David Hubel: The Scientist
By: Howard Akler
When David Hubel and Torsten Wiesel first began to collaborate, visual physiology was unknown territory. They had no hypotheses on the workings of the visual cortex, the part of the brain that processes images. Their work was pure exploration. As Hubel recalled in his Nobel lecture, they worked “in a dark and dingy inner windowless room of the Wilmer Institute basement, deemed ideal for visual studies.”
Their idea was to display visual stimuli to a cat and then record the electrical activity in its brain. The cat would respond to whatever it saw, and this response would activate the corresponding cell in the visual cortex. To do so, they applied a Tungsten electrode, which Hubel had devised during his army days, to the base of the cat’s skull. This electrode was sensitive enough to capture the blip from a single brain cell. Any neuronal activity would be amplified by an audio monitor. The cat felt no pain; in fact, the audio was sometimes drowned out by the sound of purring.
They showed the cat a variety of visual stimuli on a slide projector. Very often, there would be no response. The cat would see a dot, and nothing. A bright light, and nothing. Hubel waved his hand back and forth, and nothing. One time, the scientists even did a dance in front of the perplexed feline. The experiments went on and on. They were patient, and often worked well into the early morning hours. “I knew we were losing traction in an experiment when Torsten began to talk to me in Swedish; usually this was around 3 a.m.,” Hubel later said.
Then, one day, by accident, they were successful. Somehow, the edge of a slide got jammed in the projector. The cat saw the edge of the slide, a small straight line at a specific angle, and the cell fired like crazy. They studied the responses from this single brain cell for nine hours. They felt more and more confident with their findings, and then, finally certain, ran down the hallway, screaming with joy.
The scientists had discovered that specific cells respond to very specific visual information. Pattern, colour, contrast, angle: every minutiae is analyzed and then assembled in the brain, creating detailed mental images of the world. Hubel and Wiesel determined that vision cells with similar functions are grouped together in tight vertical clusters, or columns, and that this structure creates an almost unimaginable level of connectivity. They now understood that visual processing is extremely specialized. Systematically, painstakingly, they mapped out the entire visual cortex.
This research led to another discovery. They had already located which columns receive information from the left eye and which ones from the right eye. Now, they wondered what might happen if one eye was covered shortly after birth. Tests on kittens and baby monkeys proved that columns associated with the covered eye withered, while the eye that retained visual stimuli became dominant. From this they deduced that babies born with amblyopia (“lazy eye”), or strabismus (“cross eye”) needed timely corrective treatment; otherwise, their vision would not develop normally.
Forty years after his famous discovery, Hubel reminisced about the drama of scientific research. “When we succeed and can suddenly make a cell fire like a machine gun, it can be thrilling — and on a good day, the thrill may come every few hours.”