Cortical correlates of semantic classical conditioning.

Event-related potentials to visually displayed pseudowords were registered from 13 individuals. In a differential conditioning paradigm, half of the pseudowords had previously been paired with a painful electric shock (shock words) and the other half had been presented without shock (nonshock words). Participants were asked to decide if the words had been presented during the conditioning phase or not. Larger N100 amplitudes and a more negative-going slow wave 400-800 ms after word presentation were found for shock as compared with nonshock words. This effect was stronger over the left than over the right hemisphere. This left-lateralized negativity might reflect the activation of a cell assembly representing the memory of the learned word-shock contingency. Furthermore, the increased N100 amplitude elicited by shock as compared with nonshock words may be interpreted as an increased attentive facilitation for aversive pain-related information as a consequence of conditioning.