Inhibiting saccades to a social stimulus: a developmental study.

Faces are an important source of social signal throughout the lifespan. In adults, they have a prioritized access to the orienting system. Here we investigate when this effect emerges during development. We tested 139 children, early adolescents, adolescents and adults in a mixed pro- and anti-saccades task with faces, cars or noise patterns as visual targets. We observed an improvement in performance until about 15 years of age, replicating studies that used only meaningless stimuli as targets. Also, as previously reported, we observed that adults made more direction errors to faces than abstract patterns and cars. The children showed this effect too with regards to noise patterns but it was not specific since performance for cars and faces did not differ. The adolescents, in contrast, made more errors for faces than for cars but as many errors for noise patterns and faces. In all groups latencies for pro-saccades were faster towards faces. We discuss these findings with regards to the development of executive control in childhood and adolescence and the influence of social stimuli at different ages.

Social perception drives eye-movement related brain activity: Evidence from pro- and anti-saccades to faces.

Social stimuli such as faces attract and retain attention to a greater extent than other objects. Using fMRI, we investigated how the activity of oculomotor and visual brain regions is modulated when participants look towards or away from visual stimuli belonging to different categories (faces and cars). We identified a region within the superior frontal sulcus showing greater difference between anti- and pro-saccades to faces than to cars, and thereby supporting inhibitory control in a social context. In contrast, ventral occipito-temporal regions and the amygdala, which are associated with face perception, showed higher activity for pro-saccades than anti-saccades for faces, but the reverse for cars, suggesting that contextual, top-down mechanisms modulate the functional specialisation of areas involved in perception. In addition, during saccades in the presence of faces, we found increased functional connectivity between the frontal eye-fields and other cortical and subcortical oculomotor structures, namely the inferior frontal eye field, the posterior parietal cortex and the basal ganglia, possibly reflecting the higher demand put on the oculomotor system to inhibit responses to socially salient stimuli. For the first time, these data highlight neural bases for the different orienting responses towards or away from faces as compared to other objects.

Human cortical networks for new and familiar sequences of saccades.

Visual exploration is organized in sequences of saccadic eye movements that depend on both perceptual and cognitive context. Using functional magnetic resonance imaging, we studied the neural basis of sequential oculomotor behavior and its dependence on different types of memory by analyzing cerebral activity during performance of newly learned and familiar sequences of eye movements. Compared to a resting condition, both types of sequences activated a common fronto-parietal network, including frontal and supplementary eye fields, and several parietal areas. Within this network, newly learned sequences induced stronger activation than familiar sequences, probably reflecting higher attentional demands. In addition, specific regions were recruited for the performance of new sequences, including pre-supplementary eye fields, the precuneus and the caudate nucleus. This indicates that in addition to attentional modulation, novelty of saccadic sequences requires specific cortical resources, probably related to effortful sequence preparation and coordination as well as to spatial working memory. For familiar sequences, recalled from long-term memory, we observed specific right medial temporo-occipital activation in the vicinity of the boundary between the parahippocampal and lingual gyri, as well as an activation site in the parieto-occipital fissure. We conclude that neuronal resources recruited by the gaze system can change with the familiarity of the scanpath to be executed. This study is important to better understand how the brain implements memorized scanpaths for visual exploration and orienting.

An anatomical landmark for the supplementary eye fields in human revealed with functional magnetic resonance imaging.

Together with the frontal and parietal eye fields, the supplementary eye field (SEF) is involved in the performance and control of voluntary and reflexive saccades and of ocular pursuit. This region was first described in non-human primates and is rather well localized on the dorsal surface of the medial frontal cortex. In humans the site of the SEF is still ill-defined. Functional imaging techniques have allowed investigation of the location and function of the SEF. However, there is great variability with regard to the published standardized coordinates of this area. We used here the spatial precision of functional magnetic resonance imaging (fMRI) in order to better localize the SEF in individuals. We identified as the SEF a region on the medial wall that was significantly activated when subjects executed self-paced horizontal saccades in darkness as compared to rest. This region appeared to be predominantly activated in the left hemisphere. We found that, despite a discrepancy of >2 cm found in the standardized Talairach coordinates, the location of this SEF-region could be precisely and reliably described by referring to a sulcal landmark found in each individual: the upper part of the paracentral sulcus.