Hippocampal–scalp alpha synchrony did not significantly increase with working-memory load in nine patients

We tested whether hippocampal–scalp alpha phase synchrony during verbal working-memory maintenance increases with memory load, as previously reported. Using one session from each of nine patients in OpenNeuro ds004752 version 1.0.1, we analyzed 21 left anterior hippocampal bipolar pairs and 200-Hz scalp EEG. The preregistered-style primary contrast, alpha (9–12 Hz) pairwise phase consistency (PPC) at P3/P4/Pz/O1/O2 during maintenance (3–6 s), was higher for set size 8 than 4 in 7/9 patients, but the mean difference was small (+0.0060; 95% CI −0.0006 to +0.0126) and not significant (exact sign-flip p=0.13; Holm-adjusted p=0.64). The all-electrode alpha contrast was +0.0061 (p=0.031 unadjusted; Holm p=0.19). Late-maintenance minus encoding PPC did not differ in alpha (p=0.82) or theta (p=0.96). Unexpectedly, theta (4–8 Hz) PPC over all scalp electrodes was lower for set size 8 than 4 in all nine patients (mean −0.0066; p=0.0039; Holm p=0.031). Trial-shuffle controls did not materially change load contrasts. The sample included one session per patient and 1–3 left anterior hippocampal pairs per patient; power for small effects is low. PPC was small, volume conduction or common-reference artefact may contribute, and the measure differs from the earlier study. Thus, this analysis does not provide significant evidence for the primary alpha load effect, while showing a corrected secondary theta decrease.

hippocampus · scalp EEG · phase synchrony · pairwise phase consistency · working memory · memory load · theta · alpha · replication