Reliability of early cortical auditory gamma-band responses

Abstract

Objective: To evaluate the test-retest reliability of event-related power changes in the 30-150 Hz gamma frequency range occurring in the first 150 ms after presentation of an auditory stimulus.

Methods: Repeat intracranial electrocorticographic (ECoG) recordings were performed with 12 epilepsy patients, at ≥1-day intervals, using a passive odd-ball paradigm with steady-state tones. Time-frequency matching pursuit analysis was used to quantify changes in gamma-band power relative to pre-stimulus baseline. Test-retest reliability was estimated based on within-subject comparisons (paired t-test, McNemar's test) and correlations (Spearman rank correlations, intra-class correlations) across sessions, adjusting for within-session variability. Reliability estimates of gamma-band response robustness, spatial concordance, and reproducibility were compared with corresponding measurements from concurrent auditory evoked N1 responses.

Results: All patients showed increases in gamma-band power, 50-120 ms post-stimulus onset, that were highly robust across recordings, comparable to the evoked N1 responses. Gamma-band responses occurred regardless of patients' performance on behavioral tests of auditory processing, medication changes, seizure focus, or duration of test-retest interval. Test-retest reproducibility was greatest for the timing of peak power changes in the high-gamma range (65-150 Hz). Reliability of low-gamma responses and evoked N1 responses improved at higher signal-to-noise levels.

Conclusions: Early cortical auditory gamma-band responses are robust, spatially concordant, and reproducible over time.

Significance: These test-retest ECoG results confirm the reliability of auditory gamma-band responses, supporting their utility as objective measures of cortical processing in clinical and research studies.

Figure 1

Test-retest results for 12 patients showing largest gamma-band responses to the 1200-Hz infrequent tone for both sessions. Corresponding patient numbers are listed in the upper left corner. Time-frequency plots of gamma-band responses for each session are in inset boxes labeled 1 and 2 with arrows pointing from the corresponding electrode (depicted by red circles) on a left or right lateral view of the volumetric 3D MRI reconstruction of each patient’s brain co-registered with electrode locations (depicted with white circles). Electrodes covering basal temporal cortex are not shown. Plots of the time-frequency spectra are shown with time on the X-axis from 0–180 ms and frequency on the Y-axis from 30–150 Hz (gamma band). In the color spectrum, dark blue represents no significant change in logpower from the pre-stimulus baseline; all other colors represent significant changes, with red representing the maximum change (dB/Hz). Note: All patients showed statistically significant increases in gamma-band power (p <0.05), although smaller changes may not be clearly visible in the individual plots.

Figure 2

Test-retest results for 12 patients showing largest gamma-band responses to the 1000-Hz frequent tone across both recording sessions. Figure layout and color coding is identical to Figure 1. Note: All patients showed statistically significant increases in gamma-band power (p <0.05), although smaller changes may not be as clearly visible in the individual plots.

Figure 3

Test-retest response reproducibility results for infrequent tones plotted by session for: A) Gamma-band logpower density estimates (dB/Hz); B) Gamma-band logpower latencies (ms); C) N1 peak amplitudes (dB); and D) N1 peak latencies (ms). Each patient is represented by a blue dot. Session 1 is on the x-axis; Session 2 is on the y-axis. Diagonal lines in each plot are identity lines.

Figure 4

Test-retest response reproducibility results for frequent tones plotted by session for: A) Gamma-band logpower density estimates (dB/Hz); B) Gamma-band logpower latencies (ms); C) N1 peak amplitudes (dB); and D) N1 peak latencies (ms). Each patient is represented by a blue dot. Session 1 is on the x-axis; Session 2 is on the y-axis. Diagonal lines in each plot are identity lines.