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.