<p>Slow cortical potentials are slow event-related direct-current shifts of the electroencephalogram. Slow cortical potential shifts in the electrical negative direction reflect the depolarization of large cortical cell assemblies, reducing their excitation threshold. They change periodically from being electrically positive to electrically negative. They are described as a phasic tuning mechanism related to activities in the brain stem reticular process, the thalamus and the basal ganglia. These dc shifts are reflected in the superficial cortical layers and represent synaptic activities in the apical dendrites in those layers. Negative shifts represent increased probability of firing while positive shifts represent decreased probability or inhibition. Negative shifts are described as related to the utilization of resources for attention, memory, and other related cognitive mechanisms.<br></p>