Edit: There's a blog post on the failings of the study and the communication around it: Clickbait Neuroscience: Lessons from “Your Brain on ChatGPT” – Mind Brain Education

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.

Over four months, LLM users consistently underperformed at neural, linguistic, and behavioral levels.