F142. Corpus callosum and amblyopia: New evidence for an old debate. (May 2018)

• Record Type: Journal Article
• Authors: Bocci, Tommaso; Caleo, Matteo; Restani, Laura; Barloscio, Davide; Ferrucci, Roberta; Priori, Alberto; Nardi, Marco; Maffei, Lamberto; Sartucci, Ferdinando
• Is Part Of: Clinical neurophysiology. Volume 129(2018)Supplement 1
• Page Start: e120
• Page End: e121
• Publication Date: 2018-05
• Subjects: Neurophysiology -- Periodicals; Electroencephalography -- Periodicals; Electromyography -- Periodicals; Neurology -- Periodicals; 612.8
• DOI: 10.1016/j.clinph.2018.04.305
• Languages: English
• ISSNs: 1388-2457

Abstract

Abstract : Introduction: Amblyopia is a neurodevelopmental disorder characterized by visual acuity and contrast sensitivity loss, refractory to pharmacological and mechanical treatments in adulthood. In animal models, the corpus callosum (CC) plays a critical role in the development of the ocular dominance, thus strengthening the hypothesis of an involvement of both striate and extrastriate areas in the pathogenesis of amblyopia. To investigate the role of interhemispheric pathways in amblyopia, we studied the response of the visual cortex to transcranial Direct Current Stimulation (tDCS) applied over the primary visual area (V1) contralateral to the amblyopic eye. Methods: Visual evoked potentials (VEPs) triggered by grating stimuli of different contrasts (K90%, K50%, K20%) were recorded in both hemispheres before and after inactivation of the occipital cortex of one side via cathodal tDCS (2.0 mA, 20′). VEPs were recorded before (T0), immediately after (T1) and 60′ following tDCS (T2). The display was either centered on the vertical meridian (central stimulation) or positioned in the right hemifield (with its inner edge at a distance of 1 degree from the fixation point). Visual acuity was tested at each time interval, to assess behavioral changes between active and sham stimulation. Results: Cathodal tDCS improved visual acuity respect to baseline (recovery of 8.4 ± 3.3 letters, Holm-Sidak post hoc method p < 0.01), whereas sham polarization had no significant effect. At T1, tDCS produced an inhibitory effect on VEPs amplitudes at all contrasts in the targeted side and a concurrent facilitation of responses in the hemisphere ipsilateral to the amblyopic eye; compared with controls, the facilitation persisted at T2 for mid-high contrasts (K50%-K90%; Holm-Sidak post hoc method, p < 0.001), while the stimulated hemisphere recovered more quickly from the inhibition. Conclusion: tDCS is a promising treatment for amblyopia in adults. The rapid recovery of excitability and the persistent transcallosal disinhibition following perturbation of cortical activity strongly supports a critical role of interhemispheric balance in the pathophysiology of amblyopia.