Magnetoencephalography (MEG) was recorded during aversive classical conditioning in an attempt to elucidate the temporal coding of primary somatosensory cortex (SI) activation previously found with positron emission tomography. Four healthy volunteers participated in the experiment. The reinforced conditioned stimulus was displayed on a screen for 2 s, and as it disappeared an unconditioned electric shock to the right middle finger followed. A control stimulus, not paired with a shock was also presented. With MEG, we observed a conditioned magnetic response located in the SI. The conditioned response predated the shock presentation and is interpreted as evidence for functional control of nociception mediated by corticothalamic projections.