Down-regulation of early visual cortex excitability mediates oscillopsia suppression.

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  • Hena Ahmad
    Imperial College London
  • Ed Roberts
    Imperial College London
  • Mitesh Patel
    Imperial College London
  • Rhannon Lobo
    Imperial College London
  • Barry Seemungal
    Imperial College LondonImperial College Healthcare NHS Trust
  • Qadeer Arshad
    Imperial College London
  • Adolfo M Bronstein
    Imperial College LondonImperial College Healthcare NHS Trust
Objective: To identify in an observational study the neurophysiologic mechanisms that mediate adaptation to oscillopsia in patients with bilateral vestibular failure (BVF). Methods: We directly probe the hypothesis that adaptive changes that mediate oscillopsia suppression implicate the early visual-cortex (V1/V2). Accordingly, we investigated V1/V2 excitability using transcranial magnetic stimulation (TMS) in 12 avestibular patients and 12 healthy controls. Specifically, we assessed TMS-induced phosphene thresholds at baseline and cortical excitability changes while performing a visual motion adaptation paradigm during the following conditions: baseline measures (i.e., static), during visual motion (i.e., motion before adaptation), and during visual motion after 5 minutes of unidirectional visual motion adaptation (i.e., motion adapted). Results: Patients had significantly higher baseline phosphene thresholds, reflecting an underlying adaptive mechanism. Individual thresholds were correlated with oscillopsia symptom load. During the visual motion adaptation condition, no differences in excitability at baseline were observed, but during both the motion before adaptation and motion adapted conditions, we observed significantly attenuated cortical excitability in patients. Again, this attenuation in excitability was stronger in less symptomatic patients. Conclusions: Our findings provide neurophysiologic evidence that cortically mediated adaptive mechanisms in V1/V2 play a critical role in suppressing oscillopsia in patients with BVF.
Original languageEnglish
JournalNeurology
Volume89
Issue number11
Publication statusPublished - 16 Aug 2017
Externally publishedYes
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