Neurobiologists at the University of Maryland have discovered information about how the brain processes sound that challenges previous understandings of the auditory cortex, which had 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 associate, describe a much more complex picture of neuronal activity. Their findings are published in the January 31 online edition of Nature Neuroscience.
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.
This "in vivo 2-photon calcium imaging" technique was developed by German researchers and advanced by Harvard scientists who used it to study the visual cortex in the mid-2000s. Kanold's study is the first to apply this technique to the auditory cortex and provides an unprecedented amount of detail about how hearing happens.
Dr. Andrew King, Professor of Neurophysiology at the University of Oxford, explains that "The functional organization of the auditory cortex has remained unclear and a matter of some controversy, despite the efforts of many labs over a number of years. The approach used by Dr. Kanold and colleagues is an important advance in this field."
"We discovered that the organization of the cortex does not look as pretty as it does in the textbooks, which surprised us," explains Kanold. "Things are a lot messier than expected." And we don't see evidence of the maps previously proposed using less precise techniques."
But the disorder they found could indicate that the brain is far more adaptable than previously thought. "These results may rewrite our classical views of how cortical circuits are organized and what functions they serve," suggests Dr. Shihab Shamma, whose previous research has involved mapping responses in the auditory cortex using traditional microelectrodes.
By using different dyes, this study measured differences in how the neurons receive sound information (the inputs), and how they process that sound (the outputs). It was previously assumed that neighboring neurons receiving the same inputs would also produce the same outputs, but Kanold's research found something very different. "Neighboring neurons do their own thing by creating different outputs," Kanold explains. "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."
This is the first time that this level of individuality has been observed in neighboring neurons. Dr. Kanold, who is an expert in neuroplasticity, the brain's ability to reorganize neural pathways, believes that there is a tremendous advantage in this apparent disorder. "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," he says. For example, it is well known that we can quickly listen in on a variety of conversations around us, the so-called "cocktail party effect." It may be that neurons having access to a large range of inputs might be able to quickly change which inputs they are responding to.
This suggests that there is very little redundancy in the function of cells in the auditory cortex, which differs notably from the visual cortex, in which neighboring neurons perform the same function as one another. This could be because our acoustic environment, such as the speech we hear, changes much faster than our visual environment, so we have to constantly adapt to new situations.
Kanold continues to study the mechanisms of brain circuitry involved in early development to gain a better understanding of why we can learn so well in early development but lose some of this ability as we age. For example, why can children easily learn new languages, while adults often struggle? Kanold's work has been focusing on identifying circuits in the young brain that mediate this remarkable ability. He is also working to apply his knowledge of developmental brain circuitry to the prevention and treatment of diseases such as cerebral palsy and epilepsy, which can be caused by early brain injuries. With his collaborator Shihab Shamma, who is studying adult mechanisms of plasticity and hearing, he is exploring how brain circuitry and learning changes over time.
Dr. Kanold is also an affiliate of the Institute for Systems Research (ISR) and is associated with the Center for the Comparative and Evolutionary Biology of Hearing (C-CEBH).
Kelly Blake | Newswise Science News
Meadows beat out shrubs when it comes to storing carbon
23.11.2017 | Norwegian University of Science and Technology
Migrating Cells: Folds in the cell membrane supply material for necessary blebs
23.11.2017 | Westfälische Wilhelms-Universität Münster
Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
23.11.2017 | Information Technology
23.11.2017 | Physics and Astronomy
23.11.2017 | Life Sciences