Auditory stimulation brain map.
The topography of auditory evoked potentials (AEPs) was studied in 12 neurologically normal, adult, right-handed subjects of either sex. The AEPs were recorded with seventeen active electrodes in response to 500 Hz tone bursts with a level of 75 dB HL presented either to the left or the right ear. AEP brain maps were obtained with the BRAIN ATLAS III system. A region of maximum negativity was obtained corresponding to N1 at vertex and defined as focus of N1 (FN1). The reproducibility within and between sessions of FN1 was studied and found to be good for most of the subjects. The interindividual variability was moderate and the centre of FN1 on the map was localized 7 mm in front of the vertex electrode and 8.4 and 8.0 mm to the contralateral side of the vertex electrode upon stimulation of the left and the right ear, respectively. The approximate position of the skull surface is obtained by multiplication by a factor of 3. It was concluded that a standardized test session including six single maps based on 50 stimuli each gives an average map with identifiable and reproducible focus. The basis seems to be fulfilled to use the brain map in further analysis on clinical material.