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Related Experiment Video

Updated: Jul 2, 2026

Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings

Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings

Published on: August 1, 2018

Brainstem circuits controlling lid-eye coordination in monkey.

Anja K E Horn¹, Jean A Büttner-Ennever

¹Institute of Anatomy, Ludwig-Maximilians University of Munich, Pettenkoferstr. 11, Munich, Germany. Anja.Bochtler@med.uni-muenchen.de

Progress in Brain Research

|August 23, 2008

Summary

The M-group in primates connects eyelid and eye movements during vertical saccades. New research reveals its afferent connections, suggesting it

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Published on: March 30, 2016

Area of Science:

Neuroscience
Ophthalmology
Primate Neuroanatomy

Background:

The M-group, a mesencephalic cell cluster in primates, contains premotor neurons for the levator palpebrae (LP) and upward-pulling eye muscles.
This M-group is hypothesized to be involved in coordinating eyelid and eye movements during vertical saccades.

Purpose of the Study:

To investigate the afferent connections to the M-group and LP motoneurons in monkeys.
To further elucidate the role of the M-group in lid-eye coupling during vertical saccades.

Main Methods:

Anterograde tracer injections were administered into three eye-movement-related areas: superior colliculus (SC), interstitial nucleus of Cajal (INC), and the omnipause neuron (OPN) region.
Afferent pathways to the M-group and LP motoneurons were analyzed based on tracer labeling.

Main Results:

Medial SC injections (upward saccades) labeled the ipsilateral M-group and rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF); lateral SC injections (downward saccades) labeled only RIMLF.
Both RIMLF and M-group received bilateral projections from INC.
The OPN region projected to RIMLF (glycinergic input) and, uniquely, selectively to LP motoneurons, not other oculomotor neurons.

Conclusions:

The M-group likely mediates lid-eye coupling during vertical upgaze, indirectly driven by RIMLF saccadic burst neurons.
A subset of OPNs may directly trigger saccade-related blinks via selective projections to LP motoneurons.