Sample characteristics
| Placebo | Doxycycline | |||||
|---|---|---|---|---|---|---|
| Sex | Male (n = 24) | Female (n = 24) | Male (n = 24) | Female (n = 25) | ||
| Mean | SD | Mean | SD | p-value | Cohen’s d | |
| Age (years) | 24.98 | 4.04 | 24.35 | 3.76 | 0.43 | 0.16 |
| Weight (kg) | 71.86 | 11.74 | 69.44 | 13.55 | 0.35 | 0.19 |
| US intensity (mA) | 4.88 | 2.97 | 5.13 | 2.74 | 0.67 | 0.09 |
| Pain ratings pre vs post | 13.06 | 13.43 | 8.10 | 14.21 | 0.080 | 0.36 |
| Accuracy acquisition (%) | 96.93 | 3.54 | 97.35 | 3.97 | 0.58 | 0.11 |
| Accuracy recall (%) | 96.18 | 5.54 | 97.35 | 4.36 | 0.25 | 0.23 |
| Response rate acquisition (%) | 98.65 | 2.52 | 98.83 | 2.80 | 0.74 | 0.07 |
| Response rate recall (%) | 98.82 | 2.00 | 99.12 | 2.02 | 0.47 | 0.15 |
| Differential arousal acquisition (%) | 43.09 | 36.80 | 31.75 | 41.06 | 0.16 | 0.29 |
| Differential arousal recall (%) | 17.59 | 31.03 | 13.71 | 27.74 | 0.52 | 0.13 |
| Differential valence acquisition (%) | −40.68 | 36.06 | −37.60 | 41.53 | 0.70 | 0.08 |
| Differential valence recall (%) | −18.30 | 29.30 | −12.93 | 26.05 | 0.34 | 0.19 |
| State anxiety preacquisition | 31.65 | 6.37 | 30.53 | 5.46 | 0.37 | 0.19 |
| State anxiety prerecall | 31.65 | 6.72 | 28.09 | 4.38 | 0.004* | 0.62 |
| Trait anxiety preacquisition | 30.94 | 6.53 | 30.29 | 6.88 | 0.64 | 0.10 |
| BDI screening | 3.02 | 3.09 | 2.73 | 2.21 | 0.60 | 0.11 |
| BDI postrecall | 2.92 | 4.21 | 3.02 | 3.63 | 0.90 | 0.03 |
US intensity: electric current used in experiment; pain ratings pre vs post: difference in average pain ratings of 14 stimuli before and after the acquisition test; accuracy: % of correct responses in identification task, average of acquisition (visit 2) and recall (visit 3); performance: % of responses in identification task, average of acquisition (visit 2) and recall (visit 3); arousal: difference in arousal ratings between CS+/CS− after the acquisition session (visit 2), and after the recall session (visit 3); valence: difference in valence ratings between CS+/CS− after the acquisition session (visit 2), and after the recall session (visit 3); state anxiety: measured with State-Trait Anxiety Inventory (STAI; Laux et al., 1981); trait anxiety: measured with State-Trait Anxiety Inventory (STAI; Laux et al., 1981); BDI: Beck Depression Inventory (Beck and Hautzinger, 2001); p-value: two-sample t test; Cohen’s d: Cohen’s d effect size of the group difference. SD: standard deviation; ‘*’ significant (p < 0.05) difference between placebo and doxycycline group.