Repetition suppression dissociates spatial frames of reference in human saccade generation

Area of Science:

• Neuroscience
• Cognitive Science
• Systems Neuroscience

Background:

• Perception-action transformations rely on processing information across different reference frames.
• Understanding the reference frames used in sensorimotor transformations is crucial for deciphering neural coding.

Purpose of the Study:

• To determine the reference frame(s) used for cortical activity during saccade (eye movement) generation.
• To investigate reference frame coding in the intraparietal sulcus (IPS), frontal eye field (FEF), and supplementary eye field (SEF) during sensory processing, planning, and execution phases.

Main Methods:

• Functional magnetic resonance imaging (fMRI) with a repetition suppression paradigm.
• Subjects performed delayed saccades to peripheral targets under a 2x2 factorial design (retinal/nonretinal coordinates, novel/repeated locations).
• Analysis of blood oxygenation level dependent (BOLD) signal changes to identify coding frames.

Main Results:

• A significant attenuation of the fMRI signal was observed when target locations repeated in retinal (eye-centered) coordinates across all three regions (IPS, FEF, SEF).
• Retinal coding showed the strongest suppression during the saccade planning phase.
• Nonretinal (head-centered) coding exhibited only weak evidence in these regions.
• IPS and FEF demonstrated an orderly representation of retinal target location with a contralateral bias, unlike the SEF.

Conclusions:

• Sensorimotor processing in the IPS, FEF, and SEF for saccade generation predominantly utilizes eye-centered (retinal) coordinates.
• The findings suggest that saccade planning and execution are primarily coded in a retinal reference frame, regardless of the brain region's topographic organization.