Asymmetry of the Brain: Development and Implications

Abstract

Although the left and right hemispheres of our brains develop with a high degree of symmetry at both the anatomical and functional levels, it has become clear that subtle structural differences exist between the two sides and that each is dominant in processing specific cognitive tasks. As the result of evolutionary conservation or convergence, lateralization of the brain is found in both vertebrates and invertebrates, suggesting that it provides significant fitness for animal life. This widespread feature of hemispheric specialization has allowed the emergence of model systems to study its development and, in some cases, to link anatomical asymmetries to brain function and behavior. Here, we present some of what is known about brain asymmetry in humans and model organisms as well as what is known about the impact of environmental and genetic factors on brain asymmetry development. We specifically highlight the progress made in understanding the development of epithalamic asymmetries in zebrafish and how this model provides an exciting opportunity to address brain asymmetry at different levels of complexity.

Early Environmental Enrichment Enhances Abnormal Brain Connectivity in a Rabbit Model of Intrauterine Growth Restriction

“…These results suggested the presence of less mature connections since FA has been related to axonal packing, neuronal density, and myelination of fiber tracts [39]. Predominant changes affecting one of the brain hemispheres are coherent with the idea that some neural functions tend to be more dominant in one hemisphere than in the other [40]. In particular, the left hippocampus has been described to be related to memory and neurobehavioral impairments in the considered rabbit model [29] as well as in rodents [41,42].…”

Anticlockwise or clockwise? A dynamic Perception-Action-Laterality model for directionality bias in visuospatial functioning

“…Taken together, we propose that for the development of a bias the two forces of influence (neurobiological and cultural) work in an interactive rather than mutually independent fashion. More precisely, in order to determine directionality biases in visuospatial functioning, the unlearned, neurobiological or neurogenetic factors indexed by lateralization (handedness, footedness, eye dominance, genes, and DA asymmetry) that have been probably evolved through evolution (Duboc, Dufourcq, Blader, & Roussigné, 2015; Lalan, 2008; MacNeilage, Rogers, & Vallortigara, 2009; Rogers & Vallortigara, 2015; Vallortigara, Chiandetti, & Sovrano, 2011) interact in a very complex and dynamic manner with the learned factors(reading/writing direction, traffic rules), under ‘cultural’ practice or ‘social’ selection pressure (Ghirlanda & Vallortigara, 2004). This interaction probably occurs in a biased competition framework where the extent and direction of biases and the proportion of biased people in the population are determined, by the relative strength and direction of the two forces of influence, via neural plasticity of the brain (analogous to the biased competition process used to determine attentional allocation in perception; cf.…”

Nodal signalling and asymmetry of the nervous system

“…behavioural performance (for recent reviews, see [6][7][8]). Remarkably, several cases of nervous system asymmetry are linked with the asymmetric expression of Nodal during the development of deuterostomes and protostomes (figure 1).…”

“…Consequently, both loss (Nodal absent) and gain (Nodal bilateral) of function approaches result in the uncovering of the underlying Nodal-independent asymmetry. The zebrafish epithalamus contains the best (and perhaps the only) example to date of asymmetric Nodal signalling working as a true laterality modulator [6,7,51,57]. Asymmetry in this brain region comprises the bilaterally paired Hb and the midline-unpaired parapineal organ (PpO), a pineal complex-derived structure [40].…”