Marc Dax (27 December 1770 – 3 June 1837) was a French neurologist, sometimes credited for discovering the link between neurological damage to the left hemisphere, right-sided hemiplegia, and a loss of the ability to produce speech (aphasia).
He submitted his discovery, based on the observations of three patients in Montpellier, to the French Academy of Sciences and two previous notes were published in 1836, 25 years before Paul Broca's more famous description.
The publication included the 1836 memoir of Marc Dax, his deceased father, and additional clinical observations of his own on 140 patients.
In consequence, today the discovery of the link between the left hemisphere and speech is typically credited to Paul Broca.
According to authors Cubelli and Montagna, the Broca's theory should be renamed: The medical historians S. Finger, M. Crichtley and A. L. Benton were responsible for bringing to light the role and importance of the Daxes for neurolinguistics, in a number of papers.