Imagine a friend meets you at the train station and shows you the way to their house. You need to find your way back on your own. If afterwards you only remember the smell of a freshly baked bun from a kiosk or the noise from a building site, that won't help you find your way. So, what happens in the brain when it must prioritise among the flood of impressions it receives?
In a new study in Nature Communications, researchers at the University of Oslo reveal that brain cells have a kind of volume control. It can be turned up to prioritise and amplify certain signals over others when we concentrate on a task.
Mice in the 'Matrix'
To understand the process, the researchers had mice run on a styrofoam wheel while navigating a virtual maze, similar to a VR game. At the same time, a microscope monitored the signals of the nerve cells in their brains. When the mice reached certain points, for example between two green towers, they would receive a reward in the form of a drop of sugar water.
"At first, the mice licked for rewards randomly, but they gradually learned specific locations where they would receive sugar water, forming a spatial memory," says Koen Vervaeke. He is a professor in the Department of Molecular Medicine at the Institute of Basic Medical Sciences.
Brake on the brake
Certain brain cells that act as "brakes" to keep neuronal activity in check. When the mouse focuses on the task of finding its way, VIP cells step in. They act as a "brake on the brake".
"By inhibiting the cells that normally keep activity down, the important signals get through with increased strength," explains Vervaeke.
"What sets this function apart from a passive volume control is that it becomes more like an intelligent amplifier. VIP cells ensure that the important signals you take in about place become clear and strong, while irrelevant background noise is suppressed."
This way we can begin the return journey to the train station instead of just retaining memories of freshly baked buns.
Focus governs the process
When the mouse is engaged in hunting for sugar water, this amplifier mechanism ensures that information about place is prioritised over irrelevant noise.
"It appears that the process is governed by how focused you are on the task you are performing," says the researcher.
By observing only the activity of the nerve cells, the researchers could see exactly where the mouse was in the virtual maze. This was simply because the signals became so clear and precise when the intelligent amplifier was activated.
Implications for dementia research
The brain regions that govern spatial sense and navigation were thoroughly mapped by the Nobel Prize-winning Moser team. These regions are among the very first affected when a person develops dementia.
"By understanding how these amplifier mechanisms function in a healthy brain, we can better understand what happens when the control systems fail and memories begin to break down," says Vervaeke.
