Ver como o cérebro ouve revela surpresas sobre como o som é processado

quarta-feira, fevereiro 10, 2010

Seeing the Brain Hear Reveals Surprises About How Sound Is Processed

ScienceDaily (Feb. 10, 2010) — New research shows our brains are a lot more chaotic than previously thought, and that this might be a good thing. Neurobiologists at the University of Maryland have discovered information about how the brain processes sound that challenges previous understandings of the auditory cortex that suggested an organization based on precise neuronal maps. In the first study of the auditory cortex conducted using advanced imaging techniques, Patrick Kanold, Assistant Professor of Biology, Shihab Shamma, Professor of Electrical and Computer Engineering, and Sharba Bandyopadhyay, post-doctoral.

The left shows thousands of dye-loaded cells in the mouse auditory cortex over a large area. The right shows the preferred frequency of many cells, and shows that neighboring cells can have dramatically different frequency preference. (Credit: Image courtesy of University of Maryland)

"The organization of the cortex does not look as pretty as it does in the textbooks," says Dr. Kanold. "Things are a lot messier than expected." Images above: The left shows thousands of dye-loaded cells in the mouse auditory cortex over a large area. The right shows the preferred frequency of many cells, and shows that neighboring cells can have dramatically different frequency preference.

All our knowledge of how the brain really works has been based on taking a small sampling of all available neurons and making inferences about how the other neurons respond, Dr. Kanold explains. "This is like showing someone who wants to know how America looks, 'Here is one person from New York City and one person from California.' You don't get a very good picture of what the country looks like from that sampling," says Kanold, originally from Germany.

In contrast, Kanold and colleagues were able to look at the activity of all the neurons in a large region of the auditory cortex simultaneously. To get the highest resolution picture to date of how auditory cortex neurons are organized, the researchers used a technique to fill neurons in living mice with a dye that glows brightly when calcium levels rise, a key signal that neurons are firing. They then selectively illuminated specific regions of the cortex with a laser and measured the neuronal activity of hundreds of neurons in response to stimulation by simple tones of different frequencies.
...
Read more here/Leia mais aqui: Science Daily

+++++

Article abstract

Nature Neuroscience
Published online: 31 January 2010 | doi:10.1038/nn.2490

Dichotomy of functional organization in the mouse auditory cortex

Sharba Bandyopadhyay1,2, Shihab A Shamma2,3 & Patrick O Kanold1,2

Abstract

The sensory areas of the cerebral cortex possess multiple topographic representations of sensory dimensions. The gradient of frequency selectivity (tonotopy) is the dominant organizational feature in the primary auditory cortex, whereas other feature-based organizations are less well established. We probed the topographic organization of the mouse auditory cortex at the single-cell level using in vivo two-photon Ca2+ imaging. Tonotopy was present on a large scale but was fractured on a fine scale. Intensity tuning, which is important in level-invariant representation, was observed in individual cells, but was not topographically organized. The presence or near absence of putative subthreshold responses revealed a dichotomy in topographic organization. Inclusion of subthreshold responses revealed a topographic clustering of neurons with similar response properties, whereas such clustering was absent in supra-threshold responses. This dichotomy indicates that groups of nearby neurons with locally shared inputs can perform independent parallel computations in the auditory cortex.

1. Department of Biology, University of Maryland, College Park, Maryland, USA.

2. Institute for Systems Research, University of Maryland, College Park, Maryland, USA.
3. Department for Electrical and Computer Engineering, University of Maryland, College Park, Maryland, USA.

Correspondence to: Patrick O Kanold1,2 e-mail: pkanold@umd.edu

+++++