In two SEEG patients, posterior sites lacked a clear onset response gradient, while W2 responses tracked sentence identity

We tested whether speech high-frequency activity (HFA) in stereoelectroencephalography (SEEG) showed the posterior onset and anterior sustained response pattern reported with ECoG, and whether responses in W2 tracked sentence identity. Using bipolar pairs from two patients listening to TIMIT sentences in OpenNeuro ds004993, we selected responsive pairs on odd trials and measured an onset index on even trials. The pre-registered onset-gradient hypothesis was not supported: among 33 responsive pairs in W2, Spearman rho was +0.08 (one-sided p = 0.68; Holm p = 1.0); among 46 in W3, rho was -0.25 (p = 0.051; Holm p = 0.10). Shaft-level tests were also not significant (W2 rho = -0.43, p = 0.15 across 8 shafts; W3 rho = -0.15, p = 0.35 across 10 shafts). The onset index was positive in 21% of W2 and 35% of W3 responsive pairs (median -0.18 and -0.13). In W2, HFA time courses were more similar across repeats of the same sentence than across different sentences (D = +0.021 mean correlation difference, permutation p = 0.0005; 26 of 33 pairs had D > 0). The results are within-subject observations from two patients, not population estimates. SEEG sampled few STG surface sites; many responsive pairs were in white matter or deep sulci, and pairs on one shaft are not independent. W3 had a 20 Hz VNS artifact, and residual artifact may remain. Coordinates were native ACPC, and the onset index was a window contrast rather than the NMF clustering used in the prior ECoG study. The analyzed files came from the live OpenNeuro S3 path, described by the original report as its latest snapshot on 2026-10-11; the exact dataset release is uncertain.

stereoelectroencephalography · speech · high-frequency activity · sentence identity · TIMIT · OpenNeuro · onset response · sustained response