Scientists have found that stimulating the brain with magnets can bring back forgotten memories, an advance that may help people suffering from schizophrenia or depression.
"A lot of mental illness is associated with the inability to choose what to think about," said Brad Postle, a professor at the University of Wisconsin-Madison in the US.
"What we're taking are first steps toward looking at the mechanisms that give us control over what we think about," said Postle.
Researchers found that brains tuck less-important information away beyond the reach of the tools that typically monitor brain activity, and then they snapped that information back into active attention with magnets.
They conducted a series of experiments in which people were asked to remember two items representing different types of information.
When the researchers gave their subjects a cue as to the type of question coming - a face, for example, instead of a word - the electrical activity and blood flow in the brain associated with the word memory disappeared.
However, if a second cue came letting the subject know they would now be asked about that word, the brain activity would jump back up to a level indicating it was the focus of attention.
"People have always thought neurons would have to keep firing to hold something in memory. Most models of the brain assume that," said Postle.
"But we are watching people remember things almost perfectly without showing any of the activity that would come with a neuron firing," he said.
"The fact that you are able to bring it back at all in this example proves it is not gone. It is just that we can not see evidence for its active retention in the brain," he added.
The researchers were able to bring the seemingly abandoned items back to mind without cueing their subjects.
Using a technique called transcranial magnetic stimulation (TMS) to apply a focused electromagnetic field to a precise part of the brain involved in storing the word, they could trigger the sort of brain activity representative of focused attention.
Furthermore, if they cued their research subjects to focus on a face (causing brain activity associated with the word to drop off), a well-timed pulse of transcranial magnetic stimulation would snap the stowed memory back into attention, and prompt the subjects to incorrectly think that they had been cued to focus on the word.
The study suggests a state of memory apart from the spotlight attention of active working memory and the deep storage of more significant things in long-term memory.
The study was published in the journal Science.
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