A 64-year-old woman has 6 weeks of unsteadiness, episodic diplopia and downbeat nystagmus. MRI shows a small infarct in the cerebellar nodulus. RCT gain is normal but Tc is 34 s and she cannot suppress nystagmus when asked to fixate.
RCT pattern
Three-panel SHA summary. Shaded green = published normal band. Solid marker = patient/archetype curve; dashed = overlaid reference if shown.
Question
Which mechanism best explains the long Tc and failed suppression?