Notes
Horizontal Saccades: Details
SUPRA-OCULAR COMMAND CENTERS FOR HORIZONTAL SACCADES
- Comprises the...
- Frontal Eye Fields (the frontal eye field, the supplementary eye field, and dorsolateral prefrontal cortex) (altogether, think posterior middle frontal gyrus)
- Superior colliculus
- Cerebellum
- Anterior Cingulate Cortex
- Basal Ganglia
- Frontal eye fields and superior colliculus drive the eyes to the contralateral side.
- Injury to these structures produces contralateral volitional horizontal gaze palsy.
EXCITATORY BURST NEURONS
- Lie within the nucleus reticularis pontis caudalis of the paramedian pontine reticular formation (PPRF).
- The nucleus reticularis pontis caudalis lies within the mid-pons, anterior to the superior aspect of the abducens nucleus.
- The excitatory burst neurons activate the ipsilateral abducens nucleus and the ipsilateral inhibitory burst neurons, which inhibit the contralateral abducens nucleus.
- Excitatory burst neurons also inhibit the omnipause neurons and innervate the neural integrator.
- Injury to the PPRF produces ipsilateral horizontal gaze palsy.
INHIBITORY BURST NEURONS
- Lie within the nucleus paragigantocellularis dorsalis of the medullary reticular formation.
- The nucleus paragigantocellularis dorsalis lies within the rostral medulla, anterior to the plane of the abducens nucleus.
- The inhibitory burst neurons, most notably, suppress the contralateral abducens nucleus from firing, which prevents antagonist forces on the intended horizontal saccade movement.
- Injury to the inhibitory burst neurons is hypothesized to produce ocular flutter, high-frequency conjugate horizontal saccades without an intersaccadic interval.
NEURAL INTEGRATOR
- Lies within the medial vestibular nucleus and the nucleus prepositus hypoglossi of the perihypoglossal complex, which lie along the dorsal tegmentum of the upper medulla just anterior to the fourth ventricle.
- The neural integrator produces gaze holding.
- Injury to the neural integrator causes a leaky integrator, which means that the eyes do not remain in the intended direction of gaze but instead drift back to center, prompting a corrective saccade.
OMNIPAUSE NEURONS
- Lie within the nucleus raphe interpositus, which sits in midline in between the rootlets of the abducens nerves in the pontine tegmentum.
- Omnipause cells tonically suppress the excitatory and inhibitory burst neurons except immediately before and during saccadic eye movements.
- Injury causes a slowing of saccades.