Copyright 2012 Aileen M. Echiverri-Cohen - University of Washington

iomarker approach may elucidate mechanisms underlying inhibitory therapeutic change and
identify components for the development of more targeted interventions.
Several limitations are worth noting. The sample size for the present study was small.
Large effects were observed but they may potentially be not stable, thus merit replication in
larger samples. There was no control condition in the present study, therefore does not permit the
isolation of the effects from pre- to post-treatment beyond time. However, the design was
designed to specifically examine differential treatment effects between PE and SER. Related to
this, other comparison groups (other inhibition-related disorders) that might be expected to show
similar modulations in inhibition were not included and thus it is unknown whether the pattern of
findings are specific to PTSD or not. Also, conclusions can only be made on the short-term
effects of these treatments and cannot speak to the long term, maintenance of symptom
improvement. It also remains to be determined whether the inhibitory deficits existed prior to
PTSD or whether it developed with the disorder. Although multi-level modeling analytic
methods do not require complete data on all participants on all outcome measures, these analytic
methods assume the missing data is missing at random (MAR). MAR assumes that the
missingness is not related to the outcome. In the case where missingness is information (i.e., not
randomly missing), the robustness of the analytical results may be in question. Future research
may assess potential informativeness of the missing data with methods such as the pattern-
mixture model approach (Hedeker & Gibbons, 1997). Finally, AB and PPI are theoretically
indexes of inhibition, however, are also affected by other functions (e.g., vigilance, attention)
and as such the role of other functions cannot be ruled out. Similarly, the construct validity of
commonly used inhibition tasks, including AB, are not yet well established (Friedman &
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