Instability of R3 response of the blink reflex in patients with HAM/TSP.

HAM/TSP patients presenting interneuronal hyperexcitability of the brainstem displayed the R3 response with closed eyes but this was either diminished or disappeared contralaterally to the stimulation side when they were tested with their eyes open. Lack of regulation of the interneuronal network between R1 and R3 could be the most probable cause of these features.