Role of cerebellum in motion perception and vestibulo-ocular reflex-similarities and disparities.

Vestibular velocity storage enhances the efficacy of the angular vestibulo-ocular reflex (VOR) during relatively low-frequency head rotations. This function is modulated by GABA-mediated inhibitory cerebellar projections. Velocity storage also exists in perceptual pathway and has similar functional principles as VOR. However, it is not known whether the neural substrate for perception and VOR overlap. We propose two possibilities. First, there is the same velocity storage for both VOR and perception; second, there are nonoverlapping neural networks: one might be involved in perception and the other for the VOR. We investigated these possibilities by measuring VOR and perceptual responses in healthy human subjects during whole-body, constant-velocity rotation steps about all three dimensions (yaw, pitch, and roll) before and after 10 mg of 4-aminopyridine (4-AP). 4-AP, a selective blocker of inward rectifier potassium conductance, can lead to increased synchronization and precision of Purkinje neuron discharge and possibly enhance the GABAergic action. Hence 4-AP could reduce the decay time constant of the perceived angular velocity and VOR. We found that 4-AP reduced the decay time constant, but the amount of reduction in the two processes, perception and VOR, was not the same, suggesting the possibility of nonoverlapping or partially overlapping neural substrates for VOR and perception. We also noted that, unlike the VOR, the perceived angular velocity gradually built up and plateau prior to decay. Hence, the perception pathway may have additional mechanism that changes the dynamics of perceived angular velocity beyond the velocity storage. 4-AP had no effects on the duration of build-up of perceived angular velocity, suggesting that the higher order processing of perception, beyond the velocity storage, might not occur under the influence of mechanism that could be influenced by 4-AP.

International Classification of Functioning, Disability and Health (ICF) Core Set for patients with vertigo, dizziness and balance disorders.

Vertigo, dizziness and balance disorders have major impact on independence, employability, activities and participation. There are many measures for the assessment of the impact of vertigo, but no consensus exists on which aspects should be measured. The objective of this study was to develop international standards (ICF Core Sets) for patients with vertigo and dizziness to describe functioning. The development of the ICF Core Sets involved a formal decision-making and consensus process, integrating evidence from preparatory studies including qualitative interviews with patients, a systematic review of the literature, a survey with health professionals, and empirical data collection from patients. Twenty-seven experts selected 100 second level categories for the comprehensive Core Set and 29 second level categories for the Brief Core Set. The largest number of categories was selected from the ICF component Activities and Participation (40). Twenty-five categories were selected from the component Body Functions, six from Body Structures, and 29 from Environmental Factors. The ICF Core Set for vertigo is designed for physicians, nurses, therapists and other health professionals working in inpatient or ambulatory settings. ICF Core Sets create patient-relevant outcomes that can be used as evidence for the success of treatments.

Central and peripheral visual interactions in disparity-induced vergence eye movements: I. Spatial interaction.

PURPOSE: To evaluate the interaction between central and peripheral disparities in the initiation of vergence eye movements. METHODS: Eye movements were recorded in eight normal subjects using an infrared limbus tracker. Three-dimensional visual stimuli were back projected onto a tangent screen by using two liquid crystal display (LCD) projectors through crossed polarizers. The central target was a vertical bar, which always jumped from 2 to 1 m. The peripheral target was a random-dot pattern that jumped from 2 to 0.75, 1, or 1.5 m (near planes), 2 m (no change), or 3 m (far plane) simultaneously with the central target jump. Latency, amplitude at 150 ms, and average amplitude over 1 to 2 seconds after vergence onset; peak velocity; and the main-sequence relationship of the initial vergence response were calculated. How far the central target appeared to jump was scored subjectively. RESULTS: In half of the subjects, there was a clear effect of the peripheral disparity on the dynamics of the vergence response to the central disparity. The amplitude of vergence at 150 ms, as an index of open-loop gain, was significantly greater when the peripheral target moved closer, but steady state amplitude (average during 1-2 seconds) did not change, and the vergence latency was significantly greater when the peripheral target jumped away. There was no obvious relationship between the perceived amount of movement of the central target and the parameters of the dynamic properties of the vergence response. CONCLUSIONS: Peripheral disparity can modulate the dynamics of the initial vergence response to a central disparity and is probably independent of the perception of motion in depth.

Evaluating the dizzy patient: bedside examination and laboratory assessment of the vestibular system.

Dizziness and imbalance are common presenting complaints to the neurologist. The lack of a systematic approach to the examination and laboratory evaluation of the vestibular system often leads to incorrect diagnoses and suboptimal care. With a basic understanding of vestibular physiology and proper examination techniques, a correct diagnosis can generally be made at the bedside. We review the principles of the neuro-otological examination, including assessment for static vestibular imbalance, dynamic vestibular function, provocative maneuvers, ocular motor examination, and vestibulospinal testing. The use of additional vestibular laboratory testing and neuroimaging is then considered to further localize and quantify abnormalities.