| Paramedian pontine reticular formation | |
|---|---|
 Axial section of thepons at the level of thefacial colliculus (PPRF not labeled, but region is visible, nearabducens nucleus) | |
| Details | |
| Part of | Brain stem |
| Artery | Pontine arteries |
| Vein | Transverse and lateral pontine veins |
| Identifiers | |
| Latin | formatio reticularis pontis paramediana |
| NeuroNames | 1399 |
| Anatomical terms of neuroanatomy | |
Theparamedian pontine reticular formation (PPRF) is a subset of neurons of theoral andcaudal pontine reticular nuclei. With theabducens nucleus it makes up thehorizontal gaze centre.[1] It is situated in thepons adjacent to theabducens nucleus.[2] It projects to the ipsilateral abducens (cranial nerve VI) nucleus, and contralateraloculomotor (cranial nerve III) nucleus[note 1] to mediateconjugate horizontal gaze andsaccades.
The PPRF is situated in thepons just[3] ventralmedial to theabducens nucleus.[2] It is locatedanterior and lateral to themedial longitudinal fasciculus.[citation needed] It is continuous caudally with thenucleus prepositus hypoglossi.[4]
The PPRF (and adjacent regions of the pons) are traversed by fibers projecting to the abducens nucleus that mediate smooth pursuit, vestibular reflexes, and gaze holding.[5]: 498
The PPRF receives afferents from:
The PPRF mediateshorizontal conjugate gaze (i.e. simultaneous horizontal movement of both eyes) by projecting to both:[6][7]
The pararaphal nucleus - one of distinct neuron population in the PPRF - projects to theflocculus of thecerebellum.[5]: 498
The PPRF mediates horizontal conjugate eye movements.[3] It is important in mediatingsaccadic eye movements.[2] It is probably not involved insmooth pursuit.[2]
The PPRF generates excitatory bursts that are delivered to the ipsilateral abduecens nucleus to drive ipsilateral saccades (inhibitory saccadic stimuli are meanwhile delivered to the abducens nucleus from the contralateral medulla oblongata).[5]: 499
Destructive lesions of the PPRF cause ipsilateral horizontal conjugate gaze palsy and mostly impair ipsilateral horizontal saccades, however, other horizontal and vertical eye movements may also be affected as the PPRF contains multiple distinct populations of neurons important in saccade generation, as well as being traversed by nerve fibers involved in eye movements that elsewhere; dysfunction of horizontal saccades will additionally also indirectly disrupt (slow and misdirect) vertical saccades[5]: 498-499 (though slowing of all saccades may also be accounted for by destruction of adjacent omnipause neurons of the interposited raphe nucleus[5]: 221 ).
In the short-term, unilateral lesions of the PPRF may be characterised clinically by contralateral deviation of the eyes; looking contralaterally inducesnystagmus characterised by quick twitches directed contralaterally whereas ipsilateral twitches are slow and do not move beyond the midline. More extensive lesions will also affect inhibition of antagonists, abolishing ipsilateral saccades.[5]: 499
Lesions of the medial pontine regions are relatively common. Due to the small size of the arteries in the area, the most common cause of a local lesion is an infarction due tolipohyalinosis andhypertension. Like other small arteries of the brain, these vessels are vulnerable tomicroemboli, especially those generated due toturbulence or low-flow states in those withartificial heart valves orarrhythmias, respectively.[8] Unilateral lesions of the PPRF produce characteristic findings:[1]
