Splitting Hairs – The Role of New Adult Brain Cells

§ July 10th, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

A study published in the July 10, 2009, issue of the journal Science shows that new brain cells help us find our way around.

According to senior author Fred Gage of the Salk Institute new brain cells “help us to distinguish between memories that are closely related in space.”

“Adding new neurons could be a very problematic process if they don’t integrate properly into the existing neural circuitry,” says Gage. “There must be a clear benefit to outweigh the potential risk.”

Most neurogenesis happens in the hippocampus, a small horn-shaped region in the brain’s interior. The hippocampus prepares information for recall and then send it off for storage. Experiences involving time, emotion, intent, touch, smell etc., arise in the cortex and gets channeled to the hippocampus.

Previous studies had indicated that new neurons contributed to learning and memory but the details were unclear.

The dentate gyrus divides and distributes incoming signals. This process, known as pattern separation, increases the number of active cells by a factor of ten. To find out whether the brain was using new cells to aid in pattern separation, the study team devised two sets of experiments:

1. To find food presented relative to the location of an earlier meal within an eight-spoke radial maze. “Mice without neurogenesis had no trouble finding the new location as long as it was far enough from the original location,” says Clelland, “but couldn’t differentiate between the two when they were close to each other.”

2. To differentiate close points on a touch screen. Again, mice in which neurogenesis had been curtailed could not discriminate between closely set points on the screen, but had no trouble recalling spatial information in general.

“Neurogenesis helps us to make finer distinctions and appears to play a very specific role in forming spatial memories,” says Clelland. Adds Gage, “There is value in knowing something about the relationship between separate events and the closer they get the more important this information becomes.”

Obviously, it is very unlikely that new cells only assist with pattern separation.  For instance, the researchers also discovered that “newborn neurons actually form a link between individual elements of episodes occurring closely in time,” says Gage.

Gage and his team will go on to investigate whether neurons also enable the encoding of relationships of time and context.

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