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Temporal sensitivity in a hemianopic visual field can be improved by long-term training using flicker stimulation
  1. A Raninen1,
  2. S Vanni2,
  3. L Hyvärinen3,
  4. R Näsänen4
  1. 1Department of Bio and Environmental Sciences, Physiology, Biocentre 3, University of Helsinki, Helsinki, Finland
  2. 2Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland
  3. 3Faculty of Behavioural Sciences, University of Helsinki, Helsinki, Finland
  4. 4Finnish Institute of Occupational Health, Helsinki, Finland
  1. Correspondence to:
 A Raninen
 Department of Bio and Environmental Sciences, Physiology, Biocentre 3, PO Box 65, University of Helsinki, FI-00014, Finland;raninen{at}mappi.helsinki.fi

Abstract

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° or with flickering letters at 10° 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° eccentricity in one participant and 20° eccentricity in the other. Flickering letters were recognised equally at 10° eccentricity in the blind and intact hemifields. Improvement spread from the stimulated horizontal meridian to the whole hemianopic field within 30°. 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.

  • fMRI, functional magnetic resonance imaging
  • MEG, magnetoencephalography

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Footnotes

  • Published Online First 4 September 2006

  • Funding: This study was supported by the Academy of Finland grant number 105628, the Sigrid Juselius Foundation, the Finnish Medical Foundation and the De Blindas Vänner rf - Sokeain Ystävät ry.

  • Competing interests: None.

  • Ethical approval: The study was approved by the ethics committee of the Hospital District of Helsinki and Uusimaa. Tenets of the Declaration of Helsinki were followed.

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