Velocity Storage Integrator (VSI): Mechanisms, circuits, and clinical implications A narrative review

Area of Science:

• Neuroscience
• Vestibular System Physiology
• Computational Neuroscience

Background:

• The velocity storage integrator (VSI) is a neural network essential for prolonging and orienting vestibular and optokinetic signals.
• Classical models viewed VSI as a leaky integrator in an indirect pathway, complementing a direct pathway for rapid gaze stabilization.

Purpose of the Study:

• To synthesize evidence localizing the VSI's spatiotemporal core to commissural vestibular-nuclei networks.
• To elucidate the role of cerebellar nodulus-uvula (NU) in controlling VSI via internal-model feedback.
• To differentiate the VSI's function from the nucleus prepositus hypoglossi (NPH/PPH) in velocity-to-position integration.

Main Methods:

• Review and synthesis of anatomical, physiological, computational, and clinical evidence.
• Analysis of unit recordings, lesion studies, and computational modeling.
• Pharmacological studies using GABA_B agonists and altered-gravity experiments.

Main Results:

• The VSI's core is localized to vestibular-nuclei networks (VO, VPS) under NU control, which regulates gravity alignment and time constants.
• Pharmacological manipulation (baclofen) affects VSI time constants and motion sickness susceptibility.
• Gravity significantly influences VSI persistence and Coriolis cross-coupling, with afferent-class mapping explaining stimulus-dependent behaviors.

Conclusions:

• A unified framework for velocity storage is presented, distinguishing the VSI (neural substrate) from the VSM (phenotype).
• The VSI's gravity dependence and multisensory updating are highlighted.
• This framework provides biomarkers and therapeutic targets for vestibular disorders.