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University of Basel

How the brain learns to see

Christoph Dieffenbacher

Sonja Hofer’s research focuses on how the brain processes visual information and how the underlying networks of neurons are altered by new experiences and learning – in short, how vision works. She communicates willingly about her work, and not just in student seminars: She publishes articles in specialist journals and has even appeared on local television talking about everyday life in the lab.

Watching brain activities: Sonja Hofer in her laboratory.
Watching brain activities: Sonja Hofer in her laboratory. © University of Basel, Andreas Zimmermann

Sixth floor of the Biozentrum; the view to the south extends as far as the Jura mountains. The small office may seem somewhat makeshift to the visitor’s eye: a desk with two large screens, above it a two-shelf bookcase with just a few books, a conference table and chairs, some boxes stacked in the corner. “That’s all the space I need,” laughs Sonja Hofer, neurobiologist and for the past one and a half years Assistant Professor at the Biozentrum. She deems it much more important that her doctoral researchers have enough space to work. And different instruments and microscopes take up quite a bit of space, too.

100 billion nerve cells

A white board hangs on the office wall with pen sketches of various brain regions to serve as memory aids. When discussing her research, Sonja Hofer comes across as dedicated and down-to-earth. Just occasionally she hesitates when the English term comes to mind faster than the German. When talking about her private life, the 37-year-old is a bit more reserved. She is a distinguished scientist with some prestigious scientific awards under her belt and papers in internationally renowned publications such as Nature, Nature Neuroscience and Neuron. And this is not the only arena in which she passes on her knowledge. She also knows how to present her work in a relaxed and understandable style, for example in interviews for the local TV station “Telebasel”.

“Basically, I keep asking myself the same questions I asked during my PhD,” she explains: What happens in the brain when we see something? How exactly do these processes work in the visual part of the cerebral cortex? What happens with our nerve cells and their connections, the synapses? It’s a really complex business – the human brain is made up of an estimated 100 billion nerve cells and 100 trillion synapses, and on top of that there are many different types of cells. Sonja Hofer addresses two more specific issues: The first, more basic one, is how the visual system develops, how the nerve cells are structured and linked together, and how these networks evolve over our lifetime. The second topic follows on from this: How do the connections between the nerve cells change when we learn, make new experiences or our environment changes?

“We still know little”

We already know something about the plasticity of the brain, that is: its ability to change and adapt, the professor explains. It is possible to learn new things at any stage of life, as we retain the capacity to do so even at an advanced age. “The visual system – which takes up a relatively large part of our brain – provides us with a model to study precisely how networks of brain cells work and how they change.” Thanks to research conducted over the last few years, it has become increasingly clear that vision is a very active process and not just a passive response to external stimuli. Non-sensory information such as expectations, previous knowledge and experience play a significant role and are integrated within the visual information. “But,” says Hofer, “we still know little about how these various pieces of information are combined in the brain and how they lead to our perceptions.”

Sonja Hofer and her team work with mice, using the latest imaging techniques to monitor their brain activity. Specific cells and synapses in the animals’ brains light up in different colors and to different levels of brightness depending on whether they are activated or communicating with others. This allows the team to watch in high resolution how activity in the brain changes when the animals experience something new, for example when they react to images: “The mice need to learn to associate a particular optical stimulus with a reward,” she explains. When they do, they are given a few drops of tasty soya milk.

Complex microscopes allow the team to observe over long periods how the cells and even their synapses change when the mice learn something new. Scientists hope to learn more about the mechanisms of learning in the brain in these experiments. Although this basic research may not be directly transferable to practical applications, one long-term objective is to establish how to better counteract learning disabilities or neurological disorders such as dementia.

An interest in nature

So how did she, a young woman born and raised in Munich, come to study biology? Even at school she had an interest in nature, she says, in how it all works – the behavior of animals, ecological systems, but also how individual cells and their smallest building blocks (such as DNA) are structured. Later, as a student at the Technische Universität München, she specialized more and more and became increasingly interested in the brain. “If you want to understand animal behavior, you need to know more about the brain.” This was a key insight as she began to study sensory systems and the plasticity of the brain.

It was not until university that she first discovered what research actually is and what exactly it entails, she says with a smile. Things progressed after she completed her studies: Her desire to learn more took her to Martinsried near Munich, her hometown, and to the Max Planck Institute for Neurobiology, where she wrote her doctoral thesis. She then moved to University College London, one of the capital’s renowned universities, for her postdoctoral studies. In her last two years at the institution, she led a small research group before being appointed to the Biozentrum and moving to Basel together with her husband.

Funded together

Her husband, Thomas Mrsic-Flogel, has an office right next door. An associate professor, he has his own team that also researches neurological networks using very similar methods. The couple was appointed to the Biozentrum as part of a dual career program, a fairly new concept that enables the University of Basel to fund highly qualified and internationally renowned scientist couples – who are often being wooed by other global research institutes – and allows them to pursue their careers together.

The couple live in Basel, a city they really enjoy, says Sonja Hofer. Much about their everyday life is easier here than in London, not least because of the short distances. It would not be entirely wrong to assume that she and her husband also spend a lot of time at home discussing their research, particularly since they also have some joint publications. When not engaged in her time-consuming scientific research, Hofer occasionally likes to switch off from work. For her, the best way to relax and unwind, but also to find new energy and inspiration is to hike in the mountains – in nature. Something she not only studies but can also enjoy.

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