Brain topography
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Temporal summation is a potent central somatosensory mechanism and may be a major mechanism involved in e.g. neuropathic pain. This study assessed the long-latency somatosensory evoked potentials (SEPs) in response to trains of repeated painful electrical stimulation of human skin and muscle in order to investigate the cerebral representation of temporal summation. Forty series of stimuli were delivered at stimulus intensities corresponding to moderate pain levels in 20 young men. ⋯ In the muscle, the fifth stimulus was associated with a marked reduction of the frontal positivity at contralateral F4 site in the early stages at 100 and 140 ms, and with a total disappearance of positive source at Cz. In summary, this study demonstrated a clear temporal summation of psychophysical ratings, reduction of the peak amplitudes in the last of the first stimuli, dissociation from simple amplitude increase of the cerebral responses to pain, and a concurrent transformation of the CSD patterns. This change in "rapid cortical dynamics" of short-term plasticity could be an important mechanism for wind-up and pain processing in the brain.