A neuropsychiatric perspective on traumatic brain injury.

Traumatic brain injury (TBI) due to closed mechanisms causes strain injuries to axons that increase in number and severity as injury severity increases. Axons that project up from the brain stem are vulnerable, even in milder concussive injuries, and include axons that participate in key monoaminergic pathways. Although called diffuse axonal injury, the supra-tentorial injury component typically shows an anterior preponderance in humans. As the injury forces increase, cerebral contusions may be superimposed on the axonal strain injuries, and these contusions show an anterior preponderance as well. The chronic neuropsychiatric manifestations of TBI reflect this injury distribution. In the cognitive sphere, these manifestations almost always include power function disturbances marked by difficulties with cognitive processing speed, multitasking, and cognitive endurance. These disturbances may then be followed by disturbances in executive function and self-awareness as injury severity increases. In the behavioral sphere, mood disturbances and disorders of behavioral control and regulation are particularly common.