Spectral responses in the gamma-band: physiological signs of higher cognitive processes?

It has recently been proposed that brain responses in the gamma-range (> 20 Hz) include information about specific cognitive processes in the human brain. Empirical data substantiating this assumption come from EEG and MEG recordings during visual and language processing. For example, 30 Hz activity has been found to be stronger during processing of words than during processing of meaningless but pronounceable pseudo-words. However, it has been reported that power changes in the gamma-band are sometimes artefacts of changes taking place in other frequencies, such as the alpha-band. In this study, we investigated power changes in frequency bands outside the gamma-range and found no evidence that such changes are related to the dynamics in gamma-power distinguishing between words and pseudowords. These results are consistent with the view that gamma-band responses are an indicator of lexical processing and other cognitive processes related to binding of stimulus features into a whole (Gestalt), as proposed by Singer.