Response suppression induced by afferent stimulation in the superficial and deep layers of the hamster's superior colliculus.

Stimulation of the optic chiasm (OX) or visual cortex (VC) elicited a burst of impulses from visual cells in the superficial layers of the hamster's superior colliculus which was followed by a period of response suppression which lasted from 50-200 ms. During this period responses to normally suprathreshold OX and VC shocks, spontaneous activity and even injury discharges were markedly attenuated. For approximately 50% of the visual cells tested VC stimulation also reduced responses to visual stimuli. No correlations between receptive field properties and whether or not VC shocks diminished a given cell's visual responses were noted. Stimulation of either the cervical spinal cord (SC) or somatic sensory cortex (SMCTX) evoked action potentials from somatosensory neurons in the deep tectal laminae. These responses were followed by a period of suppression identical to that seen in the superficial layers after OX or VC shocks. SMCTX stimulation attenuated responses to tactile stimuli for 30% of the cells tested in the deep layers. Again, no correlation was observed between somatosensory response characteristics and whether or not a given cell exhibited response suppression.