Ragnar Granit demonstrated the importance of cones to colour vision

Human vision works by the light around us being captured by a large number of light-sensitive cells located in the retinas at the back of our eyes. The activation of these photoreceptors produces signals that are sent to the brain. On the way, they pass various switching stations that convert them into information that the brain can interpret as an image.

The 1967 Nobel Prize in Physiology or Medicine rewarded discoveries on how this works. The prize was awarded to Ragnar Granit, then professor of neurophysiology at Karolinska Institutet, Keffer Hartline and George Wald for “their discoveries concerning the primary physiological and chemical visual processes in the eye”.

Early interest in colour vision

Ragnar Granit concentrated his work on colour vision, a field that captured his interest back when he was a doctoral student of medicine in Helsinki. Many of the discoveries that earned him the Nobel Prize were made in the 1930s at Helsinki University.

Together with a colleague, Granit developed an electrode so thin and sharp that it was able to register signals from individual neurons in the frog retina. With it, he succeeded in demonstrating that different cells are selectively sensitive to light within specific wavelength bands.

His results clarified experimentally how the eye transmits colour information to the brain. He went on to demonstrate the presence of a variety of retinal cells – cones – each sensitive to a different wavelength.

Opted for Karolinska Institutet

Ragnar Granit also provided experimental evidence that illumination of the eye not only stimulates but also inhibits impulses along the optic nerve. When his team flashed light into the eye while the off-impulses were active, they found that these impulses were inhibited.

At the end of the 1930s, Granit was an internationally sought-after scientist, but when the opportunity to head up the newly established Neurophysiology Department at Karolinska Institutet presented itself, he opted to move to Sweden.

Granit’s decision had a major impact on the development of neurophysiology as a discipline at Karolinska Institutet, where he and his group continued to study the eye and to map retinal colour coding in a wide range of vertebrates.

His department was eventually incorporated into the Medical Nobel Institute, and in 1946 Ragnar Granit was made professor of neurophysiology. The following year, the Nobel Institute relocated to new premisses on what is now Karolinska Institutet’s Solna campus.

Switched research tracks

At the end of the 1940s, Granit left vision research to devote his time instead to the neurophysiology of motor control, building up around it another successful research environment at Karolinska Institutet.

Ragnar Granit was born in 1900 and died in 1991. He had a life-long interest in the humanities and wrote cultural texts for the newspapers as well as books on a range of subjects, including life in research and a biography of neurophysiologist and 1932 Nobel laureate in Physiology or Medicine Charles Sherrington, in whose lab he worked as a young scientist and who remained his mentor and friend.

In his acceptance speech at the Nobel Prize ceremony in Stockholm, Granit admitted that he, like Charles Darwin before him, would go cold all over at the thought of the eye’s complexity. “But right now,” he said in closing, “I’m just feeling the warmth that the eye can emit, and am basking in it. Thank you.”