ABSTRACT The goal of this administrative supplement is to support research training and mentoring for Ms. LeeAnne Tunstall in the post-baccalaureate category. Ms. Tunstall graduated from Virginia Tech in May 2023 with a Bachelor of Science in Psychology and minor concentration in Adaptive Brain and Behavior. Long-term, she is interested in pursuing a research career in neuroscience. Ms. Tunstall’s research experience will be considerably enhanced by dedicated mentoring by the PI, intellectually stimulating scientific and clinical environment at Duke, formal and informal educational experiences, and peer networking opportunities with post-baccalaureate, graduate, and post-doctoral trainees at Duke. The parent grant will investigate resting- state functional connectivity in PTSD, but does not change or duplicate the overall goals or hypotheses of the parent award. The parent project aims to identify resting-state fMRI neural signatures that are common and unique across DSM diagnoses of PTSD and MDD, compares comorbid PTSD and MDD, pure PTSD, pure MDD, and Controls in functional brain networks involved with arousal, fear, salience, and executive processing, and finally investigates trans-diagnostic symptoms shared by PTSD and MDD. The goal of Specific Aim 1 is: Investigate the relationship between PTSD re-experiencing symptoms and DMN / CEN connectivity, and the relationship between PTSD hypervigilance symptoms SN connectivity. Hypothesis: We predict that re-experiencing symptoms will be positively associated with DMN activity and re-experiencing symptoms will be negatively associated with CEN activity. Thus, there will be a reciprocal relationship between DMN and CEN activity. We predict that patients with more severe re-experiencing symptoms will spend greater time in a DMN-dominant state whereas patients with mild re-experiencing symptoms will spend relatively less time in a DMN-dominant state, effectively modulating DMN-CEN network imbalance. The goal of Specific Aim 2 is: Investigate the relationship between PTSD re-experiencing symptoms and DMN-cerebellar / DMN-cerebellar subregions, CEN-cerebellar / CEN-cerebellar subregion / SN-cerebellar / SN-cerebellar subregion connectivity. Hypothesis: We predict altered CEN, SN, and DMN connectivity to cerebellum and cerebellar sub-structures in PTSD. We hypothesize that the PTSD effects will be more pronounced in the neocerebellum than the archicerebellum (i.e. diagnosis x sub-structural interaction). We expect more severe PTSD re-experiencing symptoms will tip the balance to stronger DMN-cerebellar and DMN-cerebellar sub-structural connectivity, but weaker CEN-cerebellar, CEN-cerebellar sub-structural connectivity in PTSD. We expect more severe PTSD hypervigilance symptoms will tip the balance to stronger SN-cerebellar and SN-cerebellar sub-structural connectivity in PTSD.