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).