Spontaneous spike activity of spinoreticular tract neurons during sleep and wakefulness

Sleep mentation studies infer that pain sensation in humans may be reduced during active REM sleep. However, to provide a mechanistic explanation for this phenomenon, few, if any neurophysiological studies have been performed at the lumbar level from neurons comprising classical pain pathways during sleep and wakefulness. The spinoreticular tract is one such classical path way that has been implicated in the rostral transmission of nociceptive inf ormation. The present study was performed to determine if the activity of s pinoreticular tract (SRT) neurons is dependent upon behavioral state. Accor dingly, extracellular recording techniques were used to monitor the activit y of identified SRT neurons in unanesthetized chronic cats during sleep and wakefulness. The ongoing spike activity of SRT neurons was found to be rel atively uniform when the states of quiet wakefulness and quiet sleep were c ompared. However, during active sleep, the majority of the SRT neurons samp led underwent a sustained reduction in spike activity. Marked facilitation of SRT cell activity occurred in a few instances. These data provide the fi rst unitary evidence supporting earlier evoked potential, psychophysical an d clinical studies that ascending sensory information in a classical pain p athway is regulated in a state-dependent fashion.