In order to guide us accurately through space, the brain needs a
“sense” of the speed of our movement. But how do such stimuli actually
reach the brain? Researchers at the German Center for Neurodegenerative
Diseases (DZNE) have now identified a signal pathway in mice that feeds
speed information directly into the brain’s navigation system.
Scientists led by Stefan Remy
report on this in the journal “Nature Neuroscience”. Similar neural
pathways exist in humans. They are known to be damaged by Alzheimer’s
disease – a possible explanation why spatial orientation is frequently
impaired in this form of dementia.
In this study, the researchers
stimulated specific areas in the brains of mice and recorded the evoked
brain activity. “In previous studies, we found specific cells in the
medial septum that fire at higher rates when the mouse moves faster.
They function as ‘speedometer cells’. Possibly, they receive their input
from deeper brain areas that are involved in motion control”, explains
Professor Remy.
Neuronal data bus
These neurons are connected to other brain regions via long-range
projections. This includes an area called the “entorhinal cortex” which
is considered to be the brain’s navigation center. “The computations
needed to navigate in space are ultimately made in this area of the
brain,” says Remy. “We have now been able to show that the rate at which
the speedometer cells fire influences neuronal activity in the
entorhinal cortex. When the firing rate increases, activity in the
entorhinal cortex increases too. The speedometer cells act like a data
bus, an interface that relays speed information directly to the brain’s
navigation center.”
Cause of spatial orientation disorders?
Humans have similar neural pathways connecting the medial septum and
entorhinal cortex. Their function has not yet been investigated in
detail; however, in the brains of Alzheimer’s patients these connections
are known to degenerate early in the progress of the disease. “The
symptoms of Alzheimer’s disease include spatial memory impairments. In
such cases, it might happen that an affected person cannot find the way
home,” says Remy. “Our results now provide a possible explanation for
these symptoms: Information about the ongoing speed of movement is
withheld and does not reach the brain’s navigation center.”
