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. 2007 Aug 14;8:66.
doi: 10.1186/1471-2202-8-66.

Activation of Superior Colliculi in Humans During Visual Exploration

Free PMC article

Activation of Superior Colliculi in Humans During Visual Exploration

Marc Himmelbach et al. BMC Neurosci. .
Free PMC article


Background: Visual, oculomotor, and - recently - cognitive functions of the superior colliculi (SC) have been documented in detail in non-human primates in the past. Evidence for corresponding functions of the SC in humans is still rare. We examined activity changes in the human tectum and the lateral geniculate nuclei (LGN) in a visual search task using functional magnetic resonance imaging (fMRI) and anatomically defined regions of interest (ROI). Healthy subjects conducted a free visual search task and two voluntary eye movement tasks with and without irrelevant visual distracters. Blood oxygen level dependent (BOLD) signals in the SC were compared to activity in the inferior colliculi (IC) and LGN.

Results: Neural activity increased during free exploration only in the SC in comparison to both control tasks. Saccade frequency did not exert a significant effect on BOLD signal changes. No corresponding differences between experimental tasks were found in the IC or the LGN. However, while the IC revealed no signal increase from the baseline, BOLD signal changes at the LGN were consistently positive in all experimental conditions.

Conclusion: Our data demonstrate the involvement of the SC in a visual search task. In contrast to the results of previous studies, signal changes could not be seen to be driven by either visual stimulation or oculomotor control on their own. Further, we can exclude the influence of any nearby neural structures (e.g. pulvinar, tegmentum) or of typical artefacts at the brainstem on the observed signal changes at the SC. Corresponding to findings in non-human primates, our data support a dependency of SC activity on functions beyond oculomotor control and visual processing.


Figure 1
Figure 1
Experimental conditions. An initial baseline period of fixation was followed by visual exploration (VE). A letter array of 24 × 35 cm2 (~9° × 13°) was presented consisting of about 370 letters set in Arial font with a vertical size of 0.95 cm (~0.36°) per letter at a viewing distance of 150 cm. In the saccade block with visual background (VEC), a cross of red circles was presented in front of the same letter field. In the saccade block without visual background (SC), the same cross was presented, but without the letter field. Each line consisted of 9 dots of a size of 0.5 cm (0.2°) at a distance of 2.75 cm (1°) from each other. A cycle consisting of these three conditions interleaved with baseline periods was repeated 5 times during each of the three experimental runs.
Figure 2
Figure 2
Anatomical regions of interest. Overlap of superior (A) and inferior (B) colliculus ROIs of all subjects illustrated on a sagittal slice of the group's mean brain (x = 4 mm). (C, D) Overlap of LGN ROIs illustrated on a transversal (C, z = -6) and coronal (D, y = -25) slice of the group's mean brain. The number of overlapping ROIs is colour coded, from violet (n = 1) to red (n = 13).
Figure 3
Figure 3
BOLD signal changes. Estimated marginal means of BOLD signal changes across all subjects with 95% confidence interval for each experimental condition in the superior colliculi (A), inferior colliculi (B), and lateral geniculate nuclei (C).

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