs like resveratrol, which mimic the effect or caloric restriction in animal tests. A companion article by Arnquist notes the proliferation of web sites making unproven health claims and using false celebrity product endorsements for anti-aging and weight-loss pills made from resveratrol. (previous MindBlog postings in this areas can be found by clicking on aging in the topics list in the left column of this web page.) Here are clips from the Wade article which point out reservations about the existing studies:

...the whole phenomenon of caloric restriction may be a misleading result unwittingly produced in laboratory mice. The mice are selected for quick breeding and fed on rich diets. A low-calorie diet could be much closer to the diet that mice are adapted to in the wild, and therefore it could extend life simply because it is much healthier for them...To decide whether life extension by caloric restriction is an artifact of mice in captivity, why not try it on wild mice? Just such an experiment has been done by Steven N. Austad of the University of Texas Health Science Center. Dr. Austad reported that caloric restriction did not extend the average life span of wild mice, suggesting the diet’s benefits are indeed an artifact of mice in captivity. But others interpret his results differently. Richard A. Miller of the University of Michigan, says the maximum life span of the wild mice was extended, and so the experiment was a success for caloric restriction.

With reference to the study at Wisconsin on caloric restriction in monkeys:

The monkeys who had spent 20 years on caloric restriction were in better health than their normally fed counterparts, and suffered less diabetes, cancer and heart disease, apparently confirming that caloric restriction holds off the degenerative diseases of aging in primates as well as rodents...But as for life span, the diet extended life significantly only if the researchers excluded deaths that were apparently unrelated to aging, such as under the anesthesia necessary to take blood samples. When all deaths were counted, life span was not significantly extended...Some researchers think it is perfectly valid to ignore such deaths. Others note that in mouse studies one just counts the numbers of dead mice without asking what they died of, and the same procedure should be followed with monkeys, since one cannot be sure if a death under anesthesia might have been age related.

Another point:

...last month the results with another substance, the antifungal drug rapamycin, were published (see my July 22 post) Rapamycin was found to extend mice’s lives significantly even though by accident the mice were already the equivalent of 60 years old when the experiment started...Rapamycin has nothing to do with caloric restriction, so far as is known, but the study provided striking proof that a chemical can extend life span.

A nation's mood from its songs and blogs?

As a followup on monday's post on happiness and the blogosphere, Benedict Carey points to researchers who suggest that linguistic analysis — of song lyrics, blogs and speeches — could add a new and valuable dimension to a growing area of mass psychology: the determination of national well-being.

Bilingual infants are more flexible learners.

From Kovács and Mehler:

Children acquire their native language according to a well-defined time frame. Surprisingly, although children raised in bilingual environments have to learn roughly twice as much about language as their monolingual peers, the speed of acquisition is comparable in monolinguals and bilinguals. Here, we show that preverbal 12-month-old bilingual infants have become more flexible at learning speech structures than monolinguals. When given the opportunity to simultaneously learn two different regularities, bilingual infants learned both, whereas monolinguals learned only one of them. Hence, bilinguals may acquire two languages in the time in which monolinguals acquire one because they quickly become more flexible learners.

Even cockroaches get lonely.

The research highlights section of the July 29 Nature points out an interesting study from Lihoreau et al. suggesting why, when you find cockroaches in your home, "there's never just one."

Even cockroaches develop psychological problems if they are denied a normal social life. Animals reared in solitude are less likely to explore new environments or search for food, are more timid when approaching other cockroaches and are less able to spot the signs of a good mate. The effects of solitary confinement parallel those of 'isolation syndrome' described in a variety of vertebrates, and the suggestion is that it may develop when any group-living species is denied company.

Here is the abstract from the Lihoreau et al study:

Social isolation has dramatic consequences on the development of individuals of many vertebrate species, and it induces a set of behavioural disturbances rending them unable to process environmental as well as social stimuli appropriately. We hypothesized that isolation syndrome is a ubiquitous trait of social life that can be observed in a wide array of species, including invertebrates. Here we report that gregarious cockroaches (Blattella germanica) reared in isolation showed (i) stronger exploration-avoidance, (ii) reduced foraging activity, (iii) reduced willingness to interact socially, and (iv) reduced ability to assess mating partner quality than conspecifics reared in groups. We demonstrate the occurrence of a behavioural syndrome induced by social isolation, similar to syndromes described in vertebrates, revealing the importance of social interactions and group-living in this non-eusocial insect species. We suggest that investigating social isolation effects on individual development should provide interesting results to assess social cohesion of species and thus constitute an additional tool for comparative studies focusing on the evolution of social life.

Brain activity accociated with honest and dishonest decisions.

Greene and Paxton make some interesting observations:

What makes people behave honestly when confronted with opportunities for dishonest gain? Research on the interplay between controlled and automatic processes in decision making suggests 2 hypotheses: According to the “Will” hypothesis, honesty results from the active resistance of temptation, comparable to the controlled cognitive processes that enable the delay of reward. According to the “Grace” hypothesis, honesty results from the absence of temptation, consistent with research emphasizing the determination of behavior by the presence or absence of automatic processes. To test these hypotheses, we examined neural activity in individuals confronted with opportunities for dishonest gain. Subjects undergoing functional magnetic resonance imaging (fMRI) gained money by accurately predicting the outcomes of computerized coin-flips. In some trials, subjects recorded their predictions in advance. In other trials, subjects were rewarded based on self-reported accuracy, allowing them to gain money dishonestly by lying about the accuracy of their predictions. Many subjects behaved dishonestly, as indicated by improbable levels of “accuracy.” Our findings support the Grace hypothesis. Individuals who behaved honestly exhibited no additional control-related activity (or other kind of activity) when choosing to behave honestly, as compared with a control condition in which there was no opportunity for dishonest gain. In contrast, individuals who behaved dishonestly exhibited increased activity in control-related regions of prefrontal cortex, both when choosing to behave dishonestly and on occasions when they refrained from dishonesty. Levels of activity in these regions correlated with the frequency of dishonesty in individuals.

Our bias blind spot.

Pronin et al carry out three studies that suggest that knowledge of particular biases in our judgment and inference, and the ability to recognize the impact of those biases on others, neither prevents us from succumbing nor makes us aware of having done so. Indeed, participants in their research denied that their assessments of their personal qualities and their attributions for a particular success or failure had been biased even after having displayed the relevant biases and reading descriptions of them.

Mindblog is back...

Still jet-lagged, I'll be taking some time to cobble myself back together again. Here are a few vacation photos of Deric in London, and Len and Deric in Hagley (Hagley is a far western surburb of Birmingham where we used a colleague's house as a base to explore some spots in the Cotswolds). If I ever needed more personal objective data on the decay of one's brain plasticity on aging, I sure got it when I started to drive on the left after a 14 year absence from the UK! What I recalled as being rather fun and effortless (negotiating complex roundabouts, etc.) now went with much more energy, concentration, focus, and stress. This, I presume, reflects the difference between the 67 year old and the 53 year old versions of Deric's brain.

Why health care reform is paralyzed...

In the Aug. 3 issue of the New Yorker, Hertzberg writes a concise and lucid description of why we are the only wealthy democracy on this planet that has failed to get either universal health care or some form of guaranteed health insurance. Other democracies can actually make democratic decisions, we appear to be unable to:

A president may fancy that he has a mandate (and, morally, he may well have one), but the two separately elected, differently constituted, independent legilatures whose acquiescence he needs are under no compulsion to agree. Within those legilatures, a system of overlapping committees dominated by powerful chairmen creates a plethora of veto points where well-organized special interest can smother or distort a bill meant to benefit a large but amorphous public. In the smaller of the two legislatures - which is even more heavily weighted toward conservative rural interests than is the larger one, and where one member may represent as little as one-seventieth as many people as the member in the next seat - an arcane and patently unconstitutional rule, the filibuster, allows a minority of members to block almost any action. The process that results is less like the Roman Senate than like the Roman Games: a sanguinary legislative Colosseum where at any moment some two-bit emperor is apt to signal the thumbs-down.

Happiness increasing in the blogosphere...

The following is from the "Random Samples" section of the Aug. 7 issue of Science. This may be just a tad simplistic??

Day in, day out, bloggers pour their feelings onto the Web. Now researchers are mining those outpourings to track society's mood swings.

Peter Dodds and Christopher Danforth, applied mathematicians at the University of Vermont, Burlington, automatically searched 2.4 million blogs, via the Web site www.wefeelfine.org, for phrases containing the words "I feel." Their computers then scanned those phrases for 1034 emotionally charged words that a 1999 psychology study had ranked on a happiness scale from 1 (miserable) to 9 (ecstatic). From the words' frequency and scores, an algorithm calculated a net feel-good factor for each day and month.

For the past 4 years, happiness has steadily increased in the blogosphere, Dodds and Danforth reported online recently in the Journal of Happiness Studies. Spirits spike on Christmas and Valentine's Day but dip on 11 September. The happiest day since 2005 was 4 November 2008, the day of the U.S. presidential election. In contrast, Michael Jackson's death in June triggered a 3-day trough.

The Vermont scientists are now studying Twitter feeds. James Fowler, a social scientist at the University of California, San Diego, says the new method will enable scientists "to take the pulse of the whole world, assessing the mood of human society."