Why do we remember some seemingly mundane details of our day while forgetting others? Researchers from Caltech are chipping away at this question by studying the brains of epilepsy patients undergoing a procedure to locate the source of their seizures.

Ueli Rutishauser, a researcher at the California Institute of Technology, in Pasadena, recorded electrical activity from single neurons in part of the brain responsible for memory in these patients as they looked at a series of pictures. He later showed the patients another set of pictures, some new and some previously shown, and asked them which they had seen before. He then searched for differences in the brain activity recorded when the patients were shown pictures that would later be forgotten or remembered.

Rutishauser found that a patient was highly likely to remember a picture if the activity of a single neuron was correlated to a broader electrical rhythm in the brain called the theta rhythm--this four-to-eight hertz rhythm results from large populations of neurons firing synchronously. The correlation "also predicts the confidence that they will remember it," he says. "If they remember it strongly, the correlation will be even stronger. If they are guessing, the correlation will be weak."

It's not yet clear what regulates the phenomena, it might be a function of attention, motivation or some unknown property of the internal circuit dynamics of the brain, says Rutishauser. "We want to figure out what regulates it so that we can change it, perhaps allowing for the creation of stronger memories." The research was presented at the Society for Neuroscience conference in Chicago this week.