Open-loop 50 Hz stimulation showed no reliable onset-versus-sustained recall cost difference in RAM FR2

This study tested whether recall cost differed between the first word, at train onset, and the second word, during sustained stimulation, in 50 Hz open-loop stimulation blocks covering two words. In depth-anode RAM FR2 sessions (29 subjects), the pre-registered onset-minus-sustained contrast was −2.32 percentage points (95% CI −5.71 to +1.11; sign-flip p = 0.20). The same contrast in catFR2 (10 subjects) was −1.22 points (95% CI −4.73 to +3.42; p = 0.63). Against no-stimulation lists, both onset and sustained words lost about 3.6 points in FR2. A post hoc analysis found lower recall for the unstimulated word just before a train in FR2 (−3.44 points, p = 0.027, uncorrected); the word just after a train showed no difference. This may reflect a retrograde train effect or a list-level design effect and only generates a hypothesis. The study used event and behavioral data only, did not analyze iEEG signals, included mixed stimulation sites and amplitudes, and did not correct secondary or post hoc p values for multiple tests. Each train covered two words, so onset and sustained timing were paired and a one-word train was not tested.

memory · free recall · intracranial stimulation · SEEG · closed-loop brain-computer interface · FR2 · catFR2