Traumatic brain injury (TBI) contributes a major cause of death, disability, and mental health disorders. Most TBI patients suffer long-term post-traumatic stress disorder, cognitive dysfunction, and disability. The underlying molecular and cellular mechanisms of such neuropathology progression in TBI remain elusive. In part, it is due to non-standardized classification of mild, moderate, and severe injury in various animal models of TBI. Thus, a better diagnosis and treatment requires a better understanding of the injury mechanisms in a well-defined severity of mild, moderate, and severe injury in different models that may potentially reflect the various types of human brain injuries. The purpose of this review article is to highlight the classification of mild, moderate, and severe injury in various animal models of TBI with special focus on mixed injury that represents a translational concussive head injury. We will classify animal models of TBI broadly into focal injury, diffuse injury, and mixed injury. Focal injury, a localized injury, is represented by animal models of controlled cortical impact, penetrating ballistic-like brain injury, and Feeney or Shohami weight drop injury. A global diffuse injury is best represented by shock tube model of primary blast injury, and Marmarou or Maryland weight drop model. A mixed injury consists of focal and diffuse injury which reproduces the concussive clinical syndrome, and it is best studied in animal model of lateral fluid percussion injury.
Keywords: Animal models; Diffuse injury; Focal injury; Injury severity; Mixed injury; Traumatic brain injury.