Can imaginary head tilt shorten postrotatory nystagmus?

Area of Science:

• Vestibular System Physiology
• Neuroscience
• Oculomotor Control

Background:

• Postrotatory nystagmus duration is shortened by head tilt after yaw rotation.
• This effect is attributed to otolith organ input discharging horizontal semicircular canal velocity storage.
• The role of cortical signals in modulating this response remains unclear.

Purpose of the Study:

• To investigate whether imagined head orientation tasks influence postrotatory nystagmus.
• To determine if cortical neural signals modulate the velocity storage mechanism.

Main Methods:

• Healthy subjects underwent yaw rotation in the dark.
• Subjects performed tasks involving actual head tilt or imagined head orientations upon cessation of rotation.
• Eye movements were recorded using an infrared video camera to measure average eye velocity (AEV).

Main Results:

• Actual head tilt significantly reduced postrotatory nystagmus (ratio of 0.414).
• Imagination tasks (watching TV, viewing art, imagining floating) did not significantly alter postrotatory nystagmus (ratios near 1.0).
• The ratio of postrotatory AEV to perrotatory AEV was 1.1 when subjects kept their head erect.

Conclusions:

• Actual head tilt effectively modulates postrotatory nystagmus, supporting the role of otolith input.
• Imagined head orientation tasks do not significantly affect postrotatory nystagmus.
• Velocity storage appears to be independent of cortical neural signals during imagined prone orientation.