Imaging techniques reveal new picture of sound processing

February 2nd, 2010 - 4:04 pm ICT by ANI  

London, Feb 2 (ANI): Researchers from the University of Maryland have come up with a surprising picture of neuronal activity after using advanced imaging techniques to see how the brain processes sound.

The study was conducted by Patrick Kanold, Assistant Professor of Biology, Shihab Shamma, Professor of Electrical and Computer Engineering and Institute for Systems Research (ISR), and Sharba Bandyopadhyay, Assistant Research Scientist (ISR).

Dr. Kanold said all our knowledge of the brain’s functioning has been based on taking a small sampling of all available neurons and making inferences about how the other neurons respond.

He explained: “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.”

However, Kanold and his team 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 ever taken of how auditory cortex neurons are organized, the scientists 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.

Thereafter, they 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. Kanold’s research is the first to apply this technique to the auditory cortex and reveals an unprecedented amount of detail about how hearing happens.

Dr. Kanold said: “We discovered that the organization of the cortex does not look as pretty as it does in the textbooks, which surprised us.

“Things are a lot messier than expected.” And we don’t see evidence of the maps previously proposed using less precise techniques.”

Dr. Shihab Shamma said: “These results may rewrite our classical views of how cortical circuits are organized and what functions they serve.”

The study used different dyes to measure differences in how the neurons receive sound information (the inputs), and how they process that sound (the outputs).

Earlier it was believed that neighbouring neurons receiving the same inputs would also produce the same outputs, but Kanold’s study discovered something very different

Dr. Kanold said: “Neighboring neurons do their own thing by creating different outputs…You can imagine that you and your neighbor both receive water to your houses from the same pipe, but you do different things with it - you might cook with it while your neighbor waters the lawn. You can’t assume that they are doing the same thing just because they are neighbors.”

He added: “Each individual neuron is getting inputs from a wide range of frequencies, and by selecting which frequencies they are strongly responding to, they might be very easily able to shift their function.”

The findings of the study have appeared in the January 31 online edition of Nature Neuroscience. (ANI)

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