Magneto- and electroencephalographic correlates of the processing of visual verbal, and non-verbal information

A reliable method for he clinically useful assessment of brain structures involved in language processing would be highly desirable. Ideally, the outcome of the diagnostic procedure would show negligible dependence on the current cognitive state of a : patient. To approach this goal, we studied brain activational patterns during language processing on a rather basic revel, i.e. we examined secondary processing of lexical information when words were visually presented to the subject. This condition was compared to three other experimental conditions requiring the secondary processing of non-lexical and non-verbal information in Visual stimuli. The primary task for subjects was target detection. Electric and magnetic brain activity differentiated the experimental conditions starting at about 150 ms after stimulus onset. Amplitudes of components of event-related potentials and fields, as well as the similarity of magnetic field distributions between experimental conditions (as evaluated by cross-correlation) differed significantly between mainly verbal and the non-verbal conditions. This reflects presumably that secondary processing of verbal and non-verbal information in visual stimuli involves different neuroanatomical structures. Attempts to reinforce this result with source analysis techniques failed to reveal systematic effects. Possible reasons might be the inadequacy of the applied distributed source analysis model as well as interindividual variability of neuroanatomical structures involved in the processing of information.