Article: Aphasia

Aphasia (also Aphemia - from Greek α, without, and φημη, speech), is a loss or impairment of the ability to produce and/or comprehend language, due to brain damage. It is usually a result of damage to the language centres of the brain (like Broca's area). These areas are almost always located in the left hemisphere, and in most people this is where the ability to produce and comprehend language is found. However in a very small number of people language ability is found in the right hemisphere. Damage to these language areas can be caused by a stroke, traumatic brain injury or other head injury. Aphasia may also develop slowly, as in the case of a brain tumor. Depending on the area and extent of the damage, someone suffering from aphasia may be able to speak but not write, or vice versa, understand more complex sentences than he or she can produce, or display any of a wide variety of other deficiencies in reading, writing, and comprehension.

Aphasia may co-occur with speech disorders such as dysarthria or apraxia of speech, which also result from brain damage.

The brains of young children with brain damage sometimes restructure themselves to use different areas for speech processing, and regain lost function; adult brains are less "plastic" and lack this ability.

Aphasia can be assessed in a variety of ways, from quick clinical screening at the bedside to several-hour-long batteries of tasks that examine the key components of language and communication.

Classification of Aphasia

The Locationist Model

The locationist model attempts to classify the aphasia by major characteristics and then link these to areas of the brain in which the damage has been caused. The initial two categories here were devised by early neurologists working in the field, however, since then, more researchers have added to the model, resulting in it often being referred to as the "Boston-Neoclassical Model". The most prominent writers on this topic have been Howard Goodglass and Edith Kaplan.

Individuals with Broca's aphasia have damage to the frontal lobe of the brain. These individuals frequently speak in short, meaningful phrases that are produced with great effort. Broca's aphasia is thus characterized as a nonfluent aphasia. Affected people often omit small words such as "is", "and", and "the". For example, a person with Broca's aphasia may say, "Walk dog" meaning, "I will take the dog for a walk". The same sentence could also mean "You take the dog for a walk", or "The dog walked out of the yard", depending on the circumstances. Individuals with Broca's aphasia are able to understand the speech of others to varying degrees. Because of this, they are often aware of their difficulties and can become easily frustrated by their speaking problems. Individuals with Broca's aphasia often have right-sided weakness or paralysis of the arm and leg because the frontal lobe is also important for body movement.

In contrast to Broca's aphasia, damage to the temporal lobe may result in a fluent aphasia that is called Wernicke's aphasia. Individuals with Wernicke's aphasia may speak in long sentences that have no meaning, add unnecessary words, and even create new "words". For example, someone with Wernicke's aphasia may say, "You know that smoodle pinkered and that I want to get him round and take care of him like you want before", meaning "The dog needs to go out so I will take him for a walk". Individuals with Wernicke's aphasia usually have great difficulty understanding speech and are therefore often unaware of their mistakes. These individuals usually have no body weakness because their brain injury is not near the parts of the brain that control movement.

Working from Wernicke's model of aphasia, Ludwig Lichtheim proposed five other types of Aphasia but these were not tested against real patients until modern imaging made more indepth studies available. The other five types of aphasia in the locationist model are:

1. Pure Word Deafness (all understanding impaired, but expressive channels intact).
2. Conduction Aphasia (speech, writing and silent reading intact, but repetition, reading aloud and dictation impaired).
3. Apraxia Which is now considered a separate disorder in itself.
4. Transcortical Motor Aphasia (Understanding of speech, writing, repetition and reading intact, but impaired voluntary speech and writing).
5. Transcortical Sensory Aphasia,(Impaired comprehension of speech and writing, but writing, reading aloud and speech spared).

Anomia is another type of aphasia proposed under what is commonly known as the Boston-Neoclassical model, which is essentially a difficulty with naming. The sufferer may have difficulties naming certain words, linked by their grammatical type (e.g. difficulty naming verbs and not nouns) or by their semantic category (e.g. difficulty naming words relating to photography but nothing else) or a more general naming difficulty. Sufferers are usually aware and it is comprarable to a 'tip of the tongue' sensation experienced by most people.

A final type of aphasia, global aphasia, results from damage to extensive portions of the language areas of the brain. Individuals with global aphasia have severe communication difficulties and will be extremely limited in their ability to speak or comprehend language.

In practice however, very few patients fit one of the types perfectly, and so an alternative model was proposed.

The Cognitive Neuropsychological Model

The Cognitive Neuropsychological model builds on cognitive neuropsychology. It assumes that language processing can be broken down into a number of modules, each of which has a specific function. Hence there is a module which recognises phonemes as they are spoken and a module which stores formulated phonemes before they are spoken. Use of this model clinically involves conducting a battery of assessments (usually from the PALPA), each of which test one or a number of these modules. Once a diagnosis is reached as to where the impairment lies, therapy can proceed to treat the individual module.

Types of aphasia

Any of the following can be considered aphasia:

• inability to comprehend speech
• inability to read (alexia)
• inability to write (agraphia)
• inability to speak, without muscle paralysis
• inability to form words
• inability to name objects (anomia)
• poor enunciation
• excessive creation and use of personal neologisms (jargon aphasia)
• inability to repeat a phrase
• persistent repetition of phrases
• other language impairment

The common types of aphasia are

• Broca's aphasia (expressive aphasia)
• Wernicke's aphasia (receptive aphasia)
• Nominal aphasia (anomic aphasia)
• Global aphasia
• Conduction aphasia

It is worth noting that a combination of the above is possible.

A few less common varieties include

• Transcortical motor aphasia
• Subcortical motor aphasia
• Transcortical sensory aphasia
• Subcortical sensory aphasia
• Mixed transcortical aphasia
• Acquired eleptiform aphasia (Landau Kleffner Syndrome)