Abstract
Complex visuospatial processing relies on distributed neural networks involving occipital, parietal and frontal brain regions. Effects of physiological maturation (during normal brain development) and proficiency on tasks requiring complex visuospatial processing have not yet been studied extensively, as they are almost invariably interrelated. We therefore aimed at dissociating the effects of age and performance on functional MRI (fMRI) activation in a complex visual search task. In our cross-sectional study, healthy children and adolescents (n = 43, 19 females, 7-17 years) performed a complex visual search task during fMRI. Resulting activation was analysed with regard to the differential effects of age and performance. Our results are compatible with an increase in the neural network's efficacy with age: within occipital and parietal cortex, the core regions of the visual exploration network, activation increased with age, and more so in the right than in the left hemisphere. Further, activation outside the visual search network decreased with age, mainly in left inferior frontal, middle temporal, and inferior parietal cortex. High-performers had stronger activation in right superior parietal cortex, suggesting a more mature visual search network. We could not see effects of age or performance in frontal cortex. Our results show that effects of physiological maturation and effects of performance, while usually intertwined, can be successfully disentangled and investigated using fMRI in children and adolescents.
Highlights
Visuospatial processing encompasses a multitude of functions with varying degrees of complexity, such as visual perception, visuospatial attention, object categorization, spatial transformation, occulomotor planning and execution, etc. [1]
The top-down control of visuo-spatial attention [9,13,14,15,16,17,18] and the representation of spatial coordinates [19] on the other hand, have been associated with bilateral superior parietal lobule (SPL) and intraparietal sulcus (IPS) in functional MRI (fMRI) studies using a number of basic visual search tasks
Studying the effects of age and performance on fMRI activation during a complex visual search task, our main finding was an increase of activation with age in bilateral occipital cortex and right superior parietal lobule
Summary
Visuospatial processing encompasses a multitude of functions with varying degrees of complexity, such as visual perception, visuospatial attention, object categorization, spatial transformation, occulomotor planning and execution, etc. [1]. It is well known that visual exploration relies on a predominantly right-hemispheric and densely interconnected perisylvian network (i.e., superior / middle temporal, inferior parietal, and ventrolateral prefrontal cortex of the right hemisphere, including the corresponding fibre-tracts) Disruptions of this network lead to the core symptoms of spatial neglect (i.e., contra-lesionally biased gaze orientation and visual exploration [26]). With the clear preponderance of righthemispheric lesions leading to spatial neglect, it is somewhat puzzling that studies with healthy participants rarely find a strong lateralization of the above-mentioned functions This may be related to task demand, since task complexity or increased processing demands were associated with a more bilateral activation pattern in complex visual search [27,28] and in mental rotation [29]. To basic and complex visual search tasks [9,13,14,15,16,17,18], fMRI studies with the EFT highlight a bilateral parietooccipital network comprising mainly SPL and precuneus [31]
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