Literature Review: Brain Function

by Carl Strang

Some of these notes pertain to the Winter Campfire series of a few years ago.

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Alexander, David M., et al. 2013. Traveling waves and trial averaging: The nature of single-trial and averaged brain responses in large-scale cortical signals. NeuroImage 73: 95 DOI: 10.1016/j.neuroimage.2013.01.016 They find that brain function is better understood as wave activity that involves the entire organ, rather than separate bits of the brain specializing in separate activities. The wave is modified as different specific actions take place, and the focus of each modification may involve certain anatomical areas, but functionally these are not properly understood as isolated from one another.

Gross, J., et al. 2013. Speech rhythms and multiplexed oscillatory sensory coding in the human brain. PLoS Biol 11(12): e1001752. doi:10.1371/journal.pbio.1001752 Brain cortical cells fire in patterns that produce brain waves of different frequencies (slowest delta waves, slow theta waves and fast gamma waves). Spoken sentences also are made up of components that change at different rates (slowest prosody, such as intonation and other meaning conveying elements; slow syllable utterance; and fast phoneme production, the individual sounds that make up speech). This study found a correlation between the two that allows parallel processing of different speech components. The slower, meaning conveying components of speech are entrained with slower brain waves in the right hemisphere, while the faster phonemes are in synch with gamma waves in the left hemisphere. When speech is interrupted then resumes, the waves re-align with the new rhythm.

Healy, Kevin, et al. 2013. Metabolic rate and body size are linked with perception of temporal information. Animal Behaviour, DOI: 10.1016/j.anbehav.2013.06.018 Different animal species perceive time at different rates that vary according to the pace of their lives and other needs. Fast-moving animals with high metabolic rates, like birds, collect more information per unit time than we do, for instance. From the ScienceDaily article describing the study: “This time perception ability can be shown to vary across all animals, using a phenomenon called the critical flicker fusion frequency. The phenomenon, based on the maximum speed of flashes of light an individual can see before the light source is perceived as constant, is the principle behind the illusion of non-flashing television, computer and cinema screens. This is also the reason pet dogs see flickering televisions, as their eyes have a refresh rate higher than the screen of the TV.”

Xie, Lulu, et al. 2013. Sleep drives metabolite clearance from the adult brain. Science 342: 373-377. A study of mice revealed that brain tissues shrink and a significant increase of cerebrospinal fluid takes place around them during sleep, suggesting that a function of sleep is to flush out accumulated metabolites.

Gabel, Harrison W., and Michael E. Greenberg. 2013. The maturing brain methylome. Science 341:626-627. This is a review-interpretive article outlining the significance of a study published on-line by Science of the developing brain and its function. During development, neurons (but not other kinds of cells) in different parts of the brain acquire different patterns of methylation, epigenetic changes through chemical attachments that suppress the expression of certain genes. This appears to control patterns of synapse development, and thus is fundamental to brain function. Upon maturation, this methylation levels off.

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