Temporal Sensitivity in a Hemianopic Visual Field Can Be Improved by Long-term Training Using Flicker Stimulation

Background: Blindness of a visual half-field (hemianopia) is a common symptom after postchiasmatic cerebral lesions. Although hemianopia severely limits activities of daily life, current clinical practice comprises no training of visual functions in the blind hemifield.

Objective: To find out whether flicker sensitivity in the blind hemifield can be improved with intensive training, and whether training with flicker stimulation can evoke changes in cortical responsiveness.

Methods: Two men with homonymous hemianopia participated in the experiments. They trained with flicker stimuli at 30 degrees or with flickering letters at 10 degrees eccentricity twice a week for a year, and continued training with more peripheral stimuli thereafter. Neuromagnetic responses were registered at 1-2-month intervals, and the Goldmann perimetry was recorded before, during and after training.

Results: Flicker sensitivity in the blind hemifield improved to the level of the intact hemifield within 30 degrees eccentricity in one participant and 20 degrees eccentricity in the other. Flickering letters were recognised equally at 10 degrees eccentricity in the blind and intact hemifields. Improvement spread from the stimulated horizontal meridian to the whole hemianopic field within 30 degrees. Before training, neuromagnetic recordings showed no signal above the noise level in the hemianopic side. During training, evoked fields emerged in both participants. No changes were found in the Goldmann perimetry.

Discussion: Results show that sensitivity to flicker could be fully restored in the stimulated region, that improvement in sensitivity spreads to the surrounding neuronal networks, and that, during training, accompanying changes occurred in the neuromagnetic fields.