Receptive field profiles and integrative properties of spinocervical tract cells in the cat

The receptive fields of sixteen spinocervical tract (s.c.t.) cells whose responses were recorded extracellularly were mapped using discrete and uniform jets of air given at equally spaced locations on the clipped fur of cats anaesthetized with chloralose. All the cells whose receptive fields were on the thigh or upper hind limb showed approximately unimodal gradients of sensitivity to stimulation within their excitatory receptive fields. The response magnitudes declined steadily as the stimuli were moved sequentially from the centres to the peripheries of the fields and abrupt edges were not found. Spatial summation from within the excitatory receptive field was studied in twelve s.c.t. cells. These cells showed a poor ability to summate the responses to two spatially separated air jets when these stimuli were applied simultaneously within their receptive fields. No significant summation was found in twenty-five out of thirty-one trials and in six of these trials (four cells) the responses were significantly reduced. Summation was found in six trials (four cells). Lack of summation or response reduction was more prevalent when the individual response levels were low (less than impulses stimulus-1). These results are discussed in relation to similar findings for cells of somatosensory relay nuclei and cortex.