Tuesday, April 22, 2008
Mistakes, music, language, and individuality
It's Tuesday and you know what that means.... the Science Times. A few articles caught my eye today, one by Karren Barrow about a man who lost his ability to speak following a stroke (aphasia) and was able to learn to speak again with the help of melodic intonation therapy. This therapy seems to take advantage of the fact that certain aspects of singing, especially the melodic part, are typically accomplished by the right hemisphere of the brain while most language functions are housed on the left, where this patient experienced damage from the stroke. It's almost as if the right hemisphere is dragging the left along. It seems to be particularly helpful with speech spontaneity.
There is a little blurb by Henry Fountain that describes a study by Tom Eichele, a Norwegian researcher, and his colleagues that images the brain prior to making errors to learn what is different from when we perform well. There were two things I appreciated about this article. One was a few simple words in the writing which did not use the typical language of popular science with regard to fMRI.
** a little lecture about fMRI follows, which you are welcome to skip**
Usually authors describe the brain "lighting up" and make a direct link between the brain's relative use of oxygen in some parts of the brain as compared to others and its activation. The basis of this type of fMRI (there are several but this is a pretty common one), is that the 'f,' standing for functional, gives us a picture of a brain in action. It does this by measuring which regions of the brain are metabolizing the most oxygen at a certain moment in time, and describes those as the regions which are most active. Not an unreasonable assumption. The fMRI is a giant magnet, sensitive to the oxygen level of hemoglobin - the chemical in our blood which carries oxygen. That chemical is more strongly magnetic in its deoxygenated state than when it is bound to oxygen. That difference is what the magnet senses, and tiny regions measuring only a millimeter by a millimeter can be coded as to their relative blood oxygen levels. There has to be an adjustment for the time lag that exists between the metabolism of the oxygen and the blood oxygen level which is not directly measured, rather the fMRI is sensing the by-product that remains once the oxygen is used up. This is one of the many complications inherent in designing a meaningful fMRI experiment. There is in addition some disagreement as to exactly what physiological state is being reflected by the difference in oxygenation level. Most fMRI literature suggests that blood oxygen level is directly analogous to 'activation' of brain regions but what does that mean? The firing of a nerve cell or many cells within that 1mm volume (known as a voxel)? Neurons can be excitatory or inhibitory. Are those neurons all excitatory? Doesn't an inhibitory neuron firing also use up energy? Are we seeing a net measure of activation? My point is that fMRI is a complex measure. What a given series of brain images suggest should be described thoughtfully as the brain is not actually 'lighting up' at all. This article chooses to do that by carefully describing fMRI as a 'measure of oxygenation' and I appreciated that. Whew long tangent.
**Lecture ends here**
The other thing I liked about this article was the science itself. This experiment makes use of a fairly controversial idea - the so-called default mode region - which is a network of brain regions that are more relatively active when a person is relaxed and "at rest." Don't get me started with the scientific and philosophical problems of measuring rest. I won't go there today. This study suggest that those regions become more activated just prior to an error. As problematic as the whole default-mode idea can be, I enjoy the scientific sense behind the idea that a brain preparing to rest rather than to perform an activity would perform it less well. It almost sounds liking going to sleep at the wheel!
I also really enjoyed the article by Christine Kenneally on the impact of language on thought. One of my main research interests is top-down impact on perception - how an individual brain's experiences mold perception. This article about is written in a thorough format and offers a reading list on language and thought that many of you might enjoy.
Finally, Carl Zimmer writes interestingly and amusingly on diversity at the bacterial level. With the simplicity of a bacterial life form, you wouldn't expect much possibility of individuation, but research on the E. Coli belies that expectation.