Vestibular Signals during Active and Passive Head Movements

Active and passive head movements both generate sensory signals in the vestibular system, yet require completely different reactions to this input. Here we investigate the context-dependent processing of vestibular signals with a variety of methods. To clarify the role of vestibular sensory information during active head movements, we measured eye and head movements in healthy subjects and patients without vestibular function. We challenged the head-motor system by artificially increasing the head moment of inertia. While active head movements were unaffected by the intervention in healthy subjects, the head markedly oscillated in patients, demonstrating that vestibular feedback plays a role in active movements. To reveal the processing from sensory input to motor output, we examined and modelled secondary neurons and their connectivity in the vestibular nuclei (cooperation with Hans Straka, CNRS Paris). The results emphasize a synergistic role of both membrane and network properties. Finally, we continued our modelling efforts of downbeat nystagmus, an ocular motor syndrome that was previously considered to be of vestibular origin. We could show that damage of cerebellar Purkinje cells in the floccular lobe responsible for smooth pursuit and gaze holding explains all symptoms related to downbeat nystagmus.

Modelling of 2nd-order vestibular neurons.

Upper row: schematic experimental setup: pulse train applied as stimulus to the vestibular nerve;intracellular recording of the 2nd-order neuron.

Middle row: example data from the two types of neurons measured.

Lower row: model responses.