Insulin sensitivity, antioxidants, and memory function in aging

Insulin resistance has been associated with dysfunction of mitochondria. Iwabu et al have an article showing that this may be transduced at the molecular level by the adiponectin receptor 1 (AdipoR1). From the abstract:

Suppression of AdipoR1 also resulted in decreased PGC-1α expression and deacetylation, decreased mitochondrial content and enzymes, decreased oxidative type I myofibres, and decreased oxidative stress-detoxifying enzymes in skeletal muscle, which were associated with insulin resistance and decreased exercise endurance. Decreased levels of adiponectin and AdipoR1 in obesity may have causal roles in mitochondrial dysfunction and insulin resistance seen in diabetes.

This short essay explains the age-dependent differences in cognitive changes following caloric restriction via insulin sensitivity. People age 50 +  have benefits in recall (~ 30% more words remembered after 30 mins) following CR while people ages 25 – 45 see no significant benefits. This makes sense if CR improves insulin sensitivity, leading to increased protection from oxidative stress (more evidence for which Iwabu et al provide above), leading to less neural damage (antioxidants have much increased neuroprotective effects in older cohorts), leading to improved memory.

Reference

Iwabu M, et al. 2010 Adiponectin and AdipoR1 regulate PGC-1α  and mitochondria by Ca2+ and AMPK/SIRT1. doi:10.1038/nature08991

Advertisement

Mortality priming modulates children preferences

What reason do we have to fight through struggles when we know that we will one day die? Terror management theory (TMT) posits that when people experience existential angst they will mitigate this angst in a number of predictable ways. Wisman and Goldenberg (2005) examine the evidence for one surprising prediction for TMT: when primed to consider their own mortality, people will show a preference for more children to reduce angst by gaining symbolic or genetic “immortality.”

The researchers primed to think of death by asking subjects to describe their emotions surrounding death and imaging their own death, as opposed to control questions about TV shows. Although women who had been primed to think of death showed no significant increase in number of desired children, men did: they preferred a mean of 2.00 with an SD of 0.87 in the control condition and 2.78 with an SD of 0.82 in the death primed condition, which was a significant interaction in the ANOVA, p = 0.006.

Previous research has found that when primed for death people show no extra desire for the physical connection of sex, so the authors dismissed the explanation of “comfort sex” as a potential confound.

Is this an evolutionarily adaptive mechanism? In some sense it may make sense to prefer more children when death is imminent but there are two problems with this theory:

1) The most adaptive mechanism is to prefer as many children as possible and humans living in more modern cultures simply do not show any indication of wanting this. If our baseline desire for children is not influenced by evolutionary psychology, then why should we expect that any changes in this self-reported value would be?

2) If it were an adaptive mechanism, why would it work for men but not women?

TMT has a good explanation for this discrepancy: women can also subjugate existential angst through career success, and they are cognizant of the fact that children may stifle their career success. So while children lead to immortality in one pathway they may hinder the quest for it through their careeer.

Men, who traditionally have had less trouble balancing family with career success, do not see this discrepancy and therefore see more children as a net positive in dimishing their existential angst. The evolutionary psychological explanation, on the other hand, is less able to explain away this discrepancy.

Reference

Wisman A, Goldenberg JL. 2005 From the grave to the cradle: evidence that mortality salience engenders a desire for offspring. Journal of Personality and Social Psychology 89:46-61.

More evidence for lack of predictive abilities in humans

The predictive abilities of humans under uncertainty is a hot area of research today. Lots of time is spent determining how we go about making decisions, at least in part so that one day we will know how to improve these abilities.

Brown and Steyvers (2008) formulated an experimental design where subjects were asked to determine the hidden state of the process determining the shade of a particle when the only visible outputs were subject to noise. You can view the type of experiment here. In their first experiment, their subjects averaged an accuracy of about 70%, and the accuracy decreased as the noise increased, which is to be expected.

Aside from misinterpreting how many times the system changed its underlying state, they provided conditionally optimal answers. The success of these subjects was staggering in comparison to other tests under uncertainty, and the authors hypothesized that it was because most of those studies asked for predictions, while this study merely asked to explain what had already happened.

In their second experiment, they put this hypothesis to the test by comparing the prescriptive abilities of the subjects to their abilities to predict. In addition to being asked for the hidden state, subjects were also asked to predict where the next stimulus would fall. Mathematically the variability in the answers to these answers should be the same. Given the same sequences of stimuli, the answer to the prediction should be based on the same distribution of the hidden state of the last stimulus.

However, this is not what the researchers found. Not only were the subjects much less accurate on the prediction than the inference task (that was to be expected), but the subjects averaged 15 “response changes” in the predictive task compared with only 11 in the inference task. That means that the subjects were changing their responses more than they ought to have. In fact, if the subjects had simply re-produced the logical extension for the predictive task that they gave for the inference task, their answers would have been 73% better.

If humans truly were “prediction machines,” as so many philosophers have noted, then it would make sense for them to make sound predictions as compared to their retrodictions. But the empirical results, once again, do not support this hypothesis.

Reference

Brown SD, Steyvers M. 2008 Detecting and predicting changes. Cognitive Psychology 58:49-67. doi:10.1016/j.cogpsych.2008.09.002.

How the Mind Works book notes

This is perhaps Pinker’s most famous book, and it encompasses a broad range of topics, touching on lots of evolutionary psychology to explain a plethora of cultural phenomena. I enjoyed it, but I thought that the chapters on vision and the last part about music were a tad too long and probably could have been condensed. Here are some of my notes:

• “The stuff of life turned out to be not a quivering, glowing, wondrous gel but a contraption of tiny jigs, springs, hinges, rods, sheets, magnets, zippers, and trapdoors, assembled by a data tape whose information is copied, downloaded, and scanned.”
• The Profet hypothesis is an evolutionary explanation of pregnancy sickness that explains a lot of otherwise incomprehensible facts.
• “There are really not many jobs that actually require a penis or vagina, and all the other occupations should be open to everyone.” – Gloria Steinem
• The icheneumon wasp paralyzes a caterpillar and lays eggs in its body so her hatchlings can slowly devour its living flesh from the inside; the natural world is beautiful
• “Computation has finally demystified mentalistic terms. beliefs are inscriptions in memory, desires are goal inscriptions, thinking is computation, perceptions are inscriptions triggered by sensors, trying is executing operations triggered by a goal”
• “The history of science has not been kind to intuitions of common sense”
• Reasons to question Penrose’s idea of quantum effects in the brain: “Quantum effects almost surely cancel out in nervous tissue…  microtubules are ubiquitous among cells and appear to play no role in how the brain achieves intelligence… there is not even a hint as to how conciousness might arise from quantum mechanics”
• “Recent thinking about zebra stripes is that they are not for blending in with stripey tall grass–always a dubious explanation–but for turning the zebras into a living shell game, baffling lions and other predators as they try to keep their attention on just one zebra.”
• Consciousness can refer to intelligence, self-knowledge, access to self-information, and/or sentience (”what it feels like”)
• “The technique of functional imaging of brain activity (PET and MRI) depends on the fact that working brain tissue calls more blood its way and consumes more glucose”
• “Natural intelligence does nothing even close to striving for intelligence. The process is driven by differences in the survival and reproduction rates of replicating organisms in a particular environment. Over time the organisms acquire designs that adapt them for survival and reproduction in that environment, period; nothing pulls them in any direction other than success there and then.”
• “Evolution is constrained by the legacies of ancestors and the kinds of machinery that can be grown out of protein.”
• “If you converge your eyes on a nerby point to eliminate double vision, the eyes squeeze the lens to close-up focus; if you diverge your eyes on a distant point, they relax for distant focus.”
• “The genome builds as much of the animal as it can, and for the parts of the animal that cannot be specified in advance (such as the proper wiring for two eyes that are moving apart at an unpredictable rate), the genome turns on an information-gathering mechanism at the time in development at which it is most needed.”
• We see in 2 1/2 dimensions, cool way of thinking about vision.
• “…problem faced by Ingrid Bergman in Notorious: how do you know when you have been poisoned? Your judgment would be addled, but that would affect your judgment about whether your judgment had been addled!”
• “Shape recognition jis such a hard problem that a single, general-purpose algorithm may not work for every shape ujnder every viewing condition.” We use mental rotation, object-centered vision (geon theory), and multiple views.
• Our main criteria for designating an “object” is parts moving together.
• “Our minds explain other people’s behavior by their beliefs and desires because other people’s behavior is in fact caused by their beliefs and desires. The behaviorists were wrong, and everyone intuitively knows it.” This is not exactly a fair treatment of behaviorism! Behaviorism is a scientific standpoint; obviously people have goals, but how much do those goals actually control behavior?
• The state lottery could also be called a “stupidity tax.”
• “Creative people are at their most creative when writing their autobiographies.”
• The reptilian/neocortex brain dichotomy is ill-founded, evolution modifies existing structures instead of making completely new ones.
• You need emotions to have goals, the idea of Spock having no emotions but being completely rational is ridiculous. Check out this description of the prototypical “rational man” as a popular conception.
• Disgust towards certain foods is irrational. Ie, insects, they are fine to eat.
• “Anger has moral overtones; almost all anger is righteous anger. Furious people feel they are aggrieved an must redress an injustice.”
• “Usually people do not want any suitor who wants them too bad too early, because it shows that the suitor is desperate (so they should wait for someone better), and because it shows that the suitor’s ardor is too easily triggered (hence too easily triggerable by someone else).”
• “Perhaps grief is an internal doomsday machine, pointless once it goes off, useful only as a deterrent.”
• “In real life, villains are convinced of their rectitude. Many biographers of evil men start out assuming that their subjects are cynical opportunists and reluctantly discover that they are ideologues and moralists.”
• “The kinship metaphors have a simple message: treat certain people as kindly as you treat your blood relatives. We all understand the presupposition. The love of kind comes naturally; the love of non-kin does not. That is the fundamental fact of the social world, steering everything from how we grow up to the rise and fall of empires and religions.”
• Looking at historical evidence from opinions on scientific revolutions, members of the French National Convention from 1793-1794, and various American revolutions, Sulloway found that later borns (ie, past the first child), are ten times more likely to support a revolution than first borns.
• “Sex is useful as a defense against parasite and pathogens…. By swapping half the genes out for a different half, an organism gives its offspring a head start in the race against the local germs. Its molecular locks have a different combination of pins, so the germs have to start evolving new keys from scratch.”
• “Men are about 1.15 times as large as women, which tells us that they have competed in our evolutionary history, with some men mating with several women and some men mating with none… Men have smaller testicles for their body size than chimpanzees but bigger ones than gorillas and gibbons, suggesting that ancestral women were not wantonly promiscuous but were not always monogamous either.”
• “Trend-setters are members of upper classes who adopt the styles of lower classes to differentiate themselves from middle classes, who woulnd’t be caught dead in lower-class styles because they’re the ones in danger of being mistaken for them”
• “Believers also avoid working out the strange logical consequences of these piecemeal revisions of ordinary things. They don’t pause to wonder why a God who knows our intentions has to listen to our prayers, or how a God can both see into the future and care about how we choose to act.”

Overall, this is a fascinating book. If I could only bring three books to a desert island, this might be one of them, because there are so many parts of the book that can be pondered further.

Does primacy trump recency?

One of the more nuanced critiques of the literature on human cognitive biases is that some of them posit conflicting effects. Probably the most glaring discrepancy is the difference between the primacy and the recency effect in hypothesis formation. Which factor is more important? Marsh and Ahn take on the challenge in their 2006 paper,

Some studies have shown a recency effect: Information that is presented later in a sequence is more heavily reflected in judgments than is information that is presented earlier. Other studies have shown a primacy effect: Early-presented information is reflected in judgment more than is later information…

Throughout this study, we have maintained the position that the primacy effect is obtained because people form a hypothesis from earlier data and underadjust this hypothesis… The primacy effect was found to be moderated by the cognitive load required by the hypothesis-testing nature of the task and by the size of the verbal working memory capacity available to process information.

Unless the subject is overloaded with information, the primacy effect is dominant. A real world application can be found in the work of Trevon Logan, who analyzed college football votes in order to see which games had more of an impact on the rankings of AP voters. Consistent with the idea that primacy is more salient than recency, he found that it is better to lose later in the season than earlier.

In order to be rational, you must obfuscate your initial opinions and see the whole story before you begin to draw conclusions. If you must choose, err on the side of weighing the later data more heavily in order to compensate for your cognitive flaws.

Reference

Marsh JK, Ahn, W. 2006 Order effects in contingency learning: The role of task complexity. Memory & Cognition 34:568-576. Abstract.

Nonevidence for temporal asymmetry

Scientists often assume that the human brain is inherently designed for prediction. But there have been precious few behavioral studies giving evidence for this thesis.

Jones and Pashler of UCSD attempt to create a model for this in their recent paper, by looking at whether individuals are more skilled at prediction or retrodiction. In their experiment, they found no statistical differences between these two skills. This is a fascinating result, as it suggests that the assumed paradigm of temporal assymetry may have to be overturned. The paper is freely available online, and it is nice and short, so you should read it for yourself.

Reference

Jones J, Pashler H 2007 Is the mind inherently forward looking? Comparing prediction and retrodiction. Psychonomic bulletin and Review, article in press. Available here.

Individual over group bias

The claim that individuals believe themselves to be better drivers than average is one of the common pieces of evidence used to show the effect of overconfidence bias. The BPS Research Digest reports that the experimental method of these results may be slightly flawed.

Instead of asking students to compare themselves to the overall group (or average), they asked the students to compare somebody else to the group. By this manipulation, they found that students still showed a preferential bias towards the individual over the group whether they were that individual or somebody else was.

This result doesn’t imply that individuals are not overconfident–we still are–but merely that the cause of that overconfidence may not be narcissism but instead a failure to compare an individual to a fair population mean.