The Macaque Cerebellar Flocculus Outputs a Forward Model of Eye Movement

Area of Science:

• Neuroscience
• Motor Control
• Oculomotor System

Background:

• The central nervous system (CNS) uses predictive forward models for motor control and learning.
• Identifying neuronal correlates of these forward models has been challenging.
• The oculomotor system offers a unique model to study forward models due to inherent eye movement mechanics.

Purpose of the Study:

• To investigate the role of the cerebellar flocculus complex (FL) in generating forward models of eye movements.
• To identify neuronal signals related to torsional eye movements within the FL.
• To differentiate between motor command signals and predictive forward model signals in the oculomotor system.

Main Methods:

• Examining neuronal responses in the cerebellar flocculus complex (FL) during smooth pursuit eye movements at eccentric positions.
• Analyzing responses of mossy fibers (MFs) and Purkinje cells (PCs) in the FL.
• Utilizing the half-angle rule governing torsional eye movements during pursuit.

Main Results:

• Mossy fibers (MFs) in the FL did not show altered responses with pursuit eccentricity, indicating they do not carry torsional eye movement information.
• Vertical Purkinje cells (PCs) in the FL exhibited a preference for counter-clockwise (CCW) eye velocity, corresponding to ipsilateral eye extorsion.
• Torsional eye movement information was present in FL output (PCs) but not in its input (MFs).

Conclusions:

• The cerebellar flocculus complex (FL) likely computes an estimate of torsional eye movement, acting as a forward model.
• These findings support the existence of predictive signals within the CNS constructed from motor command information.
• The study provides evidence for the FL's role in generating predictive signals essential for fine motor control.