Why the left brain hemisphere matches the right
Long-range connections between neurons coordinate the development between different brain regions
The activity of the nerve cells contributes to the formation of the brain structure so that the processing of information eventually is learned by practice. For a long time, scientists assumed that such an activity-dependent structure formation has only local effects, while the rough architecture of the brain already exists at the time of birth. This idea is now challenged by scientists from Göttingen and Jena. They show that long-range connections between neurons help to coordinate the development of different brain regions and even of the two brain hemispheres. This process continues for many weeks after the onset of vision (PNAS, October 6, 2009). Scientist Fred Wolf of the Max Planck Institute for Dynamics and Self-Organization and Bernstein Center for Computational Neuroscience and Siegrid Löwel of the University of Jena have investigated areas of the cortex that process information received from the eyes: the primary visual cortex (V1), which is specialized in processing fine contours and the secondary visual cortex (V2), which reacts to larger and to fast moving stimuli. In both of these areas, information from the retina of the eyes is transmitted to the visual cortex in such a way that neighboring spots on the retina activate neighboring regions of the visual cortex. In the course of visual development, so called columns form in the visual cortex – groups of neighboring nerve cells that provide an aspect of visual performance together. Even if primary and secondary visual cortex are specialized in different aspects of visual perception, they still work closely together and are connected with each other via long-range neuronal connections: Regions of V1 and V2 that analyze the same area of the visual field are strongly interconnected. Using complex image analysis methods, Fred Wolf and his colleagues have now discovered that these long-range connections influence the size of the columns and thus the structure of the brain regions. "The sizes of the columns vary strongly – within the visual cortex as well as from individual to individual," explains Jena professor Siegrid Löwel, who carried out the experiments. Nevertheless, certain rules could be identified: For example, if in one animal certain V1 areas have columns that are particularly large, the corresponding V2 areas – which process the same image area – also have columns that are particularly large. This means that exactly those areas, which are linked by far-reaching neural connections, are similar in size. Moreover, the scientists observed symmetries in the column sizes between the visual cortex in the left and in the right brain hemisphere – but only in those parts that are strongly interconnected.
Also long-range correlations need to be learned
These correlations do not exist from birth on, but are only developed during the first weeks after the opening of the eyes. Right after birth, humans cannot yet see perfectly well. Perception is acquired as the respective neural connections in the brain form. “This first phase of learning how to see takes us humans six months and cats approximately 18 weeks. For a long time it has remained unclear why these development processes take so long,” Fred Wolf says. Apperently, during this learning phase, the architecture of completely different brain areas is coordinated, so that in the end the left brain hemisphere matches the right one. “Just as in a globalized world, which is characterized by equally important local and far-reaching contacts, also the exchange of information during the development of the brain is based on an interplay of short and a far-reaching neural connections," Wolf says.
Joint research project will investigate the basis of learning and memory
Within the funding initiative “Bernstein Focus: Neuronal Basis of Learning”, a new research association, coordinated by Siegrid Löwel from the University of Jena, builds on these research results. The Federal Ministry of Education and Research (BMBF) approved more than 3 Million Euro for this project, of which more than 500,000 Euro are allotted to the subproject at the Max-Planck-Institute for Dynamics and Self-Organization in Göttingen led by Fred Wolf. Further cooperation partners are the professors Otto Witte, Knut Holthoff and Christian Hübner at the University Hospital Jena. The research project aims at getting a better understanding of the neural mechanisms that underlie long-range interactions in the brain and of how they influence plasticity and restructuring in the healthy and in the diseased brain.
The Bernstein Focus is part of the Bernstein Network Computational Neuroscience, which is funded by the BMBF and also includes the Bernstein Center and Bernstein Focus Neurotechnology in Göttingen
Matthias Kaschube, Michael Schnabel, Fred Wolf and Siegrid Löwel. Interareal coordination of columnar architectures during visual cortical development. PNAS, 2009 Oct 6;106(40): 17205-10.
Prof. Dr. Fred Wolf
Max Planck Institute for Dynamics and Self-Organization
Bunsenstrasse 10 37073 Göttingen
Orientation preference map: Nerve cells in the visual cortex preferentially respond to contours in a particular orientation. Cells of the same orientation preference are depicted in the same color.
(c) Siegrid Löwel