Brainstem neurons without spontaneous unit discharge

Abstract

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.

Fig. 1.

Activity of a representative NSA unit during waking and sleep. During waking, when the proper stimulus is present, the cell discharges in sustained high-frequency bursts. During waking without stimulation, slow-wave sleep, and REM sleep, the unit is silent. Abbreviations: EEG, electroencephalogram; EOG, electrooculogram; LGN, lateral geniculate nucleus; and EMG, electromyogram. The unit channel displays the pulse output of a window discriminator.

Fig. 2.

Unit activity before and after a 23-minute silent period. Note the stability of sp.ke amplitude and waveshape. The low-speed tracings are computer plots of digitized data.