For anyone who's ever forgotten something or someone they wish they could remember, a bit of solace: Though the memory is hidden from your conscious mind, it might not be gone.

In a study of college students, brain imaging detected patterns of activation that corresponded to memories the students thought they'd lost.

"Even though your brain still holds this information, you might not always have access to it," said neurobiologist Jeffrey Johnson of the University of California, Irvine. His remarks appeared in the study he co-authored, published Wednesday in Neuron.

That recalling a memory triggers the neurological patterns encoded when the memory was formed is a tenet of cognitive science. Less understood, however, is what becomes of those patterns at moments of incomplete recall.

Maybe you remember breakfast at a certain restaurant, but not what you ate; perhaps you recall a particular conversation, but not what you said. It's not known whether those details vanish from the mind altogether, or are subsumed by some larger pattern, or remain intact but inaccessible.

"It wasn't quite clear what happens to them," said Johnson of lost details. "But even when people claim that there are no details attached to their memories, we could still pick some of those details out."

Of the the forgotten breakfast, he said that "we might still be able to pick up information about what you ate from brain activity, though you can't access it consciously."

Johnson's team put eleven female and five male college students inside an fMRI machine, which measures real-time patterns of blood flow in the brain. Each student was shown a list of words, then asked to say each word backwards, think of how it could be used, and imagine how an artist would draw it.

Twenty minutes later, the researchers showed them the list again, and asked the students to remember what they could of each word.

Recollection triggered the original learning patterns, a process known technically as reinstatement; the stronger the memory, the stronger the signal.

"What I think is cool about the study is that the degree of cortical reinstatement is related to the strength of our subjective experience of memory," said Anthony Wagner, a Stanford University memory researcher who wasn't involved in the experiment.

But at the weak end of the gradient, where the students' conscious recall had faded to zero, the signal was still there.

It's possible that the students lied about what they remembered. But if not, then memory may truly persist. The question then is how long memories could last — weeks, months, even years.

"We can only speculate that this is the case," said Johnson, who plans to run brain-imaging studies of memory degradation over days and weeks.

As for whether those memories could be intentionally guided to the surface, Johnson says that "at this stage, we're just happy to be able to find evidence of reinstatement at a weak level. That would be something down the line."

See Also:

*Citation: "Recollection, Familiarity, and Cortical Reinstatement: A Multivoxel Pattern Analysis." By Jeffrey D. Johnson, Susan G.R. McDuff, Michael D. Rugg, and Kenneth A. Norman. Neuron, Vol. 63 Issue 5, September 8, 2009. *

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