Transforming absolute value to categorical choice in primate superior colliculus during value-based decision making

Involvement of superior colliculus in complex figure detection of mice

Object detection is an essential function of the visual system. Although the visual cortex plays an important role in object detection, the superior colliculus can support detection when the visual cortex is ablated or silenced. Moreover, it has been shown that superficial layers of mouse SC (sSC) encode visual features of complex objects, and that this code is not inherited from the primary visual cortex. This suggests that mouse sSC may provide a significant contribution to complex object vision. Here, we use optogenetics to show that mouse sSC is involved in figure detection based on differences in figure contrast, orientation, and phase. Additionally, our neural recordings show that in mouse sSC, image elements that belong to a figure elicit stronger activity than those same elements when they are part of the background. The discriminability of this neural code is higher for correct trials than for incorrect trials. Our results provide new insight into the behavioral relevance of the visual processing that takes place in sSC.

Collicular circuits supporting the perceptual, motor and cognitive demands of ethological environments

Animals evolve to survive in their environment. Accordingly, a reasonable hypothesis is that brain evolution prioritises the processing of useful sensory information over complete representation of the surroundings. The superior colliculus or tectum is a brain area that processes the animal's surroundings and directs movements in space. Here, we review recent studies on the role of the superior colliculus to assess the validity of this "utility hypothesis". We discuss how the response properties of collicular neurons vary across anatomical regions to capture ethologically relevant stimuli at a given portion of the sensory field. Next, we focus on the recent advances dissecting the role of defined types of sensory and motor neurons of the colliculus in prey capture. Finally, we discuss the recent literature describing how this ancient structure, with neural circuits over 500 million years old, implements the necessary degree of cognitive control for flexible sensorimotor transformation.

Inhibitory tagging in the superior colliculus during visual search

Inhibitory tagging is an important feature of many models of saccade target selection, in particular those that are based on the notion of a neural priority map. The superior colliculus (SC) has been suggested as a potential site of such a map, yet it is unknown whether inhibitory tagging is represented in the SC during visual search. In this study, we tested the hypothesis that SC neurons represent inhibitory tagging during search, as might be expected if they contribute to a priority map. To do so, we recorded the activity of SC neurons in a multisaccade visual-search task. On each trial, a single reward-bearing target was embedded in an array of physically identical, potentially reward-bearing targets and physically distinct, non-reward-bearing distractors. The task was to fixate the reward-bearing target. We found that, in the context of this task, the activity of many SC neurons was greater when their response field stimulus was a target than when it was a distractor and was reduced when it had been previously fixated relative to when it had not. Moreover, we found that the previous-fixation-related reduction of activity was larger for targets than for distractors and decreased with increasing time (or number of saccades) since fixation. Taken together, the results suggest that fixated stimuli are transiently inhibited in the SC during search, consistent with the notion that inhibitory tagging plays an important role in visual search and that SC neurons represent this inhibition as part of a priority map used for saccade target selection.NEW & NOTEWORTHY Searching a cluttered scene for an object of interest is a ubiquitous task in everyday life, which we often perform relatively quickly and efficiently. It has been suggested that to achieve such speed and efficiency an inhibitory-tagging mechanism inhibits saccades to objects in the scene once they have been searched and rejected. Here, we demonstrate that the superior colliculus represents this type of inhibition during search, consistent with its role in saccade target selection.