In college I tried a medication called Topamax (Topiramate) for migraine prevention. Topamax has a low-occurrence side effect of “language impairment”. After 10 days or so it became clear that I was particularly susceptible to this phenomenon.
It was a terrifying experience, but it was also a valuable one as it changed the way I view intelligence.
When I was in the thick of it, my writing and speech skills had devolved to that of a primary school aged child. I’ll never forget trying to type a text message and struggling to come up with simple words like “and”. My speech slowed down considerably and I was having trouble with verbal dictation.
The terrifying thing was that my internal world was still as complex and meaningful as it was before. All of the emotions I felt were real and legitimate. My cognition outside of communication was intact, I could do math just fine and conceptualize and abstract problems.
In spite of this, I was unable to convey what I was feeling and thinking to the outside world. It felt like I was trapped inside my own body.
I thankfully made a full recovery. However, my intuitive understanding of the link between language and intelligence was completely severed. While I believe there’s likely a high degree of correlation between the two in populations, on an individual level one’s language skills mostly represent one’s ability to communicate with the outside world, not their ability to understand complex information or process it.
See the following for more info on Topamax/Topiramate language impairment: https://link.springer.com/article/10.1007/s10072-008-0906-5