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.
Because I found it now and searching didn't show anyone posting it before…