Aphasia is an inability to comprehend or formulate language usually due to damage to specific brain regions responsible for these processes. 

There are two important points here to note: 

1. Aphasia is the consequence of another brain disorder such as stroke, brain tumor, traumatic brain injury, viral infections like HSV or neurovegetative process (think dementia here). 

2. There are different types of aphasias, most notably they can be broken down into expressive and receptive aphasia

To be diagnosed the person must have significant impairment in one or more of the following

1. Auditory comprehension

2. Verbal expression

3. Reading and writing

4. Functional communication

About 2 million people are affected by this disorder in the U.S. and strokes account for most of the documented cases. 

One of the most common presentations is anomic aphasias where individuals have word retrieval failures and cannot express the words they want to say (usually nouns and verbs). Some level of this is seen in all types of aphasia.

There can be many other presentations including: 

-inability to comprehend language 

-inability to pronounce words

-inability to speak spontaneously

-inability to read 

-inability to write 

The two most common examples: 

Receptive aphasia (Wernicke’s):

This is a fluent aphasia where the person can speak in sentences but there is no meaning, unnecessary words, and possibly the creation of new words called neologisms. 

-They have poor auditory and reading comprehension.

-There is fluent but nonsensical written or oral expression.

-Since thy do not comprehend language well they are often unaware of their mistakes. 

-The area of the brain affected is well known and established it’s the left temporal lobe as indicated in the picture. 

Expressive aphasia: Broca’s 

-These individuals will speak in short, meaningful phrases with great effort. It will be noticeable how much effort they are putting into speaking. 

-They are usually able to understand the speech of others and are aware of the difficulties they are having leading to frustration. 

-The location of the brain injury is well established, damage to the frontal lobe causes this presentation 

Primary progressive aphasia 

-This is a form of dementia 

-Characterized by gradual loss of language functioning while other cognitive domains such as personality and memory are mostly preserved 

-It usually starts with sudden word finding difficulties and progresses to reduced ability to form grammatically correct sentences, and impaired comprehension