What is Concussion?

The Basics

Mild traumatic brain injury (MTBI), commonly known as concussion, is defined as a head injury with a temporary loss of brain function causing a variety of physical, cognitive, and emotional symptoms. There is no overt physical evidence of trauma, and the victim may immediately appear to be confused, disoriented, dazed or even experience a brief loss of consciousness. These symptoms often resolve within a brief period of time or may last for days, weeks, months and even years after the incident. Clinical experience shows that fatigue becomes a notable factor over time with reports of decreased performance and needing more rest.

Current diagnosis of MTBI include observation and behavioral checklists. Long-term symptoms may be examined with a CT scan or MRI and neuropsychological testing. Presently the quantitative EEG (qEEG) is one of few techniques to accurately diagnose MTBI as other methods do not pick up bruising or microscopic tears within the brain. Concussions consequences can vary from mild to fatal. Historically, the brain was thought to be "hardwired" with each area of the brain responsible for certain functions. For example, the occipital lobe of the brain’s involvement in visual perception. Damage to this area will cause issues with vision.

Skull Brain Interface

MTBI occurs when the brain hits the inside of the skull. This happens when a body (skull) stops suddenly, changes direction suddenly, or is repeatedly exposed to micro traumas. The brain is enclosed in cerebral spinal fluid, which acts to cushion the brain from hitting the skull. If the change in direction or force is too great, the brain will collide with the skull.

The sinus cavity is at the front of the skull; above, around and below the eyes and along the sides of the skull towards the ears. These structures are jagged and sharp. When these structures impact the brain, they tear and causing micro bleeding. The areas most commonly affected are the prefrontal, frontal and temporal lobes. The back of the skull is quite smooth and curved and collisions with it will instead cause extensive bruising. Injuries caused by hitting the sinus cavities are usually quite discrete (specific as to effect), whereas injuries caused by hitting the back of the skull are quite diffuse.

Physiological Effects of Concussion

As the skull stops moving, the brain continues to move subject to the laws of physics. The sudden change(s) in direction and the impact upon the inside of the skull lead to several potentially traumatic events occurring. Based upon the physics, verified by MRIs we know that:

1. Brain cells communicate through a cascade of electrical charges down a long stem, called an axon. Axons contain pumps and channels that allow ions, such as sodium and calcium, to go in and out of the cell when needed. The forceful impact of a concussion causes diffuse damage occurs in ionic channels, resulting in a reduction of general intelligence, information processing and slowness of thought.

2. Bruising and micro-tearing of impacted regions of the brain, resulting in short-term memory reduction, reduced self-awareness, reduced social acuity, and depression.

3. Shear forces on grey and white matter, resulting in the stretching of axons. This occurs when different parts of the brain slide by each other, and the long stems of the brain cells (described above) are damaged. Injuries of this sort lead to reduced clarity and slowness of thought.

4. Rotational forces can damage the connections between the area of the brain for vision and the inner brain stem connections. Areas of the brainstem are responsible for basic functioning, such as body temperature, heart rate, and control of hormones and bodily signals. These sorts of damages results in problems with balance, sleep, and vision.

Functional Modules of the Brain

Current research suggests MTBI is even more complex than we previously thought. Behaviours are organized as “hubs” or “functional modules”. A hub consists of the parts of the brain that work together to produce a thought, behavior or emotion. While there are numerous hubs, seven have been extensively studied. These are the hubs for: addiction, anxiety, attention, default network, depression, pain, and schizophrenia.

The default network appears at rest, when not engaged in a task and not ruminating about the past/present. This network involves the cingulate gyrus, hippocampus, medial frontal lobes, temporal lobes, and parietal lobes. Injury to any one of these areas, or damage to the axons running between these organs, can disrupt the activity of the default network. The image below shows just a few parts of the default network, illustrating the location of associated regions and the distances between them.

A Mild Traumatic Brain Injury (MTBI), also known as a concussion, can occur any time the brain impacts upon the skull. The nature of impact is determined by a varying degree of external forces such as blows to the head, a sudden stop, bouncing up and down or repeated impact. The most commonly thought of MTBIs are motor vehicle accidents; however, there are several ways for a concussion to occur. The following material discusses both the causes and impact of concussion.