Now, collaboration between researchers at the Salk Institute for Biological Studies and Weill Cornell Medical College has revealed that brain cells processing visual information adjust their filtering properties to make the most sense of incoming information.
“We are best at discriminating the facial features that are typical of our neighbors, and if they happen to be parrots, we become very good at recognizing individual birds,” explains Tatyana Sharpee, Ph.D., an assistant professor in the Laboratory for Computational Biology and the lead author on the current study, which has been published in the August 5 online edition of the Journal of Computational Neuroscience.
Neurobiologists are on a perennial quest to understand how the brain codes and processes information. In the past, they had to rely on simplified objects on a computer screen or random stimuli to garner information on how the brain’s visual circuitry works. “Ultimately we are interested in what happens in a natural environment,” explains Sharpee, “but some questions require more control over the properties of visual stimuli than a picture of a natural scene would allow.”
Neurons in the primary visual cortex only respond when a stimulus appears within a window covering a small part of the visual field that the eye sees. This window is known as the neuron’s “receptive field.” Whenever a stimulus enters the neuron’s receptive field, the cell produces a volley of electrical spikes, known as “action potentials” that can be recorded.
But these neurons don’t react to just anything. Instead they are highly specialized and can only “see” a single attribute such as color, motion, or a specific luminance pattern. By measuring a certain neuron’s action potentials in response to random visual stimuli the researchers can infer the profile of its receptive field.
But growing evidence hints that this simple picture is incomplete. “The response of individual neurons can be strongly influenced by simple stimuli in the surround of the receptive field, a phenomenon known as contextual modulation,” explains Sharpee.
To unveil how contextual modulation shapes the apparent profile of neurons specialized in recognizing luminance patterns, Sharpee teamed up with Jonathan D. Victor, Ph.D., Fred Plum Professor of Neurology and Neuroscience at Weill Cornell Medical College in New York. The study made use of two sets of visual stimuli that were first introduced to neurophysiology by Victor. These stimuli matched in size, contrast, and luminance but differ in higher-order statistics leading to oriented checkerboard-like patterns in one case and pinwheel patterns in the other (see image). Single neurons’ responses to individual patterns were recorded in Victor’s laboratory.
Using complimentary methodologies developed by the two authors, who are leaders in applying information theory to extract meaning from a cacophony of signals, they then parsed the code for systematic, context-dependent changes in the neurons’ responses. Maybe not surprisingly, they found that larger receptive field components were more susceptible to contextual modulation and adjusted more than smaller ones.
But more importantly, they discovered that odd-symmetric components induced systematic changes across the whole population of neurons in the V1 area of the visual cortex, whereas even-symmetric components did not.
Odd-symmetric components are patterns that turn into their opposite when rotated by 180 degrees, such as a white and a black bar that are arranged parallel to each other. Even-symmetric components (such as a white bar sandwiched between two black bars) remain unchanged with this rotation.
“Context is an important part of how we perceive visual stimuli,” says Sharpee, “and these results show how individual neurons might adjust their properties in different natural environments, such as on a beach or in a forest.”
The research was supported by a grant from the Swartz Foundation and the National Institutes of Health.
The Salk Institute for Biological Studies in La Jolla, California, is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health and the training of future generations of researchers. Jonas Salk, M.D., whose polio vaccine all but eradicated the crippling disease poliomyelitis in 1955, opened the Institute in 1965 with a gift of land from the City of San Diego and the financial support of the March of Dimes.
Gina Kirchweger | Newswise Science News
Further reports about: > Wild Parrots
Amputees can learn to control a robotic arm with their minds
28.11.2017 | University of Chicago Medical Center
The importance of biodiversity in forests could increase due to climate change
17.11.2017 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong
Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
12.12.2017 | Physics and Astronomy
12.12.2017 | Earth Sciences
12.12.2017 | Power and Electrical Engineering