Stimulus Frequency Dependence of the Transient Oscillatory Auditory Evoked Responses (40 Hz) Studied by Electric and Magnetic Recordings in Human

In the last years, several studies aimed to propose a specific functional role to electrical brain activities characterized by oscillations around 40 Hz, the so-called gamma-band activity. Eckhorn et al. (1988) and Gray et al. (1989) have shown that, in the visual cortex, a spatially disparate subset of cells fires in coherent bursts (in the range 40–60 Hz) after appropriate visual stimuli. It has thus been suggested that these synchronous gamma-band activities participate to fundamental mechanism underlying feature binding in object recognition. The observation of oscillatory response in the gamma-band has also been reported in human auditory modality, elicited by either steady-state (Galambos et al. 1981) or transient stimulation (Pantev et al. 1991) recorded over the scalp. How these gamma-band responses, recorded on the head surface and certainly due to large populations of neurons, relate to the synchronous rhythmic activities recorded intracranially and representing few neurons in very focal cortical area, is still a question of debate.