Rats have too much on their minds

Science News, Oct 17, 1998 by John Travis

Students cramming for an exam sometimes feel as if their brains can't absorb any more information. That overloaded feeling is shared by rodents studied by Edvard I. Moser of the Norwegian University of Science and Technology in Trondhelm and his colleagues. The scientists used electrodes to stimulate memory-forming regions of rat brains. The stimulated animals fared poorly on a spatial-learning task that involves swimming for a hidden platform in a water tank, the researchers report in the Sept. 25 SCIENCE.

The overstimulation seems to prevent a strengthening of the connections between brain cells, known as synapses, that occurs after repeated stimulation. Many neuroscientists now believe that this strengthening, called long-term potentiation or LTP, is the primary mechanism by which animals form memories. The overstimulation experiments confirm that LTP can strengthen the synaptic connections between brain cells only so much. Moreover, if a brain reaches maximum stimulation, any learning is difficult if not impossible. "People are now focusing on how such changes in synaptic strength allow memories to form. That's the next issue, and it's a formidable question," says Moser.