Alteration in the response properties of primary somatosensory cortex related to differential aversive Pavlovian conditioning

The effects of differential aversive Pavlovian conditioning on the functional organization of primary somatosensory cortex (SI) were examined in 17 healthy participants. Neuroelectric source imaging from 60 electrodes was employed while nine subjects received an innocuous electric stimulus (conditioned stimulus, CS) to one finger (left or right) that was followed by painful electric shock to the lower back (unconditioned stimulus, US) and an innocuous stimulus to the other finger that was never followed by pain. Eight subjects received a presentation of the innocuous and painful stimuli with equal probability to both fingers (control group). The data included the electromyogram (EMG) from the left m. corrugator, and judgments of intensity, aversiveness, and CS-US contingency. Only the experimental group displayed EMG conditioning, differential contingency judgments, as well as a change of dipole orientation for the CS and an enhanced dipole moment for the US in the electroencephalogram. Intensity and unpleasantness ratings were altered in a more unspecific manner and did not differ between groups and stimulus conditions. The data suatiest that SI contributes to memory processes in associative learning. Pavlovian conditioning of tactile responses might be important in the altered processing of painful stimuli in chronic pain patients where enhanced conditioning has been demonstrated. (C) 2007 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.