What is a Mild Brain Injury?

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By Michael Howard, Ph.D.

The Mild Traumatic Brain Injury (MTBI) Working Group of the CDC (Center for Disease Control) in Atlanta has defined MTBI as an injury to the head resulting from blunt trauma or acceleration or deceleration forces with one or more of the following conditions:

  • transient confusion, disorientation, or impaired consciousness.
  • dysfunction of memory around the time of injury.
  • loss of consciousness lasting less than 30 minutes.

Mild traumatic brain injury is also called concussion.  Traumatic brain injury results when the neurons inside the brain are damaged from acceleration-deceleration forces during impact.  When the head is struck or moved violently, the gel-like brain is rapidly displaced or concussed back and forth within the skull.  The brain is distorted in shape and the fragile, thread-like neuron cells inside the brain can be stretched, torn, or traumatized by the mechanical forces.

Typically, the long axon of the neuron is most susceptible to injury.  The phenomenon is called axonal shearing.  This type of traumatic injury can result in the neuron’s death or temporary loss of function.  When, by head trauma, a number of neurons is disabled in such a manner, disruption or alteration of brain functions can occur.  This is the major mechanism behind MTBI.

Traumatic brain injury can result in the skull being broken or fractured (penetrating head injury) or the skull remaining intact (closed head injury).  In MTBI, closed-head injuries are by far the most common.  It is not necessary for the head to be physically struck to result in mild traumatic brain injury.  Violent back-and-forth movement of the head, called whiplash, can also result in neuronal damage.  The MTBI that is due to proximity to a blast explosion that many soldiers and others in Iraq have sustained is another example of an MTBI occurring without the head being physically struck.

WHAT ARE THE SYMPTOMS OF A MILD BRAIN INJURY?

It is common for individuals to have immediate symptoms of brain impairment after a mild traumatic brain injury.  These symptoms can be physical, cognitive, and behavioral in nature and can occur in any combination. They typically last up to a few weeks.  Although there is no “typical” MTBI patient, headaches, dizziness, insomnia, and intermittent confusion are commonly seen in the first days or weeks after the injury.  These symptoms are most severe immediately after the injury.

Over the few days or weeks following the injury, the symptoms should diminish in number and intensity.  Whether or not an individual will have symptoms persisting beyond the first few weeks or months is very difficult to predict and may depend on a number of factors, including the presence of co-existing conditions like depression, anxiety, chronic pain, prior head traumas, or involvement in personal-injury litigation.