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The brain swims alone in its cranial cavity. Were it not for the senses, it would not know what is happening to it. But how does a stimulus become a perception? For example, how does the brain generate a coherent image from light waves? David Hubel and Torsten Wiesel shed light on this problem from 1958 - and were honored with a Nobel Prize in 1981 for their findings.

Seeing borders on a miracle: Light in the form of its smallest particles, the photons, falls on the light-sensing cells of the retina in the eye. As with a camera, an image is created that is upside down. And it's also pixelated, because each individual cell of the retina covers a small area of the visual field. When stimulated, it sends a nerve impulse along the visual pathway across the brain to the primary visual cortex. There, the signals are decoded pixel by pixel and put together to form an image of the outside world. But how exactly does information processing work?

what happened before

Some things about the visual processes were already known before Hubel and Wiesel entered the scene: in the retina, several receptor cells - the cones for color information, the rods for light-dark and movements - are connected to a ganglion cell via horizontal and bipolar cells. As early as 1950, the Hungarian-born American neurologist Stephen Kuffler investigated how these react to stimuli. Among other things, he discovered that they cover certain regions in the field of vision: If a stimulus occurs here, the cell produces a whole salvo of electrical impulses.

The axons of the ganglion cells form the optic nerve of each eye. Both cross at the optic chiasm, exchanging around 50 percent of their fibers. You then reach the lateral geniculate body of the thalamus (corpus geniculatum laterale, CGL for short), the only switchover station between the retina and the cortex. The Irishman Gordon Morgan Holmes and the Englishman Henry Head had already investigated the function of the CGL in 1908: its cells also react to punctiform light stimuli - just like the rods and cones of the retina.

Information travels further via visual radiation directly to the primary visual cortex (V1) where processing begins. But "no one had a clear idea of how to interpret this chain-like transmission of information from one stage to the next," David Hubel later wrote. The few scientists who tried to unravel the secret of the V1 in the 1950s had discovered nothing illuminating. In retrospect, Hubel was not surprised: the cells in V1 "...were much too picky to pay attention to something as gross as diffuse light".

David Hunter Hubel

Hubel met Torsten Wiesel in Kuffler's laboratory in 1958 - a Swede and a... Canadian? American? David Hubel was born in Ontario in 1926. This made him Canadian, which is why he was forced to serve in the Canadian Training Corps during the final stages of WWII. However, since his parents were Americans, he was drafted into the US Army in 1954 and served at Walter Reed Hospital. The Royal Society later stumbled upon this dual citizenship, not knowing whether to accept him as a regular or foreign member.

Hubel was already interested in science as a child. This was reflected not only, but also, in the mixing of explosives. He took physics and mathematics at McGill University in Montréal – not least to have enough time to play the piano. Rather on a whim, he also enrolled in medical school – and was accepted. Eventually, he decided to focus entirely on medicine. When he shared this with his physics professor, he replied, "Well, I admire your courage - I wish I could say the same about your judgment."

The physics professor was wrong: At the Walter Reed Hospital, Hubel began researching the cat's primary visual cortex. To this end, he developed the modern microelectrode made of metal and was thus able to measure the activity of individual cells.

Torsten Nils Wiesel

Wiesel, in his autobiography for the Nobel Foundation, describes himself as a rather lazy, mischievous student who was more interested in sports than anything else. This did not prevent him from doing his doctorate in medicine at the Stockholm Karolinska Institute and going to New York to work with Kuffler in 1955.

As inconspicuous as Wiesel's biography may have been in his youth, in old age he stood out for his commitment to human rights.