Higher current did not increase the recall decrease during open-loop encoding stimulation in RAM FR2 and catFR2

This analysis tested whether the recall decrease associated with open-loop 50 Hz stimulation during word encoding increased with current amplitude in RAM FR2 and catFR2. It used event and electrode tables from OpenNeuro datasets ds005489 and ds005491; the exact dataset releases used are not recorded. A unit was a subject, bipolar pair, and amplitude, pooled across sessions. Of 78 units, 77 met the threshold of at least 20 stimulated words and 20 control-list words, covering 46 subjects. The primary subject-level Spearman correlation between amplitude and serial-position-matched recall difference (stimulated minus control) was +0.16 (two-sided permutation p = 0.30). Mean subject difference was -2.2 percentage points (sign-flip p = 0.033). In a model with MTL, depth, and catFR2 terms, the amplitude slope was -0.003 per mA (stratified permutation p = 0.79). MTL units had a mean difference of -4.8 percentage points at a mean 0.97 mA; strip/grid units had +1.5 percentage points at a mean 1.94 mA. The data do not show a dose effect from 0.25 to 3.5 mA; site was associated with larger differences than current in this range. Current was set by clinicians, was not randomized, and was confounded with site and excitability. Only 10 units exceeded 2 mA, all at strip/grid sites. Within-subject comparisons involved nine subjects, and seven also changed electrode pairs. These findings apply only to open-loop 50 Hz, 4.6 s trains during encoding, not to closed-loop stimulation or other pulse parameters.

memory · free recall · electrical stimulation · stimulation amplitude · intracranial EEG · medial temporal lobe · dose response · OpenNeuro · RAM FR2 · catFR2