Associative learning in humans - conditioning of sensory-evoked brain activity

A classical conditioning paradigm was employed in two experiments performed on 35 human volunteers. In nine subjects, the presentation of Landolt ring s (conditioned stimuli, CS +) was paired with an electric stimulus (uncondi tioned stimuli, UCS) applied to the left median nerve. Neutral Visual contr ol stimuli were full circles (CS -) that were not paired with the UCS. The skin conductance response (SCR) was determined in a time interval of 5 s af ter onset of the Visual stimuli, and it was measured in the acquisition and test phase. Associative learning was reflected by a SCR occurring selectiv ely with CS +. The same experiment was repeated with another group of 26 ad ults while electroencephalogram (EEG) was recorded from 30 electrodes. For each subject, mean evoked potentials were computed. In 13 of the subjects, a conditioning paradigm was followed while the other subjects served as the control group (non-contingent stimulation). There were somatosensory and v isual brain activity evoked by the stimuli. Conditioned components were ide ntified by computing cross-correlation between evoked somatosensory compone nts and the averaged EEG. In the Visual evoked brain activity, three compon ents with mean latencies of 105.4, 183.2, and 360.3 ms were analyzed. Somat osensory stimuli were followed by major components that occurred at mean la tencies of 48.8, 132.5, 219.7, 294.8, and 374.2 ms latency after the shock. All components were analyzed in terms of latency, held strength, and topog raphic characteristics, and were compared between groups and experimental c onditions. Both visual and somatosensory brain activity was significantly a ffected by classical conditioning. Our data illustrate how associative lear ning affects the topography of brain electrical activity elicited by presen tation of conditioned visual stimuli. (C) 2000 Elsevier Science B.V. All ri ghts reserved.