Study clarifies process controlling night vision

October 17, 2012
Sensory rhodopsin II (rainbow colored) embedded in a lipid bilayer (heads red and tails blue) with Transducin (Gt) below it. Credit: Wikipedia.

On the road at night or on a tennis court at dusk, the eye can be deceived. Vision is not as sharp as in the light of day, and detecting a bicyclist on the road or a careening tennis ball can be tough.

New research reveals the key chemical process that corrects for potential visual errors in low- conditions. Understanding this fundamental step could lead to new treatments for visual deficits, or might one day boost normal to new levels.

Like the mirror of a telescope pointed toward the , the eye's capture the energy of photons - the individual particles that make up light. The interaction triggers a series of that ultimately translate the photons into the light we see.

The key in rod cells is a protein called rhodopsin. Each rod cell has about 100 million rhodopsin receptors, and each one can detect a single photon at a time.

Scientists had thought that the strength of rhodopsin's signal determines how well we see in . But UC Davis scientists have found instead that a second step acts as a gatekeeper to correct for rhodopsin errors. The result is a more accurate reading of light under dim conditions.

A report on their research appears in the October issue of the journal Neuron in a study entitled "Calcium feedback to cGMP synthesis strongly attenuates single photon responses driven by long rhodopsin lifetimes."

Individual rhodopsin errors are relatively small in magnitude - on the order of a few hundredths of a second - but even this much biological noise can affect how well the signal gets transmitted to the rest of the brain, the researchers said.

The gatekeeper protects us from "seeing" more light than is actually there - a misreading that would have endangered an ice-age hunter, as it would a driver at dusk today. The correction may prevent the photon receptor from swamping the intricate chemical apparatus that leads to accurate .

"The rhodopsin receptor is the site where physics meets biology - where a photon of light from the physical world must get interpreted for the nervous system," said Marie Burns, professor of ophthalmology and vision science at UC Davis School of Medicine and lead author of the study. "Biology is messy. Rhodopsin does a remarkable but not perfect job."

Burns and her colleagues studied rod cells in the laboratory and discovered that calcium plays the gatekeeper role.

They found that rhodopsin activity changed calcium levels in the cells and that over-active rhodopsins changed calcium levels at a faster rate than normal. This faster change led calcium to trigger a series of chemical steps to counter the over-active rhodopsin signal by producing an equal and opposite signal, thereby correcting false information before it gets sent on to the rest of the visual system.

They uncovered this fundamental new level of control by measuring how long individual rhodopsin remained active in response to flashes of light, and then determining how much calcium's gatekeeping function modified the rhodopsin signals.

"Basic research like ours often doesn't translate to immediate clinical treatments for known diseases, but understanding fundamental processes has long-term significance," Burns said. "In the case of our research, this understanding can prove essential for progress on a range of vision deficits that are currently poorly understood and untreatable."

Explore further: Why animals don't have infrared vision

Related Stories

Why animals don't have infrared vision

June 9, 2011
On rare occasion, the light-sensing photoreceptor cells in the eye misfire and signal to the brain as if they have captured photons, when in reality they haven't. For years this phenomenon remained a mystery. Reporting in ...

Geometry plays a role in GPCR transmembrane signaling

September 26, 2012
A recent study in The Journal of General Physiology characterizes the movement of rhodopsin, a GPCR and member of a large family of transmembrane receptors responsible for many cellular responses and involved in many human ...

Recommended for you

Researchers find monkey brain structure that decides if viewed objects are new or unidentified

August 18, 2017
A team of researchers working at the University of Tokyo School of Medicine has found what they believe is the part of the monkey brain that decides if something that is being viewed is recognizable. In their paper published ...

Artificial neural networks decode brain activity during performed and imagined movements

August 18, 2017
Artificial intelligence has far outpaced human intelligence in certain tasks. Several groups from the Freiburg excellence cluster BrainLinks-BrainTools led by neuroscientist private lecturer Dr. Tonio Ball are showing how ...

How whip-like cell appendages promote bodily fluid flow

August 18, 2017
Researchers at Nagoya University have identified a molecule that enables cell appendages called cilia to beat in a coordinated way to drive the flow of fluid around the brain; this prevents the accumulation of this fluid, ...

Study of nervous system cells can help to understand degenerative diseases

August 18, 2017
The results of a new study show that many of the genes expressed by microglia differ between humans and mice, which are frequently used as animal models in research on Alzheimer's disease and other neurodegenerative disorders.

Researchers make surprising discovery about how neurons talk to each other

August 17, 2017
Researchers at the University of Pittsburgh have uncovered the mechanism by which neurons keep up with the demands of repeatedly sending signals to other neurons. The new findings, made in fruit flies and mice, challenge ...

Neurons involved in learning, memory preservation less stable, more flexible than once thought

August 17, 2017
The human brain has a region of cells responsible for linking sensory cues to actions and behaviors and cataloging the link as a memory. Cells that form these links have been deemed highly stable and fixed.

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

ThanderMAX
not rated yet Oct 17, 2012
Wow, so our retina has better low-noise performance ?

Great
MrVibrating
not rated yet Oct 17, 2012
Exactly - this inhibitory action helps maintain an equilibrium baseline of responsiveness.

As ever, have to take this opportunity to give G. C. Huth's seminal work on the quantum mechanics of retinal function a quick plug... if you found this article interesting, check this out: http://www.ghuth.com/
PJS
not rated yet Oct 18, 2012
i never realized careening tennis balls were such a problem

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.