Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Brain can be trained to process sound in alternate way

13.12.2004


UCSF scientists have found that the brains of rats can be trained to learn an alternate way of processing changes in the loudness of sound. The discovery, they say, has potential for the treatment of hearing loss, autism, and other sensory disabilities in humans. It also gives clues, they say, about the process of learning and the way we perceive the world.



"We addressed a very fundamental question," says Daniel B. Polley, PhD, lead author of the study. "When we notice a sound getting louder, what happens in our brain so that we know it’s getting louder?"

Polley is a postdoctoral research fellow in the laboratory of senior author Michael M. Merzenich, PhD, co-director of the Coleman Memorial Laboratory in the UCSF Keck Center for Integrative Neuroscience and UCSF professor of otolaryngology.


The study was published recently in Proceedings of the National Academy of Sciences (November 16, 2004).

"This is a very old idea," Polley notes. "How to relate the bigness of a stimulus to the bigness of its internal representation in the brain." Over the centuries, philosophers and scientists have put together a picture of how our brains model the world through the mechanism of our senses. Physical stimuli such as light, sound, and touch are converted by our sensory organs -- eyes, ears, and skin -- into electrical signals, which are processed by neurons in different areas of the brain. As those neurons fire, we see, hear, and feel. When the light or sound changes in intensity, our neurons fire faster or slower in direct ratio to the change. That ratio varies depending on the sense involved, but is constant for each sense: the louder a sound, the faster the neurons in the auditory cortex fire.

But now that picture has changed. Polley trained two groups of rats to become " experts" at discriminating between very small differences in loudness -- an ability that untrained rats do not have. He then looked at how the expert rats processed changes in loudness compared to two groups of untrained rats, and found that the auditory cortex in the expert rats contained groups of neurons that had become selective for specific volume levels -- they fired only at those levels and were quiet otherwise. This physiological change in the brain, called "plasticity," has been widely observed in humans and animals who have learned new skills.

Then came the breakthrough discovery: the expert rats were processing volume changes in a new and different way. In the brains of the untrained rats, the overall neural response rate increased as the sound got louder and louder, as the classical model would predict. In the expert rats, however, the overall response rate of the selective neurons increased until the sound reached a loudness threshold of 40 decibels -- and then leveled off while the loudness increased 100-fold, from 40 to 80 decibels. "At first glance, this was not good," observes Polley: If their neurons were not increasing their firing rate, how were the expert rats registering the increase in volume? David T. Blake, PhD, UCSF assistant research physiologist and a co-author of the study, cracked the puzzle. Instead of looking for a simple increase in firing rate, Blake measured the rate at which the firing changed, either up or down. This rate turned out to be in exact proportion to the increase in volume -- and at the same ratio as the firing rate increase. Tests confirmed that the untrained rats’ brains were not registering volume increases in this new way; it had been learned by the expert rats as they became better at discriminating changes in volume.

Polley concludes, "There is still proportionality between response strength in the brain and the stimulus. But now neurons are much more selective, and can represent sound intensity with decreasing firing rates as well as increasing firing rates." This system is "optimal" for representing subtle changes in loudness, reasons Polley, because "it gives you two directions to change through," making it many times more responsive than a simple firing rate increase. "And it becomes optimized through learning."

The discovery has several implications. From a practical viewpoint, "I think it has quite a bit to offer," says Christoph E. Schreiner, UCSF professor of otolaryngology and a co-author of the study. In particular, it might present a technique for retraining people with partial hearing loss, who often cannot hear very soft sounds but have normal hearing at higher volume levels.

"There’s a very steep volume curve that goes from soft to very loud right away, and people have a hard time with that," Schreiner explains, "especially for hearing-aid users." However, they -- or their auditory cortexes -- might be trained to be more sensitive to minor volume changes at the lower threshold of hearing, "so this steep transition doesn’t bother them anymore." Similarly, such training might be of value to profoundly hearing-impaired people with cochlear implants, which replace the function of the inner ear but are not as sensitive to small volume changes.

Another group that might be helped is children with sensory-modulation disorders, including children with autism. These children are "overwhelmingly sensitive" to changes in their environment, explains Polley. "So when presented with a moderate stimulus -- a sound, a touch, a flash of light -- they respond as if their entire sensory systems have become overwhelmed. What might be needed in their brains is greater selectivity." Potentially, they could be trained to distinguish smaller degrees of change in their environments. Being perceived as gradual, these changes would be less overwhelming.

From a psychological viewpoint, the study says something about how we acquire and refine new skills. When we speak of training a musician’s ear or a painter’ s eye, speculates Polley, we may be referring to the alternate sensory processing system employed by the expert rats. "This is implicit learning," he says. "How do we learn the skills that distinguish one tradesman from another tradesman? These processes are undoubtedly operating in these types of learning behaviors, and they most likely are responsible for expertise. We are looking at the neural substrate for these lifelong learning processes."

Jennifer O’Brien | EurekAlert!
Further information:
http://www.ucsf.edu

More articles from Studies and Analyses:

nachricht Drone vs. truck deliveries: Which create less carbon pollution?
31.05.2017 | University of Washington

nachricht New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>