Structural and functional brain rewiring clarifies preserved interhemispheric transfer in humans born without the corpus callosum

Abstract

Why do humans born without the corpus callosum, the major interhemispheric commissure, lack the disconnection syndrome classically described in callosotomized patients? This paradox was discovered by Nobel laureate Roger Sperry in 1968, and has remained unsolved since then. To tackle the hypothesis that alternative neural pathways could explain this puzzle, we investigated patients with callosal dysgenesis using structural and functional neuroimaging, as well as neuropsychological assessments. We identified two anomalous white-matter tracts by deterministic and probabilistic tractography, and provide supporting resting-state functional neuroimaging and neuropsychological evidence for their functional role in preserved interhemispheric transfer of complex tactile information, such as object recognition. These compensatory pathways connect the homotopic posterior parietal cortical areas (Brodmann areas 39 and surroundings) via the posterior and anterior commissures. We propose that anomalous brain circuitry of callosal dysgenesis is determined by long-distance plasticity, a set of hardware changes occurring in the developing brain after pathological interference. So far unknown, these pathological changes somehow divert growing axons away from the dorsal midline, creating alternative tracts through the ventral forebrain and the dorsal midbrain midline, with partial compensatory effects to the interhemispheric transfer of cortical function.callosal agenesis | callosal plasticity | human connectome

Long‐term acclimatization to high‐altitude hypoxia modifies interhemispheric functional and structural connectivity in the adult brain

“…2009; Tovar‐Moll et al. 2014), and it is widely assumed that structural connectivity is relatively stable over time, whereas functional connectivity is more variable (Zhang et al. 2011).…”

Split-brain syndrome and extended perceptual consciousness

“…I agree with her on this point-(1) makes best sense of why acallosals perform the same as normal subjects in split-brain experiments and it is backed up with neurophysiological evidence (Tovar-Moll et al 2014). Although Hurley thinks that interpretation (1) provides the best explanation of acallosals, she does argue that interpretation (2) should be taken seriously as a nomological possibility.…”

How Can Development and Plasticity Contribute to Understanding Evolution of the Human Brain?

“…They have large brains with many billion neurons and glial cells (Lent et al, 2012), trillions of synapses and besides all, a plastic hardware that may change either subtly or strongly in response to the external or internal environment (Tovar-Moll et al, 2014). With this hypercomplex apparatus, they are capable of very sophisticated inward computations and outward behaviors that include self-recognition, metacognition, different forms of language expression and reception, prediction of future events, planning and performing long streams of motor acts, subtle emotional feelings, and many other exceedingly complex properties.…”

“…This evolutionary trajectory as related to developmental mechanisms is reviewed by Rodrigo Suarez and his colleagues from Queensland Brain Institute, Australia. The corpus callosum, in particular, is the target of their interest, and the knowledge of the developmental events underlying its formation is instrumental to unravel its striking long-distance plasticity, as shown in cases of humans born without it (Tovar-Moll et al, 2014).…”