Endogenous Attention Signals Evoked by Threshold Contrast Detection in Human Superior Colliculus

Abstract

Human superior colliculus (SC) responds in a retinotopically selective manner when attention is deployed on a high-contrast visual stimulus using a discrimination task. To further elucidate the role of SC in endogenous visual attention, high-resolution fMRI was used to demonstrate that SC also exhibits a retinotopically selective response for covert attention in the absence of significant visual stimulation using a threshold-contrast detection task. SC neurons have a laminar organization according to their function, with visually responsive neurons present in the superficial layers and visuomotor neurons in the intermediate layers. The results show that the response evoked by the threshold-contrast detection task is significantly deeper than the response evoked by the high-contrast speed discrimination task, reflecting a functional dissociation of the attentional enhancement of visuomotor and visual neurons, respectively. Such a functional dissociation of attention within SC laminae provides a subcortical basis for the oculomotor theory of attention.

On the Role of Suppression in Spatial Attention: Evidence from Negative BOLD in Human Subcortical and Cortical Structures

“…By alternating stimulation from one hemifield to the other, without a baseline condition, the approach used by could capture both modest attention-dependent increases (Schneider and Kastner, 2009), along with perhaps larger effects reflecting a release from suppression that we measure here. We did, however, detect an attention-dependent increase in the superior colliculus contralateral to the stimulus, consistent with literature highlighting an attentional role of this structure (Schneider and Kastner, 2009;Katyal et al, 2010;Lovejoy and Krauzlis, 2010;Krauzlis et al, 2013;Katyal and Ress, 2014).…”

Selective reduction of fMRI responses to transient achromatic stimuli in the magnocellular layers of the LGN and the superficial layer of the SC of early glaucoma patients

“…In the present study, we measured neural signals from different depth in the human SC. Voxels in the superficial layer of the SC showed the strongest response to visual stimuli, which is consistent with primate physiology and recent fMRI studies [Katyal and Ress, ; Katyal et al, ]. In glaucoma patients, the superficial voxels showed significant reduction of fMRI response to the M stimulus but not to the P stimulus (Fig.…”

“…2 shows the depth map of the SC), which is consistent with the fact that the superficial layer is mostly composed of visual sensory neurons. This finding is also consistent with recent fMRI studies on the SC showing that high contrast visual stimuli evoked strongest response in the superficial layer of the SC [Katyal and Ress, 2014;Zhang et al, 2015]. FMRI signals measured at the superficial voxels (depth 5 0 mm) showed a significant interaction between stimulus conditions (M/P stimuli) and subject groups (controls/patients) [F (1,70) 5 5.94, P < 0.02].…”

Depth‐dependence of visual signals in the human superior colliculus at 9.4 T

“…Katyal and Ress [2014] recently reported high-resolution functional measurements of the human SC that represent the current standard of functional midbrain imaging at 3 T. They acquired 68 minutes of data with a voxel volume of 1.7 mm 3 for a successful depth mapping of collicular signals. At 9.4 T, we used 1 mm 3 corresponding to a reduction of the SNR far greater than the increase in magnetic field strength in comparison to standard fMRI at 3 T with comparable experimental designs and GLM analyses.…”

“…Differences in the anatomy, afferents, and efferents between other mammalian species question a complete congruence of macaque and human SC [May, 2006]. Specific functional properties of the SC investigated with fMRI include a preference for temporal versus nasal stimulation [Sylvester et al, 2007], shifts and allocation of attention [Katyal and Ress, 2014;Katyal et al, 2010;Schneider and Kastner, 2009], and execution of upper limb movements [Himmelbach et al, 2013;Linzenbold and Himmelbach, 2012]. Specific functional properties of the SC investigated with fMRI include a preference for temporal versus nasal stimulation [Sylvester et al, 2007], shifts and allocation of attention [Katyal and Ress, 2014;Katyal et al, 2010;Schneider and Kastner, 2009], and execution of upper limb movements [Himmelbach et al, 2013;Linzenbold and Himmelbach, 2012].…”