Researchers discover 'speedometer' in brain

Scientists have discovered nerve cells in the brains of mice that trigger locomotion and also supply the brain with speed-related information.
Scientists at the German Center for Neurodegenerative Diseases and the University of Bonn led by Professor Stefan Remy said the findings give new insights into the workings of spatial memory.
The findings could also help improve our understanding of movement related symptoms associated with Parkinson's disease.
It has been known for some time that the hippocampus - the part of the brain that controls memory, particularly spatial memory - adjusts to the speed of locomotion.
"The electrical activity of the hippocampus undergoes rhythmic fluctuations. The faster we move, the faster certain nerve cells are activated," said Remy.

"This increased activation rate sensitises the brain. It becomes more receptive to the changing sensory impressions that have to be processed when moving," Remy said.

But how does the brain actually know how fast a movement is? Previously there was no answer to this question.
Now, Remy and his colleagues have decoded the mechanism. For this, they stimulated specific areas within the mouse brain and recorded the ensuing 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," Remy said.
The cells in question are located in the "medial septum," a part of the brain directly connected to the hippocampus. They make up a relatively small group comprising a few thousand cells.
"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 optimised processing of sensory stimuli during locomotion," said Remy.
"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," he said.

These newly discovered nerve cells are linked with areas of the brain that are affected by Parkinson's in humans. This disease is associated with movement-related symptoms and can 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," said Remy.
The study is published in the journal Neuron.