Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers find essential brain circuit in visual development

26.08.2013
NIH-funded study could lead to new treatments for amblyopia

A study in mice reveals an elegant circuit within the developing visual system that helps dictate how the eyes connect to the brain. The research, funded by the National Institutes of Health, has implications for treating amblyopia, a vision disorder that occurs when the brain ignores one eye in favor of the other.


To trace the connections of the eyes to the brain in a mouse, different dyes can be placed into each eye. The left eye (red) and right eye (blue) mostly connect in separate territories. But they can both connect to the binocular zone (green-yellow). Amblyopia occurs when one eye is impaired and the other takes over this zone.

Credit: Image courtesy of Dr. Joshua Trachtenberg, UCLA.

Amblyopia is the most common cause of visual impairment in childhood, and can occur whenever there is a misalignment between what the two eyes see—for example, if one eye is clouded by a cataract or if the eyes are positioned at different angles. The brain at first has a slight preference for the more functional eye, and over time—as that eye continues to send the brain useful information—the brain's preference for that eye gets stronger at the expense of the other eye.

Patching the strong eye can help correct amblyopia. But if the condition isn't caught and corrected during childhood, visual impairment in the weaker eye is likely to persist into adulthood.

"Our study identifies a mechanism for visual development in the young brain and shows that it's possible to turn on the same mechanism in the adult brain, thus offering hope for treating older children and adults with amblyopia," said Joshua Trachtenberg, Ph.D., an associate professor of neurobiology at the David Geffen School of Medicine, University of California, Los Angeles (UCLA). The study was published in Nature.

Within the brain, cells in a limited region called the binocular zone can receive input from both eyes. During brain development, the eyes compete to connect within this zone, and sometimes one eye prevails—a process known as ocular dominance.

Ocular dominance is a normal process and is an example of the brain's ability to adapt based on experience—called plasticity. But it can also set the stage for amblyopia. If one eye is impaired and can't effectively compete, it will lose space in the binocular zone to the other eye. Also, this competition takes place during a limited time called the critical period. Once the critical period closes—around age 7 in kids—the connections are difficult to change. Some studies have shown, however, that it's possible to partially correct amblyopia in the teenage years.

"The new study identifies a key step in ocular dominance plasticity," Dr. Trachtenberg said. It was funded by the National Eye Institute (NEI) and the National Institute of Neurological Disorders and Stroke (NINDS), both part of NIH.

Much is known about the mechanisms behind ocular dominance. Fifty years of research on it has even led to a general theory of plasticity called the sliding threshold model. The new study tested a fundamental piece of this model that at first seems at odds with ocular dominance.

According to the model, plasticity can only proceed if the activity—or firing rate—of cells in the brain is above a certain threshold. Below this threshold, strong connections won't be made stronger and weak ones won't be eliminated. This is where it's difficult to fit ocular dominance to the model: If the binocular zone cells are only being driven by one eye, then their firing rate should drop by about half—below the threshold.

Working with the lab of Xiangmin Xu, Ph.D., at the University of California, Irvine, Dr. Trachtenberg and his team at UCLA investigated this problem in mice. To induce changes in ocular dominance, they temporarily patched one eye in young mice. After 24 hours, they removed the patch and recorded how the firing rate of binocular zone cells changed in response to vision through each eye.

They found that the cells' firing rates immediately dropped by half when vision was restricted to one eye, as expected. But over the next 24 hours, the cells responding to either eye—even the eye that had been temporarily patched—increased their firing rate back to the normal range.

The team's next goal was to explain the increased firing rate. "Since the signals from the patched eye to the binocular zone are reduced, we wanted to know what drives the increase," Dr. Trachtenberg said.

First, they investigated the possibility that the binocular zone cells were getting more stimulation from other parts of the brain, but that wasn't the case. Instead, the key turned out to be a brain circuit that normally inhibits the cells. When vision through one eye is impaired, the inhibition from that circuit gets weaker. This loss of inhibition restores the cells' firing rate to the range where their connections can be remodeled.

By manipulating this circuit, the researchers were able to prevent ocular dominance in young mice and induce it in older mice that were already beyond the critical period. If this circuit could be controlled in the human brain—for example, with a drug or with implants of the kind sometimes used to treat Parkinson's—it would open the door to correcting amblyopia years later than is currently possible, Dr. Trachtenberg said.

This work was supported by NEI grant EY016052 and NINDS grant NS078434. For more information about amblyopia, visit NEI's website at http://www.nei.nih.gov/health/amblyopia.

Reporters: To set up an interview with Dr. Trachtenberg, please contact Elaine Schmidt at UCLA (eschmidt@mednet.ucla.edu, 310-794-2272).

Reference: Kuhlman SJ et al. "A disinhibitory microcircuit initiates critical period plasticity in visual cortex." Nature, August 2013. DOI: 10.1038/nature12485.

NEI leads the federal government's research on the visual system and eye diseases. NEI supports basic and clinical science programs that result in the development of sight-saving treatments. For more information, visit http://www.nei.nih.gov/.

NINDS is the nation's leading funder of research on the brain and nervous system. The NINDS mission is to reduce the burden of neurological disease – a burden borne by every age group, by every segment of society, by people all over the world.

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.

NIH...Turning Discovery Into Health®

Dan Stimson | EurekAlert!
Further information:
http://www.nei.nih.gov

More articles from Studies and Analyses:

nachricht Europe’s Demographic Future. Where the Regions Are Heading after a Decade of Crises
10.08.2017 | Berlin-Institut für Bevölkerung und Entwicklung

nachricht Scientists reveal source of human heartbeat in 3-D
07.08.2017 | University of Manchester

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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>