Investing on a Whiff


Chemical Spray Shows Power as Trust Booster

Trust, but verify.

- Ronald Reagan

by Bruce Bower

Some people smell fear in potential business partners.  Others smell a rat.  But individuals who smell a certain brain hormone become unusually trusting of others in financial transactions, according to a new report.  Men who inhale a nasal spray spiked with oxytocin give more money to partners in a risky investment game than do men who sniff a spray containing no active ingredient, say economist Ernst Fehr of the University of Zurich and his colleagues.

Previous studies of nonhuman animals had suggested that oxytocin in the brain encourages long-term mating in pairs of adults and nurturing behaviours by mothers toward their offspring.  This substance, which works as both a hormone and a neurotransmitter, fosters the trust needed for friendship, love, families, economic transactions, and political networks, Fehr proposes.  "Oxytocin specifically affects an individual's willingness to accept social risks arising through interpersonal interactions," he and his colleagues conclude in the 2 June Nature.

The scientists studied oxytocin's influence on male college students playing an investment game.  Each of 58 men was paid $64 to participate in the experiment.  The volunteers were paired up, and one man in each pair was randomly assigned to play the role of an investor and the other to play the role of a trustee.  Each participant received 12 tokens, valued at 32 cents each and redeemable at the end of the experiment.  The investor in each pair decided how many tokens to cede to the trustee.  Both participants, sitting face to face, knew that the experimenters would quadruple that investment.  The trustee then determined whether to keep the entire, enhanced pot or give some portion of the proceeds - whatever amount seemed fair - to the investor.  Among the investors who had inhaled oxytocin, about half gave all their tokens to trustees, and most of the rest contributed a majority of their tokens.  In contrast, only 1/5 of investors who had inhaled a placebo spray forked over all their tokens, and another 1/3 parted with a majority of their tokens.  Oxytocin influenced only investors.  Trustees returned comparable amounts of money after inhaling either spray.  The trustee responses were generous when the investors offered most of their tokens and were stingy when the investment was small, Fehr and his coworkers report.  The influence of oxytocin was limited to social situations.  In another part of the study, oxytocin didn't affect isolated investors who received randomly assigned amounts of money after making their contributions.

The oxytocin influence is "a remarkable finding," says neuroscientist Antonio Damasio of the University of Iowa College of Medicine in Iowa City in an editorial published with the new report.  Damasio had previously argued that the hormone acts somewhat as a love potion.  "It adds trust to the mix, for there is no love without trust," he says.  Worries may arise that crowds of people will be sprayed with oxytocin at political rallies or other events to induce trust in speakers, Damasio notes.  However, he proposes that slick marketing strategies for political and other products probably already trigger oxytocin release in many consumers.

Fehr's group plans to determine what brain networks participate in oxytocin-inspired trust decisions and to consider whether oxytocin might counter social phobia and other mental disorders that result in social avoidance.


Damasio, A. 2005. Brain Trust. Nature 435(June 2):571.

Kosfeld, M. ... and E. Fehr. 2005.  "Oxytocin Increases Trust in Humans".   Nature 435(June 2):673-676.  Abstract available at


Antonio Damasio
Department of Neurology
University of Iowa
College of Medicine
200 Hawkins Drive
Iowa City, Iowa 52242

Ernst Fehr
University of Zurich
Institute for Empirical Research in Economics
Blumlisalpstrasse 10
CH-806 Zurich

Source: Science News Volume 167 Number 23 on 4 June 2005 page 356 © Science Service all rights reserved

Parkinson's Medication Can Trigger Gambling

Trust everybody, but cut the cards.

- Finley Peter Dunne

Rochester, Minnesota - Compulsive gambling with losses up to $200,000 within 6 months by people who never or rarely gambled has been tied to Parkinson's disease drugs called dopamine agonists, according to a Mayo Clinic analysis to be published in Archives of Neurology,

J Eric Ahlskog, MD, PhD is the Mayo Clinic neurologist who treated most of the patients.  He and M Leann Dodd, MD, the Mayo Clinic psychiatrist who spearheaded the analysis, say that the behaviour only occurs in a small number of patients and stops when they stop taking the drug.  Eleven of the patients had started gambling; all were taking dopamine agonist medications for Parkinson's treatment and 8 pf those also took carbidopa/levodopa.  The researchers found other cases in medical literature associating Parkinson's treatment with gambling.  Excessive gambling stopped in all within months of discontinuing medication.

Other patients experienced compulsive eating with weight gain, increased alcohol consumption and hypersexuality (increased use of pornography, more extramarital affairs or increased sex drive to the point of being bothersome to the spouse) but these behaviours ceased when the medication was changed.

Parkinson's patients have lower-than-normal levels of brain dopamine.  The primary treatment for years was levodopa, which replenishes brain levels.  Dopamine agonists are different - they mimic the effect of dopamine in the brain - they aren't as potent but they last longer.  The dopamine agonist drugs associated with pathological gambling specifically target the dopamine receptors located in the limbic system of the brain controlling the emotions and the internal "reward system."  When this area is overstimulated, it can lead to impulsive behaviours which produce feelings of pleasure.

"I'd want patients to be very forthcoming with their doctors about gambling," said Dr Dodd.  "If they or family members detect any behaviors that don't seem characteristic - problematic gambling, excessive eating or alcohol consumption - they should bring it up to their [doctors]."

Source: excerpted from 11 July 2005

Flies on Speed Offer Insight into Role of Dopamine in Sleep and Arousal

Methamphetamine, the drug of choice for long-distance truckers and college students pulling all-nighters, appears to do a similar trick for fruit flies, too.  This finding is one of several in a new study that demonstrates a critical role for the neurotransmitter dopamine in the modulation of sleep, wake, and arousal states.  The work was reported by Dr Ralph Greenspan and colleagues at The Neurosciences Institute in San Diego.

The researchers found that long, sleepless nights, heightened locomotor activity, frenetic brain activity, and frenzied (but ultimately ineffective) courtship behaviour are all characteristics of fruit flies on methamphetamine, the effects of which are known to act through the neurotransmitter dopamine.  In the new work, the researchers showed that genetically engineered flies whose dopamine cells could be turned off experimentally, or flies that have received dopamine inhibitors, show converse behavioural effects to those seen in normal flies that have ingested methamphetamine.  The results suggest that the right balance of dopamine is necessary for proper brain functioning, as has been seen in human studies of attention and distraction. Dopamine has been implicated in numerous aspects of brain function in humans and other animals, and many of these brain functions involve the modulation of neuronal activity and the ability to assign proper saliency (or relevance) to sensory stimuli.

The researchers include Rozi Andretic, Bruno van Swinderen, and Ralph J Greenspan of the The Neurosciences Institute.  This work was supported by the Neurosciences Research Foundation.

Source: 11 July 2005

From Diseasing of America

by Stanton Peele

[A]ddiction is not a chemical side effect of a drug.  Rather, addiction is a direct result of the psychoactive effects of a substance — of the way it changes our sensations.  The experience itself is what the person becomes addicted to.  In other words, when narcotics relieve pain, or when cocaine produces a feeling of exhilaration, or when alcohol or gambling creates a sense of power, or when shopping or eating indicates to people that they are being cared for, it is the feeling to which the person becomes addicted.  No other explanation — about supposed chemical bondings or inbred biological deficiencies — is required.  And none of these other theories comes close to making sense of the most obvious aspects of addiction.

Some people seem to behave excessively in all areas of life, including using drugs heavily.  This even extends into legal drug use.  For example, those who smoke also drink more coffee.  But this tendency to do unhealthy or antisocial things extends beyond the simple use of drugs.  Illicit drug users have more accidents even when not using drugs. Those arrested for drunk driving frequently also have arrest records for traffic violations when they aren't drunk.  In other words, people who get drunk and go out on the road are frequently the same people who drive recklessly when they're sober.  In the same way, smokers have the highest rates of car accidents and traffic violations, and are more likely to drink when they drive.  That people misuse many drugs at once and engage in other risky and antisocial behaviors at the same time suggests that these are people who don't especially value their bodies and health or the health of the people around them.


Beauty Is in the Nose of the Beholder

by Andy Coghlan

Facial attractiveness and smell give us contradictory messages about how to select mates, new research has revealed.  Previous research on smell suggests that humans prefer odours from potential partners who are genetically dissimilar.  But new research in which women rated the facial attractiveness of men suggests the exact opposite.  So sight and smell appear to be giving contradictory messages about which partners to choose.

The new research investigated possible links between mate preference and the major histocompatibility complex (MHC) - the huge molecule on cells, unique to each individual, which helps our immune systems to distinguish native from alien cells.  The underlying theory is that humans avoid the dangers of inbreeding, and maximise the chances of having genetically fitter children, by selecting partners who have a vastly different MHC from their own.  That way, there is more chance of one parent’s genes compensating for faulty genes in the other.  But how the senses pick up subliminal cues about someone else’s MHC is still something of a mystery.

Most research so far has focused on smell, especially in rodents, and has backed up this basic assumption.  Male and female mice, for example, usually select mates with different MHC, which they judge by smelling each others’ urine.  Smell experiments in humans have broadly given the same message, showing that body odour is more appealing in people with vastly differing MHC.  But new research in which women rated the attractiveness of men’s faces has bucked the trend, showing that women preferred faces of men with similar MHC.

“It’s a subtle effect,” says Craig Roberts of the University of Liverpool, who led the team which made the discovery.  “We’re not saying it’s something that rules who we find attractive.”  Roberts and colleagues recruited 92 women and 75 men, and recorded differences in their MHC by analysing DNA from blood samples.  Then each woman was asked to rate photographs of 6 men, 3 with similar and 3 with different MHC.  The results showed that, visually, the women preferred men with similar MHC.  The preference applied both to long and short relationships, but was strongest for potential long term relationships.  Although the results appear to contradict those applying to smell, Roberts and his colleagues offer an explanation to resolve the paradox, based on the notion that kith and kin - despite having similar MHC - can offer cultural and social advantages in child rearing.

The team suggests that “filtering” for mates takes place at two levels - the first based on facial likeness to select someone not too distantly related, and the second based on smell, essentially to avoid in-breeding.  “It is a plausible explanation,” says Claus Wedekind, now visiting Harvard University in Cambridge, Massachusetts, and whose research provides the strongest evidence that on smell alone, humans and mice prefer mates with different MHC.  “It could be explained by a desire for cultural ‘sameness’, but you could build up 20 or more equally plausible scenarios to explain it,” he adds, citing evidence that, in general, Americans prefer to marry within ethnic groups.

But even incorporating smell research, the picture remains unclear.  A study by Martha McClintock and colleagues at the University of Chicago, US, showed that women preferred odours matching the MHC of their fathers.  And Wedekind showed that women taking contraceptive pills switched to preferring odours of men with similar MHC, an effect also seen in pregnant mice.

Journal reference: Biology Letters (DOI: 10.1098/rsbl.2005.0343)

Source: 13 July 2005

See also:

bulletHot on the Scent (in the section on Men) - for several articles on similar topics - including one that proposes that cells from babies women have had may stick around to assist her immune system - so that what sort of immune system her mate has may indeed matter very much...

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