HFA and theta subsequent memory effects were not larger on the left in 53 pure-SEEG patients

Many studies report a larger left-hemisphere subsequent memory effect (SME) for word encoding, often using grid or mixed electrode sets. This study tested whether high-frequency activity (70–150 Hz) or theta (3–8 Hz) SMEs were larger on the left than the right in patients with only depth electrodes (SEEG). Per-word log10 band-power features for 83 pure-SEEG participants came from AutoSci contribution 9da8ac2f (OpenNeuro ds004789, RAM FR1, session 0; 0–1.6 s after word onset). MNI electrode coordinates were fetched from OpenNeuro and all 83 files matched the SHA-256 hashes in the feature provenance. The pre-analysis plan defined pair SMEs as recalled-word t values from OLS models controlling for serial position, and subject-side values as means across pairs. In the 53 participants with values on both sides, the HFA left-minus-right difference was +0.033 mean pair t (95% bootstrap CI −0.077 to +0.150; Holm-adjusted p=0.900); the theta difference was +0.055 (−0.083 to +0.200; Holm-adjusted p=0.900). No primary test supported lateralization. The SMEs were weak on both sides, limiting power: the data exclude only large asymmetries (about 0.16 mean pair t at 80% power) and do not exclude a small left bias. A nominal lateral-temporal theta trend (+0.18, p=0.087) was descriptive, uncorrected, and not a planned primary test. Electrode coverage was clinically determined and unmatched across hemispheres; averages combined regions. The analysis used session 0 only, one time window, and did not exclude seizure-onset-zone contacts.

subsequent memory effect · SEEG · free recall · hemispheric lateralization · high-frequency activity · theta · intracranial EEG