Rationale: Due to combat and training operations, military Service Members are frequently exposed to repeated injurious events making them very susceptible to recurring mild traumatic brain injury (mTBI). Prolonged symptoms are common among military Service Members and Veterans with mTBI. One of these symptoms involves problems with emotional control, often characterized as irritability. Poorly managed irritability contributes substantively to personal distress, interpersonal dysfunction, and limitation in personal and work- related activities, making post-service transition to family life and integration into society problematic. The causes of chronic irritability following mTBI is poorly understood, making effective treatment difficult. This suggests that current standard of care is not consistently targeting the underlying causes of post-mTBI irritability. Understanding what the causes are is a required first step towards developing more targeted and effective treatments for post-mTBI irritability. Problems with standing balance and hearing and understanding words or sounds while in rooms or spaces that are busy and noisy, referred to as auditory processing, are likely reasons for persistent irritability in persons with mTBI, including military Veterans and Service Members.

Objective: The research team’s objective is to research the FY21 TBIPHRP “Understanding of biological factors contributing to an individual’s response, recovery, and long-term outcomes following a brain injury or traumatic event” Focus Area by comparing differences in measures of irritability, upright balance control and sound-in-noise processing between 63 military Veterans with extended history of mTBI (e.g. > 3 months) and 63 Veteran and non-Veteran persons without history of mTBI (healthy controls). The team will determine whether irritability is related to upright balance control and auditory processing in Veterans with extended history of mTBI and explore whether the relationship for Veterans with extended history of mTBI is different when compared to the relationship for healthy controls. The team will also explore what brain structures and connections between the structures relate to irritability in each of the two study groups.

Short-term and long-term outcomes and contributions of the proposed study. In the current study, the research team will administer standardized measures of irritability and implement state-of-the-art technology to measure upright balance control and auditory processing accurately and completely. The team expects to find significant differences in these measures in Veterans with history of mTBI compared to Veterans and non- Veterans without history of mTBI. The team also anticipates finding that impaired upright balance control and auditory processing contributes to posttraumatic irritability in Veterans with history of mTBI.

Clinicians such as psychologists, physicians, and rehabilitation specialists continue to require standard tools and procedures to better identify and treat mTBI-related posttraumatic symptoms. The most immediate impact of the current study will be to inform clinical personnel that posttraumatic irritability is a chronic problem in persons with history of mTBI that requires early detection and purposeful assessment of upright balance control, auditory processing as possible contributors that can lead to more timely and effective therapy for this problem. Additionally, knowing what areas of the brain relate to posttraumatic irritability, clinicians will be better equipped to educate their patients about the neurological underpinnings of their chronic posttraumatic irritability and the prognosis of improving it.

Results of the study will immediately guide the team and other researchers in designing follow-up studies including larger studies that will attempt to replicate the findings found in the current study, studies to improve posttraumatic irritability, and studies that apply brain imaging as an outcome to test the effectiveness of treatment approaches aimed at improving posttraumatic irritability. The research team plans to collaborate with local and national military operating bases and networks to replicate the study in Service Members.

Results from the current study and follow-up studies will pioneer an initial paradigm shift in standard-of-care assessments, setting the foundation for the development of treatments that will lead to improved and potentially more sustainable psychological health and overall quality of life for military Service Members and Veterans with prior history of mTBI. Other populations and professions such as first responders (e.g., local, state, federal law enforcement officers/agents, firefighters) have comparable exposures and related head injuries. Also similar to military Service Members and Veterans, psychological and mental health problems including anxiety, depression, posttraumatic stress and emotional dyscontrol (e.g., irritability) are among the most common symptoms in first responders. However, less is known about upright balance control and auditory processing and how impairment in these areas may contribute to chronic irritability in first responders with history of mTBI. As such, study findings will also be applied to investigate posttraumatic irritability and how upright balance control and auditory processing contribute to irritability in first responders with prior mTBI.