Figure 50: Anatomy and Physiology of the Saccadic Pathways

When a saccade is desired (or reflexively triggered), signals project from the saccade-related cortical eye fields to the superior colliculus, which serves to integrate and relay commands to the saccade generating brainstem circuitry. The inferior cerebellar peduncle (ICP) carries climbing fibers to the dorsal vermis, which has an inhibitory influence over the Purkinje cells. These Purkinje cells normally inhibit the ipsilateral fastigial nucleus, and the fastigial nucleus sends excitatory fibers to the contralateral excitatory burst neuron (EBN)/inhibitory burst neuron (IBN) pair within the paramedian pontine reticular formation (PPRF). The IBN project contralaterally to inhibit the VIth nucleus to prevent unwanted saccades in this direction, while the EBN project ipsilaterally to excite the VIth nucleus to facilitate saccades in this direction (an example of reciprocal innervation).