The responses to somatic stimuli of deep spinothalamic tract cells in the lumbar spinal cord of the cat.

1. The responses to natural somatic stimuli of thirty-seven antidromically identified spinothalamic tract (s.t.t.) cells in Rexed's laminae VII and VIII of the lumbar spinal cord of the cat have been studied. A further twenty-eight s.t.t. cells were identified antidromically.2. Cells were activated from sites in, or close to, one of the following locations: nucleus (n.) parafascicularis or n. centrum medianum, magnocellular part of the medial geniculate or the medial leminiscus, n. ventralis posterior medialis, n. lateralis posterior.3. The majority (84%) of s.t.t. cells showed spontaneous discharge at 1-67 Hz.4. Somatic stimuli excited 81% of s.t.t. cells but gave rise to inhibition of spontaneous discharge in 54% of cells. Only 8.1% of cells gave only inhibitory responses while 35.1% gave only excitatory responses and 45.9% gave both inhibitory and excitatory responses. No response could be elicited in 10.8% of cells.5. The proportion of s.t.t. cells giving inhibitory and excitatory responses to hair movement, light touch or tap, innocuous pinch, noxious pinch, joint movement, twisting of and intense pressure on joints, flicking, palpation or deflexion of large muscles, skin cooling and warming and noxious heat are documented. Of these stimuli, only skin cooling and warming failed to produce a response in any cell.6. Many cells showed convergence from receptors in muscles, joint and skin although 29.7% responded exclusively to innocuous cutaneous stimuli.7. Convergence from receptors on wide, and sometimes quite separate, areas of the hind quarters was common but exclusively contralateral receptive fields were not found and for none of the above stimuli was the contralateral side more effective than the ipsilateral side.