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Your Brain on ChatGPT: Accumulation of Cognitive Debt when Using an AI Assistant for Essay Writing Task
(arxiv.org)
This is a paper for a MIT study. Three groups of participants where tasked to write an essay. One of them was allowed to use a LLM. These where the results: 
The participants mental activity was also checked repeatedly via EEG. As per the papers abstract:
EEG revealed significant differences in brain connectivity: Brain-only participants exhibited the strongest, most distributed networks; Search Engine users showed moderate engagement; and LLM users displayed the weakest connectivity. Cognitive activity scaled down in relation to external tool use.
I hate to have to be the one to tell you this, but... just copy-pasting is how a lot of people use LLMs.
Yep, and they fuck themselves over academically because lecturers notice how their time spent in online-learning platforms doesn't match their assessment submissions.
Students inevitably get questioned about their content, only for the lecturer to discover they don't know shit, because they cheated. Had the student actually used it properly, they might know enough about the content to scrape by.
In any case, I've seen this happen five times lol. One of them because my lecturer asked one of my classmates what 'frivolous' and 'multifaceted' meant, and fumbled before saying they used a thesaurus.
She was then asked in plain speech what she intended to say, and ended up with an "I don't know" - boom. Academic integrity compromised, investigation into her Learnline metrics, and cross referencing her work from two years earlier. Termination of her course followed two weeks after.
Most students use it; the lecturers know this. The difference is whether people use it as a tool, or a replacement.
In any case, essays are supposed to be a metric of knowledge and evidence of independent research. In practice? A good essay really only reflects one thing - the student is good at writing essays. I know people in early childhood education who suffered through university, who have more intuition and emotional intelligence than people who got by on academic prowess.