John Graham Nicholls FRS (19 December 1929 – 13 July 2023) was a British, American and Swiss physiologist and neuroscientist.

[1] He received his MD from Charing Cross Hospital and a PhD from the Department of Biophysics at University College London in 1955.

After reaching emeritus status in 1998, he was professor of neurobiology at the International School for Advanced Studies in Trieste, Italy, where he lived until his death.

The International Brain Research Organization named a fellowship in his honor and he was a Fellow of the Royal Society.

In invertebrate and mammalian nervous systems he studied synaptic transmission[7] as well as the problem of why neurons in the mammalian brain and spinal cord fail to regenerate after injury, in contrast to the precise regeneration of synaptic connections that he was the first to demonstrate using the leech.