Month: April 2019

Evolution of the neocortex: Perspective from developmental biology by Pasko Rakic

The enlargement and species-specific elaboration of the cerebral neocortex during evolution holds the secrets of humans’ mental abilities; however the genetic origin and cellular mechanisms generating the distinct evolutionary advancements are not well understood. If any organ of our body should be substantially different from any other species, it is the cerebral neocortex, the center of extraordinary human cognitive abilities.

This article describes how novelties that make us human may have been introduced during evolution, based on findings in the embryonic cerebral cortex in different mammalian species. The data on the differences in gene expression, new molecular pathways and novel cellular interactions that have led to these evolutionary advances may also provide insight into the pathogenesis and therapies for human- specific neuropsychiatric disorders.

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Functional anatomy of visual search: regional segregations within the frontal eye fields and effective connectivity of the superior colliculus

The ability to find targets embedded within complex visual environments requires the dynamic programming of visuomotor search behaviors. Functional magnetic resonance imaging was used to image subjects while they visually searched for targets embedded among foils.

Visuomotor search activated the posterior parietal cortex and the frontal eye fields. Both regions showed a greater number of activated voxels on the right, consistent with the known pattern of right hemispheric dominance for spatial attention. The superior colliculus showed prominent activation in the search versus eye movement contrast, demonstrating, for the first time in humans, activation of this region specifically related to an exploratory attentional contingency. An analysis of effective connectivity demonstrated that the search-dependent variance in the activity of the superior colliculus was significantly influenced by the activity in a network of cortical regions including the right frontal eye fields and bilateral parietal and occipital cortices. These experiments also revealed the presence of a mosaic of activated sites within the frontal eye field region wherein saccadic eye movements, covert shifts of attention, and visuomotor search elicited overlapping but not identical zones of activation. In contrast to the existing literature on functional imaging, which has focused on covert shifts of spatial attention, this study helps to characterize the functional anatomy of overt spatial exploration.

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Superior Colliculus, vision, mind, self

The superior colliculus is an important provider of visual maps and even has the ability to relate those visual maps to auditory and body-base maps. The inferior colliculus is dedicated to auditory processing. The activity of the superior colliculi may be a precursor of the mind and self processes that later blossom in the cerebral cortices.