Late cortical-evoked responses in clinical use

Direct-current (dc) deflections in the EEG in response to sensory stimuli were first described by Köhler who, however, employed relatively high intensities. Gumnit, as well as Caspers, working with physiological stimulus intensities in animals, and recording from the primary projection areas of the different sensory modalities then showed that the evoked dc potentials during stimulation were restricted to a relatively small area of the animal's cortex which conformed well to the locus of the chosen modality. In our laboratory, using a fully computerized dc recording averaging system with Beckman electrodes, placed normally on the vertex, we have developed a routine technique adapted for clinical use. By this means, all types of electric responses obtainable from the intact human skull so auditory, gustatory and olfactory stimuli can be plotted simultaneously including the dc shift duirng a relatively long-lasting train of clicks (perstimulatory dc shift). This technique has been applied both in normal and in pathological subjects in various hospitals (ENT and children's clinics, in our country. The results obtained using this technique are described in our contribution.