Functional analysis of primary visual cortex (V1) in humans

Functional analysis of primary visual cortex (V1) in humans

Nuclear Magnetic Resonance Center, Massachusetts General Hospital, 149 13th Street, Charlestown, MA 02129

Abstract

Human area V1 offers an excellent opportunity to study, using functional MRI, a range of properties in a specific cortical visual area, whose borders are defined objectively and convergently by retinotopic criteria. The retinotopy in V1 (also known as primary visual cortex, striate cortex, or Brodmann’s area 17) was defined in each subject by using both stationary and phase-encoded polar coordinate stimuli. Data from V1 and neighboring retinotopic areas were displayed on flattened cortical maps. In additional tests we revealed the paired cortical representations of the monocular “blind spot.” We also activated area V1 preferentially (relative to other extrastriate areas) by presenting radial gratings alternating between 6% and 100% contrast. Finally, we showed evidence for orientation selectivity in V1 by measuring transient functional MRI increases produced at the change in response to gratings of differing orientations. By systematically varying the orientations presented, we were able to measure the bandwidth of the orientation “transients” (45°).

Footnotes

↵ * To whom reprint requests should be addressed. e-mail: tootell{at}nmr.mgh.harvard.edu.
This paper was presented at a colloquium entitled “Neuroimaging of Human Brain Function,” organized by Michael Posner and Marcus E. Raichle, held May 29–31, 1997, sponsored by the National Academy of Sciences at the Arnold and Mabel Beckman Center in Irvine, CA.
ABBREVIATIONS:

MR,

magnetic resonance;

MRI,

MR imaging;

fMRI,

functional MRI