Hippocampal spectral power rises during verbal memory maintenance but does not track load in 14 SEEG patients

In 14 patients with stereoelectroencephalography (SEEG) performing a verbal Sternberg working-memory task, hippocampal low- and mid-frequency power and the aperiodic exponent were higher during maintenance than fixation, but no spectral feature tracked memory load after correction and fixation-baseline control. We analyzed OpenNeuro ds004752 v1.0.1: 97 bipolar pairs and 1,275 artifact-free trials from up to two sessions per patient. For correct trials, we computed 1-s periodograms and tested Spearman correlations of set size (4, 6, or 8 letters) with six spectral features using exact sign-flip tests and Holm correction. Accuracy decreased from 0.974 to 0.835 and median response time increased from 1.165 to 1.443 s between set sizes 4 and 8 (p=0.00024 for both). Maintenance power increased in theta, alpha, beta, gamma, and high gamma bands (Holm p=0.001, 0.001, 0.001, 0.001, and 0.008); the exponent steepened (p=0.003). Maintenance theta and beta had small uncorrected load correlations, but neither survived correction; similar theta correlation was present in fixation, before set size was shown. Load correlations for maintenance minus fixation were near zero (all p≥0.19). Within this analysis of bipolar local field potential spectra in 14 patients, spectral power and the aperiodic exponent did not track verbal working-memory load. The study used 1-s windows, up to two sessions per patient, and atlas-labeled contacts in patients with epilepsy; it did not measure neuronal firing or hippocampal-cortical synchrony.

hippocampus · stereoelectroencephalography · working memory · spectral power · aperiodic exponent · OpenNeuro · verbal memory