Differences between post-traumatic stress disorder with military background patients and healthy people during early auditory processing : neural markers of resilience and vulnerability to trauma (Hebrew)

The Mismatch Negativity (MMN) evoked event-related potential (ERP) component is a central neurophysiological index of early auditory processing in humans, representing an electrophysiological brain response (e.g. mean MMN amplitude size) to an unexpected or deviant acoustic stimulus versus a standard expected acoustic stimulus across many ERP trials. MMN responses reflect excitatory neural reactivity in the primary auditory cortex (activation of excitatory post-synaptic receptors) to an unexpected transient deviation in ongoing auditory stimuli. Since the MMN embodies cognitive processes of sensory change detection, attentional regulation, and pre-attentive auditory processing, studies indicate an association between its characteristics and behavioral-clinical features across different neuropsychiatric populations. The present study examined early auditory processing by evaluating the MMN component in combat history army veterans, with the aim of identifying early neural response patterns that may distinguish between soldiers diagnosed with PTSD, soldiers at subclinical risk for developing PTSD, and versus healthy soldiers without risk. The main goal of the study was to test whether the amplitude and latency MMN component could serve as markers differentiating between groups of healthy soldiers at risk versus those without risk, as well as to examine the association between MMN measures and the extent of PTSD symptoms and psychological resilience among the healthy army-veteran participants. Three groups were classified as a between-group factor within the total sample of the study: soldiers diagnosed with PTSD, healthy soldiers at risk (PCL-M > 34), and healthy soldiers without risk. After completing personal questionnaires, all participants completed the PCL questionnaire assessing PTSD symptom severity and the psychological resilience questionnaire (CD-RISC), which was followed by a passive MMN task paradigm during online EEG recording noting all auditory ERP events and ongoing EEG activity. The findings indicated that in the healthy, undiagnosed sample participants at risk (high risk) exhibited significantly higher MMN amplitude compared to participants without risk (low risk), providing preliminary evidence for excessive neural reactivity in the higher-risk group, closer in magnitude to MMN amplitudes in the group diagnosed with PTSD. No differences were found in MMN latency between groups. A significant overall difference in MMN amplitude was observed among the three groups; however, post hoc comparisons did not reveal significant pairwise differences. Mean amplitudes nevertheless tended to be higher in the diagnosed group, close to those observed in the high-risk soldiers.

 A negative association was also found between psychological resilience and MMN amplitude among healthy soldiers, such that lower resilience was associated with increased MMN amplitudes, also supported by larger MMN amplitudes in high-risk individuals versus low-resilience individuals. The findings support the idea that increased MMN amplitude may reflect hyper-reactivity of early auditory processing mechanisms in high-risk PTSD individuals versus low-risk individuals. Exaggerated responses in the auditory cortex in pre-attentive processing windows may reflect heightened arousal in early sensory pathways and impaired activation of post-synaptic NMDA receptors. This pattern, which appears among subclinical-risk soldiers as well as among those diagnosed with PTSD, may represent an early neural-processing response that differentiates between varying levels of vulnerability or risk for developing PTSD. Additionally, the association between low psychological resilience and high MMN amplitude highlights that resilience is not only a psychological trait but is possibly linked to the responsiveness of early neural regulatory pre-attentive mechanisms for detecting unexpected changes in the environment. The findings emphasize the importance of event-related EEG measures, and specifically the MMN ERP component, as sensitive neurophysiological markers of subclinical differences among soldiers before the onset of more debilitating PTSD symptoms such as anxiety, restlessness, and impaired emotional and sensory regulation (e.g., hyperarousal symptoms). Integrating these neural measures with resilience and psychological symptom scores across individuals at risk for the development of PTSD (such as soldiers with elevated subclinical symptoms) may enable earlier and more accurate identification of soldiers at risk for developing PTSD, thereby supporting the use of auditory neural-response profiling as an objective and reliable tool for mental-health professionals in the IDF and in educational systems that assess and train future soldiers or monitor soldiers at-risk for PTSD following their military service, and following early treatment interventions.