Development of the brain’s visual cortex depends on experience with light

Tiny molecular signals that govern how the connections between brain cells mature when the eyes first see light have now been identified by a research team in MIT’s Picower Institute for Learning and Memory and the Department of Brain and Cognitive Sciences.

Working with the brains of mice, the researchers identified small molecules whose presence helped develop the connections between cells responsible for perceiving and processing signals from light. When the matures normally, these micro-RNAs allow visual brain regions to preferentially strengthen certain connections in response to the light they experience from their surroundings, a process known as synaptic plasticity. However, when one or both eyes are deprived of light, levels of these micro-RNAs are reduced and the connections don’t develop properly.

“Our study is the first to demonstrate the existence of numerous experience-dependent micro-RNAs in the , and to demonstrate that inhibition of one of these small RNAs causes a profound loss in the ability of neurons to adjust to changes in their input,” says postdoc Nikolaos Mellios, the lead author of a research report appearing in the current issue of the scientific journal Nature Neuroscience.

Such research is important because neuroscientists see increasing evidence that abnormalities during the development of the brain’s basic wiring play some role in brain disorders. Too-high or too-low levels of micro-RNA molecules could contribute to these abnormalities.

The report’s 12 authors did their work in the laboratory of Mriganka Sur, the Paul E. Newton (1965) Professor of Neuroscience at MIT, and at several research centers overseas.

Their studies focused on a micro-RNA molecule called miR-132, which was shown to steadily increase in abundance as the brain region responsible for vision, primary visual cortex, matured. Conversely, levels of miR-132 were reduced when animals were reared in darkness.

To study how miR-132 could impact the ability of this brain region to adapt to changing conditions, the scientists temporarily stitched closed one eyelid in mice, to stop the nerve signals from that eye from reaching neurons in the visual cortex. Because the other eye remained open, transmitting information to cortex normally, the scientists could study how the visual cortex responded to the mixed signals, offering clues about the brain’s capacity to adapt to changes in input. Using an innovative technique to measure real-time activity in the brains of live mice, conducted by co-first author Hiroki Sugihara, the authors demonstrated that reducing miR-132 in neurons delayed their maturation and made them unable to respond to the changes in signals from the two eyes.

Scientists are aware that micro-RNAs orchestrate gene expression and coding proteins in cells, but little has been known about how these molecules contribute to processes of brain development that are dependent on experience and external surroundings. This research shows that they do, in fact, play an important role in synaptic plasticity, especially during sensitive periods of early maturation.

Micro-RNA was discovered only a dozen years ago, yet studying these molecules has led to a whole new understanding of how genes and genetic systems communicate with each other inside living organisms. There is, of course, much yet to be learned.

Related Stories

Team IDs binocular vision gene

Sep 14, 2007

In work that could lead to new treatments for sensory disorders in which people experience the strange phenomena of seeing better with one eye covered, MIT researchers report that they have identified the gene responsible ...

What drives brain changes in macular degeneration?

Mar 03, 2009

In macular degeneration, the most common form of adult blindness, patients progressively lose vision in the center of their visual field, thereby depriving the corresponding part of the visual cortex of input. Previously, ...

Disinhibition plus instruction improve brain plasticity

Apr 12, 2011

(PhysOrg.com) -- The healthy brain has balance of excitatory and inhibitory signals that stimulate activity but also keep it under control. Some brain diseases, like autism and Down's syndrome, have too much inhibition, which ...

Picower research finds unexpected activity in visual cortex

Mar 16, 2006

For years, neural activity in the brain's visual cortex was thought to have only one job: to create visual perceptions. A new study by researchers at MIT's Picower Institute for Learning and Memory shows that visual cortical ...

Scientists make brain signal discovery

Jul 06, 2011

(Medical Xpress) -- A Murdoch University scientist is closer to understanding why early brain development is so critical to mental health and function in the long term.

Recommended for you

'Trigger' for stress processes discovered in the brain

5 hours ago

At the Center for Brain Research at the MedUni Vienna an important factor for stress has been identified in collaboration with the Karolinska Institutet in Stockholm (Sweden). This is the protein secretagogin ...

New research supporting stroke rehabilitation

Nov 26, 2014

Using world-leading research methods, the team of Dr David Wright and Prof Paul Holmes, working with Dr Jacqueline Williams from the Victoria University in Melbourne, studied activity in an area of the brain ...

User comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.