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In all vertebrates, visual signals from each visual field project to the opposite midbrain tectum (called the superior colliculus in mammals). The tectum/colliculus computes visual salience to select targets for context-contingent visually guided behavior: a frog will orient toward a small, moving stimulus (insect prey) but away from a large, looming stimulus (a predator). In mammals, visual signals competing for behavioral salience are also transmitted to the visual cortex, where they are integrated with collicular signals and then projected via the dorsal visual stream to the parietal and frontal cortices. To control visually guided behavior, visual signals must be encoded in body-centered (egocentric) coordinates, and so visual signals must be integrated with information encoding eye position in the orbit—where the individual is looking. Eye position information is derived from copies of eye movement signals transmitted from the colliculus to the frontal and parietal cortices. In the intraparietal cortex of the dorsal stream, eye movement signals from the colliculus are used to predict the sensory consequences of action. These eye position signals are integrated with retinotopic visual signals to generate scaffolding for a visual scene that contains goal-relevant objects that are seen to have spatial relationships with each other and with the observer. Patients with degeneration of the superior colliculus, although they can see, behave as though they are blind. Bilateral damage to the intraparietal cortex of the dorsal stream causes the visual scene to disappear, leaving awareness of only one object that is lost in space. This tutorial considers what we have learned from patients with damage to the colliculus, or to the intraparietal cortex, about how the phylogenetically older midbrain and the newer mammalian dorsal cortical visual stream jointly coordinate the experience of a spatially and temporally coherent visual scene. [ABSTRACT FROM AUTHOR]

The superior colliculus (SC) plays a critical role in mediating reflexive eye movements. Under optimal conditions, for example including a temporal 'gap' of 200 ms after fixation offset and prior to target onset, it is possible to isolate a population of 'express saccades' with very short latencies between 80 and 120 ms. Ablation of the SC abolishes express saccades in monkeys. However, it remains to be established whether express saccade generation is dependent upon visual afferents transmitting direct retinal projections to SC via the retinotectal tract (RTT). In nineteen healthy human participants, we used a gap paradigm to investigate whether express saccades demonstrate shorter latencies to targets in the temporal hemifield, a marker for RTT function. A population of predominantly reflexive saccades (with latencies between 70 and 150 ms) was isolated in which latencies toward temporal hemifield targets were shown to be shorter than toward nasal hemifield targets. The advantages for reflexive saccades toward temporal hemifield targets suggest that visual efferents from the retina to the superior colliculus contribute to generating reflexively triggered saccades. • Reflexive saccade latency is shorter toward temporal versus nasal hemifield targets. • Temporo-nasal asymmetry is not present for regular, voluntary saccades. • Retinal efferents to superior colliculus contribute to generating reflexive saccades. [ABSTRACT FROM AUTHOR]

Probabilistic diffusion tractography was used to provide the first direct evidence for a subcortical pathway from the retina to the amygdala, via the superior colliculus and pulvinar, that transmits visual stimuli signaling threat. A bias to orient toward threat was measured in a temporal order judgement saccade decision task, under monocular viewing, in a group of 19 healthy participants who also underwent diffusion weighted MR imaging. On each trial of the behavioural task a picture depicting threat was presented in one visual field and a competing non-threatening stimulus in the other. The onset interval between the two pictures was randomly varied and participants made a saccade toward the stimulus that they judged to have appeared first. The bias to orient toward threat was stronger when the threatening stimulus was in the temporal visual hemifield, suggesting that afferents via the retinotectal tract contributed to the bias. Probabalistic tractography was used to virtually dissect connections between the superior colliculus and the amygdala traversing the pulvinar. Individual differences in microstructure (fractional anisotropy) of the streamline predicted the magnitude of the bias to orient toward threat, providing supporting evidence for a functional role of the subcortical SC-amygdala pathway in processing threat in healthy humans. • First direct evidence for subcortical pathway transmitting visual threat. • Orienting is biased to threatening compared to pleasant stimuli. • Bias to threat is greater in the temporal visual hemifield. • Microstructure (FA) of SC-Amygdala pathway predicts threat bias. [ABSTRACT FROM AUTHOR]

An ongoing debate exists regarding the possible existence of a retino-tectal visual pathway projecting to the amygdala, which would rapidly process information involving threatening or behaviorally-relevant stimuli. It has been suggested that this route might be responsible for the involuntary capture of attention by potentially dangerous stimuli. In separate studies, anatomical evidence has suggested that the retino-tectal pathway relies essentially on projections from the nasal hemiretina (temporal visual field). In this study, we chose to take advantage of this anatomical difference to further investigate whether emotional facial expressions are indeed processed through a subcortical pathway. Using EEG, participants performed a monocular spatial attention paradigm in which lateralized, task-irrelevant distractors were presented, followed by a target. The distractors were fearful faces that appeared either in nasal or temporal visual hemifield (by virtue of their monocular presentations), while the neutral face was presented simultaneously on the opposite side. Participants were asked to identify a target letter that appeared subsequently in the nasal or temporal visual hemifield. Event-related potentials (ERPs) results revealed that fearful faces appearing in the temporal visual hemifield produced a strong inhibitory response, while a negative deflection reflecting attentional capture followed presentations of fear in the nasal hemifield. These effects can be explained by a greater sensitivity of the subcortical pathway for emotional stimuli. Fearful faces conveyed through this route are processed more effectively, consequently necessitating more vigorous suppression in order for targets to be dealt with adequately. [ABSTRACT FROM AUTHOR]

It has been suggested that some cortically blind patients can process the emotional valence of visual stimuli via a fast, subcortical pathway from the superior colliculus (SC) that reaches the amygdala via the pulvinar. We provide in vivo evidence for connectivity between the SC and the amygdala via the pulvinar in both humans and rhesus macaques. Probabilistic diffusion tensor imaging tractography revealed a streamlined path that passes dorsolaterally through the pulvinar before arcing rostrally to traverse above the temporal horn of the lateral ventricle and connect to the lateral amygdala. To obviate artifactual connectivity with crossing fibers of the stria terminalis, the stria was also dissected. The putative streamline between the SC and amygdala traverses above the temporal horn dorsal to the stria terminalis and is positioned medial to it in humans and lateral to it in monkeys. The topography of the streamline was examined in relation to lesion anatomy in five patients who had previously participated in behavioral experiments studying the processing of emotionally valenced visual stimuli. The pulvinar lesion interrupted the streamline in two patients who had exhibited contralesional processing deficits and spared the streamline in three patients who had no deficit. Although not definitive, this evidence supports the existence of a subcortical pathway linking the SC with the amygdala in primates. It also provides a necessary bridge between behavioral data obtained in future studies of neurological patients, and any forthcoming evidence from more invasive techniques, such as anatomical tracing studies and electrophysiological investigations only possible in nonhuman species [ABSTRACT FROM AUTHOR]

The article presents a study on the reach target selection deficits in hand-reaching movements during the temporary localized inactivation of the midbrain's superior colliculus (SC). It states that rhesus monkeys could perceive the target even at the inactivated part of the visual field. It says that results indicate that SC is a part of target selection system affecting the choice of targets for other acts such as hand-reaching.