Figure 2.

Paired presentations of CS and US result in stable conditioned fear responses (fear learning group) in comparison to explicitly unpaired presentations of CS and US (control group). Upper Panel (a and b): Mean shock expectancy ratings at the start of acquisition training (first two trials averaged) and at the end of the acquisition training (last two trials averaged) for the sham stimulation (blue) and tVNS condition (red) in the fear learning group (a: left) and in the control group (b: right). Error bars represent the standard error of the means (SEM). Participants of the fear learning group, receiving paired presentations of the CS and the electrical shock, showed an increase in rated shock expectancy from the start to the end of acquisition training. Participants of the control group, receiving explicitly unpaired presentations of the CS and the electrical shock, showed a decrease in rated shock expectancy from the start to the end of acquisition training. Lower Panel (c and d): Mean startle potentiation scores (standardized (T-scores) blink magnitudes elicited during the CS minus standardized (T-scores) blink magnitudes elicited during the inter-trial intervals) averaged across the magnitudes at the start of acquisition (first two probes in either condition (CS and ITI)) and at the end of acquisition training (last two probes in either condition (CS and ITI)). Potentiation scores are presented for sham stimulation (blue) and the tVNS condition (red) in the fear learning group (c: left) and in the control group (d: right). Again, error bars represent SEM. Participants of the fear learning group, receiving paired presentations of the CS and the electrical shock, showed stable fear potentiated startle responses at the end of the acquisition training. Participants of the control group, receiving explicitly unpaired presentations of the CS and the electrical shock, did not show fear potentiated startle responses at the end of the acquisition training.