Duke Institute for Brain Sciences

Watching Brain Circuits Develop

November 05, 2008

By Len White

At birth or soon thereafter, most mammals open their eyes for the first time and experience the shapes, colors, textures and patterns of motion that define the visual environment. But are the visual centers of the brain ready to receive and process such fundamental signals that provide the foundation for visual perception and visually guided behavior? The conventional wisdom in developmental neuroscience would answer “yes;” but recent evidence has begun to challenge the notion that the brain possesses the capacity to process and analyze most — if not all — fundamental visual cues at the onset of visual experience. Now, a new paper published in Nature, authored by Li et al. from the Department of Neurobiology and the Duke Institute for Brain Sciences, takes this challenge one important step further. This paper shows that the neural circuits in the visual cortex that discriminate directions of motion develop after eye opening. But this is no coincidence; the study shows that neural circuits learn to discriminate opposite directions of motion only if they are exposed to those patterns of motion in an early, critical phase of visual experience.

The study used cutting-edge methods of brain imaging, making it possible to literally watch the development of direction selectivity in a population of neurons in the visual cortex. Direction selectivity refers to the ability of neurons in the visual centers of the brain to respond preferentially to one direction of stimulus motion more so than any other (for example, “up” versus “down”). When the scientists examined the direction selective responses of animals that had very little visual experience, only a very small minority of neurons could reliably discriminate opposite directions of motion. By contrast, most neurons in more mature animals show reliable responses that prefer just one direction of motion over any other. Remarkably, as the investigators exposed the immature animals to stimulus patterns that moved in one direction and then the opposite direction, they were able to observe – in a matter of hours – a rapid emergence of responses that indicate the development of direction selectivity. This was observed both at the level of individual neurons and at the level of columnar circuits that organize direction selectivity across the entire network of neurons in the visual cortex.

Significantly, this study shows how structured sensory experience in early life alters the response properties of individual neurons and the functional organization of neural circuits in the cerebral cortex. This discovery could prove to be invaluable for understanding ongoing brain development in infancy, the formative impact of early sensory experience, and the neurobiological mechanisms that could go awry in a broad spectrum of developmental brain disorders that affect the construction of circuitry in the cortex. Read the press release from the Duke Office of News and Communications.