In accordance with the expected RP effects, the N1m showed a clear
decrement with increasing number of repetitions. A large body of literature
has previously reported N1 adaptation with stimulus repetition
during oddball presentations. Such strong finding has led
to the alternative interpretation that non-specific N1 adaptation can
account for the whole of sensory memory-based effects of the MMN or partially concur
with them (Garrido et al., 2009b). Suppression of the N1m component
is a relatively stable effect observed in most roving standard studies
and constitutes an essential part of the RP effects Comparable effects were observed at the anatomical level in
our study, with RS found in auditory and non-auditory regions during
the N1m time range. Similarly reported a strong
N1 suppression of frontal, parietal and cingulate areas that exceeded
suppression found in typically auditory areas. In most cases, RS was
stronger on the right hemisphere. In line with this previous research,
results presented here indicate a strong suppression of the bilateral
precuneus, located in the medial wall of the parietal cortex, and to a
lesser degree in typical auditory regions like the HG, STG, and MTG
during the early N1m interval. Both ROI and whole-brain analyses
consistently showed that the precuneus was capable to track sound repetition aftermany presentations, as evidenced by themiddle vs. late
contrast. This might suggest that while rapid adaptation after fewstimuli
occurred in secondary auditory areas, non-auditory regions—and the
HGas revealed in the ROI analysis—developed a slower long-termadaptation
during the early N1m time range. Such notion would be in line
with previous findings showing that auditory HG responses exhibit adaptation
on multiple timescales in animals and
humans In addition,
some empirical support for the separationwemade of the N1m component
in two different subcomponents was found. In the right hemisphere,
dSPM estimates revealed a peak of activation in anterior areas
of the STG during late N1m interval, whereas the early N1m interval
had its loci located in the posterior STG reported
a similar pattern for N1mto novel sounds and suggested that anterior
N1m sources might bemore narrowly tuned to sound frequency,
and thus, reflect a lesser degree of adaptation. Similarly, our results
showfewRS effects in the late N1mtime range as compared to the posterior,
early N1m subcomponent.