Brain injury forces of moderate magnitude elicit the fencing response

Traumatic brain injury is heterogeneous, both in its induction and ensuing neurological sequelae. In this way, medical care depends on accurately identifying the severity of injury-related forces. Clinically, injury severity is determined by a combination of the Glasgow Coma Scale, length of unconsciousness, posttraumatic amnesia, and persistence of neurological sequelae. In the laboratory, injury severity is gauged by the biomechanical forces and the acute suppression of neurological reflexes. The present communication describes and validates the "fencing response" as an overt indicator of injury force magnitude and midbrain localization to aid in injury identification and classification.

Using YouTube, the Internet video database, videos were screened for head injury resulting in unconsciousness and documented for the fencing response. Adult male rats were subjected to midline fluid percussion brain injury at two severities, observed for acute neurological reflexes and the midbrain evaluated histopathologically.

Tonic posturing (fencing response) has been observed to precede convulsions in sports injuries at the moment of impact, where extension and flexion of opposite arms occurs despite body position or gravity. Of the 35 videos identified by an impact to the head and period of unconsciousness, 66% showed a fencing response at the moment of impact, regardless of the side of impact, without ensuing convulsion. Similarly, diffuse brain-injured rats demonstrate a fencing response upon injury at moderate (1.9 atm, 39/44 animals) but not mild severity (1.1 atm, 0/19 animals). The proximity of the lateral vestibular nucleus to the cerebellar peduncles makes it vulnerable to mechanical forces that initiate a neurochemical storm to elicit the neuromotor response, disrupt the blood-brain barrier, and alter the nuclear volume.

Therefore, the fencing response likely indicates neurological disturbance unique from convulsion associated with mechanical forces of moderate magnitude imparted on the midbrain and can assist in guiding medical care after injury.