Neuronal Responses in the Parieto — Insular Vestibular Cortex of Alert Java Monkeys (Maccaca Fascicularis)

The awake subject is aware of the space coordinates (vertical and horizontal plane) and the spatial relationship between the objects of the extrapersonal space. This percept remains approximately invariant when the subject moves or changes his position in space, a procedure requiring a continuous readjustment between personal space and extrapersonal space perception. This readjustment relies on input signals from different sensory modalities: the teleceptive modality of vision, the vestibular signals (otolith signals for static position, cupula receptor signals for dynamic position changes) and mechanoreceptor input from the body. The deep mechanoreceptors from the neck region (joints, tendon organs, muscle spindles (?)) are especially important since they signal the relative position between head and trunk. In addition the force (pressure) gradient over the whole body is an important component in the perception of space coordinates. When this force gradient caused by the effect of gravity on the body mass is substantially altered, spatial orientation is impaired, as everybody can experience when he dives for the first time.