Friday, September 28, 2007

Music and Language: dissociation between rule-crunching and memory-retrieval systems

I have previously written about how concepts are stored in the brain: they involve rule-based systems (A is bachelor if A is Single AND A is male) and memory based systems (prototypes and exemplars). I have also looked at how language involves both rules (the syntax of the language) as well as memory (semantics or word meanings) systems and our normal language comprehension as well as productions engages both types of systems.

It is a popular paradigm in cognitive linguistic research to present unexpected words in sentences (such as, “I’ll have my coffee with milk and concrete”), while monitoring brain activity using ERP, and find that the presentation of an unexpected word leads to a N400 peak in the temporal lobe areas. This violation of semantics is differentiated from when the syntax of the sentence is wrong, in which case we get changed activity in frontal lobes.

“Up until now, researchers had found that the processing of rules relies on an overlapping set of frontal lobe structures in music and language. However, in addition to rules, both language and music crucially require the memorization of arbitrary information such as words and melodies,” says the study’s principal investigator, Michael Ulmann, Ph.D., professor of neuroscience, psychology, neurology and linguistics.

For the first time , similar results have been obtained for music. If one assumes that changing an in-key note in a familiar melody is akin to an unexpected word in a sentence, then the same N400 peak is observed. Also , if a violation of harmonical rules , like an off-key note in an unfamiliar harmony, is akin to violations of linguistic syntax, then here too similar changes in frontal lobe activity were observed.

The subjects listened to 180 snippets of melodies. Half of the melodies were segments from tunes that most participants would know, such as “Three Blind Mice” and “Twinkle, Twinkle Little Star.” The other half included novel tunes composed by Miranda. Three versions of each well-known and novel melody were created: melodies containing an in-key deviant note (which could only be detected if the melody was familiar, and therefore memorized); melodies that contained an out-of-key deviant note (which violated rules of harmony); and the original (control) melodies.

For listeners familiar with a melody, an in-key deviant note violated the listener’s memory of the melody − the song sounded musically “correct” and didn’t violate any rules of music, but it was different than what the listener had previously memorized. In contrast, in-key “deviant” notes in novel melodies did not violate memory (or rules) because the listeners did not know the tune.

Out-of-key deviant notes constituted violations of musical rules in both well-known and novel melodies. Additionally, out-of-key deviant notes violated memory in well-known melodies.

Miranda and Ullman examined the brain waves of the participants who listened to melodies in the different conditions, and found that violations of rules andmemory in music corresponded to the two patterns of brain waves seen in previous studies of rule and memory violations in language. That is, in-key violations of familiar (but not novel) melodies led to a brain-wave pattern similar to one called an “N400” that has previously been found with violations of words (such as, “I’ll have my coffee with milk and concrete”). Out-of-key violations of both familiar and novel melodies led to a brain-wave pattern over frontal lobe electrodes similar to patterns previously found for violations of rules in both language and music. Finally, out-of-key violations of familiar melodies also led to an N400-like pattern of brain activity, as expected because these are violations of memory as well as rules.

“This tells us that these two aspects of music, that is rules and memorized melodies, depend on two different brain systems – brain systems that also underlie rules and memorized information in language,” Ullman says. “The findings open up exciting new ways of thinking about and investigating the relationship between language and music, two fundamental human capacities.”

To me this seems exciting. My thesis has been that Men are better at rule-based things (syntax and harmony); while women are better at memory-based things (semantics and melody), so I'll like to know whether the authors observed any gender effects. If so, this would be further proof for abstract vs concrete gender difference theory.

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Monday, September 10, 2007

Schizophrenia fact sheet

This is just an FYI post regarding a great Schizophrenia fact sheet that is available on the net. do have a look and provide more facts as to what we know and what we do not know about this illness.

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Schizophrenia and plasticity/neurogenisis: a case for positive selection?

A recent study has unearthed the normal function of a gene involved in Schizophrenia susceptibility. This gene called DISC 1(Disrupted in Schizophrenia 1) is now though to orchestrate the neuronal migration process of new neurons that are created in the adult human brain.

It turns out that this gene, called disc1, makes a protein that serves as a sort of musical conductor for newly made nerve cells in the adult brain, guiding them to their proper locations at the appropriate tempo so they can seamlessly integrate into our complex and intertwined nervous system. If the DISC1 protein doesn't operate properly, the new nerves go hyper.

It is believed that the allele that raise susceptibility to Schizophrenia , also speed up the neuronal migration process. Thus, the fact, that as we progress towards more and more neoteny , and towards a brain that is plastic and undergoes neurogeneisis, even in adulthood, so too the burden of this trait- some of us who are the forerunner for this increased neurogeneisis and speedy neural migration, also have to pay the cost for that behavior.

While it may not be obvious why high-speed integration would be detrimental, Song notes that because of the complexity of the brain, timing is critical to ensure that new nerves are prepared to plug into the neural network.

Another related article , brings to light the fact that some of the genes most strongly implicated in schizophrenia susceptibility, have also been under positive selection recently. Thus, it is evident that Schizophrenia is a cost we have to play for the creativity that might result from increased learning potential vis-a-vis more and faster neurogenesis and speedy neural migration.

Several genes with strong associations to schizophrenia have evolved rapidly due to selection during human evolution, according to new research in the Proceedings of the Royal Society B (Wednesday 5 September 2007).

To me, this is further evidence for the fact that Schizophrenia is just an extreme end of a particular creative thinking style and which has as a basis differential connectivity patterns in the brain.

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Wednesday, September 05, 2007

Obesity: The Dopamine Connection

In a recent news article, there is a surprising revelation, that obese people have fewer dopamine receptors. The article author links this to a state akin to addiction (with amphetamine etc) as in addicted individuals too the dopamine system is involved and after prolonged usage of the drug, the dopamine receptors become less in the system.

It turns out that food also affects the brain's dopamine systems. When Volkow, who is also director of the National Institute on Drug Abuse, and her colleagues compared brain images of methamphetamine users with obese people, they found both groups had significantly fewer dopamine receptors than healthy people. Even more interesting: The higher the body mass index, the fewer the dopamine receptors -- a finding that may open the door to a better understanding of why it is so difficult for some people to lose weight and keep it off.

What role dopamine may play in obesity -- and how eating affects it -- is still to be determined. No one knows when the obese people in the study lost their dopamine receptors in the brain or if that loss could be reversed with weight loss. Are some people more susceptible to the effects of eating sugary, high-fat fare because they start out with lower levels of dopamine receptors in the brain? Or could eating those foods decrease dopamine receptors? Might food additives, preservatives and other substances also have an effect on dopamine receptors?

While several alternatives are provided above as to why this link exists, I would like to advance my own thoughts on the matter. First and foremost, I would like to speculate that when we eat something , we get a dopamine rush, and all of us carve food (get hungry) when we haven't had a food-associated-dopamine-rush for a long time. Now, if the dopamine rush that we feel, when eating, is not strong enough, we would still feel hungry. This cycle may lead to obesity. Now, from the above study it is clear, that obese people have fewer Dopamine receptors than the rest of us. thus, when they eat something, though the dopamine released in synapses may be the same as that in normal people, due to lesser dopamine receptors, they will experience a subdued dopamine rush. To compensate for this they may overeat and thus gain weight.

This theory (which seems so obvious, once stated) also explains the fact that why people on anti-psychotics sometimes gain weight as a side effect. the anti-psychotics (most of them) work as dopamine antagonist; i.e. they bind to the dopamine receptors and thus make fewer dopamine receptors available. Thus, with reduced bind able dopamine receptor sites, the food we eat, would not lead to a dopamine rush of great magnitude; thus causing overeating and weight gain.

Here, I would like to highlight that dopamine and serotonin system interact a lot, and as indicated in a previous post, those people who have low serotonin levels in brain (i.e. are depressed) also have reduced sensitivity to sweet taste. Thus, they too overeat sweet items to compensate for their reduced sweet taste. Having low serotonin and fewer D2 receptors, may be a potentially deadly condition that may lead to more food craving (especially sugary food) and may lead to obesity.

Hat tip: Center for emotional wellbeing.

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