Modulation of central nystagmus by vision, proprioception, and efference copy signals: a systematic evaluation.

Non-vestibular sensorimotor signals modulate the vestibular nucleus neuron to achieve current behavioral goals, and may generate or modulate nystagmus. In central lesions affecting the vestibular nuclei, non-vestibular signals such as mastication or swallowing may induce nystagmus. However, the influence of non-vestibular signals on these types of nystagmus has not been investigated in a systematic way and the underlying mechanisms of the modulation are poorly understood. In this study, several non-vestibular sensorimotor stimuli were applied to evaluate the patterns of nystagmus modulation in a patient with suspected rhombencephalitis or imaging negative small infarction, probably involving the left dorsolateral medulla. The nystagmus was induced or significantly modulated by (1) visual inputs, and (2) combined proprioceptive and efference copy signals (during voluntary motion) unrelated to body or head orientation. In contrast, isolated proprioceptive signal, mental set, or non-proprioceptive somatosensory inputs showed a negligible effect on the induction of nystagmus. Based on these modulations, we suggest that (1) the visually mediated nystagmus is due to a lesion-induced pursuit asymmetry, and (2) the nystagmus induced during voluntary motion is due to erroneous contribution of combined proprioceptive and efference copy signals during integration of non-vestibular signals for ocular motor control. Various non-vestibular sensorimotor stimulations may induce nystagmus due to dysfunction of the central vestibular neural circuity.