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While I do find my peers' posts fascinating, all this talk of neo-cortex has left something a bit wanting - without all that "useless" white matter, cells in various regions of the neo-cortex couldn't even hope to talk to each other. Those globs of white matter are the axons of somas in the neo-cortex, their white color springing from the fatty sheath of myelin which allow electrical signals to travel faster along the nodes of Ranvier rather than measly simple conduction.

While CAT scans, MRIs and, more recently, fMRIs have begun to illuminate the space between our ears, not much could be said of the white-jumble between various processing centers thought to be responsible for various. Thought about how the brain worked leaned towards localizing processes to specific regions of the brain, and the methods of neuroimaging available to researchers at the time supported such hypotheses by providing data on the grey matter structures of the brain. This, however, only told half the story, as can be seen by a more recent move away from localization theories after the incredible plasticity of the brain came to light.

Enter diffusion tensor imaging, a form of neuroimaging I find so freaking cool that I actually mention it on a dating website profile. By measuring the movement of water molecules across tissues, the tracks of myelinated axons can be traced and the connectedness of structures in the brain observed. The applications of this new imaging technique are only now being realized; from tracking plaque development in multiple sclerosis to observing abnormal connections in the brains of schizophrenics.

My absolute favorite application of DTI has been in the study of the underlying physiology of synesthia. Two warring camps attempting to explain this abnormal union of sensation developed over the years: one arguing that it was due to poor feedback inhibition which allowed activation to spill backwards to other “associated” areas, the other arguing that synesthesia resulted from a higher degree of connectivity in the brains of synesthetes presumably from a failure in the first cell apoptosis in infants. By comparing connectivity in normal humans and color-grapheme synesthetes, Romke Rouw and Steven Sholte were able to show that at the very least synesthetes DO show a higher degree of connectivity in their brains. Another influential researcher in synesthia, Dr. Cytowic, argues that synesthesia is an inherently “mammalian” state and that humans are alone in not experiencing their worlds in a synesthetic sense. He cites some very difficult to understand studies which show that neonates seem to experience their world synesthetically, a trait which disappears as the child develops.

Interesting Reads:

Increased structural connectivity in grapheme-color synesthesia.

http://www.nature.com/neuro/journal/v10/n6/full/nn1906.html

Diffusion Tensor Imaging

http://www.technologyreview.com/read_article.aspx?ch=specialsections&sc=emergingtech&id=16473

Cytowic’s Website on Synesthesia

http://cytowic.net/Synesthesia/synesthesia.html