Abstract
Research on rodents and non-human primates has established the involvement of the superior colliculus in defensive behaviours and visual threat detection. The superior colliculus has been well-studied in humans for its functional roles in saccade and visual processing, but less is known about its involvement in affect. In standard functional MRI studies of the human superior colliculus, it is challenging to discern activity in the superior colliculus from activity in surrounding nuclei such as the periaqueductal gray due to technological and methodological limitations. Employing high-field strength (7 Tesla) fMRI techniques, this study imaged the superior colliculus at high (0.75 mm isotropic) resolution, which enabled isolation of the superior colliculus from other brainstem nuclei. Superior colliculus activation during emotionally aversive image viewing blocks was greater than that during neutral image viewing blocks. These findings suggest that the superior colliculus may play a role in shaping subjective emotional experiences in addition to its visuomotor functions, bridging the gap between affective research on humans and non-human animals.
Highlights
A midbrain structure in the oculomotor system, the superior colliculus (SC) receives direct retinal input and contains visual neurons with retinotopically organized receptive fields[1,2]
We first examined whether visual processing selectively elicited greater activation in the SC compared to a control region, the inferior colliculus (IC)
The SC showed, as predicted, greater activation during aversive image viewing blocks compared to neutral image viewing blocks [paired t(10) = 2.2889, p = 0.0451, dz = 0.6901] (Fig. 2, panel b)
Summary
A midbrain structure in the oculomotor system, the superior colliculus (SC) receives direct retinal input and contains visual neurons with retinotopically organized receptive fields[1,2]. A recent study involving human participants has found greater activity in the SC when snake images are presented in the foveal compared to the peripheral visual field, consistent with the central bias in processing ecologically relevant threat stimuli[25]. In vivo diffusion tensor imaging and probabilistic tractography studies have predicted fiber connections between the human SC and the amygdala via the pulvinar, providing anatomical evidence supporting the SC’s role in threat detection[22,26,27,28]. Extrastriate cortex, the midtemporal area, and the motor and premotor cortices in the primate brain[8,29] In both cases, SC activity may be expected to be modulated during affective processing especially when the visual stimulus requires orienting to threat. Most fMRI methods cannot discern PAG response from SC response when viewing aversive vs. neutral images, as standard normalization and smoothing procedures introduce significant partial-volume issues
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