Activity in the human superior colliculus relating to endogenous saccade preparation and execution

Area of Science:

• Neuroscience
• Ophthalmology
• Cognitive Science

Background:

• The human superior colliculus (SC) is known for visual processing, but its oculomotor functions, particularly during saccade preparation, are less understood.
• Previous functional imaging studies have primarily focused on visual responses in the SC, with limited investigation into its role in eye movement control.

Purpose of the Study:

• To investigate hemodynamic activity in the human SC associated with endogenous saccade preparation and execution using functional magnetic resonance imaging (fMRI).
• To determine if preparatory activity exists in the human SC prior to saccade initiation and to characterize its laterality and amplitude dependence.

Main Methods:

• Utilized 3-Tesla fMRI to record hemodynamic activity in the SC during saccade preparation and execution in two experiments.
• Participants performed saccadic eye movements, and brain activity was analyzed for increases related to preparation and execution across various saccade amplitudes.

Main Results:

• Both saccade preparation and execution led to increased hemodynamic activity in the SC.
• Saccade-related activity was observed in both the contralateral and, to a lesser extent, the ipsilateral SC.
• This bilateral activity was consistent across a range of saccade amplitudes, suggesting it is not solely due to small saccades targeting the foveal region.

Conclusions:

• This study provides the first evidence of presaccadic preparatory activity in the human SC.
• fMRI can detect activity in the human SC consistent with buildup neurons identified in nonhuman primate studies.
• The findings highlight the SC's crucial role in both the preparation and execution of voluntary eye movements.