© Nature/ReutersA Princeton University and National Institutes of Health study suggests that our response to stressful situations originates from structural changes in our brain that allows us to adapt to turmoil. Adult rats with disruptions in their social hierarchy produced far fewer new neurons in the hippocampus, the part of the brain responsible for certain types of memory and stress regulation. They also reacted to the disruption by favoring the company of familiar rats. Their behavior manifested six weeks after social disruption, during which time brain-cell growth, or neurogenesis, had decreased by 50 percent. The photo shows adult hippocampal neurons that are less than two weeks old.
The study involves rats running on treadmill, and focuses on specific neurons called grid cells which support navigation in time and space, even without visual landmarks and the optic flow.
Until now, there was no direct evidence demonstrating that the grid cells help the brain determine the distance and time passed.
To prove the contrary, researchers put rats on treadmills and recorded the activity of grid cells, keeping either distance or duration of running unchanged, and only varying the speed.
As a result, 92% of grid cells in rats emitted signals at specific moments: for instance, one cell would fire 8 seconds into the run, not taking into account speed or distance covered, and another cell would emit a signal every 400 cm, not depending on speed or duration of the run.
50 percent of the cells were affected by distance, another half by time, and around 40 percent by both factors.
"Space and time are ever-present dimensions by which events can be organized in memory," senior study author Howard Eichenbaum, a psychologist and neuroscientist at Boston University, said in the official press release.
"These findings support the view that memory evolved as a common function in mammals using circuits that organize events in space, time, and potentially many other dimensions of experience," he added.
Earlier, grid cells were regarded as the indicators of location only. However, with the new study, scientists have discovered that when the place remains unchanged, grid cells keep track of the time and distance.
Thus, grid cells play "a much broader role for the medial entorhinal cortex than solely mapping space", Eichenbaum said.
What could humanity do with these findings? Actually,this knowledge could help deal with and prevent memory and cognitive disorders - for example, Alzheimer's disease, researchers say.
"If we can understand the circuits better, it could help us to tease them back into normal function. If we can get to the cell level, now we can tune them back up again," Eichenbaum said, as quoted by The Discover magazine.
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