Role of vision in the development of inhibitory networks
Brain function, like many other areas of life, is all about balance. Excitatory neurons that increase the activity of connected neurons are balanced by inhibitory neurons that dampen this activity. In this way, excitation and inhibition work together throughout the brain to process information and guide behavior. An imbalance of these systems, which can sometimes occur during development, contributes to neurodevelopmental disorders such as autism. Until recently, researchers have mainly focused on excitatory neurons, while the function and development of inhibitory neural circuits have been little studied.
New research from the Max Planck Florida Institute for Neuroscience demonstrates that the inhibitory and excitatory neural circuits of the visual system develop through different processes, even though the organization of the mature circuit is similar. These results, published in Nature Communications, underline the importance of continuing to study the development of these two systems, the understanding of which is fundamental to understanding neurodevelopmental disorders.
An area of the brain that processes visual information, the primary visual cortex, is highly organized, forming patches of neighboring neurons that tend to be active together and respond to similar visual characteristics. In mammals, these modular functional maps consist of both excitatory and inhibitory neurons that work together to create an accurate representation of the world.
Scientists Jeremy Chang and David Fitzpatrick have now characterized the development of these functional maps for inhibitory neurons in the primary visual cortex. Although excitatory and inhibitory functional maps are paired at maturity, their development occurs through different parallel processes.
Excitatory neurons exhibit a modular organization early on, before the eyes open and visual input is received. Neighboring neurons respond to visual images in a correlated manner and show similar preferences for stimuli presented in specific orientations. While the visual experience refines particular properties of these maps, such as the alignment of visual information from each eye, the basic features of modular organization are present before the visual experience.
Dr. Chang found that inhibitory neurons, on the other hand, lack much of this modular activity prior to visual experience. “It was a surprise,” he admitted. “We did not expect the functional maps seen before eye opening in excitatory neurons to be nearly absent in inhibitory neurons.” This suggests that the development of a mature functional organization of inhibitory neurons requires visual experience. In fact, if visual input was delayed, the development of many features of functional inhibitory neural maps was also delayed.
This work contributes to the fundamental understanding of larger questions about the role of inhibition in the cortex, which the lab will continue to explore. “New techniques developed over the past decade have allowed us to image the activity of inhibitory neurons in response to visual images. We are beginning to understand the functional importance of inhibition in visual processing and how the role of inhibition changes throughout development. During development, inhibitory and excitatory neurons have to solve different puzzles to find each other in the right place, connect to the right partners, and fine-tune their connections in response to experience,” Chang said. Future work will focus on understanding how these puzzles are solved.
This research was supported by the National Eye Institute of the National Institutes of Health under award numbers EY011488 and EY026273 and the Max Planck Florida Institute for Neuroscience. This content is the sole responsibility of the authors and does not necessarily represent the official views of the funders.
Chang, JT and Fitzpatrick, D. (2022). Development of visual response selectivity in cortical GABAergic interneurons. Nature Communications, 13(1), 3791. Link