Vestibulo-ocular reflex.

The vestibulo-ocular reflex (VOR) ensures best vision during head motion by moving the eyes contrary to the head to stabilize the line of sight in space. The VOR has three main components: the peripheral sensory apparatus (a set of motion sensors: the semicircular canals, SCCs, and the otolith organs), a central processing mechanism, and the motor output (the eye muscles). The SCCs sense angular acceleration to detect head rotation; the otolith organs sense linear acceleration to detect both head translation and the position of the head relative to gravity. The SCCs are arranged in a push-pull configuration with two coplanar canals on each side (like the left and right horizontal canals) working together. During angular head movements, if one part is excited the other is inhibited and vice versa. While the head is at rest, the primary vestibular afferents have a tonic discharge which is exactly balanced between corresponding canals. During rotation, the head velocity corresponds to the difference in the firing rate between SCC pairs. Knowledge of the geometrical arrangement of the SCCs within the head and of the functional properties of the otolith organs allows to localize and interpret certain patterns of nystagmus and ocular misalignment. This is based on the experimental observation that stimulation of a single SCC leads v ia the VOR to slowphase eye movements that rotate the globe in a plane parallel to that of the stimulated canal. Furthermore, knowledge of the mechanisms that underlie compensation for vestibular disorders is essential for correctly diagnosing and effectively managing patients with vestibular disturbances.

Saccade velocity is controlled by polyglutamine size in spinocerebellar ataxia 2.

We assessed maximal saccade velocity (MSV) in 82 spinocerebellar ataxia type 2 (SCA2) patients and 80 controls, correlating it to disease duration, polyglutamine expansion size, age at onset, ataxia score, age, and sex. Little overlap with normal values was found even at earliest stages. Stepwise linear regression analysis showed that 60-degree MSV was strongly influenced by polyglutamine size and less by disease duration, whereas the reverse was found for ataxia score. Saccade velocity thus is a sensitive, quite specific, and objective endophenotype, useful to search polyglutamine modifier genes.

Cortical vestibular representation in the superior temporal gyrus.

We present the unique case of a patient with a circumscribed solitary cerebral metastasis of a malignant melanoma extending from the medial part of the superior temporal gyrus to the lower part of the 1st long insular gyrus causing gait and stance instability and an ipsiversive tilt of the subjective visual vertical. Oculomotor disorders could not be detected. We suggest that the superior temporal gyrus is likely to be involved in spatial orientation presumably using otolithic information.