Even if you can't consciously remember a face you've seen once before, your brain remembers it. Scientists interested in this phenomenon have proven that there's strong evidence that our brains hold far more memories than we're aware of. New Scientist has the story:
[University of California, Davis, neuroscientists] Deborah Hannula and Charan Ranganath first trained volunteers by showing them images of faces paired with background scenes. Then they ran tests in which the volunteers were shown one of the scenes, to cue their memories, followed by the same scene superimposed with three previously learned faces.
The volunteers correctly identified the face previously paired with the scene nearly two thirds of the time. But careful analysis of the volunteers' eye movements, combined with measurements of brain activity using functional magnetic resonance imaging, revealed that the hippocampus was often retrieving memories even if these recollections didn't make it to the level of consciousness.
Somehow the hippocampus is able to retreive memories without that acitivity making it into your conscious mind. This work suggests a number of future areas of research. First of all, could we figure out a way to make the activity of the hippocampus touch the conscious mind, and improve our memories? And second, is it possible that we're acting on unconscious memories all the time, letting them color our decisions and calling them "intuition" or "just a feeling"?
This research is forthcoming in Neuron.