Modulation of the spontaneous and evoked discharges of ventral posterior thalamic neurons during shifts in arousal

Abstract

The responses of 154 ventral posterior thalamic neurons to a variety of somatic stimuli and to electrical stimulation of the midbrain spinal lemniscus were recorded in the awake squirrel monkey during varying states of arousal. Many VP () neurons showed changes in somatosensory responsiveness which correlated with shifts in arousal. Arousal related modulation (ARM) of somatic responses were not selective for any specific stimulus modality. Most cells (N = 36) responded maximally during quiet waking with responses significantly reduced during drowsiness or periods of waking movement. Other neurons (N = 5) responded maximally during drowsiness, and gave decreased responses as the level of arousal increased. Similar changes were seen for neurons driven by spinal lemniscal (SL) stimulation. All changes in evoked responses were independent of prestimulus background discharge frequency. At least one site of ARM takes place at the level of the VP thalamus.