Localization of event-related magnetic fields during speech processing by magnetoencephalography

In this study the authors investigated several approaches to localize cortical areas activated during speech processing. The event-related activation was elicited by visually presented stimuli. One paradigm consisted of written mono syllable nouns where the subjects were asked to read the words and imagine the described object. Another task was to silently name objects presented to them. The magnetic evoked activity of 13 normal subjects (9 right handed, 4 left handed) was recorded with the 37 channel biomagnetic system KRENIKON^R (Siemens). The time course of the averaged evoked signals showed a high inter-individual variability. However they had two features in common, a wave starting at approximately 350 ms and a wave starting at 500 ms after the stimulus onset. The cortical representation of the waves in the cases with a high signal to noise ratio was found in the Wernicke´s area and Broca´s area respectively