Neuronal activity in superior colliculus signals both stimulus identity and saccade goals during visual conjunction search

Abstract

Although we know that the process of saccade target selection is reflected in the activity of sensory-motor neurons within saccade executive centers, the description of this process at the neural level has yet to fully account for all selection outcomes. The current study sought to determine how neuronal activity in the intermediate layers of the superior colliculus (SC) determines correct saccade target selection by examining the activity of visuomovement neurons during both correct and error trials of monkeys performing a relatively difficult visual conjunction search task. We found that a stimulus presented in a neuron's response field, but not foveated, was associated with greater activity if it was the search target instead of a distractor, indicating that SC neurons could represent stimulus identity. Nevertheless, activity was greater when a saccade was made to a stimulus than when it was not, further implicating these neurons in selecting the saccade goal. Together with the related observation that, when the target fell in their response fields, SC neurons discharged significantly more if the monkey correctly selected it instead of a distractor, these results suggest that visual stimuli are selected when these neurons reach a critical activation level. Our findings show that the outcome of all visual search trials, regardless of the stimulus being selected, is predicted by SC neuronal activity.