Each ECoG trial was transformed into the time–frequency domain using a complex demodulation technique (Papp and Ktonas, 1977 (link)) incorporated in BESA® EEG V.5.1.8 software (BESA GmbH, Gräfelfing, Germany; Hoechstetter et al., 2004 (link); Brown et al., 2008 (link)). A given ECoG signal was assigned an amplitude (a measure proportional to the square root of power) as a function of time and frequency at each trial. The time–frequency transform was obtained by multiplication of the time–domain signal with a complex exponential, followed by a low-pass filter. The low-pass filter used here was a finite impulse response filter of Gaussian shape, making the complex demodulation effectively equivalent to a Gabor transform. The filter had a full-width at half-maximum of 2 × 15.8 ms in the temporal domain and 2 × 7.1 Hz in the frequency domain. At each time–frequency bin at each electrode site, we measured the amplitude change at the bands, in steps of 5 Hz and 10 ms, relative to the mean amplitude in a resting period between 600 to 200 ms prior to stimulus onset. Time–frequency analysis was repeated with a time-lock to (i) stimulus onset; (ii) stimulus offset; and (iii) response onset. The per cent changes in high-gamma (70–110 Hz) and beta amplitudes (15–30 Hz) at each electrode site and each moment were spatially presented with a Gaussian half-width at half-maximum of 7.5 mm, and sequentially animated on the average FreeSurfer pial surface image as a function of time throughout the task. Grand-averaging of all available patients’ data finally yielded a 4D map showing ‘when’ and ‘where’ high-gamma and beta activities are augmented and attenuated during the auditory-naming task in each of the older and younger groups.