Acquisition (Day 1)
We examined the maximum SCRs to the CS+ and CS- during the last 4 of the 5 acquisition trials (). There was significant a Stimulus effect, with SCRs to the CS+ greater than to the CS-: F1,11.3=8.6, p=0.007.
Figure 1 Intact fear acquisition and extinction learning but impaired extinction recall (retention) in PTSD. A. Largest skin conductance response (SCR) to the conditioned stimulus paired with the shock (CS+) and to the conditioned stimulus not paired with the (more ...)
Extinction Learning (Day 1)
We examined the average SCRs to the last two late Extinction Learning Phase trials (). Subjects in all groups extinguished approximately 70% of the acquired conditioned responses. There were no significant differences in the levels of extinction across all groups.
Extinction Recall (Day 2)
We examined the average SCRs to the first two Recall Phase trials (). There was a significant Stimulus main effect, with SCRs to the CS+ greater than to the CS-: F1,11.0=16.9, p<0.001. There was also a significant Diagnosis × Exposure interaction: F1,12.1=4.3, p=0.03, with ExP+ subjects showing larger SCRs than ExP- subjects: F1,12=7.1, p=0.01, and larger SCRs than UxP+ subjects: F1,7.2=5.2, p=0.03.
We examined these indices as defined above (). There was a significant Diagnosis × Exposure × Phase interaction: F1,11.1=4.3, p=0.03, with overall greater extinction retention during the Learning than the Recall Phase, reflecting some return of the SCRs to the CS+ on Day 2. Analyzing the two phases separately, for ELI (-left), there were no significant results. However, for ERI (-right) there was a significant Diagnosis × Exposure interaction: F1,11.1=4.2, p=0.03, with ExP+ subjects showing (nearly significantly) less extinction retention than ExP- subjects: F1,12=3.0, p=0.06, and less extinction retention than UxP+ subjects: F1,5.7=4.9, p=0.04. These results paralleled the results obtained with the SCR analyses.
Figure 2 Extinction Learning and Extinction Retention Indices (see text for definition) demonstrate intact extinction learning across all groups but impaired extinction retention in PTSD twins only. *p<0.05. ExP+: PTSD twins, UxP+: their combat-unexposed (more ...)
Analyses Addressing Potentially Confounding Factors
The significant Diagnosis × Exposure interaction for SCRs during Extinction Recall was not explained by: 1.) SCRs during Acquisition; 2.) SCRs during Extinction Learning; 3.) Age; 4.) Combat Severity (Ex subjects only); 5.) number of Potentially Traumatic, Lifetime, Non-Combat Events; 6.) reported use of one or more potentially confounding Medications or Substances (including antihistamines, sympathomimetics, sympatholytics, parasympathomimetics, parasympatholytics, skeletal muscle relaxants, hypotensive agents, vasodilating agents, pressor agents, β-blockers, antiarrhythmics, calcium channel blockers, narcotics, anticonvulsants, antidepressants, neuroleptics, benzodiazepines, other psychotherapeutic agents, cerebral stimulants, sedatives, and hypnotics) during the month prior to testing, or a “dirty” urine specimen (i.e., containing amphetamines, barbiturates, cocaine, opiates, benzodiazepines, methaquolone, propoxyphene, phencyclidine, methadone, or cannabinoids; and number of 7.) Alcoholic Beverages, 8.) Caffeinated Beverages, or 9.) Cigarettes consumed used during the 24 hours preceding testing. The significant Diagnosis × Exposure interaction for ERI was similarly robust. However both interactions were no longer significant after adjusting for the presence of a current, comorbid mental disorder. The reason for this was that the three ExP+ subjects with a current, comorbid mental disorder showed larger SCRs during Recall (mean 0.48 μS collapsed across Stimulus type) than the four comorbidity free ExP+ subjects (mean 0.32 μS).
Analyses Addressing Type II Error
For each negative result, we calculated the 90% upper confidence limit (UCL) of the estimate. In every case, the UCL was greater than trivial, i.e., >0.05 μS (or >20% for ELI and ERI). Therefore we were unable to conclude that any of the negative results were significant.