The association between concussion and autonomic nervous system responses to a cognitive stressor

Objective: Investigate the association between concussion and reactivity of cardiovascular, salivary, and electrodermal indicators of autonomic nervous system (ANS) function in the context of cognitive stress. Method: Individuals (N = 37) with concussion were prospectively recruited from a level 1 trauma center emergency department, along with 23 uninjured community controls (UC). Participants were assessed twice (1-week and 1-month post-injury for the concussion group). Electrocardiogram, impedance cardiography, electrodermal skin conductance, and saliva samples were collected before, during, and after a modified Paced Auditory Serial Addition Test. Analyses evaluated the effect of Group, Visit, and task Event on behavioral and physiological variables. Physiological reactivity to the task was correlated with Rivermead Post Concussive Symptom Questionnaire (RPQ) total scores. Results: The UC group showed augmented heart rate (HR) task responses when compared to the concussion group (effect ranging from d = 0.53 to 0.82). Similarly, the UC group had reduced high-frequency HR variability (HF-HRV) task response, indicating parasympathetic (PNS) withdrawal during cognitive engagement (effects ranging from d = 0.25 to 0.80). The concussion group displayed no significant HF-HRV changes during the task. There were no reliable group differences in sympathetic nervous system measures (i.e. PEP, skin conductance, and salivary alpha amylase). Among concussed individuals, greater increase in HR task response at 1 week was associated with lower concussion symptom burden at 1 month. Conclusions: Findings indicate that blunted ANS, and especially PNS, reactivity to cognitive stress is associated with concussion in community adults and that ANS dysfunction may be prognostic of symptom recovery.