Structural mediation of the default-mode network in children with callosal agenesis.

Agenesis of the corpus callosum is a neurodevelopmental condition characterized by the partial or complete absence of the corpus callosum, the largest white matter bundle connecting the cerebral hemispheres. The default-mode network comprises bilateral frontal, temporal, and parietal regions that exhibit correlated activity at rest. Previous studies show that individuals with agenesis of the corpus callosum show overall preserved default-mode network functional connectivity, suggesting compensatory mechanisms for maintaining bilaterally correlated activity. In this study, we aimed to explore white matter pathways that support default-mode network-related networks in 15 children with agenesis of the corpus callosum and 27 typically developing controls, using combined diffusion and functional magnetic resonance imaging. A seed-based and dynamic functional connectivity approach enabled us to examine default-mode network spatial and temporal properties and their white matter substrates. While spatial default-mode network patterns were similar across groups, we found differences in temporal dynamics of 1 network and in white matter-default-mode network correspondence. These differences were either observed in white matter tracts directly associated with complete or partial absence of the corpus callosum or in white matter tracts such as the fornix and the anterior and posterior commissures, which have been previously implicated in neuroplasticity in agenesis of the corpus callosum. Our findings show that default-mode network dynamics can remain functionally preserved despite significant white matter alterations

Left Hemisphere Specialization for Oro-Facial Movements of Learned Vocal Signals by Captive Chimpanzees

The left hemisphere of the human brain is dominant in the production of speech and signed language. Whether similar lateralization of function for communicative signal production is present in other primates remains a topic of considerable debate. In the current study, we examined whether oro-facial movements associated with the production of learned attention-getting sounds are differentially lateralized compared to facial expressions associated with the production of species-typical emotional vocalizations in chimpanzees.Still images captured from digital video were used to quantify oro-facial asymmetries in the production of two attention-getting sounds and two species-typical vocalizations in a sample of captive chimpanzees. Comparisons of mouth asymmetries during production of these sounds revealed significant rightward biased asymmetries for the attention-getting sounds and significant leftward biased asymmetries for the species-typical sounds.These results suggest that the motor control of oro-facial movements associated with the production of learned sounds is lateralized to the left hemisphere in chimpanzees. Furthermore, the findings suggest that the antecedents for lateralization of human speech may have been present in the common ancestor of chimpanzees and humans approximately 5 mya and are not unique to the human lineage

Evolutionary origins of human handedness : evaluating contrasting hypotheses

Variation in methods and measures, resulting in past dispute over the existence of population handedness in nonhuman great apes, has impeded progress into the origins of human right-handedness and how it relates to the human hallmark of language. Pooling evidence from behavioral studies, neuroimaging and neuroanatomy, we evaluate data on manual and cerebral laterality in humans and other apes engaged in a range of manipulative tasks and in gestural communication. A simplistic human/animal partition is no longer tenable, and we review four (nonexclusive) possible drivers for the origin of population-level right-handedness: skilled manipulative activity, as in tool use; communicative gestures; organizational complexity of action, in particular hierarchical structure; and the role of intentionality in goal-directed action. Fully testing these hypotheses will require developmental and evolutionary evidence as well as modern neuroimaging data.Publisher PDFPeer reviewe