How does amnesia not affect language and speech?
In: Biology
Different “kinds” of memories are stored in different places in the brain. Movement, speech, emotions, senses, tasks & skills, history, working memory, and all those sorts of things each have a different, localized area, and damage to that specific area generally impairs that function and not much else (for example, look at the case of [Phineas Gage](https://en.wikipedia.org/wiki/Phineas_Gage), who had a rail spike go through his head and lost basically all his emotional control but retained a good bit of his original mind).
All of that is to say, unless a brain injury specifically damages the areas responsible for higher cognitive functioning, language (words & grammar), or speech (converting mental words into vocal sounds), you generally won’t lose the ability to speak.
As a quick aside, there’s also two major forms of amnesia: retrograde, in which you forget your history from before the incident but can still make new memories, or anterograde, in which you remember everything but can’t make new memories – as soon as something in your present leaves short-term memory, it’s gone forever.
Language and speech aren’t the same kind of memory as learning geometry. Your brain figures out what phonemes you need for your language before you’re a year old, and you’ll talk before you’re two. That’s the time when your brain is still rewiring itself, mostly cutting unneeded connections and also adding new ones. To some extent, your first language is hardwired in. It’s not just data storage.
Amnesia can be caused by many different things and can effect different parts of the brain.
Some people do forget, such as with amnesia aphasia.
They can also forget as part of late stages of dementia, specifically alzheimer’s, which often works backwards, causing people to forget their most recent memories first (that is a very very simplified explanation). Since language and speech are one of our oldest memories, they’re usually the last to go and often people suffering from dementia die before reaching this stage.
Because if it did it would be called aphasia instead.
Jokes aside, words mean what we want them to mean, and, especially for technical contexts like medicine, narrow, highly specifc meanings are more useful than looser, vaguer meanings. In this case, it’s useful to have separate words for losing “biographical” memory and losing “language” memory.
In practice, the two things often go together, in the same way that, if you get hit by a heavy object, oedema (swelling caused by accumulated fluids) often goes together with haematoma (bruising caused by ruptured capillaries), and it’s more useful to think in terms of where those conditions come from: e.g. a stroke can cause amnesia and/or aphasia.
Amnesia is a very specific form of brain damage where other faculties are not affected. It’s also extremely rare.
When people suffer from a stroke though, they sometimes have to relearn how to speak and/or how to walk.
So Amnesia is really the exception, rather than the rule of brain injury.
Typically amnesia affects areas in the medial temporal lobe (roughly to the lower sides of your brain), such as the hippocampus. Your speech and language centers are in different areas of the brain.
Of course, amnesia can be accompanied with language processing or producing problems (seen with strokes).
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