In this review, Martina develops an overarching model to explain the ontogeny of neuronal asymmetries combining data from human and animal research. It suggests a multi-level model for asymmetry formation whereby the relative impact of genetic and nongenetic factors varies between different developmental phases and neuronal structures. The basic lateralized organization of a brain is already established through genetically controlled embryonic events. During ongoing development, hemispheric specialization increases for specific functions and subsystems interact to shape the final functional organization of a brain. In particular, these developmental steps are influenced by environmental experiences, which regulate the fine-tuning of neural networks via processes that are referred to as ontogenetic plasticity.

This review is part of the Special Issue “Cognitive and Neurophysiological Models of Brain Asymmetry” edited by Sebastian Ocklenburg & Onur Güntürkün

Manns M (2021). It Is Not Just in the Genes. Symmetry 13: 1815

https://doi.org/10.3390/sym13101815

The current group of Master students Louisa Wagner, Kevin Haselhuhn and Stefanie Herrmanns (from right to left) is working together with Martina to gain a deeper understanding how two specialized brain sides interact for adaptive decision making and behaviour.

In her comment on the target article of Ocklenburg et al. (2020), Martina points out the relevance of studies in non-human species within natural settings for understanding the ecological pressures, which shape the direction and degree of brain asymmetries. The opinion paper of Ocklenburg et al. outlines ten trends, which potentially shape laterality research in the 2020s. These ideas inspired eleven commentary papers from experts in the field. This collection is published in the journal “Laterality: Asymmetries of Brain, Behaviour, and Cognition”, which celebrates its 25th anniversary in 2021.

Martina Manns (2021) Laterality for the next decade: Costs and benefits of neuronal asymmetries – putting lateralization in an evolutionary context, Laterality, 26:3, 315-318,

DOI: 10.1080/1357650X.2021.1886110

Sebastian Ocklenburg, Gesa Berretz, Julian Packheiser & Patrick Friedrich (2021) Laterality 2020: entering the next decade, Laterality, 26:3, 265-297, DOI: 10.1080/1357650X.2020.1804396

Mice and rats are among the most common animal model species in both basic and clinical neuroscience. Despite their ubiquity as model species, many clinically relevant brain-behaviour relationships in rodents are not well understood. In particular, data on hemispheric asymmetries, are conflicting as existing studies are often statistically underpowered due to small sample sizes. Paw preference is one of the most frequently investigated forms of hemispheric asymmetries on the behavioural level. Here, a team from Bochum used meta-analysis to statistically integrated findings on paw preferences in rats and mice. For both species, results indicate significant hemispheric asymmetries on the individual but not population level. In mice, 81% of animals showed a preference for either the left or the right paw, while 84% of rats show this preference. These results are particularly significant as they point out that paying attention to potential individual hemispheric differences is important in both basic and clinical neuroscience.

Manns M, Basbasse YE, Freund N, Ocklenburg S. Paw preferences in mice and rats: Meta-analysis. Neurosci Biobehav Rev. 2021 Aug;127:593-606.

https://www.sciencedirect.com/science/article/abs/pii/S014976342100213X?via%3Dihub

What if two persons who are supposed to work together have different opinions on how to solve a problem? This problem not only arises in human interaction, but can also occur between the two halves of our brain. In this case, the brain requires efficient problem-solving mechanisms. A Biopsychology team from Bochum explored the potential mechanisms by confronted pigeons with a task in which two stimulus classes (cats and dogs) were brought into conflict. The analysis of response patterns and reaction times indicated that an individual dominance of one hemisphere for conflict decisions (meta-control) is primarily based on intrahemispheric processes. Interhemispheric mechanisms come into play for more complex decisions. This flexibility could be a crucial building block for the evolutionary success of a lateralized brain.

Manns M, Otto T, Salm L. Pigeons show how meta-control enables decision-making in an ambiguous world. Sci Rep. 2021 Feb 15;11(1):3838.

https://www.nature.com/articles/s41598-021-83406-7

In this review article, Martina summarizes methods, which temporarily or permanently silence brain structures in order to understand the functional organization of lateralized brains. This is a chapter of the highly informative book edited Lesley Rogers and Giorgio Vallortigara, which explains core methods of asymmetry research.

Manns, M., 2017. Unilateral lesions. In: Roger, L. & Vallortigara, G. (eds.) Lateralized Brain Functions – Methods in Human and Non-Human Species, New York, Springer, pp. 211–249.

https://link.springer.com/book/10.1007%2F978-1-4939-6725-4

Hemispheric asymmetries represent a fundamental organizational principle of sensory, cognitive, or motor processing in the brains of many animal species. This lateralization is related to left-right differences in the structural organization of neural circuits, but how these asymmetries emerge during ontogeny is still poorly understood. A much discussed issue is the relative importance of genetic and environmental factors. In a current neuroanatomical study, biopsychologists from Bochum therefore investigated how projection asymmetries develop in the visual system of pigeons. Retrograde tracing of the major ascending (tectorotundal) projections in light-exposed and –deprived pigeons indicates that light stimulation during embryonic development leads to a stronger innervation of the left side of the brain. However, light does not enhance stabilization of fibers within the left hemisphere but induces stronger pruning of projections to the less stimulated right hemisphere. These data illustrate how visual input during early development modifies connectivity pattern in both brain halves, which in turn profoundly affects lateralized sensory processing, and ultimately lateralized cognitive processes, decision-making, or behavioral control.

Letzner S, Manns M, Güntürkün O. Light-dependent development of the tectorotundal projection in pigeons. Eur J Neurosci. 2020 Sep;52(6):3561-3571. doi: 10.1111/ejn.14775.

https://onlinelibrary.wiley.com/doi/10.1111/ejn.14775

A new group of Bachelor students (from left to right: Heesin Yoon, Kevin Haselhuhn, Felix Brenne, Simon Gies + research assistant Laurenz Salm) work together to understand how two specialized hemispheres interact for efficient sensory processing and motor control to generate adapted behaviour.