Research from Dragoi lab on cortical adaptation published in Nature Communications
Recent research from the lab of Valentin Dragoi, PhD, Rochelle and Max Levit Distinguished Professor in the Neurosciences, on the adaptive capacity of visual cortical populations has been published in the January edition of Nature Communications.
Research performed in the Dragoi lab provides novel insight into how populations of neurons in the visual cortex undergo rapid plasticity at the same time scale of visual fixation to acquire visual information relevant to perception. The brain unconsciously accomplishes this task hundreds of thousands of times per day, and yet how this phenomenon manifests in the brain remains mysterious.
In previous studies, the focus has been on examining adaptive phenomenology along a single stimulus axis, such as orientation or color, separately. However, in their new study, titled “Adaptive coding across visual features during free-viewing and fixation conditions,” the lab conducted experiments across multiple axes simultaneously to simulate a more natural viewing experience.
Using chronically implanted Utah arrays, a high-channel count microelectrode, the Dragoi lab recorded the electrical activity of neural populations in the visual cortex of behaving animals. While animals maintained visual fixation on a computer screen, the team measured neural responses when stimuli were presented in isolation, and when they were preceded by a 300-ms oriented grating or color which were used as adaptors.
“We tested neurons’ responses to oriented or color stimuli when the population response was adapted to a stimulus that was lying across a cross-feature axis, for example testing cells to orientation while they were adapted to color,” Dragoi said. “We further employed advanced computational methods to decode the population response to extract measures of coding accuracy to each set of stimuli.”
The study from the Dragoi lab systematically examined the effects of cross-feature adaptation using a free-viewing paradigm allowing animals to voluntarily explore visual displays containing multiple stimulus features: color and orientation. The novel research showed that the accuracy of visual cortical populations to discriminate stimuli is improved after cross feature adaptation.
“Our most surprising finding is that a substantial fraction of visually-responsible neurons that were either untuned or poorly tuned for color or orientation, became tuned after adapting to stimuli lying on an orthogonal feature axis, which may lead to a major revision of sensory adaptation and its neural underpinnings,” Dragoi said.
Their research showed for the first time that untuned neurons could play a significant role in the adaptive coding of sensory inputs, despite usually being ignored in most studies of cortical function. Furthermore, following cross-feature adaptation, the remaining neurons which were either tuned to color or orientation significantly improved their stimulus tuning.
“These results also demonstrate that a mechanism previously believed to operate under particular stimulus conditions, for example, within a single feature axis, operates at a much larger scale than scientists believed,” Dragoi said. “This means that our brain networks are continuously undergoing rapid adaptation to help improve vision across a wide range of stimuli encountered during natural viewing.”
These findings from the Dragoi lab will lead to future experiments to test the perceptual effects of cross-feature adaptation by using both synthetic and natural stimuli. Furthermore, since studies from the Dragoi lab used parametrized synthetic stimuli, expansive research will need to be done using more complex, and natural stimuli.
“Adaptive changes in population coding accuracy similar to those shown here may exist in other brain areas,” Dragoi said. “Therefore, examining the adaptive properties of the neural code across the visual system, or other systems, will likely provide important clues about the link between neural population activity and perception during naturalistic viewing.”
First author for the paper is Sunny Nigam, PhD, postdoctoral research fellow in the Dragoi Lab. Other contributing authors from the Dragoi lab are Russell Milton, PhD, and Sorin Pojoga, PhD. The work was supported by NIH grants from the National Eye Institute.