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Archive for the ‘development’ Category

sadchild.jpegPhysorg reports about an interesting forthcoming MRI study linking paedophilia to regional changes in white matter. Analysing structural MRI using voxel-based morphometry, paedophiles were found to have significantly smaller white matter volumes in specific regions, as the abstract demonstrates:

The present investigation sought to identify which brain regions distinguish pedophilic from nonpedophilic men, using unbiased, automated analyses of the whole brain. T1-weighted magnetic resonance images (MRIs) were acquired from men who demonstrated illegal or clinically significant sexual behaviors or interests (n = 65) and from men who had histories of nonsexual offenses but no sexual offenses (n = 62). Sexual interest in children was assessed by participants’ admissions of pedophilic interest, histories of committing sexual offenses against children, and psychophysiological responses in the laboratory to erotic stimuli depicting children or adults. Automated parcellation of the MRIs revealed significant negative associations between pedophilia and white matter volumes of the temporal and parietal lobes bilaterally. Voxel-based morphometry corroborated the associations and indicated that the regions of lower white matter volumes followed, and were limited to, two major fiber bundles: the superior fronto-occipital fasciculus and the right arcuate fasciculus. No significant differences were found in grey matter or in cerebrospinal fluid (CSF). Because the superior fronto-occipital and arcuate fasciculi connect the cortical regions that respond to sexual cues, these results suggest (1) that those cortical regions operate as a network for recognizing sexually relevant stimuli and (2) that pedophilia results from a partial disconnection within that network.

Now, a few things strikes me odd in this analysis and interpretation. First of all, why is the comparison group nonsexual offenders? After all, that the crime is of a sexual nature is absolutely central to the present question, and especially that the sexual offender has been interested in children. The obvious choice would be to compare paedophilic sexual offenders to sexual offenders who had adult victims (typically a male offending a woman). Here, the act of sexual offence is similar between the two groups, while the sexual “object” is the vital difference. In the present study, any significant difference could just as well be explained by the nature of the crime as the sexual inclination of the subjects. It’s a classic case of poor control of confounding variables.

Second, I strongly dislike the over-interpretations offere in both the article and the news story. First, the authors find significant differences in the superior fronto-occipital and arcuate fasciculi, and link these regions to studies showing involvement in response to sexual stimuli. Following this, they suggest that paedophilia may occur due to a disconnection in this network. Just based on the reasons given in the previous section, these results may be interpreted just as well as brain alterations in sexual offence in general.

But more than this, if one just skims the literature on these regions (fasciculi), one can see that they have been implemented in language lateralization/function and hallucinations and delusions. So interpreting the differences as relevant to paedophilia is a long shot.

Furthermore, the physorg story suggest that this study:

challenges the commonly held belief that paedophilia is brought on by childhood trauma or abuse. This finding is the strongest evidence yet that paedophilia is instead the result of a problem in brain development.

This is a serious over-interpretation of the results. When understanding white matter (and any brain) changes during development, one should be cautious to claim that the changes observed are the mere cause of “brain development” and not experience-related phenomena. Here, we need to divide between two effects: neurogenetic and psychogenetic effects. Neurogenetic effects are, in this story, changes in the brain that are caused by biological factors. Age-related atrophy is a good example of this. The cause is the accumulation of junk within cells/neurons that eventually hinder cell division and function. Psychogenetic factors, on the other hand, are observed brain changes that are caused by behaviour, in its broadest sense. For example, if you learn to juggle, areas in the motor regions of the brain will alter their size and connectivity to a measurable extent. Likewise, London taxi drivers are known to have larger posterior hippocampi as a result of their prolonged training in navigation.

So in the case of paedophilia, observed changes in the brain cannot be said to support a brain-based (neurogenetic) interpretation, and to challenge psychogenetic causes. Rather, it has been suggested that many paedophiles have been subject to similar maltreatment when young. At the least, just because the brain shows a difference, one cannot conclude anything beyond this about causation.

As neuroscience enters the domain of social sciences, it holds the promise to both enlighten and naturalize these age-old discussions. However, the use of mere reporting and tailored interpretations are far from sufficient, and may even lead us astray in the goal to achieve a better understanding of these, and related, phenomena.

-Thomas

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brain_child_by_temabina.jpgIt’s really a slow digestion period, getting back from SfN in Atlanta. Other than an aching back and jet-lag the conference experience has been tremendous. But at the same time it was rather confusing. Those talks and lectures that I expected to be good turned out to be boring or far too complex (or ill presented) to comprehend. Other talks — IMO wildcards relative to my own area — were tremendously informative.

It strikes me that this year didn’t have one or more major themes that were dominating the discussion and themes as such. This very much as we’ve seen in previous conferences, and at other conferences, where topics such as e.g. stem cell research (SfN) or brain development or imaging genetics (Human Brain Mapping) was on everybody’s lips. So while I sit here back home and reflect on some highlights — other than those very technical aspects that I myself found interesting — a few come to mind.

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amygdala.jpgCan a brain scan reveal your relationship to your mother? According to a recent study, this may well be the case.

One of the theories in modern psychology is about the relationship between a child and her parent, especially the mother. Among such attachment theories is the original theory by John Bowlby. For a good description of attachment theory see Wikipedia. There’s also a good article (PDF) in Developmental Psychology on the history of attachment.
Basically, the theory of attachment demonstrated that the dyadic relationship between the infant and the mother can take the form of different styles — attachment styles. Such styles include secure attachment where the infant can use the mother as a secure base from which the immediate environment is explored. Insecure attachment, however, can come in different forms, including avoidant, ambivalent and disorganized (see also here). Studies have shown that the attachment style at birth is likely to influence the social functions in adulthood, and that the attachment style in one female is inherited by her offspring through a process called transmission (see also this excellent paper). Normally, this transmission is thought to be socially transmitted, although I think it’s a dubious conclusion since children are both genetically and socially related to their mother. However, a convincing study (PDF) in 2003 by Bokhorst showed that while genetic influence on temperament was relatively high, the influence on attatchment style was negligible.

But let’s get to the case: does attachment style demonstrate measurable effects on the brain? Indeed, this is what Erwin Lemche and colleagues found in a study using functional MRI. Based on previous findings that insecure attachment is related to heightened sympathetic nervous system activity (e.g. heart rate increase and cortisol secretion), Lemche et al. demonstrated that performance during a stress, relative to a neutral, prime stimulus condition involved bilateral amygdalae activation.

The subjects were shownn two series of 32 sentence statements describing self-centred or other-centred information. They had to report whether they agreed or disagreed with the statements by pressing a button. Before the presentation of the target sentences, subliminal messages with negative content were presented on some occasions (stress condition), or with nonsense sentence content (neutral condition). For example, the negative prime could be “My mom rejects me” presented for 30 milliseconds. In the neutral condition the prime could be “Ym umu jrecest em”, also presented for 30 milliseconds.

The activation of the amygdalae after negative primes was the same for all subjects. However, for those subjects who demonstrated an insecure attachment style (determined by the Adult Attachment Interview) the amygdalae activation levels was significantly higher when presented with the unconscious negative primes.

So having an insecure attachment style leads to higher activation to attachment-related primes. Taken together, this result demonstrates a role for amygdala in mediating attatchment relevant behaviour. Indeed, it is interesting to see how a phylogenetic “old” limbic structure is involved in an interpersonal psychological process, which is normally thought to involve more prefrontal cortical regions.

-Thomas

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Here is a great story: human imitation has been known to be present in newborns, supporting a notion of the human race being predisposed to social interaction. However, an obvious question of whether this is also the case in non-human primates below our closest evolutionary relatives has not been asked. Until now. In an excellent study by Pier Ferrari and colleagues in PLoS Biology, imitation of facial expression is demonstrated in neonatal monkeys (that disappeared after approx. 7 days).

From ScienceDaily we can read:

Ferrari et al. tested 21 baby rhesus monkeys’ response to various experimental conditions at different ages (one, three, seven, and 14 days old). Infants were held in front of a researcher who began with a passive expression (the baseline condition) and then made one of several gestures, including tongue protrusion, mouth opening, lip smacking, and hand opening.

Day-old infants rarely displayed mouth opening behavior, but smacked their lips frequently. When experimenters performed the mouth opening gesture, infants responded with increased lip smacking but did not increase any other behavior. None of the other stimuli produced significant responses. But by day 3, matched behaviors emerged: infants stuck out their tongues far more often in response to researchers’ tongue protrusions compared with control conditions, and smacked their lips far more often while watching researchers smacking theirs. By day 7, the monkeys tended to decrease lip smacking when humans performed the gesture, and by two weeks, all imitative behavior stopped.

Here is an example from the article:

And from the abstract:

Our findings provide a quantitative description of neonatal imitation in a nonhuman primate species and suggest that these imitative capacities, contrary to what was previously thought, are not unique to the ape and human lineage. We suggest that their evolutionary origins may be traced to affiliative gestures with communicative functions.

UPDATE: Jown Hawkes has an in-depth presentation and discussion of this study.

-Thomas

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greatimage.jpgA core question in the study of personality and intelligence is about the relative contribution of inherited traits and learned behaviours. How much nature vs how much nurture shapes the mind? This problem can be approached in several ways, including the study of monozygotic twins that have been reared apart, and adoption studies (e.g. comparing the IQ of the biological vs. the adoptive parents to assess genetic vs. environmental effects respectively). However, on rare occasions we get the opportunity to study extreme cases of how nature and nurture influences the human mind. Such occasions include children that have grown up without (or with very little) influence from other people.

Such stories are at the same time shockingly disturbing and at the same time truly amazing, and they provide us with insights into the development of the human mind. It has demonstrated, for example, how there is a critical period for language acquisition.

What happens to a mind that is deprived from cultural influence during childhood? This is the ultimate test of the nature-nurture debate. But it is also the ultimate non-ethical experiment. Nevertheless, on rare occasions science has been provided with cases where children have been abandoned or seriously socially deprived. We don’t have to go father than last week’s story about Natascha Kampusch, the now 18 year old woman who was kidnapped eight years ago and kept in a cramped, windowless underground bedroom during her captivity, and isolated from interactions with any other human beings. Kampusch still had interaction with her kidnapper, but she has spent her entire adolescence in social isolation, a period of development that involves the development of social skills and personality.

In Boston Review, Rebecca Saxe who is an MIT psychologist, has an excellent review of Encounters with Wild Children by Adriana S. Benzaquén. The book is about the history of scientific studies of “wild children”, or as the publisher write:

Since the early seventeenth century, stories of encounters with strange children in unusual circumstances have been recorded, circulated, and reproduced in Europe and North America not simply as myths, legends, or good tabloid copy but as occurrences deserving serious scrutiny by philosophers and scientists. “Wild children” were seen as privileged objects of knowledge, believed to hold answers to fundamental questions about the boundaries of the human, the character and significance of civilization, and the relation between nature and culture, heredity and environment.

The study of these “wild children” have thus been thought of as a genuine path to study the influence of culture (or, rather, lack thereof) on the developing mind. But as Benzaquèn argues, we should not give these studies this high rank. As Saxe writes:

But here’s the catch: the forbidden experiment may belong to a smaller group of experimental problems that persistently seem meaningful but are not. Intuitively, we expect that while human nature interacts with human society in a typical child’s development, the natural and the social are in principle independent and distinguishable. If this intuition is wrong, the forbidden experiment is incoherent. In fact, the social and the natural may be irretrievably entangled in development. In part this is because a social environment that includes other human beings is inevitably more natural for a human infant than any wholly artificial environment that could be constructed to replace it. Even the unfolding of innately determined human traits relies on a social environment. For example, virtually every human infant is exposed to a language and learns it; an infant who was never exposed to any language could not possibly speak one. Yet it is the children who do learn a language—through social interactions—who illustrate the natural human capacity.

So although we might be interested in the psychological profile and story that may eventually come from the Natascha Kampusch story, it should definitely be taken with more than a grain of salt.

-Thomas

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har1expression.jpgThe race is on to pinpoint how the human genome has changed since the last common ancestor of chimps and hominids. With more and more genomes being sequenzed it has become possible to compare species and locate the regions where DNA has remained static over the last ~5 million years, and where it has evolved rapidly. An extremely exiting paper reporting such a genome-wide scan in a range of animals, including humans, has been put on-line today at the Nature website. The paper identifies 49 so-called Human Accelerated Regions (HAR) where sequences are evolutionary conserved among many mammals but has diverged rapidly in humans since the last chimp-human ancestor. The fastest among these, dubbed HAR1, has accrued 18 changes in this time. As it turns out, HAR1 is not a protein-coding sequence but belongs to a non-coding RNA sequence. This is rather interesting since geneticists (and evolutionary psychologists) generally assume that adaptations work on protein-coding genes. This new result may indicate that many of the adaptations setting the human genome apart from the chimp genome can have taken place outside of the genome’s protein-coding sequences.

Equally interesting is the fact that one of the two RNA genes containing HAR1, HAR1F, is expressed in human Cajal-Retzius cells that are thought to play a crucial role in redirecting migrating neurons during development. Thus, HAR1F may possibly be linked to the expansion of the human cortex starting 2 million years ago. In a short news article published in today’s Nature Gerton Lunter speculates on what HAR1F‘s functional role might be:

What the gene does is a mystery, but there are some guesses. “Given that it’s changed so dramatically only for humans, it might be involved in humanspecific brain wiring,” says Gerton Lunter at the University of Oxford, UK. One thing is becoming clear: proteincoding genes may not be the movers and shakers of human evolution scientists once thought. “We should stop looking at proteins and start looking at noncoding DNA,” says Lunter. “Everything points in that direction.”

Now, if we could just manage to extract DNA samples from the various hominids fossils linked with major evolutionary changes (homo erectus and so on), we might some day end up with a clear picture of how the hominid brain has evolved. What an amazing triumph that would be!

By the way, in last week’s Science Paul Mellars had a nice review showing how genetical analysis also illuminates our understanding of the dispersal of modern human populations out of Africa some 60,000 years ago. You might want to read that as well.

References

Pollard, K. (2006): An RNA gene expressed during cortical development evolved rapidly in humans. Nature, in press.

Mellars, P. (2006): Going east: New genetic and archaeological perspectives on the modern human colonization of Eurasia. Science 313: 796-800.

-Martin

UPDATE: You can find nice comments on this truly pathbreaking paper at Carl Zimmer’s, John Hawks’ and the Gene Expression weblogs.

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beer.jpgAs noted in my previous post, the impact of alcohol on brain maturation in adolescence is still considered an open question, although studies indicate that early exposure to alcohol is even more damaging in adolescence than in adulthood. It’s not surprising at all. Alcohol crosses the blood-brain barrier to influence the function of neurons. Actually, influence is not the right term: intoxicates or poisons the brain is more correct. After all, the effect of alcohol on your state of mind is due to a state of intoxication.Alcohol is of course only one of many substances that have an impact on brain function, and that are used for recreational purposes. Other psychoactive substances include nicotine/tobacco, cannabis, cocaine and LSD. In a population of adolescents the young vary in their use of such drugs, both the debut, the regularity of use, and the combined – or polydrug – use. The question is, then, what causes this variation?

In a special issue of Behavioral Genetics the genetic and environmental causes of substance use are explored and reviewed. For example, Jason Pagan and colleagues study the causes of alcohol use in adolescence, and conclude that

(…) there was no significant evidence of shared environmental influences on alcohol problems in early adulthood. Problems were largely influenced by genetic factors that overlapped with genetic influences on frequency of use. Unique environmental factors were largely specific to each stage, with some overlap between alcohol problems and frequency of use at age 25.
Danielle Dick and her colleagues, on the other hand, find that a specific gene, GABRA2, shows two specific patterns in relation to adolescent and adult alcohol abuse. First they found that aconsistent elevation in risk for alcohol dependence associated with GABRA2 is not evident until the mid-20s and then remains throughout adulthood. On the other hand, GABRA2 was also associated with other drug dependence in their sample, both in adolescence and adulthood. So this gene can indeed be a causative factor in the forming of drug use in general, which some findings seem to indicate. GABRA2 has been shown several times to be coupled to alcoholism. For example, Danielle Dick herself has published data showing a complex relationship between martial status, alcohol dependence and GABRA2, concluding in another publication this year:

These analyses provide evidence of both gene-environment correlation and gene-environment interaction associated with GABRA2, marital status, and alcohol dependence. They illustrate the complex pathways by which genotype and environmental risk factors act and interact to influence alcohol dependence and challenge traditional conceptualizations of “environmental” risk factors.
Anyway, the special issue in Behavior Genetics has several good articles on the gene-environment interaction effects on the development of substance use disorders. It’s a must-read to anyone interested in genes, brain and behaviour.

-Thomas

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