The new findings are significant because they may help improve researchers' understanding of how memory works, and lead to a new strategy to enable epilepsy patients retain cognitive function.
The researchers recorded brain activity from 52 neurosurgical patients being treated for drug-resistant epilepsy, in order to test whether distinct patterns of electrophysiological activity prior to a response can distinguish true from false memories.
The patients were asked to perform a verbal free-recall task while researchers used an array of implanted electrodes and intracranial electroencephalographic recordings to locate where in their brains the seizures originated.
For the verbal free-recall task, the patients studied lists of words, which they were asked to recall at a later stage. It was found that the participants recalled some numbers of correct items, and also made a small number of errors while recalling words that had not appeared on the target list.
As the patients performed the memory game, the researchers observed electrical activity in their brains to determine whether specific brain waves were associated with successfully storing and retrieving memories. It was found that a fast brain wave called the gamma rhythm increased as the participants studied a word that they would later recall. The same waves, whose voltage rises and fall between 50 and 100 times per second, also rose in the half-second prior to participants correctly recalling an item.
Lead author Per B. Sederberg, a former Penn neuroscientist who is now performing post-doctoral research at Princeton University, says that the analysis reveals that the same pattern of gamma band oscillatory activity in the hippocampus, prefrontal cortex and left temporal lobe that predicts successful memory formation also re-emerged at retrieval, distinguishing correct from incorrect responses.
According to led investigator Michael Kahana, a professor of psychology in Penns School of Arts and Sciences, retrieval of true memories induced a distinct pattern of gamma oscillations in the brain as compared to retrieval of false memories. He said that gamma waves actually predicted whether or not an item that was about to be recalled was previously studied. In other words, one could see a difference in brain activity just prior to remembering something that had and had not actually happened.
The researchers say that the new findings may provide a clearer picture of how to assist people suffering from epilepsy. They say that identifying the neural signatures of successful memory storage and retrieval can help neurosurgeons reduce the cognitive deficits that might result from epilepsy surgery.
The study has been published online in the journal Psychological Science.