The open source journal Brain Science has just published a survey of literature demonstrating that a mild traumatic brain injury (mTBI) , otherwise known as concussion, is a complex pathophysiological process that can have a systemic effect on the body aside from solely impairing cognitive function. According to the article, “dysfunction in the autonomic nervous system (ANS) has been found to be a major factor in the symptomatology in TBI, including in mTBI” and can “induce abnormalities in organ systems throughout the body.”

Some Backstory on the Autonomic Nervous System

The ANS functions without voluntary control. It has two divisions, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The SNS “fight or flight” response is a whole body response that includes release of epinephrine and norepinephrine from the adrenal medulla, as well as widespread vasoconstriction in the body. The PNS “rest and digest” response decreases heart rate, which helps to conserve energy under resting conditions. The ANS is not only involved in vascular and cardiac regulation, but because it innervates cardiac muscle, smooth muscle, and various endocrine and exocrine glands, it influences the activity of most tissues and organ systems in the body. The regulation of blood pressure, gastrointestinal responses, contraction of the urinary bladder, focusing of the eyes and thermoregulation are all controlled by the ANS.

How May a TBI Affect the ANS?

A TBI can cause increased SNS activity leading to immune system depression. Endocrine abnormalities can happen as well as pathology in the hypothalamic-pituitary axis (discussed in prior posts.) ANS dysfunction has been found to correlate with irritable bowel syndrome, depression, anxiety and psychiatric disorders.

Researchers are studying various tools for assessing ANS dysfunction following concussion including

• measures of heart rate variability
• pupillary light reflex
• the arterial pulse wave (APW)
• eyeball pressure
• graded exercise testing

Further studies are needed to understand the long term effects of mTBI on the autonomic nervous system and the most effective tools for treating this dysfunction. Acknowledging this dysfunction does help us better appreciate the wide scope of physical, cognitive and emotional symptoms often experienced following concussion.