Physiological and Affective Underarousal as a function of Mild Head Injury in University Students

sk (W A IS -I II ) As expected, prior to any arousal manipulation (i.e., baseline) students with MHI performed more poorly on tasks of working memory (WAIS-III, 1997; DKEFS, 2002) and attention (DKEFS, 2002). , , implicated in the modulation of emotional and autonomic responses1. This region is particularly vulnerable in head trauma2 and, therefore, emotional responses may be at risk in this population. Consistent with this, research (see Tranel & Damasio, 19943) has shown that persons with moderate to severe traumatic brain injury (TBI) to the vPFC present with underarousal as evidenced by reduced electrodermal activation (EDA) responses and flattened affect. Furthermore, it has been suggested that individuals with moderate to severe neurological compromise are particularly vulnerable to the adverse effects of stress 4,5 . Until recently, little research has been conducted to examine the persistence of i l d i i l f ll i ild h d i j (MHI) i j i hi h University students (N = 91); 56% self-reported MHI history Measures and procedure Neuropsychological measures (memory17, 18; attention19; planning19; abstract reasoning18,19, 20; and standard intelligence18); indices of arousal/anxiety21; manipulated arousal (via psychosocial stressor22 or relaxation) Post-concussive symptoms (Post-concussive Symptom Checklist [PCSC])16 Indices of Anxiety physiological recordings of electrodermal activity [EDA] and heart rate23; STAI21; selfreported arousal levels; Everyday life stress 24 15 20 25 30 35

The prefrontal cortex (PFC), especially the ventromedial PFC (vPFC), has been implicated in the modulation of emotional and autonomic responses 1 .This region is particularly vulnerable in head trauma 2 and, therefore, emotional responses may be at risk in this population.Consistent with this, research (see Tranel & Damasio, 1994 3 ) has shown that persons with moderate to severe traumatic brain injury (TBI) to the vPFC present with underarousal as evidenced by reduced electrodermal activation (EDA) responses and flattened affect.Furthermore, it has been suggested that individuals with moderate to severe neurological compromise are particularly vulnerable to the adverse effects of stress 4,5 .
Until recently, little research has been conducted to examine the persistence of i l d i i l f ll i ild h d i j (MHI) i j i hi h p University students (N = 91); 56% self-reported MHI history Measures and procedure Neuropsychological measures (memory 17,18 ; attention 19 ; planning 19 ; abstract reasoning 18,19,20 ; and standard intelligence 18 ); indices of arousal/anxiety 21 ; manipulated arousal (via psychosocial stressor 22   However, when arousal state was manipulated students with MHI tended to perform better on a cognitive flexibility task (WAIS-III, 1997) when stressed than when relaxed in contrast to their no-MHI counterparts who performed better when relaxed than when stressed, F (1, 87) = 3.17, p = .079.emotional and cognitive sequelae following mild head injury (MHI) -injuries which can be subtle and involve alterations in consciousness without extensive neural loss 6 .Further, the findings regarding arousal have been, at best, variable 7 , and, at worst, inconclusive.
Previous research from our lab 8,9 has demonstrated that persons with a history of mild head injury (MHI) reported lower arousal and performed better on memory and attentional tasks with increased arousal.Despite reports of lessened self-perceived stress, students with MHI reported experiencing a greater level of life stressors compared to their no-MHI cohort 9 .
Furthermore, it has been typically suggested that post-concussive symptoms Overall, competent university students who acknowledge a history of MHI but have not complained of persistent effects or concerns regarding the MHI nonetheless endorsed significantly more post-concussive symptoms (e.g., headaches, concentration difficulties, irritability), t (89) = 2.29, p = .024,experienced the symptoms with greater intensity, t (89) = 2.62, p = .010,and for longer durations, t (89) = 2.24, p = .028,than their no-MHI counterparts.

Discussion
University students with self-reported MHI endorsed experiencing significantly more life stressors such as financial or relationship difficulties than their no-MHI cohort, t (89) = 2.51, p = .014. , yp y gg p y p (i.e., cognitive difficulties, altered affect, and physical complaints) subside after a three month period and functioning is assumed to return to previous abilities 10 , 11 .Yet, for some, 5% -10% 12,13 , these difficulties may not be transient 14,15,16 .

Purpose Discussion
Therefore, the purpose of the current study was to:

MHI History MHI History
Persons with mild head trauma who have not complained of, or self-identified as experiencing any neurocognitive challenges, present with a profile similar to that of persons with moderate to severe injury to the vPFC region.Despite reports of experiencing significantly more life stressors than their no-MHI cohort, students with MHI are relatively emotionally and physiologically underaroused compared to their no-MHI counterparts.Students who acknowledged a history of sustaining a MHI were significantly less physiologically responsive to the arousal manipulations of stress and relaxation and may be less responsive to stressors in their environment-which may suggest dysregulated stress responsivity.Further, cognition is advantaged by increased arousal, rather than decreased arousal, for students with MHI in contrast to those with no-MHI.Finally, increased t i t t

hih t d f t h t i M H I f t i f t h
Despite reports of increased life stress, university students with history of a previous MHI self-reported significantly lower arousal, F (1, 89) = 5.60, p = .020,and produced significantly fewer EDA responses, F (1, 89) = 28.06,p < .001,as compared to their no-MHI cohort.Overall, university students with self-reported MHI had a diminished EDA response to the arousal manipulations as compared to their no-MHI counterparts.The no-MHI group had more extreme and larger range of EDA responses than the MHI group (ps < .05).Post-hoc analysis revealed significant differences between students with no-MHI and those with MHI across age at injury groups with respect to self-reported, F (4, 86) = 3.95, p = .005,and physiological (electrodermal activity) responses, F (4, 86) = 7.95, p < .001.In short, those who sustained their head trauma at 11 to 15 years of age reported and elicited more dampened arousal than students who sustained their injury at other ages or the no-MHI group.
investigate the affective (both self-report and physiological indices [e.g., heart rate]) status of students with self-reported MHI examine possible differences in responsivity to the experimental manipulation of arousal (psychosocial stressor or relaxation) as a function of MHI history investigate effects of experimentally manipulated arousal on cognitive performance in university students with and without MHI Explore post-concussive-like symptom reports in this high-functioning population as a function of MHI history symptom reports were heightened for those reporting a MHI as a function of the more qualitative (i.e., intensity and duration of symptoms), as opposed to quantitative (i.e., frequency) aspects of PCS.Our findings are suggestive of persistent and subtle effects of neural disruption following mild head trauma.Lastly, age at sustaining the MHI, especially during the early teenage years as compared to other ages, may also play a role in arousal levels.