Hippocampal stimulation effects on recall were not confirmed in catFR2, and PAL2 lacked power for a test

A preregistered analysis tested exploratory findings from RAM FR2 using categorized free recall data (OpenNeuro ds005491 v1.0.0). In five SEEG subjects with a hippocampal stimulation anode, stimulation at encoding was associated with an 8.6 percentage point lower recall rate for stimulated words than for non-stimulated words on the same lists (four of five negative; 95% bootstrap CI −16.5 to −0.2 points; one-sided exact sign-flip p = 0.094). This did not confirm the prior result, and the confidence interval included the earlier estimate of −4.3 points, leaving the result undetermined at this sample size. Stimulation amplitude did not significantly predict the item effect across nine SEEG subjects (Spearman rho = −0.27, p = 0.24). In a separate PAL2 paired-associate analysis (OpenNeuro ds005494 v1.0.1), only three hippocampal-anode SEEG subjects were available, below the prespecified minimum of five; the planned test was not testable. Descriptive PAL2 results across seven SEEG subjects had a mean effect of −0.056 (p = 0.56). Stimulation sites and amplitudes were not randomized, only behavior was analyzed, and the pooled FR2 plus catFR2 estimate includes discovery data and is not a confirmation.

memory · word recall · intracranial stimulation · hippocampus · SEEG · confirmatory analysis · RAM catFR2 · RAM PAL2