Neuroanatomy: Vertical Saccades

Notes

Lie at the midbrain-diencephalic junction, in the plane of the mammillary bodies.
Comprises the excitatory burst neurons for vertical and torsional saccades.
Acts in similar fashion to the nucleus reticularis pontis caudalis of the PPRF for horizontal saccades.

Lie just beneath the bilateral riMLF, still in the midbrain-diencephalic junction, near midline in the dorsal tegmentum.
Acts as the neural integrator for vertical and torsional saccades, similar to the medial vestibular nucleus and nucleus prepositus hypoglossi for horizontal saccades.
Certain texts describe the INC as containing the inhibitory burst neurons for vertical and torsional saccades whereas others describe the riMLF as containing them.
For comparison, the nucleus paragigantocellularis dorsalis of the medullary reticular formation contains the inhibitory burst neurons for horizontal saccades.

Lies beneath the bilateral INCs within the dorsal tegmentum just anterior to the periaqueductal gray area.
Straddles the midline of the mid- to upper midbrain.

Lie beneath the oculomotor complex in the lower midbrain (in the plane of the inferior colliculi) in the dorsal tegmentum near midline.

Lies in midline in the pontine tegmentum in between the rootlets of the abducens nerves.
Contains the omnipause neurons for vertical and torsional saccades just as it does for horizontal saccades.

1. The riMLF produces bilateral projections for upward gaze but only ipsilateral projections for downward gaze.
- Thus, a unilateral riMLF lesion will cause isolated downward gaze palsy (observed as slowing of downward gaze), but redundant innervation for upward gaze preserves the function and speed of upward gaze.

1. Laterality of riMLF. Innervation for torsional saccades is as follows: from the subject's POV, the right riMLF produces clockwise torsional rotation of the eyes and the left riMLF produces counterclockwise torsional rotation of the eyes.

1. Whereas the frontal eye fields (think post. middle frontal gyrus) and superior colliculus project to the contralateral PPRF excitatory burst neurons for horizontal saccades, they project to the ipsilateral riMLF for vertical and torsional saccades.