Did you know that 1965 physics laureate Richard Feynman was an enthusiastic correspondent? One of the most beautiful letters he wrote was to his first love and late wife Arline Greenbaum. The letter was written on this day 80 years ago. Greenbaum was Feynman's high school sweetheart who sadly passed away at the age of 25 from lymphatic tuberculosis. Feynman wrote her a love letter around two years after her death. A segment of the letter read: “When you were sick you worried because you could not give me something that you wanted to and thought I needed. You needn’t have worried. Just as I told you then there was no real need because I loved you in so many ways so much. And now it is clearly even more true — you can give me nothing now yet I love you so that you stand in my way of loving anyone else — but I want you to stand there. You, dead, are so much better than anyone else alive. I know you will assure me that I am foolish and that you want me to have full happiness and don't want to be in my way. I'll bet that you are surprised that I don't even have a girlfriend (except you, sweetheart) after two years. But you can't help it darling, nor can I—I don't understand it, for I have met many girls and very nice ones and I don't want to remain alone—but in two or three meetings they all seem ashes. You only are left to me. You are real. My darling wife, I do adore you. I love my wife. My wife is dead. Rich P.S. Please excuse my not mailing this—but I don't know your new address." This love letter is featured in Feynman's book of letters, 'Perfectly Reasonable Deviations from the Beaten Track', where more of his correspondence can be read. Photo from the Nobel Foundation archive.

What was this year’s medicine prize about? This year's Nobel Prize in Physiology or Medicine concerns the groundbreaking technique of optogenetics, which enables researchers to control individual nerve cells using light to switch them on or off. The method is used in laboratories around the world to investigate how nerve cells shape memories, emotions and behaviour in the living brain. For laureate Peter Hegemann, it all began with the question of how the green alga Chlamydomonas can detect light and move towards it. The algae sense the light with an eyespot that contains a light-capturing molecule, retinal. Hegemann discovered electrical signals in the eyespot that occurred just half a millisecond after illumination. He proposed that a single protein could both detect light and function as an ion channel, an idea that was initially met with scepticism. After several years of research, Hegemann and his colleague Georg Nagel demonstrated that the hypothesis was correct. They discovered proteins that open in response to light and published their findings in 2003. They also suggested that the protein channelrhodopsin-2 could be used to generate electrical impulses in cells using light. The baton was then taken up by the third laureate Karl Deisseroth. During his psychiatric training, Deisseroth realised that a deeper understanding of the brain’s neurons was essential for understanding the illnesses he encountered in his patients. When Deisseroth gained access to the DNA encoding channelrhodopsin-2, his research group introduced it into rat neurons. When the cells were exposed to blue light, they responded immediately, transmitting nerve signals to other neurons. Deisseroth’s research group published their discovery in 2005. The year after, this new method was given the name optogenetics. One year later, Deisseroth successfully activated nerve cells in the brains of living mice. Today optogenetics continues to unravel one of humanity’s greatest mysteries: how the brain works. Read more: nobelprize.org/prizes/medici…