Brainstem neurons without spontaneous unit discharge.

A new class of single neurons showing no spontaneous activity in waking, rapid eye movement sleep, and slow-wave sleep was found in the brainstem of unrestrained cats. Systematic testing showed that these cells discharge only in response to specific stimuli and remain silent for as long as 40 minutes in the absence of stimulation. Silent cells were widely distributed in the pons and midbrain and constituted a major percentage of observed neurons. The economy of discharge shown by these cells contrasts with the spontaneous activity of virtually all other neurons that have been observed in the brains of unrestrained animals and suggests the widespread existence of specialized neural systems that show only phasic activity.