The electromicrophysiology of delta waves induced by systemic atropine

Delta waves in the EEG can be induced by the intravenous administration of atropine. In cats we have investigated with several computer averaging programs the relationship of extracellular unit discharge to the EEG on the surface and within the cortex. We have also studied the laminar profiles and the vertical current density profiles of these slow waves. Our results indicate that surface-positive delta waves are related to events associated with excitation of cortical neurons, while surface-negative delta waves are related to a decreased probability of unit firing suggesting the possibility of inhibition. Laminar analysis of atropine-induced slow waves indicated that these were probably generated by pyramidal cells in a similar way to delta waves induced by brain lesions. These results suggest that a disturbance in cholinergic input to the cortex might be responsible for delta waves in the EEG.