Do the congenitally blind have a stria of Gennari? First intracortical insights in vivo.

The primary visual cortex V1, when dissected, is characterized by an easily identifiable anatomical landmark: the stria of Gennari or Gennari stripe. However, the origin and function of the Gennari stripe is so far unknown. In order to shed some light on this question, we acquired 7-T magnetic resonance imaging (MRI) brain scans of congenitally blind (CB) people, who have never had visual experience. If the stria of Gennari requires visual input to develop or to maintain its homeostasis, such subjects should lack this structure. If it is reliably detectable in the CB, it must form and persist independently of visual sensation. This question has never previously been explored in living subjects. For the first time, the use of 7-T high-resolution MRI enables such investigations because of the excellent signal-to-noise ratio at this magnetic field strength. For comparison, we scanned sighted subjects using the same experimental parameters. We detected the stria of Gennari reliably in both sighted and blind subjects, showing that this anatomical feature is not a developmental result of visual input, and it does not degenerate in the absence of visual input.