The formation of echoic memory traces has traditionally been inferred from the enhanced responses to its
deviations. The mismatch negativity (MMN), an auditory event-related potential (ERP) elicited between 100
and 250 ms after sound deviation is an indirect index of regularity encoding that reflects a memory-based
comparison process. Recently, repetition positivity (RP) has been described as a candidate ERP correlate of direct
memory trace formation. RP consists of repetition suppression and enhancement effects occurring in different
auditory components between 50 and 250 ms after sound onset. However, the neuronal generators engaged in
the encoding of repeated stimulus features have received little interest. This study intends to investigate the
neuronal sources underlying the formation and strengthening of new memory traces by employing a rovingstandard
paradigm, where trains of different frequencies and different lengths are presented randomly.
Source generators of repetition enhanced (RE) and suppressed (RS) activity were modeled using magnetoencephalography
(MEG) in healthy subjects. Our results show that, in line with RP findings, N1m (~95–150ms) activity is
suppressed with stimulus repetition. In addition, we observed the emergence of a sustained field (~230–270 ms)
that showed RE. Source analysis revealed neuronal generators of RS and RE located in both auditory and
non-auditory areas, like the medial parietal cortex and frontal areas. The different timing and location of neural
generators involved in RS and RE points to the existence of functionally separated mechanisms devoted to acoustic
memory-trace formation in different auditory processing stages of the human brain.