Snap! Crackle! Pop!
Those are the sounds that Professors David Hubel and Torsten Wiesel heard in the early 1950s when they recorded from neurons in the visual cortex of a cat, as they moved a bright line across its retina. During their recordings, they noticed a few interesting things: (1) the neurons fired only when the line was in a particular place on the retina, (2) the activity of these neurons changed depending on the orientation of the line, and (3) sometimes the neurons fired only when the line was moving in a particular direction.
Turn up your volume and listen to the neuronal activity of these visual cortex neurons!
The classic experiments by Hubel and Wiesel are fundamental to our understanding of how neurons along the visual pathway extract increasingly complex information from the pattern of light cast on the retina to construct an image. For one, they showed that there is a topographical map in the visual cortex that represents the visual field, where nearby cells process information from nearby visual fields. Moreover, their work determined that neurons in the visual cortex are arranged in a precise architecture. Cells with similar functions are organized into columns, tiny computational machines that relay information to a higher region of the brain, where a visual image is formed. In all, their work revealed how visual cortical neurons encoded image features, the fundamental properties of objects that help us build our perception of the world around us.
But they didn’t start out with such clear-cut results and meticulous recordings. Rather, their initial discovery was the result of pure luck! Working in a tiny basement laboratory at Johns Hopkins, Hubel and Wiesel struggled to find any neuronal activity in cat’s brain that correlated with images of dark and light spots. Becoming increasingly frustrated, they waved their arms, jumped around, and even displayed images of glamorous women from magazines! Alas, nothing.
Then, as they shifted a slide in the ophthalmoscope, they heard a cell in the cat’s visual cortex fire. The edge of the slide had cast a faint, straight, narrow line on the cat’s retina. They studied the cell for nine hours and then ran down the hall screaming with joy!
You can hear Dr. Hubel describe it here:
Shortly after it was announced that Hubel and Wiesel would be awarded the Nobel Prize in Physiology and Medicine in 1981, Dr. Hubel said, “There has been a myth that the brain cannot understand itself. It is compared to a man trying to lift himself by his own bootstraps. We feel that is nonsense. The brain can be studied just as the kidney can.”
Touché, Dr. Hubel, touché.
Image by Jooyeun Lee.