High temporal resolution dynamic mapping of instantaneous EEG amplitude modulation after tone-burst auditory stimulation

A new method of instantaneous EEG analysis based on amplitude modulation (A M-EEG) was applied to analyze the AM-EEG changes in the alpha frequency ban d (8.20-12.89Hz) for successive 5ms epochs. Repeated auditory tone-burst st imuli (of 220 ms duration) were presented at fixed 2.56 second intervals to 12 attending right-handed young female volunteers, who were EEG-recorded o ver 19 EEG channels at 200 Hz sampling frequency. The time-course of functi onal activation was characterized in terms of percent decrease in instantan eous amplitude modulation, as compared to baseline, in analogy with the cla ssical event-related desynchronization paradigm. A dynamic sequence of the successive 122 AM-EEG maps obtained for the 610 ms from beginning of tone-b urst was stored and later animated on PC microcomputer. Topological changes among successive maps were extracted into 40 specific AM-EEG maps. Early l eft temporal and centro-temporal activation was observed, followed first by strong bilateral frontal, and then by left temporal activation. These chan ges induced by a warning tone-burst are discussed in terms of functional ne urophysiology. The present method therefore allows an improved time-resolut ion for functional brain activation paradigms.