Insight into Learning

Scientists have spent years studying an effect in the brain called long-term potentiation (LTP) in the belief that it's responsible for memory formation. Now, a research group has finally figured out a way to demonstrate that LTP is an important mechanism for memory.

Electrically stimulating neurons (nerve cells) in the hippocampus, a part of the brain involved in memory, in a certain way can strengthen the connections between those neurons. Scientists therefore thought that this was a good way to study the kinds of changes that accompany memory formation. The problem is, as much as researchers came to understand about LTP, no one had definitively connected the effect to memory formation.

A team of researchers led by Dr. Mark F. Bear of the Massachusetts Institute of Technology (MIT), supported by NIH's National Institute of Mental Health and the Howard Hughes Medical Institute, set out to connect LTP with memory formation. They trained rats by allowing them to cross from an illuminated chamber into a dark chamber where a foot shock was delivered. They measured memory as the tendency for the animals to avoid the dark side in subsequent trials. They then dissected out the hippocampus of both trained and control animals and compared them.

In the August 25th issue of Science, the team reports that an area of the hippocampus in the trained rats had the same kinds of biochemical signs of LTP that had been identified in previous electrical stimulation experiments. The signals that could pass between the neurons there were also stronger in the trained rats. The authors conclude that the rats' training caused key connections between certain neurons to grow stronger.

Dr. Bear said, “We show what everyone has always believed: LTP is indeed induced in the hippocampus when learning occurs.”

— by Harrison Wein