Interestingly, this pattern of amplitude differences reversed during the extinction phase, leading to a CS– specific enhancement [F1,25 = 12.73, P = 0.001,  = 0.34]. The suitability of the temporal window used for the overall anovas above (the final 3200 ms of each segment) was tested in an additional method check, with discrete Fourier analyses conducted for 1-s segments across the time-domain averages for each condition. The normalized amplitude (divided by the Everolimus in vitro number of time points) at the reversal rates was extracted from the spectrum in each time window and averaged

across participants to result in time-course data for each condition, across the viewing epoch. These data are shown for the acquisition phase in Fig. 6. They suggest that, in line with earlier reports, the differential ssVEP amplification for the CS+ increased over the viewing epoch and tended to reach a maximum around the termination of the CSs. In the present study, this pattern was specific to the luminance stimulus. These findings confirm that the segment chosen for the main analyses appropriately

reflects the desired variability among threat and safety cues. To control for potential confounds of stimulation type and the kind of contrast underlying the ssVEP, and to more closely parallel the Z-VAD-FMK purchase luminance stimulus condition in which the Gabor patches were reversed in anti-phase, we conducted an experiment with the chromatic TCL condition in a separate group of individuals (n = 12), where the same chromatic Gabor patches were reversed at 14 Hz, but red and green Gabor patches were presented in anti-phase, not in-phase as in the main study. Although strong

driving was observed with anti-phase chromatic reversal on an isoluminant background, no differences emerged between safe (CS–) and threat (CS+) cues; all F < 2.12, all P > 0.22. The present study examined the extent to which low-spatial-frequency luminance vs. high-spatial-frequency chromatic visual information is critical for the acquisition of low-level visual sensory biases towards threat cues. Using a differential classical conditioning design with Gabor patch stimuli designed to preferentially activate either the luminance or the chromatic-driven human visual pathways, we found that an isoluminant stimulus that relied purely on chromatic contrast did not lead to an enhancement of threat-evoked visuocortical responses. By contrast, stimulating the luminance pathway by means of grayscale low-contrast, low-spatial-frequency pattern reversal resulted in pronounced conditioning effects. Specifically, we observed selectively enhanced neural response amplitudes for the CS+ relative to CS– during the acquisition phase of the experiment. This difference between the conditioned threat and safety signals was no longer present, and was in fact reversed, during extinction.