Tip of the Month
Publishing date: January 2009
Tip Editors: Ann Hoste, John Salmon and John Thygesen
Tip reviewer: Roger Hitchings
The Science behind the Tip
Contrary to long held beliefs, cortical maps in the brain are not rigid. Extensive reorganization (i.e. brain remapping) takes place after deprivation of sensory input due to peripheral damage. Cortical plasticity enables normal cortical cells that surround a lesion to assist the deprived ones, resulting in quite dramatic effects on a patient's perception. Phantom pain in an amputated limb is a striking example. Similarly, damage to the visual system activates longe-range horizontal synapses between cells in the primary visual cortex that are normally in a subtreshold state (1). Thus, silenced areas in the visual cortex recover visually driven activity and as a result, the brain fills-in field defects (2,3).
The images with corresponding field tests demonstrate that glaucomatous defects are not perceived as black clouds because they are concealed by the brain in patterns and colours of the surround (4).
Contributor: Ann Hoste, Antwerp
Co-editors: John Thygesen and Ann Hoste
Peer reviewers: Roger Hitchings and Anders Heijl
1. Das A, Gilbert CD. Long-range horizontal connections and their role in cortical reorganization revealed by optical recording of cat primary visual cortex. Nature. 1995;375:780-4.
2. Ramachandran VS, Gregory RL. Perceptual filling in of artificially induced scotomas in human vision. Nature. 1991;350:699-702.
3. Safran AB, Landis T. Plasticity in the adult visual cortex: implications for the diagnosis of visual field defects and visual rehabilitation. Curr Opin Ophthalmol. 1996;7:53-64.
4. Hoste AM. New insights into the subjective perception of visual field defects. Bull Soc Belge Ophtalmol. 2003;287:65-71.
You can find the abstracts here.