New Memories Erase Old By Generating New Neurons

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New Memories Erase Old By Generating New Neurons

 

Scientists have found that existing memories may be erased in our brain by

a process that involves the generation of new neurons. This clearance might

be important to " make room==for the acquisition of new memories.

 

The results are reported in today's issue of Neuron.

 

The research team, led by Joe Tsien of the Department of Molecular Biology

at Princeton University, generated mice that lack a protein called

presenilin-1 throughout much of the brain. Mutations in presenilin-1 are

responsible for the majority of cases of early-onset Alzheimer's disease,

but the function of the protein in the context of the normal CNS is poorly

understood.

 

These mice were viable and grew normally, but the researchers observed that

after spending time in a rich, stimulating environment filled with

diversions and mouse toys, the brains of presenilin-1 mutant mice generated

fewer new neurons than the brains of normal mice.

 

Tsien and colleagues initially thought that this reduced neurogenesis might

cause learning deficits, but, after months of testing, none could be

detected. The researchers did observe, however, that time spent in an

enriched environment generally enhanced the retention of recent learning.

 

To their surprise, they also found that some newly formed memories were

harder to erase in the mice lacking presenilin-1 than in the control mice.

This suggested to the authors that generation of new neurons is important

for the memory-clearance process.

 

Memory retention ordinarily seems like a good thing. However, as Tsien

points out, " adding new neurons to existing networks may potentially

disrupt, rather than improve, the function of these networks==

 

These findings raise a possibility that chronic abnormalities in this

clearance process may contribute to the devastating memory disorder

associated with Alzheimer's disease.

In addition, they raise a potential cautionary note about the therapeutic

use of neural stem cell transplantation for neurodegenerative disorders.

 

[Contact: Joe Z. Tsien]

06-Dec-2001

 

 

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