Cerebral Cortex Advance Access published online on February 3, 2008
Cerebral Cortex, doi:10.1093/cercor/bhm256
V1 Projection Zone Signals in Human Macular Degeneration Depend on Task, not Stimulus
1 Psychology, Stanford University, Stanford, CA 94305, USA, 2 Ophthalmology, Jikei University, School of Medicine, Tokyo, 105-8461 Japan
Address correspondence to Yoichiro Masuda, Wandell Laboratory, Jordan Hall, Building 420, Stanford University, Stanford, CA 94305, USA. Email: massuuu{at}gmail.com.
We used functional magnetic resonance imaging to assess abnormal cortical signals in humans with juvenile macular degeneration (JMD). These signals have been interpreted as indicating large-scale cortical reorganization. Subjects viewed a stimulus passively or performed a task; the task was either related or unrelated to the stimulus. During passive viewing, or while performing tasks unrelated to the stimulus, there were large unresponsive V1 regions. These regions included the foveal projection zone, and we refer to them as the lesion projection zone (LPZ). In 3 JMD subjects, we observed highly significant responses in the LPZ while they performed stimulus-related judgments. In control subjects, where we presented the stimulus only within the peripheral visual field, there was no V1 response in the foveal projection zone in any condition. The difference between JMD and control responses can be explained by hypotheses that have very different implications for V1 reorganization. In controls retinal afferents carry signals indicating the presence of a uniform (zero-contrast) region of the visual field. Deletion of retinal input may 1) spur the formation of new cortical pathways that carry task-dependent signals (reorganization), or 2) unmask preexisting task-dependent cortical signals that ordinarily are suppressed by the deleted signals (no reorganization).
Key Words: feed-back • fMRI • human • plasticity • retinal degeneration • visual cortex