Cerebral Activation Patterns of Tactile, Phasic and Tonic Painful Stimulation in Humans

Non-painful and painful stimuli are known to activate neighboring regions or even the same areas like the somatosensory cortices. Other activation areas seem to be predominantly, or exclusively, active when a stimulus is painful. In this fMRI study we compared different cerebral activation patterns evoked by three types of stimulation. 12 healthy subjects underwent a balanced series of 1) non painful tactile stimulation with a 128 mN v. Frey hair, 2) phasic painful stimulation with a 128 mN pin prick stimulator, and 3) tonic painful stimulation using a thermode (temperature oscillation around the individual heat pain threshold, approx. 47 °C, duration 1min). fMRI measurements were carried out on a 1.5 T system using a block design and an echo-planar imaging sequence based gradient echo sequence with 23 axial 5mm slices covering the whole head. Statistical processing was done off-line using spm99 including motion correction and spatial normalization. Coordinates, T-values and the number of activated voxels were compared between the three conditions. The primary somatosensory cortex was activated during all conditions, most pronounced during pin prick stimulation. The posterior parasylvian cortex showed the strongest activation in all conditions, with a separate activation in the anterior parasylvian cortex most pronounced in thermal pain. The strong activation of anterior and posterior insula during heat pain was hardly present in the other two conditions. Activation of anterior cingulate cortex and thalamus was present during heat pain only. These activation patterns suggest that phasic pain is predominantly mediated through the lateral, and tonic pain through the medial pain system. Supported by the Deutsche Forschungsgemeinschaft (Tr236/13–3).