Visual impressions are collected and processed in the cerebral cortex, and this enables us to navigate in our surroundings. New research now shows that the visual cortex contains highly specialised nerve cells. Some only register forward movement, others lateral movements to the left or right.

2021.01.25 | Ib Salomon

Our ability to sense visual motion is crucial. For example, if you need to cross a busy road, you have to firstly make certain that there are no cars moving towards you before you begin walking and navigate safely to the other side of the road.

Navigation in our surroundings is to a great extent based on visual impressions, and our visual system must be able to deal with two general types of motion: Both that objects in our field of vision are in motion, and that we ourselves are in motion. New research from Aarhus University now contributes to a better understanding of how the visual system assists the brain's navigation system. One of the discoveries is that the visual cortex contains some highly specialised nerve cells, and these almost certainly play a crucial role:

"We found some specialised and enormously selective nerve cells in specific areas of the visual cortex which only registers one direction of self-motion, for example forward movement, while other nerve cells register whether you’re making a left or rightward turn – and this was not known before," says PhD student Rune Nguyen Rasmussen who has, as part of his PhD project, carried out a large number of laboratory experiments to uncover how visual impressions are processed in the brains of living mice. The two shared first-authors on the study were Rune N. Rasmussen and postdoc Akihiro Matsumoto, and the research was carried out in the lab of Associate Professor Keisuke Yonehara. This is pure basic research, and the results have just been published in the journal Current Biology.

The brain creates a mental map

Our visual system provides the brain with essential information about our visual surroundings. These are received on the retina of the eye and from here sent as electrical signals to the visual part of the cerebral cortex located towards the back of the brain. Here visual impressions are collected and processed, so that the brain ends up creating a mental map of the surroundings and its own movements within these surroundings.

Researchers have long known that there are special nerve cells distributed across the retina of mice which react to motion, e.g., upward or backward motion, and that information about motion was passed on from these nerve cells to the cerebral cortex.

"But what we’re now trying to understand is the function of these nerve cells in the eye in relation to the complex processing that takes place in the cerebral cortex," explains Rune N. Rasmussen. This was done with the help of experiments on live and awake mice, which were placed in front of some screens. The screens showed a simulated movement that corresponded to the mouse’s self-motion, e.g., forwards or backwards, or to the left or to the right. Using an advanced laser light microscope, the researchers were able to directly visualize the activity of the nerve cells in the mouse's visual cortex, and in this way, they discovered the movement-selective nerve cells in the mouse's cerebral cortex.

The results became even more interesting as the researchers carried out experiments with mice that have a genetic alteration which means that the nerve cells in the eye's retina, that sense motion, no longer function as they should.

"In this way, we could make a comparison with ordinary mice, and we found that the nerve cells in the retina which sense motion are crucial for the neural activity in one particular area of the visual cortex, which reacts strongly and selectively to visual movement resulting from self-motion," says Rune N. Rasmussen.

Our visual system is probably similar to that of mice

As yet, Rune N. Rasmussen and his colleagues does not know whether the new knowledge about sensory movement can be directly applied to humans, although this something that the researchers hope to clarify.

"In human eyes, the retina is much larger and in some aspects different from mice, but it’s very probable that our visual system resembles what we have found in mice and that our research therefore opens the way to a better understanding of our visual system," he says.

 

About the study:

The research is basic research.

The study is funded by the Lundbeck Foundation, the Velux Foundation, the Novo Nordisk Foundation, the Carlsberg Foundation and the European Research Council.

The study has been published in Current Biology.

Link to the study: https://www.cell.com/current-biology/fulltext/S0960-9822(20)31886-8

 

Contact:

PhD student Rune Nguyen Rasmussen

Aarhus University, Department of Biomedicine , DANDRITE

Tel.: (+45) 6133 7698

Email: runerasmussen@biomed.au.dk

 

Group Leader & Associate Professor Keisuke Yonehara

Aarhus University, Department of Biomedicine, DANDRITE

Tel.: (+45) 9350 8084

Email: Keisuke.yonehara@dandrite.au.dk