Same-polarity SEEG pulses produce more reliable CCEP maps, but pulse timing may confound polarity

We compared single-pulse cortico-cortical evoked potential (CCEP) maps from 26 electrode pairs in 3 patients using two pulses in each of two stimulation directions. Same-polarity pulses agreed more than opposite-polarity pulses for 9 of 12 computed variants (p ≤ 0.03; the three exceptions were far zones). For the RMS map with the stored reference, median correlation was 0.64 for same-polarity and 0.45 for opposite-polarity pulses. With the same four pulses, a polarity-balanced 2-v-2 split had reliability 0.70, compared with 0.54 for a split by polarity (p = 0.002); plain Spearman–Brown predicted 0.68 for either split. A three-component model predicted the direction and approximate size of the difference. The signed near-field map nearly reversed between polarities (opposite-polarity r about 0.03), while far signed maps showed no reliability with one to two pulses. These results support balancing polarity across averages when estimating pulse counts. However, same-polarity pulses were about 5 seconds apart and opposite-polarity pulses about 27–35 seconds apart, so slow state drift could explain the effect. The study included only 3 patients, 26 pairs, and 4 pulses per pair; its results do not separate polarity from timing.

SEEG · cortico-cortical evoked potentials · CCEP · pulse polarity · reliability · Spearman-Brown · intracranial EEG · effective connectivity · brain-computer interface