Women's memory enhanced by lower male voice pitch.

Women are attracted to low male voices, and a prevailing idea is that this is relevant to mate selection. Kevin Allen and colleagues now show that they are also more likely to remember what those low voices say to them. (It makes sense that memory should be sensitive towards content of adaptive value and thus help us to act in ways that enhance our reproductive fitness):

From a functionalist perspective, human memory should be attuned to information of adaptive value for one’s survival and reproductive fitness. While evidence of sensitivity to survival-related information is growing, specific links between memory and information that could impact upon reproductive fitness have remained elusive. Here, in two experiments, we showed that memory in women is sensitive to male voice pitch, a sexually dimorphic cue important for mate choice because it not only serves as an indicator of genetic quality, but may also signal behavioural traits undesirable in a long-term partner. In a first experiment, we found that women’s visual object memory is significantly enhanced when an object’s name is spoken during encoding in a masculinised (i.e., lower-pitch) versus feminised (i.e., higher-pitch) male voice, but that no analogous effect occurs when women listen to other women’s voices. A second experiment replicated this pattern of results, additionally showing that lowering and raising male voice pitch enhanced and impaired women’s memory, respectively, relative to a baseline (i.e., unmanipulated) voice condition. The modulatory effect of sexual dimorphism cues in the male voice may reveal a mate-choice adaptation within women’s memory, sculpted by evolution in response to the dilemma posed by the double-edged qualities of male masculinity.

Human genes still evolve rapidly

A Harvard group has found evolution in response to natural selection in a contemporary human population, showing a dramatic decrease in age of reproduction in a defined population since 1720. Context on the location of their study:

Ile aux Coudres is a 34-km2 island located ∼80 km to the northeast of Québec City along the St. Lawrence River (Canada). Thirty families settled on the island between 1720 and 1773 and the population reached 1,585 people by the 1950s. This population is ideal to study the genetic basis of life-history traits (LHTs). First, church registers provide exceptionally detailed records of dates of births, marriages, and deaths. Second, the long-term data and endogamy (marriages within the population) provide a deep and intricate pedigree to facilitate the separation of genetic and environmental influences on LHTs. Third, the population was very homogeneous among families, particularly in traits known to correlate with the timing of reproduction (social class, education, and religion). In addition, the split of resources among families was quite even due to the type of land distribution, and the number of professions was limited. This relative homogeneity should minimize confounding socioeconomic or shared environmental influences within quantitative genetic analyses.

Here is their abstract:

It is often claimed that modern humans have stopped evolving because cultural and technological advancements have annihilated natural selection. In contrast, recent studies show that selection can be strong in contemporary populations. However, detecting a response to selection is particularly challenging; previous evidence from wild animals has been criticized for both applying anticonservative statistical tests and failing to consider random genetic drift. Here we study life-history variation in an insular preindustrial French-Canadian population and apply a recently proposed conservative approach to testing microevolutionary responses to selection. As reported for other such societies, natural selection favored an earlier age at first reproduction (AFR) among women. AFR was also highly heritable and genetically correlated to fitness, predicting a microevolutionary change toward earlier reproduction. In agreement with this prediction, AFR declined from about 26–22 y over a 140-y period. Crucially, we uncovered a substantial change in the breeding values for this trait, indicating that the change in AFR largely occurred at the genetic level. Moreover, the genetic trend was higher than expected under the effect of random genetic drift alone. Our results show that microevolution can be detectable over relatively few generations in humans and underscore the need for studies of human demography and reproductive ecology to consider the role of evolutionary processes.

The brain's fountain of youth

Williams points to an article that suggests that Dracula may have gotten it right. Young blood can restore an aging body. Giving young blood to older mice is know to boost their immune system and muscle function, and now it turns out that it also causes the synthesis of new nerve cells, boosting the number of cells in the hippocampus involved in memory formation. Conversely, serum from older mice decreases the number of these memory cells in younger mice. Wyss-Coray and collaborators find a blood borne protein (cytokine CCL11) that increases with aging and inhibits synthesis of new nerve cells. Factors stimulating neurogenesis are being sought. Here is their abstract:

In the central nervous system, ageing results in a precipitous decline in adult neural stem/progenitor cells and neurogenesis, with concomitant impairments in cognitive functions. Interestingly, such impairments can be ameliorated through systemic perturbations such as exercise1. Here, using heterochronic parabiosis we show that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in an age-dependent fashion in mice. Accordingly, exposing a young mouse to an old systemic environment or to plasma from old mice decreased synaptic plasticity, and impaired contextual fear conditioning and spatial learning and memory. We identify chemokines—including CCL11 (also known as eotaxin)—the plasma levels of which correlate with reduced neurogenesis in heterochronic parabionts and aged mice, and the levels of which are increased in the plasma and cerebrospinal fluid of healthy ageing humans. Lastly, increasing peripheral CCL11 chemokine levels in vivo in young mice decreased adult neurogenesis and impaired learning and memory. Together our data indicate that the decline in neurogenesis and cognitive impairments observed during ageing can be in part attributed to changes in blood-borne factors.

"Neurotrash"

In The Chronicle of Higher Education Marc Parry notes the crusade of Raymond Tallis to throw out the "Neurotrash." This is the goal of his new book "Aping Mankind: Neuromania, Darwinitis, and the Misrepresentation of Humanity" (McGill-Queen's University Press). Parry describes a Tallis lecture that seeks to demolish

…two "pillars of unwisdom." The first, "neuromania," is the notion that to understand people you must peer into the "intracranial darkness" of their skulls with brain-scanning technology. The second, "Darwinitis," is the idea that Charles Darwin's evolutionary theory can explain not just the origin of the human species—a claim Tallis enthusiastically accepts—but also the nature of human behavior and institutions….Those trends, as Tallis sees them, are like "intellectual illnesses" metastasizing from academic labs into popular culture. He sees the symptoms in neuro-economic thinkers who explain our susceptibility to subprime mortgages by describing how our brains evolved to favor short-term rewards. He sees them in philosophers who claim that our primate minds admire paintings of landscapes that would have supported hunting and gathering. He sees it in neurotheologians who preach that "God is a tingle in the 'God spot' in the brain."

The points Tallis makes are good, much of the press description of 'love spots in the brain' , etc. is nonsense…but Tallis does seem to throw out the baby with the bathwater. How could we make sense of the irrational social behaviors described in the previous two mindblog posts this week outside of an evolutionary framework, and how do we explain that activities of certain brain areas, when perturbed by strokes, electrical stimulation, or drugs do alter fairly discrete classes of behaviors?

Brief neuroscience video-tutorials

I recently received an email from Aki Nikolaidis, a neuroscience graduate student at the University of Illinois, asking me to have a look some brief instructional videos he had been making over the past several years. I took a look, and found them quite engaging. Here they are:

Fluid Intelligence

Consciousness and Free Will

Non-conscious Information Processing

Electroencephalogram (EEG)

Working Memory Training

The science of irrationality.

As a followup to yesterday's post on how common sense, ideology and intuition lead us astray in our attempts to fix social problems - while social intervention programs that have been validated by true randomized experiments are ignored - I point to Jonah Lehrer's brief review of Daniel Kahneman's new book "Thinking, Fast and Slow.", which describes his work on evolved blind spots in our rational processes which appear to be virtually impossible to fix, even though we understand that they are there.

When people face an uncertain situation, they don't carefully evaluate the information or look up relevant statistics. Instead, their decisions depend on mental short cuts, which often lead them to make foolish decisions. The short cuts aren't a faster way of doing the math; they're a way of skipping the math altogether...The biases and blind-spots identified by Messrs. Kahneman and Tversky aren't symptoms of stupidity. They're an essential part of our humanity, the inescapable byproducts of a brain that evolution engineered over millions of years.

Consider the overconfidence bias, which drives many of our mistakes in decision-making. The best demonstration of the bias comes from the world of investing. Although many fund managers charge high fees to oversee stock portfolios, they routinely fail a basic test of skill: persistent achievement. As Mr. Kahneman notes, the year-to-year correlation between the performance of the vast majority of funds is barely above zero, which suggests that most successful managers are banking on luck, not talent...This shouldn't be too surprising. The stock market is a case study in randomness, a system so complex that it's impossible to predict. Nevertheless, professional investors routinely believe that they can see what others can't. The end result is that they make far too many trades, with costly consequences.

We like to see ourselves as a Promethean species, uniquely endowed with the gift of reason. But Mr. Kahneman's simple experiments reveal a very different mind, stuffed full of habits that, in most situations, lead us astray. Though overconfidence may encourage us to take necessary risks—Mr. Kahneman calls it the "engine of capitalism"—it's generally a dangerous (and expensive) illusion.

What's even more upsetting is that these habits are virtually impossible to fix. As Mr. Kahneman himself admits, "My intuitive thinking is just as prone to overconfidence, extreme predictions and the planning fallacy as it was before I made a study of these issues."...Even when we know why we stumble, we still find a way to fall.

The science of psychological change

In the Oct 14 issue of Science Magazine
Geoffrey L. Cohen reviews Timothy Wilson's new book "Redirect: The Surprising New Science of Psychological Change." The book reviews success stories in social psychology, and I thought it would be worthwhile to pass on a few clips from that review:

There are interventions that harness the power of expressive writing and volunteerism to improve happiness and health and to lessen rates of teen pregnancy. There are interventions that reduce student failure and close gaps between minority and nonminority students by inculcating in them core positive beliefs that sustain them through hardship, such as the belief that intelligence is not a fixed entity but rather like a muscle that grows with effort. There are interventions that improve intertribal trust in Rwanda by modeling cooperative intergroup relations through radio soap operas. In the United States, interventions that defuse blacks' and whites' fear of interracial rejection increase their likelihood of becoming friends. And...there are studies that cleverly manipulate social norms to reduce teen alcohol use and encourage energy conservation.

And notes:

What these interventions share is that they are grounded in science, found effective in randomized experiments, have surprisingly large and durable effects—and, by and large, aren't used. Over and over, Wilson writes, schools, government agencies, and workplaces opt for interventions that not only have never been subjected to experimental test but also, when they finally are, often yield null and even negative effects. These interventions are usually based on a combination of intuition, ideology, and good intentions. Wilson critiques several popular but unwise interventions: Drug Abuse Resistance Education (D.A.R.E., implemented in 75% of the school districts in the United States), “scared straight,” certain forms of posttraumatic grief counseling, many commonplace diversity training programs, and the self-help and positive thinking industry in general ["The Secret" book receives sustained criticism]. These are analogous, Wilson writes, to the practices of leeching and blood-letting before the scientific method took hold in medicine.

Wilson uses the thought-provoking metaphor of “story editing” to describe the ingredient common to many of the successful interventions he reviews. They alter the narratives people tell themselves about their world and their place in it: Is it safe or threatening? Do I belong or not? Am I capable or not? During sensitive periods, people's storytelling can be redirected and the change can build on itself over time. Amend the opening sentence of the story of your transition to college, or to a new job, and the arc of your story may be entirely different from what it would have been otherwise. This helps explain why seemingly simple interventions, such as writing about a traumatic experience, or volunteering for a humanitarian cause, improve health and well-being. They give people an organizing narrative that puts their lives in an optimistic context.

Dissolution of the social contract

I've been meaning to point to a very cogent essay by Marmor and Mashaw on why conditions for recovery from the great depression of the early 1930's were more propitious than those that prevail in our current recession - which promises to be very prolonged.

...there is a crucial difference between then and now: the words that our political leaders use to talk about our problems have changed. Where politicians once drew on a morally resonant language of people, family and shared social concern, they now deploy the cold technical idiom of budgetary accounting...This is more than a superficial difference in rhetoric. It threatens to deprive us of the intellectual resources needed to address today’s problems.

From the 1930s to the 1960s...American public discourse was filled with references to the social circumstances of average citizens, our common institutions and our common history. Over the last five decades, that discourse has changed in ways that emphasize individual choice, agency and preferences. The language of sociology and common culture has been replaced by the language of economics and individualism.

In 1934, the government was us. We had shared circumstances, shared risks and shared obligations. Today the government is the other — not an institution for the achievement of our common goals, but an alien presence that stands between us and the realization of individual ambitions. Programs of social insurance have become “entitlements,” a word apparently meant to signify not a collectively provided and cherished basis for family-income security, but a sinister threat to our national well-being.

Over the last 50 years we seem to have lost the words — and with them the ideas — to frame our situation appropriately.

Differences in reality monitoring correlate with prefrontal cortex variations

Here is an intriguing bit of work from Buda et al.:

Much recent interest has centered on understanding the relationship between brain structure variability and individual differences in cognition, but there has been little progress in identifying specific neuroanatomical bases of such individual differences. One cognitive ability that exhibits considerable variability in the healthy population is reality monitoring; the cognitive processes used to introspectively judge whether a memory came from an internal or external source (e.g., whether an event was imagined or actually occurred). Neuroimaging research has implicated the medial anterior prefrontal cortex (PFC) in reality monitoring, and here we sought to determine whether morphological variability in a specific anteromedial PFC brain structure, the paracingulate sulcus (PCS), might underlie performance. Fifty-three healthy volunteers were selected on the basis of MRI scans and classified into four groups according to presence or absence of the PCS in their left or right hemisphere. The group with absence of the PCS in both hemispheres showed significantly reduced reality monitoring performance and ability to introspect metacognitively about their performance when compared with other participants. Consistent with the prediction that sulcal absence might mean greater volume in the surrounding frontal gyri, voxel-based morphometry revealed a significant negative correlation between anterior PFC gray matter and reality monitoring performance. The findings provide evidence that individual differences in introspective abilities like reality monitoring may be associated with specific structural variability in the PFC.

Examples of prominent (left) and absent (right) PCS classifications. In the left panel, PCS is indicated by the red arrow.

Merging emotional information from voice and faces in the brain.

Klasen et al. find the ventral posterior cingulate to be a central structure for supramodal representation of complex emotional information. The left amygdala reflects input of happy stimuli from multiple sensory inputs:

Supramodal representation of emotion and its neural substrates have recently attracted attention as a marker of social cognition. However, the question whether perceptual integration of facial and vocal emotions takes place in primary sensory areas, multimodal cortices, or in affective structures remains unanswered yet. Using novel computer-generated stimuli, we combined emotional faces and voices in congruent and incongruent ways and assessed functional brain data (fMRI) during an emotional classification task. Both congruent and incongruent audiovisual stimuli evoked larger responses in thalamus and superior temporal regions compared with unimodal conditions. Congruent emotions were characterized by activation in amygdala, insula, ventral posterior cingulate (vPCC), temporo-occipital, and auditory cortices; incongruent emotions activated a frontoparietal network and bilateral caudate nucleus, indicating a greater processing load in working memory and emotion-encoding areas. The vPCC alone exhibited differential reactions to congruency and incongruency for all emotion categories and can thus be considered a central structure for supramodal representation of complex emotional information. Moreover, the left amygdala reflected supramodal representation of happy stimuli. These findings document that emotional information does not merge at the perceptual audiovisual integration level in unimodal or multimodal areas, but in vPCC and amygdala.

Measuring Zeitgeist from the Tweet stream.

Golder and Macy have analyzed more than 509 million Twitter posts by 2.4 million users over a 2-year period in order to study collective mood (using Twitter to track the mood of nations sort of like using satellites to track the state of the atmosphere!). They used a freely available protocol provided by Twitter to download tweets originating from 84 countries between February 2008 and January 2010, and searched these messages for roughly 1000 words on a tried-and-tested list of words associated with positive (agree, fantastic, super) and negative (afraid, mad, panic) emotion. Despite very different cultures, geographies, and religions, the U.S., Canada, the UK, Australia, India, and English-speaking Africa all showed similar mood rhythms:

We identified individual-level diurnal and seasonal mood rhythms in cultures across the globe, using data from millions of public Twitter messages. We found that individuals awaken in a good mood that deteriorates as the day progresses—which is consistent with the effects of sleep and circadian rhythm—and that seasonal change in baseline positive affect varies with change in daylength. People are happier on weekends, but the morning peak in positive affect is delayed by 2 hours, which suggests that people awaken later on weekends.

A graphic from the article:

Hourly changes in individual affect broken down by day of the week (top, positive affect, PA; bottom,  negative affect, NA). Each series shows mean affect (black lines) and 95% confidence interval (colored regions). (Experimental psychologists have repeatedly demonstrated that positive and negative affect are independent dimensions. Positive affect (PA) includes enthusiasm, delight, activeness, and alertness, whereas negative affect (NA) includes distress, fear, anger, guilt, and disgust)

Fatherhood decreases testosterone.

Gettler et al. find that, in a community-based sample from the Philippines, men with higher testosterone level are more likely to marry than men with lower testosterone; that men who marry and become fathers experience declines in testosterone; and that men who provide more paternal care have lower testosterone levels than fathers who provide less care:

In species in which males care for young, testosterone (T) is often high during mating periods but then declines to allow for caregiving of resulting offspring. This model may apply to human males, but past human studies of T and fatherhood have been cross-sectional, making it unclear whether fatherhood suppresses T or if men with lower T are more likely to become fathers. Here, we use a large representative study in the Philippines (n = 624) to show that among single nonfathers at baseline (2005) (21.5 ± 0.3 y), men with high waking T were more likely to become partnered fathers by the time of follow-up 4.5 y later (P < 0.05). Men who became partnered fathers then experienced large declines in waking (median: −26%) and evening (median: −34%) T, which were significantly greater than declines in single nonfathers (P < 0.001). Consistent with the hypothesis that child interaction suppresses T, fathers reporting 3 h or more of daily childcare had lower T at follow-up compared with fathers not involved in care (P < 0.05). Using longitudinal data, these findings show that T and reproductive strategy have bidirectional relationships in human males, with high T predicting subsequent mating success but then declining rapidly after men become fathers. Our findings suggest that T mediates tradeoffs between mating and parenting in humans, as seen in other species in which fathers care for young. They also highlight one likely explanation for previously observed health disparities between partnered fathers and single men.

Mimicry can foster both rapport and threat.

Liu does experiments that illustrate two aspects of mimicry. Mimicry can bond people by fostering rapport and liking, but appears to have the opposite effect if participants in an interaction are primed by reminders of money. Money-primed participants liked a mimicking interaction partner less than they liked a nonmimicking partner, an effect that appears to have been due to enhanced feelings of threat. Their observations are consonant with studies that have shown that reminders of money elicit a self-sufficient state characterized by two tendencies: First, eagerness to pursue personal goals and freedom, persisting longer than others on difficult tasks and hesitating to ask for help; and second, acting more insensitive to others, desiring solo versus activities and showing more indifference to social exclusion.

The Jekyll and Hyde of emotional intelligence

Côté et al. make some observations about emotional smarts:

Does emotional intelligence promote behavior that strictly benefits the greater good, or can it also advance interpersonal deviance? In the investigation reported here, we tested the possibility that a core facet of emotional intelligence—emotion-regulation knowledge—can promote both prosocial and interpersonally deviant behavior. Drawing from research on how the effective regulation of emotion promotes goal achievement, we predicted that emotion-regulation knowledge would strengthen the effects of other-oriented and self-oriented personality traits on prosocial behavior and interpersonal deviance, respectively. Among individuals with higher emotion-regulation knowledge, a first study noted that moral identity exhibited a stronger positive association with prosocial behavior in a social dilemma [i.e. the study confirmed the authors' prediction that there is an association between moral identity and prosocial behavior in a social dilemma, this association being stronger among individuals with high emotion-regulation knowledge]. A second study found that the positive relation between Machiavellianism and interpersonal deviance was stronger when emotion-regulation knowledge was high rather than when it was low, thus pointing out the dark side of emotion-regulation knowledge.

How our brain links to our immune system via vagus nerve

A large number of studies show that our psychological state can influence our immune system. Social isolation and stress weaken our immune system, and social affiliation and calm can strengthen it (the latter are associated with increased activity of the vagus nerve, which runs from the brainstem to many parts of the body). Now a multinational collaboration headed by Kevin Tracey has shown that stimulating the vagus nerve halts the pumping out of inflammatory signals by the immune system, with the neurotransmitter molecular responsible being acetyl choline - but, the Vagus nerve is not releasing it directly. Instead the splenic branch of the Vagus nerve is releasing noradrenaline in the spleen whose white blood cells (CD4 lymphocytes) are then secreting the acetyl choline which switches off production of inflammatory chemical by nearby cells. Here is the abstract:

Neural circuits regulate cytokine production to prevent potentially damaging inflammation. A prototypical vagus nerve circuit, the inflammatory reflex, inhibits tumor necrosis factor–α production in spleen by a mechanism requiring acetylcholine signaling through the  alpha 7 nicotinic acetylcholine receptor expressed on cytokine-producing macrophages. Nerve fibers in spleen lack the enzymatic machinery necessary for acetylcholine production; therefore, how does this neural circuit terminate in cholinergic signaling? We identified an acetylcholine-producing, memory phenotype T cell population in mice that is integral to the inflammatory reflex. These acetylcholine-producing T cells were required for the inhibition of cytokine production by vagus nerve stimulation. Thus, action potentials originating in the vagus nerve regulate T cells, which in turn produce the neurotransmitter acetylcholine required to control innate immune responses.

Be Happy! ... regulate your own amygdala

Not really....the conditions used in the experiments by Zotev et al.et al. - having a handy fMRI machine nearby - are not exactly accessible to most of us. Because it is known that activation of the left amygdala is associated with happy emotions, they tried a biofeedback trick:

We investigated the feasibility of training healthy humans to self-regulate the hemodynamic activity of the amygdala, which plays major roles in emotional processing. Participants in the experimental group were provided with ongoing information about the blood oxygen level dependent (BOLD) activity in the left amygdala (LA) and were instructed to raise the BOLD rtfMRI signal by contemplating positive autobiographical memories. A control group was assigned the same task but was instead provided with sham feedback from the left horizontal segment of the intraparietal sulcus (HIPS) region. In the LA, we found a significant BOLD signal increase due to rtfMRI neurofeedback training in the experimental group versus the control group...The whole brain data analysis revealed significant differences for Happy Memories versus Rest condition between the experimental and control groups...The findings demonstrate that healthy subjects can learn to regulate their amygdala activation using rtfMRI neurofeedback, suggesting possible applications of rtfMRI neurofeedback training in the treatment of patients with neuropsychiatric disorders.

Psychological resources correlate with an Oxytocin receptor gene.

Interesting work from Saphire-Bernstein et al.. An SNP is a single nucleotide polymorphism, in this case a switch at a particular site between the base adenine (A) and guanine (G) in the DNA coding for an oxytocin receptor named OXTR. Every person carries two copies of this gene (one from each parent), and the finding is that A/A or A/G individuals are less psychologically robust than G/G individuals. This suggests a strong relationship between OXTR and psychological resources. Here is the abstract:

Psychological resources—optimism, mastery, and self-esteem—buffer the deleterious effects of stress and are predictors of neurophysiological and psychological health-related outcomes. These resources have been shown to be highly heritable, yet the genetic basis for this heritability remains unknown. Here, we report a link between the oxytocin receptor (OXTR) SNP rs53576 and psychological resources, such that carriers of the “A” allele have lower levels of optimism, mastery, and self-esteem, relative to G/G homozygotes. OXTR was also associated with depressive symptomatology. Mediation analysis indicates that the effects of OXTR on depressive symptoms may be largely mediated by the influence of OXTR on psychological resources.

Income inequality, happiness, and trust.

From Oishi et al., observations that correlate with many experiments showing that people are more concerned with their relative income rank and fairness, rather than absolute income:

Using General Social Survey data from 1972 to 2008, we found that Americans were on average happier in the years with less national income inequality than in the years with more national income inequality. We further demonstrated that this inverse relation between income inequality and happiness was explained by perceived fairness and general trust. That is, Americans trusted other people less and perceived other people to be less fair in the years with more national income inequality than in the years with less national income inequality. The negative association between income inequality and happiness held for lower-income respondents, but not for higher-income respondents. Most important, we found that the negative link between income inequality and the happiness of lower-income respondents was explained not by lower household income, but by perceived unfairness and lack of trust.

Think away colds, and...Less fat, less depression

My thanks to a colleague (Ken Munkres, Emeritus Professor of Molecular Biology and Genetics at UW Madison) who sent me these two tidbits:

How to Think Away Those Cold Symptoms
Tinker Bell was right all along

Balancing Your Fat Intake Controls Depression
The intersection of diet and psychiatry

There is nothing paranormal about near-death experiences.

Mobbs and Watt argue that neuroscience can explain seeing bright lights, meeting the dead, or being convinced you are one of them, suggesting that there is nothing paranormal about these experiences. Instead, near-death experiences are the manifestation of normal brain function gone awry, during a traumatic, and sometimes harmless, event. They engage several basic features of near death experiences (awareness of being dead, out of body experiences, tunnel of light, meeting deceased people, euphoric emotions) and note the brain regions whose perturbation by electrical stimulation or ischemic strokes can induce each phenomenon. Some can be observed in normal individuals under particular conditions of sensory stimulation (I've done posts on the Blanke experiments on out of body experiences). Their arguments are of the "may be" or "could be" sort, and their summary seems to to be particularly vague hand waving...

The near-death experience is a complex set of phenomena and a single account will not capture all its components. One recent theory is that the basic arousal systems beginning in the midbrain may account for many of the components of the near-death experience. Of interest is the locus coeruleus, a midbrain region involved in the release of noradrenaline. Noradrenaline is known to be involved in arousal related to fear, stress, and hypercarbia, and is highly connected to regions that mediate emotion and memory, including the amygdala and hippocampus. Indeed, stimulation of the noradrenaline system has been shown to enhance and consolidate memory, and plays a critical role in the sleep-wake cycle, including REM sleep. Along with basic midbrain systems, such as the periaqueductal gray, a region involved in opioid analgesia and basic fear responses, and the ventral tegmental area, which is a core dopamine reward area, the noradrenaline system may be part of a basic set of systems that directly or indirectly evoke positive emotions, hallucinations and other features of the near-death experience.

Taken together, the scientific evidence suggests that all aspects of the near-death experience have a neurophysiological or psychological basis: the vivid pleasure frequently experienced in near-death experiences may be the result of fear-elicited opioid release, while the life review and REM components of the near-death experience could be attributed to the action of the locus coeruleus- noradrenaline system. Out-of-body experiences and feelings of disconnection with the physical body could arise because of a breakdown in multisensory processes, and the bright lights and tunneling could be the result of a peripheral to fovea breakdown of the visual system through oxygen deprivation. A priori expectations, where the individual makes sense of the situation by believing they will experience the archetypal near-death experience package, may also play a crucial role. If one challenge of science is to demystify the world, then research should begin to test these and other hypotheses. Only then will discussion of near-death experiences move beyond theological dialogue and into the lawful realm of empirical neurobiology.