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
WAKE-UP provides new treatment option for stroke patients | International study led by UKE
17.05.2018 | Universitätsklinikum Hamburg-Eppendorf
First form of therapy for childhood dementia CLN2 developed
25.04.2018 | Universitätsklinikum Hamburg-Eppendorf
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences