Nav: Home

Neurobiology: Fixated on food?

November 20, 2017

Contrast has an impact on the optokinetic reflex, which enables us to clearly perceive the landscape from a moving train. Researchers from Ludwig-Maximilians-Universitaet (LMU) in Munich have now shown that visual features that modulate this ability are encoded in the retina.

When we gaze out the window of a moving train, our eye muscles are constantly at work, stabilizing the gaze in order to keep the passing landscape in focus. This so-called optokinetic reflex allows us to gauge the relative velocity of the passing scene, and thus helps us to stabilize the rapidly changing images on the retina - otherwise we would perceive what moves past us beyond the carriage window as a diffuse blur. Researchers led by LMU neurobiologist Professor Hans Straka have now shown experimentally that visual image features of the environment play an important role in the analysis and assessment of relative motion. In particular, they find that the levels of contrast determine the efficiency with which the passing parade is perceived by a moving observer. The results of the new study appear in the Journal of Experimental Biology.

All vertebrates display optokinetic reflexes, which are responsible for fine-tuning the involuntary movements of the eye muscles, which in turn permit us to faithfully stabilize objects when we move. The operation of this optokinetic system depends on rapid processing of visual information, and on the ability to realistically estimate the relative velocity of the objects in the passing scene - under widely varying levels of illumination. To investigate how visual parameters such as image patterns, lighting conditions and brightness contrasts modify this capacity, Straka and his colleagues turned to the African clawed frog Xenopus laevis, a popular model system in the field of neurobiology, and used a high-resolution video camera to follow eye movements in tadpoles. They revealed that, when confronted with a large field pattern of dots that moved back and forth, the eyes of the tadpole executed movements of larger amplitude when the pattern consisted of white dots on a black background than when the "color scheme" was reversed. In other words, the polarity of the contrast had a marked influence on the efficiency of perception of the moving pattern. The structure of the pattern itself, on the other hand, was irrelevant in this context.

"We then measured the activity of the optic nerve, which transmits the visual signal from the retina to the visual centers in the brain," Straka says. "The results revealed that the difference in the efficiency of motion perception is encoded at the level of the retina: White dots on a black background generate nerve impulse rates of higher amplitude than do black dots on a white ground." Strikingly, the brain is not involved in making this distinction. It simply picks up the impulse patterns from the retina and passes them on to the nerves that control the eye muscles. "This implies that the quality of the environmental motion characterized by brightly lit structures against a darker background - and hence the ability to track objects of interest - is greater than it is in the converse situation, where dark structures are viewed in a bright setting," as Straka explains. "We were very surprised to discover this difference. It may be a reflection of the fact that tadpoles spend their lives in a relatively turbid medium, and feed on items that are brighter than pond water. It could therefore be an adaptation to their lifestyle." Mature frogs, on the other hand, tend to swim nearer the surface and obtain their food at or above it. Hence, the LMU team now believes that a pattern of black dots against a white background is likely to evoke larger eye movements in adult Xenopus. They are now engaged on testing whether the relative efficiency of pattern recognition - mediated by the connectivity of the photoreceptors in the retina - is reversed during metamorphosis when the tadpole is transformed into the mature frog. "If the adult frog is in fact better equipped to perceive dark patterns against a bright background, that would prove that the relative efficiencies of different modes of pattern recognition are defined by the animal's mode of life", Straka concludes.
-end-


Ludwig-Maximilians-Universität München

Related Neurobiology Articles:

Tone of voice matters in neuronal communication
Neuronal communication is so fast, and at such a small scale, that it is exceedingly difficult to explain precisely how it occurs.
How the brain's inner clock measures seconds
UCLA researchers have pinpointed a second hand to the brain's internal clock.
Adaptation in single neurons provides memory for language processing
To understand language, we have to remember the words that were uttered and combine them into an interpretation.
Calcium channel subunits play a major role in autistic disorders
Neurobiologists at Johannes Gutenberg University Mainz (JGU) in Germany have found new evidence that specific calcium channel subunits play a crucial role in the development of excitatory and inhibitory synapses.
The neurobiology of social distance
Never before have we experienced social isolation on a massive scale as we have during the evolving COVID-19 pandemic.
Neurobiology of Disease publishes results of AFFiRiS' antibody mAB C6-17 in Huntington's
Monoclonal antibody mAB C6-17 targeting human/mutant huntingtin protein (HTT/mutHTT) was developed and characterized.
New imaging technique sheds light on adult zebrafish brain
Cornell scientists have developed a new technique for imaging a zebrafish's brain at all stages of its development, which could have implications for the study of human brain disorders, including autism.
Worm nerve responses for good and bad
Studies on a tiny soil worm help explain how animal nervous systems translate external signals as 'good' or 'bad' in order to elicit the appropriate response.
Brain imaging may improve diagnosis and treatment of mental health disorders
Brain imaging may one day be used to help diagnose mental health disorders--including depression and anxiety--with greater accuracy, according to a new study conducted in a large sample of youth at the University of Pennsylvania and led by Antonia Kaczkurkin, PhD and Theodore Satterthwaite, MD.
Skull features among Asian and Asian-derived groups differ significantly
Forensic anthropologists have now discovered that several skull features in Asian and Asian-derived groups differ significantly with regard to shape, such that they can be distinguished using statistical analyses.
More Neurobiology News and Neurobiology Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.