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Friday, January 20, 2012

The GUIDE: The "A's" have it... [Full link to blog for email clients.][FT:C44]

I have, on many occasions, railed against "stupid movie science" in the form of getting brain science wrong, or being unimaginative regarding use of brain disorders.  As I have often said, the most misused brain disorder in TV (especially soap opera), movies and books is amnesia.  Today's blog is meant to introduce the reader (and writer) to a number of other "Axxxx" diseases that can be used with interesting consequences in fiction.

Amnesia:  Total amnesia of the sort depicted in the typical Soap-Opera head-injury scenario is rare.  Even rarer still is the fiction construct of a person living a totally different life for decades, then receiving another head injury and reverting to their original life and memories!  However, amnesia does occur, particularly with trauma or head injury, and it often encompasses about 2-3 hours before the incident, and about 1-2 days after.  The "retrograde" amnesia (forgetting past memory) is due to the fact that the normal processing of short-term to long-term memory is disrupted by injury.  The "anterograde" amnesia (inability to make new memory) is a result of swelling or infection cause pressure on the hippocampus.  With increased pressure comes decreased blood flow and decreased function.  Once the swelling goes down, the normal processes of encoding and storing memory can continue.  However, there *are* cases of surgery (deliberate or accidental), head trauma and disease that cause damage to hippocampus and produce a permanent anterograde amnesia.  I discussed such a classic case of amnesia in the epilepsy blogs last year.

Agnosia:  A special case of amnesia, agnosia results from very localized damage to the brain.  In particular, the damage occurs to the association areas of the brain that process the basic sensory information and deliver it tot he parts of the brain that make decisions and control our actions.  In the visual areas, agnosia manifests as "visual neglect" the subject ignores what is in one part of the visual field, even though the eyes and pupils react to stimulation of that part of the field, and there is evidence that *some* of the sensory information is getting through to other parts of the visual system: for example, the eyes can track a moving object through that field, and the a subject shown an embarrassing picture to that part of the field will blush and act embarrassed without being able to say why.  Neglect can apply to the body as well, a patient may not be physically aware of sensation from a limb or part of the body, even though the spinal cord, motor control, reflexes and pain reactions are intact.   Frequently the damage is to the thalamus, which relays sensory information through the brain, or to specific nerve tracts in the Parietal Lobe.

Ataxia:  Often confused with simple clumsiness, ataxia is a failure of the brain to provide coordination to movement.  Ataxia may be accompanied by tremor, rigidity or weakness, and is thus hard to diagnose differently than other diseases.  However, the key finding is the inability to coordinate the movement of more than one arm or leg at a time, clumsiness that occurs when a person stops concentrating on the movement, or the inability to stop a movement once it is started.  Ataxia usually results from damage to the cerebellum, but may also be caused by damage to deep brain nuclei or brainstem.

Apraxia:  Like ataxia, apraxia results in a failure to get the body to do what the patients wills it to do.  In a typical case, it is easy for a patient to bend down, pick up a baseball that is in their way, and toss it away.  However, if the patient is told to pick up the ball, or verbally expresses the desire to throw the ball, they cannot do it.  All of the motor and sensory abilities - including coordination - are intact, but the patient cannot turn intent into action.  Damage to the premotor areas of Frontal Lobe or the associational areas of Parietal Lobe are usually involved.  Neither the motor nor sensory cortex areas are damaged, though, and all abilities remain intact.

Aphasia: When apraxia occurs within the speech centers, it is termed "aphasia." We all experience minor bouts of aphasia that occur as "tip of the tongue" phenomenon, but these are usually due to the inability to perform the appropriate memory recall of a word.  Aphasia is different, because a patient can hear the word, write the word, choose it out of a list, but cannot speak it.  It is a specific disorder of Broca's area, which sends signals to the motor cortex for diaphragm, throat, tongue and mouth to form words.  Broca's Area is in the Frontal Lobe, just below and forward of the motor cortical areas for the face and neck, and lying just over a bundle of nerve axons (the arcuate fascilus) that run from sensory association areas of the Parietal Lobe, underneath Wernicke's Area (language), Broca's Area, and terminate in the "cognition" ares of the Frontal Lobe.  Aphasia is frequently caused by damage to Broca's Area or the arcuate fasiculus.

Alexia:  Also known as visual aphasia, this is a failure of language and speech generation - in this case the failure to recognize and understand words.  Alexia is usually visual, and shows as the inability to recognize that printed or written characters represent language, i.e. "word-blindness."  There are auditory forms, but those are usually associated with obvious hearing disorders.  If the person retains the ability to speak and write words, then they have alexia without agraphia and the damage is between the visual cortex and Wernicke's area and confined to the lateral Parietal Lobe.  Damage to Wernicke's Area also causes loss of ability to write and speak coherent language.  Note the similarity to "dyslexia" and you can see how important the Wernicke/arcuate fasciculus/Broca linkage is to transforming sensory input to language.

So there, five new "A-words" to add to amnesia and spice up the plot of that new novel or movie.  The unfortunate thing, though, is that these disorders are not new, and doctors face them every day with stroke, head trauma and battlefield trauma patients.  Then again, the best stories come from real life incidents.

Thanks for reading, and tune in next time for some book reviews and a refresher on brain basics for The Lab Rats' Guide to the Brain!


  1. Hi speaker!

    I have a couple of questions, because I'd like to clarify things in my brain.

    One is: do most of these disorders have a spectrum of severity associated with them? like, I know consistently snagging the wrong word to say when you know the right one is called 'Aphasia', but it doesn't quite seem to fit with the examples you gave above - unless there's a spectrum characteristic.

    Also, my family has Alzheimer's... I know it's a degenerative disease that eventually affects everything, but how do such diseases fit into the disorders you present here? I know it presents as... well eventually it has all these symptoms, I think, but it starts out presenting as amnesia, right?


  2. Very good question and I will be answering a bit of this in later blogs. Yes, there is definitely a spectrum associated with disorders such as aphasia. The "tip of the tongue" phenomenon, in which you know that you know the right word, just can't retrieve it, is a very mild aphasia, and usually involves failure to retrieve a memory. The most severe aphasias involve inability to even speak, with various stages of difficulty in between. Alexia is another spectrum - alexia (word blindness) at its most severe involves inability to read, write or recognize spoken words. Alexia without agraphia means a person has word blindness, but is able to write out the same words when heard. The "milder" cousin - dyslexia - is certainly severe enough on its own and is only mild in comparison with alexia. Again, there are varying degrees of severity to dyslexia, and even a few advantages. Persons with mild dyslexia may have difficulty in spelling, pronunciation and reading certain words, but are often proficient in mirror or upside-down reading.

    As for your question on Alzheimer's I am going to defer that for about two week, I have a blog or two on Alzheimer's due to run sometime around the first of Feb.

    Thanks for reading, and be sure to follow up if I don't answer your questions!


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