Dr. David Hubel, a founder of modern neuroscience who helped decipher how our brains perceive what our eyes see, passed away on Sunday, September 22. He was 87.
When Hubel was a young scientist in the 1950s, the field of “neuroscience” didn’t exist, at least not in the strictest sense. In fact, the term wasn’t even coined until the 1960s. At that time, there also weren’t any academic programs in the U.S. dedicated to neuroscience; Hubel and a small group of other scientists at Harvard University established the first one in 1966.
In collaboration with his Harvard colleague Torsten Wiesel, Hubel was among the first scientists to explore the inner workings of the cerebral cortex, the outermost layer of the brain that is responsible for higher functions like memory, planning, language, and making sense of the world around us. Without the aid of brain imaging techniques that are commonplace today, the two researchers built a functional map of the visual cortex, creating a framework to understand how simple visual sensations—essentially spots of light—are ultimately assembled into complex scenes.
The work eventually earned them the 1981 Nobel Prize in Physiology or Medicine, which they shared with Roger W. Sperry, whose work established functional differences between the right and left halves of the cortex.
Hubel and Wiesel focused on the visual cortex out of both curiosity and convenience. “It seemed most sensible to look at a primary sensory area, and the visual [cortex] was easiest” because the eyes connect directly to the brain through the optic nerve, Hubel said about winning the Nobel. Prior research on the retina also gave them a starting point to ask how retinal inputs are interpreted by the brain.
Nerve cells in the retina detect simple visual information like changes in brightness. And each cell responds to a limited area of visual space, called a receptive field. So how does the visual cortex turn this information into a visual scene?
In research on animals, Hubel and Wiesel asked that question by using fine wires to record the electrical responses of cortical cells to visual stimulation. Using a slide projector, they started with the simplest of visual objects: different-sized spots. Nothing seemed to trigger a response, until one experiment where they continued recording from a cell while they inserted a new slide into the projector. The moving edge of the slide caused the cell to fire “like a machine gun,” Hubel had said.
It was the beginning to their discovery that cortical cells have receptive fields that are exacting, complex, and diverse compared to those of retinal cells. There are cortical cells that respond best to lines at a specific angle, motion in a specific direction, objects with distinct corners and edges, or some combination of these features. Some cortical cells respond only to one eye and others respond to both eyes equally, with a range of preferences in between. In later research, Hubel also discovered dense cell clusters, called blobs, that respond to different colors. In ways that still aren’t fully understood, the merging of these responses allows us to perceive complex shapes, color palettes, movement, and depth in a visual scene.
Hubel and Wiesel were also pioneers in the study of plasticity—the brain’s ability to adapt to new experiences. By mapping how the eyes connect to the brain during development, they found that the eyes compete for limited territory based on visual experience. So if vision through one eye is temporarily impaired—by a cataract, for example—the brain begins to favor the other eye. This process is called ocular dominance. It can lead to a condition called amblyopia, in which vision through the impaired eye becomes permanently weakened, even after the original problem is corrected.
Hubel and Wiesel established that ocular dominance takes place within a limited window of early life called the critical period. Those findings had a clinical impact, encouraging eye care professionals to treat amblyopia as early as possible. The work also established the visual system as a useful model of studying limits on brain plasticity. New research on ocular dominance by Dr. Carla Shatz at Stanford, who was a graduate student with Hubel, has even pointed to a potential new drug target for restoring lost plasticity in Alzheimer’s disease.
Much of Hubel and Wiesel’s work was supported by the National Eye Institute (NEI). Hubel served on the National Advisory Eye Council from 1996 to 1999.
“All of neuroscience, and especially vision science, owes a great debt to David Hubel,” said Dr. Paul Sieving, director of the NEI. “His trailblazing and now classic work on the visual system continues to inform and inspire new generations of researchers.”