Aim: 

The integration of vestibular and somatosensory signals is necessary for spatial orientation and reflex postural control. Vestibulospinal (VS) reflexes elicited by head motion contribute to postural stability. They are related to the direction of body motion, due to somatosensory neck afferents acting through the cerebellar vermis, where they modify the labyrinthine responses of Purkinje cells. Aim of the present experiments was to investigate, whether, within the cerebellar vermal cortex and the vestibular nuclei, the neuronal responses to the labyrinthine input can be also tuned by somatosensory limb afferents.

Methods: 

Winstar rats were submitted to wobble of the whole animal (5°, 0.156 Hz), which imposes to the head a tilt of constant amplitude, whose direction changes continuously, rotating in the horizontal plane. During this stimulus, the activity of units responsive to labyrinthine stimulation reaches its peak for a particular direction (D) of head tilt. Responses to wobble were recorded i) in the control condition (both forelimbs pointing forward) and ii) following a 90° rotation of the forelimb ipsilateral to the recording side towards the tail.

Results: 

Limb-to-body rotation decreased the gain of responses to wobble in both vestibular nuclei and cerebellar vermal cortex, while the D values were affected only within the cerebellum, which indicates that the spatiotemporal characteristics of labyrinthine responses were modified in the cerebellum, but not in the vestibular nuclei.

Conclusion: 

The results show that, following limb rotation, the gain of VS reflexes can be modified by the vestibular nuclei and the cerebellar cortex, while only the cerebellum may tune their spatial organization according to the limb-to-body position.