Word onset increased theta phase locking in SEEG, while corrected recall effects were not significant

We measured theta pairwise phase consistency (PPC) and power after word onset in 3,591 bipolar SEEG pairs from 39 subjects in the OpenNeuro delayed free-recall dataset (ds004789), using the first 180 words of session 0. For each subject, PPC from 0.1–0.6 s after onset minus PPC from −0.5 to −0.1 s before onset was positive in 38 of 39 subjects (mean +0.0130, dz 1.14, sign-flip p < 1e−5, Holm p < 1e−5); group PPC peaked at about 0.2 s. A total of 847/3,591 pairs (23.6%) met the phase-locking criterion. In those pairs, theta power did not change significantly (+0.045 dB, p = 0.65), a pattern consistent with phase reset of ongoing theta, although an evoked component plus a concurrent induced power decrease cannot be excluded. The subsequent-memory PPC effect across all pairs was small and positive (+0.0013, dz 0.34, raw p = 0.046) but was not significant after Holm correction (p = 0.092). A secondary, uncorrected analysis restricted to phase-locked pairs found PPC +0.0054 (p = 0.016). The analysis covered one session and the first 180 words per subject, with no artifact rejection beyond detrending; the post-onset window includes the visual evoked response. Phase locking does not prove phase reset.

theta phase locking · pairwise phase consistency · SEEG · free recall · subsequent memory · intracranial EEG