In a recent study published in the journal Neuron, a team of researchers at the University of Bonn and at the German Center for Neurodegenerative Diseases (DZNE) led by Prof. Stefan Remy were able to identify in mice brains specific neural cells linked to movement and navigation in space. These cells are thought to also exist in humans, and be responsible for speed and locomotion information.
The brain has to process varying sensory impressions very quickly to make movement/locomotion decisions. “This is a fundamental issue our brain has to deal with. Not just on our way to the coffee machine, but any time we move in space. For example when we are on a bike or in a car,” explained Remy in a recent news release. With increasing speed, the data rate also increases, he emphasized: “The faster we move, the less time the brain has to take in environmental cues and to associate them with a location on our memorized spatial map. Our perception therefore has to keep pace with the speed of movement so that we remember the right way to go. Otherwise we end up at the copy machine instead of the coffee machine.”
The hippocampus is the area of the brain responsible for memory, particularly spatial memory, which adjusts locomotion speed. “The electrical activity of the hippocampus undergoes rhythmic fluctuations. The faster we move, the faster certain nerve cells are activated,” said Remy in the news release. “This increased activation rate sensitizes the brain. It becomes more receptive to the changing sensory impressions that have to be processed when moving.”
This discovery helps to answer the question of how the brain knows how fast a movement is. In their research, Bonn scientists stimulated specific areas within the mice’s brains and recorded brain activity and the mice’s locomotion. “We have identified the neural circuits in mice that link their spatial memory to the speed of their movement. This interplay is an important foundation for a functioning spatial memory,” said Remy. “We assume that humans have similar nerve cells, as the brains of mice and humans have a very similar structure in these regions.”
These cells are in the brain’s medial septum, an area linked to the hippocampus. “They gather information from sensory and locomotor systems, determine the speed of movement and transmit this information to the hippocampus. In this way, they tune the spatial memory systems for optimized processing of sensory stimuli during locomotion,” explained Remy. However, these circuits have even more functions. “We have found that they also give the start signal for locomotion and that they actively control its speed. Until now, this control function was almost exclusively ascribed to the motor cerebral cortex.”
The nerve cells are connected with brain areas related to Parkinson’s disease in humans, as the condition causes movement-related symptoms and can also cause dementia. “In this respect, our results go beyond the workings of spatial memory; they also have the potential to provide new insights into how memory systems and the execution of movements are affected in Parkinson’s disease,” concluded Remy in the news release.