Washington: Electrical oscillations in the brain, long thought to play a role in organizing cognitive functions such as memory, are critically important for the brain to store the information that allows us to navigate through our physical environment, according to a new study.
Biologists at UC San Diego report hat neurons called ``grid cells`` that create maps of the external environment in one portion of our brain require precisely timed electrical oscillations in order to function properly from another part of the brain that serves as a kind of neural pacemaker.
The discovery has important implications for understanding the underlying causes of neurological diseases such as Alzheimer``s disease and for restoring memory in areas of the brain that are necessary for orientation.
"This work is the first to demonstrate that oscillatory activity has a well-defined function in brain areas that store memories," said Stefan Leutgeb, an assistant professor of biology at UCSD who headed the team of researchers.
Leutgeb and his team were motivated to understand the function of electrical oscillations in the brain, which are routinely measured in clinical settings to diagnose neurological disorders.
They monitored the electrical activity of grid cells in rats that explored a small four-foot by four-foot enclosure.
Grid cells, located in the entorhinal cortex just adjacent to the hippocampus, maintain an internal representation of the external environment. This representation is a grid-like map made of repeating equilateral triangles that tile the space in a hexagonal pattern. As an animal navigates through its environment, a given grid cell becomes active when the animal`s position coincides with any of the vertices within the grid.
The scientists silenced the oscillatory input by manipulating a small group of pacemaker cells in the brain and observed a significant deterioration of the grid cells` maps of the environment.
Surprisingly, silencing the oscillatory input did not disrupt brain signals that indicate precise location (provided by place cells) and the compass signal (provided by head direction cells).
"It has been thought that the hippocampus is under control of the entorhinal cortex, so there was the assumption that grid cells would have a very large impact on place cells. We are surprised at how the function of place cells is maintained in the face of significant disruption in grid cell function," said Leutgeb.
"This important result shows that, in general, you can eliminate a substantial amount of incoming information to a brain circuit without that brain circuit losing a majority of its functionality," he said.
"Our findings are a major step towards identifying these key components in an effort to preserve memory function in aging individuals and in patients with neurodegenerative diseases," he added.
The study appears in the current issue of the journal Science.