Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study sheds light on critical relay in visual circuit of the brain

25.07.2003


Scientists at Harvard Medical School have cleared up some of the mystery surrounding a key structure in the developing brain that helps form the visual circuits. Their findings, which appear in the July 25 issue of Science, could provide new insight into early brain defects that are linked to conditions like cerebral palsy and learning disabilities.



During development, nerve cells in the eye send messages to the thalamus, a region located deep within the brain. The thalamus then passes these messages on to the area of the outer cerebral cortex that deals with vision. The connection between the thalamus and cortex initially passes through a transient and seldom studied structure called the subplate. By removing parts of the subplate in cats, the HMS researchers have shown that this structure is a key component in strengthening the thalamus to cortex connection and in mapping out further cortical wiring patterns important for vision.

The subplate neurons are acting "kind of like teachers," says senior author Carla Shatz, the Nathan Marsh Pusey professor of neurobiology and head of the HMS Department of Neurobiology. "They’re needed for the thalamic connections to strengthen and grow so that they can become strong enough to talk to the cortical neurons."


Shatz, who is also co-chair of the Harvard Center for Neurodegeneration and Repair (hcnr.med.harvard.edu), says that an intact subplate normally acts like a form of building scaffolding for the neural circuits, directing and strengthening important nerve signals, before disappearing. "You make sure all the connections in the building are really strong so the thing doesn’t fall down, and then you remove the scaffolding." Once the brain is fully developed and the subplate neurons start to die, a hand-off of sorts occurs in which the thalamus starts sending its signals directly to the developing visual cortex, bypassing the dismantling subplate.

In humans, the subplate scaffolding disappears by two years of age. But it is highly susceptible to damage even in the womb. During this developmental stage, the subplate neurons are the first to mature and thus require lots of oxygen for their many metabolic processes. Oxygen deprivation early on, as occurs in hypoxic injury in the womb or at birth, could harm the subplate and lead to defects like cerebral palsy or other disabilities later in life. If it turns out that the subplate is linked to such defects, understanding more about its function could eventually lead to new therapies.

Research looking at the subplate neurons has proven difficult in the past because of problems accessing the cells, which are located deep below the cerebral cortical plate, and because the structure disappears by adulthood. This did not deter Kanold and colleagues, who used toxins that targeted specific molecules on the subplate neurons to selectively remove parts of the structure.

The study looks closely at the neural connections that start at the lateral geniculate nucleus (LGN), a thalamic region that receives inputs from the retinal cells, and end in a late-developing area of the visual cortex labeled layer 4. From there, highly specialized columns of cells form, which are involved in analyzing visual stimuli. Nobel prize-winning work by David Hubel and Torsten Wiesel at Harvard Medical School demonstrated that the thalamic connections to the nerve cells in the cortex help form these columns. One type of column, for determining ocular dominance, forms based on visual signals it receives from either the left or right eye. Another kind of column forms in response to bars of light presented to the eyes at different orientations--for example, neurons in one such column may respond to vertical lines like telephone poles, while cells of another column may recognize horizontal lines like the wires crossing between the poles.

By examining the brains of cats with their subplate neurons removed, the researchers have shown that not only is the structure involved in strengthening the signal from the LGN to the layer 4 neurons, but without it, the distinctive ocular dominance and orientation columns do not form. "Basically, taking out the subplate arrests cortical development," says Patrick Kanold, a research fellow in neurobiology at HMS and lead author of the study. Kanold showed that neurons in the visual cortex with a disrupted subplate could not distinguish light bars of different orientations--whether the lines were vertical, horizontal, or at an angle. This was a clear indication that their orientation columns had not formed properly. By measuring neural activity, he also showed that the signals between the LGN and the layer 4 neurons were much weaker in brains with missing subplate neurons.

Contact: Alison Harris, Gaia Remerowski, John Lacey, +1-617-432-0442, public_affairs@hms.harvard.edu

John Lacey | EurekAlert!
Further information:
http://www.hms.harvard.edu/news/index.html

More articles from Studies and Analyses:

nachricht The importance of biodiversity in forests could increase due to climate change
17.11.2017 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig

nachricht Win-win strategies for climate and food security
02.10.2017 | International Institute for Applied Systems Analysis (IIASA)

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: A “cosmic snake” reveals the structure of remote galaxies

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...

Im Focus: Visual intelligence is not the same as IQ

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...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

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....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>