Quality discrimination for noxious stimuli in secondary somatosensory cortex: a MEG-study

A complex cortical network is believed to encode the multi-dimensionality of the human pain experience. In the present study, we used magnetoencephalography (MEG) to examine whether the cortical processing of noxious stimuli with different psychophysical properties differs in primary (S1) and secondary (S2) somatosensory cortices. Noxious low (condition 1) and high (condition 2) current density stimulations of equal stimulus intensities were applied at the left forearm in 12 subjects in a randomised order. Concomitantly, subjects had to evaluate the corresponding sensory-discriminative and affective-motivational pain dimensions. MEG revealed an increased activation of bilateral secondary somatosensory cortices (S2) during condition 2 compared to condition 1. Higher activations of bilateral S2 were significantly correlated with higher scores for the sensory-discriminative component during condition 2. In contrast, corresponding scores for the affective-motivational pain dimension did not differ between both conditions. Therefore, concerning the sensory dimension of the human pain experience we conclude that the S2 cortex is involved in the encoding of quality discrimination.