Electric brain response to sound repetition in humans:: an index of long-term-memory -: trace formation?

The developing auditory system is exposed to an almost endless variation of acoustic input in its every-day environment. All these different stimuli cannot, of course, be encoded in memory, however, at least not for any longer time. The present data suggest a principle that might be followed by the brain in selecting stimuli for the formation of longer-duration memory traces. Normal subjects ignoring auditory stimulation were presented with a randomized sequence of different sounds (simple tones in Experiment I and frequency glides in Experiment 2) with the exception that every now and then, randomly, one of the sounds was repeated in a row a few times. It was found that these repetitions elicited a novel electric brain response ('repetition negativity') which might be generated by neural activity forming these longer-duration traces. This would suggest that of all the different sounds, only those that soon occur again form more enduring memory traces (when sounds have no particular significance). (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.