Sir JCass has reminded me that Jean-Jacques Rousseau, in all likelihood, suffered from a paranoid disorder. One can pick out distant echoes of mental distress from this episode, as told by Mme de Genlis in her memoirs:
He [JJR] often talked to us of the manner in which he had composed the Nouvelle Héloïse. He told us that he wrote all the letters of Julie on beautiful small-letter paper with vignettes – that he afterward folded them like letters, and read them in his walks with as much transport as if he had received them from an adored mistress.
This reminded me of Dmitry Pisarev (1840-68), the radical Russian literary critic who suffered from an unidentified psychiatric illness labeled dementia melancholica. It was not dementia in the modern sense – Pisarev was a brilliant young man with a gift for languages – but it was undoubtedly a disorder. The protagonist of Nabokov’s last Russian novel, The Gift, wrote in his essay on Chernyshevsky – the (in)famous Chapter Four:
Just as, in his boyhood, he had arrayed all his notebooks in rainbow covers, so, as a grown man, Pisarev would suddenly abandon some urgent work in order to painstakingly color woodcuts in books…
(Translated by Michael Scammell.) LanguageHat has recently pointed out this sentence from Samuil Lurie‘s novel Pisarev, a Man of Letters:
He took down lectures [at St. Petersburg University] in minute handwriting in pretty little notebooks decorated with decalcomania and little sheets of pink blotting paper.
Pisarev was treated at a psychiatric clinic in 1859-60, but his mental health likely deteriorated further during his imprisonment in the Fortress of St. Peter and St. Paul (Petropavlovskaya Krepost’) in 1862-1866. He enjoyed a brief period of great influence over the Russian students and progressive youth, which did not end with his imprisonment as he was allowed to write from his cell. He drowned near Riga in 1868.