Focal Neurological Deficits Add to Multi-Attending Problems

Focal Neurological Deficits Add to Multi-Attending Problems

By Gordon Johnson

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Focal neurological deficits are one of the four acute symptoms of Mild Traumatic Brain Injury.   See the ACRM definition of Mild Traumatic Brain Injury and our treatment of MTBI discussed click here:   Yet focal neurological deficits are not just important as an acute signs of concussion. They are also create a serious logjam in the brain’s capacity to multi-attend after a mild brain injury.  In other words, they are a major drain on the brain’s RAM.

Focal Neurological Deficits caused by focal injury to the brain.

Focal Neurological Deficits can be caused by an injury to any of the brain’s structures or axonal tracts.

Focal neurological deficits are specific parts of the central or peripheral nervous systems that aren’t working correctly. For example, if there is a defect in the way the muscles of the eye are working, that would be a focal neurological deficit. Likewise, an obvious deficit after trauma is a defect in the way in which the pupils dilate.  Someone in a deep coma may have severely dilated pupils, or unevenly dilated pupils. Each cranial nerve operates a neurological function, which can cause focal neurological deficits. For our treatment of the cranial nerves, click here.

The spectrum of different focal neurological deficits is as almost as broad as everything the body does. Yet these things – when working properly – work subconsciously, without requiring significant attention. Any time the neurological system is working improperly, it will create a major drain on the brain’s attentional resources.  When the eyes aren’t focusing, all visual input will be garbled, requiring the brain to try to interpret the signals it sees. Likewise, when the ears aren’t working, or when muscle coordination is impaired.

Focal Neurological Deficits: Vestibular Disorder

Most focal neurological deficits are fairly uncommon after mild head trauma.  The one which is not is a vestibular deficit, a malfunction in the bodies balance system.  Making it particularly important in a discussion of attentional demands of focal neurological deficits, is that the vestibular system can be an attentional demanding deficit to overcome.

The vestibular system is so named because it includes the inner ear, which is located in the brain’s vestibules.  But vestibular function is also dependent upon the cranial nerves and a specific portion of the cerebral cortex.  The vestibular system is that part of the neurological system that allows the body to stay balanced and for the eyes to focus when the head is moving.  You cannot be balanced if your eyes are out of focus.  Further, imbalance is particularly distracting.

In normal situations the vestibular system runs in the background and runs fairly efficiently even though it’s doing some fairly complicated things.  The method the vestibular system uses to keep the eyes in focused is called the “vestibular ocular reflex”, (VOR).  The VOR creates a counterbalancing movement of the eyes to respond to the movement of the head. Try this to see the VOR in operation:

Stand in front of a mirror and look at your eyes, while rotating your head.  As you rotate the head, your eyes will stay in the same position.   As long as your eyes are focusing on the fixed object your eyes will not move relative to the object.  They will stay steady with that object.  In order to do what you observe, the eyes have to rotate inside the eye sockets, in the opposite direction of the head.

If you rotate your head too far you won’t be able to stay in focus, but moderate movement to the head does not affect your ability to focus.  Obviously the more coordinated you are the better your eyes are at tracking.  For example, professional football wide receivers are extremely good at maintaining focus while their head is moving.

Like other focal neurological functions, vestibular activities run in the background and run fairly efficiently.  Unfortunately, the vestibular system is one parts of our nervous system which is fairly easy to have something go wrong after trauma – even relatively mild trauma.

  • There can be problems with the inner ear.
  • There can be problems with crystals within the inner ear.
  • There can be problems with the cranial nerves that connect the inner ear to the brain; and
  • There can be problems with that portion of the cerebral cortex where the signals from the inner ear are received and interpreted.

That’s a lot that can go wrong and often it does.  For an excellent illustration of some of the things involved in the vestibular system, click here.

When the vestibular system malfunctions the brain can usually find a way to compensate, but the compensation is one of the most demanding things there is for our brain’s RAM capacity.  The reason a focal neurological deficit in the vestibular system requires so much data is that the vestibular system is crunching so much data.  What makes the vestibular processing so intensive is that visual data, especially three dimensional visual data, is far more complex than most other things the brain does. Compensating for a vestibular dysfunction is like processing an entire movie file on a computer.

Think of how much slower a computer processes video files than word processing files. The brain is similarly challenged. When the vestibular system is sending the brain bad signals, the brain has to transpose those bad signals.  The attention demands of that are extraordinary. Further, the demands are not just processing demands, but also bandwidth demands, because not only is the brain trying to translate improper stimuli, but that stimuli may be flowing into the brain at an unsynchronized rate.  Think how distracting it is to watch a movie when the sound is out of sync. The incoming nerve roots are serving the same purpose as the internet connection does to Netflix. The nerve roots are inputting the balance and visual informaiton into our central processing unit, that is the brain.  For more on the vestibular disorder click here.

So if you have an  abnormal vestibular system you may have extreme difficulty doing any other cognitive tasks when the vestibular system is acting up.  We will now continue or illustrate  how post-concussional deficits can consume the brain’s RAM.

Next – Pain Impacts Attention After Concussion


Gordon Johnson

Attorney Gordon Johnson is one of the nations leading brain injury advocates. He is Past-Chair of the TBILG, a national group of more than 150 brain injury advocates. He has spoken at numerous brain injury seminars and is the author of some of the most read brain injury web pages on the internet.

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