As part of the subcortical visual system, neurons within the<unk>  nuclei respond to varying intensities of illuminance and are primarily involved in mediating non-conscious behavioral responses to acute changes in light. In general, these responses involve the initiation of optokinetic reflexes, although the pretectum can also regulate nociception and REM sleep. Pupillary light reflex Pupillary constriction resulting from the pupillary light reflex is mediated by the olivary and posterior<unk>  nuclei. The pupillary light reflex is mediated by the pretectum. This reflex is responsible for the constriction of the pupils upon light's entering the eye. Several<unk>  nuclei, in particular the ON, receive illuminance information from the ipsilateral retina via the optic tract. Nuclei in the ON are known to gradually increase in activation in response to increasing levels of illuminance. This information is then relayed directly to the Edinger-Westphal nucleus, which proceeds to relay the command to constrict the pupils to the pupillary sphincter via the ciliary ganglion. Smooth pursuit<unk>  nuclei, in particular the NOT, are involved in coordinating eye movements during smooth pursuit. These movements allow the eye to closely follow a moving object and to catch up to an object after an unexpected change in direction or velocity. Direction-sensitive retinal slip neurons within the NOT provide ipsiversive horizontal retinal error information to the cortex through the inferior olive. During the day, this information is sensed and relayed by neurons with large receptive fields, whereas parafoveal neurons with small receptive fields do so in the dark. It is through this pathway that the NOT is able to provide retinal error information to guide eye movements. In addition to its role in maintaining smooth pursuit, the pretectum is activated during the optokinetic nystagmus in which the eye returns to a central, forward-facing position after an object it was following passes out of the field of vision. Accommodation reflex Part of the pretectum, particularly the NOT and NPP, are implicated in the accommodation reflex by which the eye maintains focus. Proprioceptive information from the retina reaches the pretectum via the occulomotor nerve and the trigeminal nerve. From that point, the mechanism by which the eye maintains focus through muscular contractions of the retina is similar to that of the pupillary light reflex. Antinociception The NPA participates in the active diminishing of the perception of pain stimuli (antinociception). Although the mechanism by which the NPA alters an organism's response to painful stimuli is not fully known, research has shown that activity in the ventral NPA triggers cholinergic and serotonergic neurons. These neurons activate descending pathways that synapse in the spinal cord and inhibit nociceptive cells in the dorsal horn. In addition to its direct antionociceptive mechanism, the NPA projects onto brain regions that, through connections to the somatosensory cortex, regulate the perception of painful stimuli. Two of these regions that the NPA is known to project to are the zona incerta and posterior thalamic nucleus. Regions of the NPA may be specialized to respond to different types of pain. Research has found that the dorsal NPA best diminished the perception of brief pain whereas the ventral NPA reduced the perception of chronic pain. Because of its role in the reduction of chronic pain, abnormal activity of the NPA is thought to be implicated in central pain syndrome. REM sleep Multiple<unk>  nuclei may be involved in regulating REM sleep and sleep behaviors. Research has shown that the pretectum, in conjunction with the superior colliculus, may be responsible for causing non-circadian changes in REM sleep behaviors.<unk>  nuclei receiving retinal input, in particular the NOT and the NPP, have been shown to be partially responsible for initiating REM sleep in albino rats. The discovery of projections from the pretectum to several thalamic nuclei involved in cortical activation during REM sleep, to be specific the projection to the superchiasmatic nucleus, which is part of a known REM sleep regulatory mechanism, supports this hypothesis.
Pretectal area
Watershed area 
Fusiform body area
Postcentral sulcus
Suboccipital triangle
Collateral eminence
Periaqueductal gray
Occipital triangle