Event-related potentials (ERPs), transient stereotypical changes in the electroencephalogram in response to particular stimuli, are widely used to measure cognitive function, but the mechanisms that generate ERPs are unclear. This study showed that the amplitude and timing of the frontal ERP response to the presentation of an 'oddball' auditory tone was coupled to neuronal activity in the basal forebrain (BF) of rats. Furthermore, BF stimulation triggered local field potentials similar to those associated with the ERP. Thus, subcortical inputs may have an important role in the generation of ERPs.