Researchers from the University of California, Irvine, have visualized brain cell connections that are modified by learning. Now neuroscientists likely can use the same method to map where memories form throughout the brain, said principal investigator Gary Lynch.

In previous studies, the scientists found markers of memory-forming synapses in the hippocampus, a brain center for memory. They electrically stimulated brain slices because naturally occurring electrical signals are believed to induce memory formation in living organisms, a process known as long-term potentiation. They discovered that spines on dendrites, or branchlike parts of neurons, become more numerous and contain more phosphorylated cofilin, a protein, as a result of long-term potentiation.

The left image shows synapses as green dots in a rat tissue section. The two right panels are pictures of a synapse (green) and a second label (red) that indicates it has been modified by long-term potentiation.

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In the current experiments, they wanted to know whether these markers naturally appear during learning. Therefore, they examined the brains of rats that had traveled through a maze as a learning activity to see whether the brains had an increase in the number of dendritic spines and phosphorylated cofilin. They labeled both and imaged the brains with a Leica wide-field microscope. They employed deconvolution software from Improvision Inc. of Lexington, Mass., to generate 3-D reconstructions of each brain image.

The scientists determined that the dendritic spines with a dense concentration of phosphorylated cofilin became more prevalent in the brains of rats that had learned the maze, as reported in the July 25 issue of the Journal of Neuroscience. Critically, they also discovered that synapses, micron-size zones that receive input from other neurons, were substantially larger on the labeled spines. These results confirmed that the markers identified in long-term potentiation studies could serve as markers for memory in a real learning task. Lynch said that similar experiments theoretically can be performed in other animals.

The researchers are so confident that they can map where in the brain memories are created that they plan to establish soon a consortium of laboratories directed at producing the first maps of memory.