As individuals we vary greatly in our emotional experiences and their form of expression. In order to investigate and subsequently characterize this variability we examined individual emotional reactivity and recovery, while taking into account the integration and segregation of multiple brain networks, multi-level indices of somatic homeostasis and perturbation (cellular, hormonal and physiological measures), as well as measures of emotional behavior (action choices, verbal replies, continuous self-reports of feelings, and/or clusters of personality tendencies).

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A robust method for delineating individual differences is by examining the above measures with regard to stressful occurrence: in real life or induced in the lab. With regard to the former, we measured neuronal reactivity among a-priori healthy IDF soldiers, before and after military combat via prospective fMRI testing. We found that higher amygdala activation prior to potentially traumatic exposure correlated with more traumatic stress symptoms among soldiers, following exposure to chronic combat stress. In contrast, activity in the hippocampus and the ventral striatum changed over time in correlation with symptoms following exposure. Intriguingly both a-priori reactivity and posteriori plasticity corresponded with ventromedial PFC co-activation and structural connectivity with limbic regions

(Admon... Hendler, 2009) , (Admon... Hendler, 2012), (Admon... Hendler 2013) (see pics 1, 2, 3).

 

Based on this series of studies, we proposed a cause and consequence model for trauma, with the amygdala predisposing emotional hyper-reactivity, and prefrontal cortex and hippocampus responsible for a resulting dis-regulation and poor adaptation to the traumatic stressor (Admon, Milad and Hendler 2015, (Hendler and Admon 2016). In another prospective fMRI study we further examined the effects of chronic military stress by examining the contribution of both personality and brain biased responses to threat. Mediation analysis revealed that only high anxious individuals showed hippocampal activity that lead to decreased symptoms via avoidance bias tendencies (Lin... Hendler 2014) (see pic 4). 

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More recently, we have looked for neural and epigenomic correlates of recovery from distress following laboratory induced social stress. Using resting state fMRI before and after the induced stress, we showed that during the second fMRI test (about approximately 40 min after the exposure to stress (during the second fMRI scan) individuals that exhibited sustained feelings of distress also showed a greater increase in  the coactivationco-activation of the amygdala (Vaisvaser... Hendler, 2013) and hippocampus, as well as a decrease amygdala-PCC connectivity (Maron Katz... Hendler and Shamir, 2016).  We also found that changes in vmPFC activation during social stress induction corresponded to with peripheral measures of prospective changes in miRNA 29c; known to be an epigenetic marker of the function of astrocytes function in the rodents' medial PFC;, most probably related to cortisol secretion. This finding points to a neuroepigenetic mechanism that may underlie the adaptation to stress in humans (Vaisvaser... Shomron and Hendler, 2016) (see pic 5, 6).  Moreover, in a study investigating the epigenetic markers of the cholinergic system, we found that increased vmPFC coactivation with the amygdala following chronic stress resulted in less stress symptoms, suggesting it may serve as a marker for resilience to stress related psychopathologies (Lin…Hendler and Soerq, 2016) (see pic 7).

 

To further examine individual differences in goal directed behavior when at risk when encountering risky situations, we used an interactive game that assesses the degree of approach towards rewarding targets when under high environmental risk for punishment.  The fMRI results demonstrated a hyper-activation of the meso-limbic system (; ventral striatum and ventral tegmental areas), in individuals with a personality tendency to high goal-approaching behavior in general, as well as during the Consistent results were observed behaviorally as well. Game itself as measured behaviorally. This study nicely links specific brain circuit function with individual behavioral tendencies, alluding to the importance of multi-level measurements when profiling pathological functions (Gonen... Hendler, 2016) (see pic 8).