Hippocampal ripple rate did not track task period, memory load, accuracy, or response time in 13 patients

We tested whether hippocampal 80–120 Hz ripple rate changed across periods of a verbal Sternberg working-memory task, with memory load, accuracy, or response time. We analyzed session 1, run 1 from OpenNeuro ds004752 in 13 epilepsy patients, using 95 bipolar SEEG pairs and 588 clean trials. A fixed threshold detector identified 4,341 ripples. The mean rate was 0.13 ripples/s per pair. Exact patient-level sign-flip tests found no significant rate difference between fixation and encoding, maintenance, or probe (p=0.54, 0.59, and 0.72), between load 8 and load 4 in maintenance or encoding (p=0.35 and 0.87), with accuracy (n=11, p=0.79), or with response time (p=0.36). Confidence intervals exclude period and load effects larger than about 0.04 ripples/s per pair, about 30% of the mean rate, but smaller effects remain possible. Continuous 80–120 Hz power was higher during maintenance than fixation (mean log-power difference +0.038, 95% CI [+0.013, +0.065], p=0.013; 9 of 13 patients). Thus, in this task, continuous band power changed while discrete ripple rate did not. The analysis used one fixed threshold detector without event-by-event visual review, dataset anatomical labels without new localization, and session 1 only. The sub-11 ripple-locked average had a large sharp deflection, so some detected events there may be sharp-wave ripples or residual interictal epileptiform discharges. Small rate effects cannot be excluded.

hippocampus · ripples · verbal working memory · intracranial EEG · SEEG · Sternberg task · memory load · closed-loop brain-computer interface