As we discussed during my lecture on sleep, slow wave sleep consists of up and down states with cortical neurons silent during the down (hyperpolarized) states. A research article in Science magazine demonstrated that a relatively small number of neurons fire during these down states. Furthermore, these “delta spikes” (so-called because the neurons fire or ‘spike’ during the down state signaled by a very low frequency delta wave) occur in neurons that were most related to a memory when the animal (rat) was in an awake state. Thus, the down state during slow wave sleep were associated with the selective activation of those neurons most involved in the memory that is presumably being consolidated.