VISCERAL PAIN EVOKED BY THALAMIC MICROSTIMULATION IN HUMANS

MICROSTIMULATION within and below the ventrocaudal nucleus (Vc) in the human thalamus typically evokes nonpainful, paraesthetic cutaneous se nsations. We now describe cases in which thalamic microstimulation evo ked visceral pains. Data were obtained during stereotactic thalamotomy procedures. Patient 211 had a history of essential tremor. At a site 0.5 mm ventroposterior to Vc, microstimulation elicited pain described as 'deep, internal, in a straight line like my appendix pain years ag o'. Patient 153 had a history of post-stroke hemibody pain. In each of two trajectories, at sites approximately 2 mm ventroposterior to Vc, microstimulation evoked pain in the groin. At one of these sites, the pain was described as 'like having a baby'. These and additional obser vations suggest that stimulation ventroposterior to Vc can evoke visce ral pain and may trigger pain 'memories'.