Rapid eye movement generation in the primate. Physiology, pathophysiology, and clinical implications

Area of Science:

• Neuroscience
• Ophthalmology
• Motor Control

Background:

• Rapid eye movements (REMs) are typically described using horizontal, vertical, and torsional components within a Cartesian coordinate system.
• Understanding the neural substrates for these movements is crucial for diagnosing and treating oculomotor disorders.

Purpose of the Study:

• To identify and localize the specific neural populations responsible for the sensory-to-motor transformations of REMs.
• To investigate the roles of the paramedian pontine reticular formation (PPRF) and rostral interstitial nucleus of the medial longitudinal fasciculus (rostral iMLF) in controlling different components of eye movements.

Main Methods:

• Localization of neuronal activity associated with horizontal REMs to the PPRF, identifying long-lead and short-lead burst neurons.
• Identification of the rostral iMLF as the key area for vertical and torsional REMs.
• Analysis of the effects of experimental inactivation of PPRF and rostral iMLF neuronal populations on eye movement generation.

Main Results:

• Unilateral PPRF lesions resulted in ipsilateral horizontal REM deficits.
• Bilateral PPRF lesions, including caudal midline structures, caused bilateral horizontal gaze palsy and disrupted vertical/torsional movements.
• Bilateral rostral iMLF lesions abolished vertical and torsional REMs, while unilateral lesions impaired ipsilateral torsional movements.

Conclusions:

• The PPRF is essential for horizontal REMs, with distinct neuronal types contributing.
• The rostral iMLF is critical for vertical and torsional REMs.
• Specific neuronal populations within the PPRF and rostral iMLF are necessary for coordinated and accurate eye movement control.