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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.
Very interesting, emphasis mine :
"findings support the view that external support tools restructure not only task performance but also the underlying cognitive architecture. The Brain-only group leveraged broad, distributed neural networks for internally generated content; the Search Engine group relied on hybrid strategies of visual information management and regulatory control; and the LLM group optimized for procedural integration of AI-generated suggestions.
These distinctions carry significant implications for cognitive load theory, the extended mind hypothesis [102], and educational practice. As reliance on AI tools increases, careful attention must be paid to how such systems affect neurocognitive development, especially the potential trade-offs between external support and internal synthesis."
Also the focus on agency and ownership is also very interesting, namely regardless of the scored outcome or how one might think the work itself changed them, or not, do they themselves feel it is their work?
Why should they care? They've gone into this artificial situation for money and they're just copying/writing words to get paid. It's similar to school in that sense. Pointless work in order to please people in power.