Abstract
Being able to effectively explore our visual world is of fundamental importance, and it has been suggested that the straight-ahead gaze (primary position) might play a special role in this context. We employed fMRI in humans to investigate how neural activity might be modulated for saccades relative to this putative default position. Using an endogenous cueing paradigm, saccade direction and orbital starting position were systematically manipulated, resulting in saccades toward primary position (centripetal) and away from primary position (centrifugal) that were matched in amplitude, directional predictability, as well as orbital starting position. In accord with earlier research, we found that fMRI activity in the superior colliculus (SC), as well as in the frontal eye fields and the intraparietal sulcus, was enhanced contralateral to saccade direction across all saccade conditions. Furthermore, the SC exhibited a relative activity decrease during re-centering relative to centrifugal saccades, a pattern that was paralleled by faster saccadic reaction times. In contrast, activity within the cortical eye fields was not significantly modulated during re-centering saccades as compared to other saccade types, suggesting that the re-centering bias is predominantly implemented at a subcortical rather than cortical processing stage. Such a modulation might reflect a special coding bias facilitating the return of gaze to a default position in the gaze space in which retinotopic and egocentric reference frames are aligned and from which the visual world can be effectively explored.
Highlights
The execution of eye movements to objects or locations of interest is carried out by a complex network of cortical and subcortical brain regions enabling a precise alignment of the observer’s fovea with the object of interest
Beyond the generation of saccadic eye movements, both the frontal eye fields (FEF) and the intraparietal sulcus (IPS) have been associated with the covert orienting of attention in a wide range of paradigms, consistent with the view that these two functions are supported by overlapping neural systems (Corbetta and Shulman, 2002)
After rejecting an average of 10% of all trials due to blinks and other artifacts in the remaining 13 data sets, the average saccade-task performance in the included trials was well above 95%
Summary
The execution of eye movements to objects or locations of interest is carried out by a complex network of cortical and subcortical brain regions enabling a precise alignment of the observer’s fovea with the object of interest (for a review see Wurtz and Albano, 1980; Sparks, 2002). The SC receives multiple cortical and subcortical inputs and represents the final relay structure for eye-movement execution (Fries, 1984; Sparks et al, 2000; Schiller and Tehovnik, 2001; Sparks, 2002; Sommer and Wurtz, 2008). Among its wide range of connections, the SC receives prominent input from two cortical regions that are linked to both overt saccades and covert attentional shifts: the frontal eye fields (FEF) located in the premotor cortex (Paus, 1996; Blanke et al, 2000; Koyama et al, 2004) and an area within the intraparietal sulcus (IPS; encompassing BA7 and BA40) considered to be the human equivalent of the primate lateral intraparietal area (LIP, Muri et al., 1996; Luna et al, 1998; Koyama et al, 2004). Beyond the generation of saccadic eye movements, both the FEF and the IPS have been associated with the covert orienting of attention in a wide range of paradigms, consistent with the view that these two functions are supported by overlapping neural systems (Corbetta and Shulman, 2002)
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