A total of 60 subjects were included in the analyses. The subjects’ ages ranged from 18–63 years old and 47.1% were female. shows the breakdown of the subjects across the different types of child abuse, as well as demographic information, and PTSD and depression symptoms. shows the rates of traumatic events experienced by the subjects in the study sample. The PSS and BDI scores were significantly correlated, r(57)=0.37, p<0.01; the association remained significant after co-varying for childhood trauma, sex and age.
The table displays the rates of three forms of reported child abuse within the total subject pool, as well as demographic information in addition to patients’ scores of depressive and PTSD symptoms.
Startle reactivity was assessed during noise-alone (NA) trials and in the presence of conditioned stimuli. The first set of results describes baseline startle magnitude, i.e. data for the NA trials across the session, as well as to the trials of the habituation phase. The second set of results focuses on fear-potentiated startle during the presentations of the CSs. These data were evaluated for fear acquisition, differential conditioning between danger and safety signals, and conditioned inhibition of fear.
Startle Magnitude to Noise Alone
A two-way mixed-model ANOVA with block and group showed a significant between groups effect for self-reported physical (F(1,58)=4.08, p<0.05) and sexual (F(1,58)=6.98,p=0.01) abuse, with high abuse subjects exhibiting greater startle magnitude (). On the other hand, self-reported emotional abuse did not show a between groups effect (). In all three types of child abuse, the severity of abuse did not affect the degree of habituation to the startle probe throughout the session. The linear trend for block was significant in physical (F(1,58)=14.48, p<0.01), sexual (F(1,58)=14.96, p<0.01), and emotional abuse (F(1,58)=10.26, p<0.01). There were no block-by-group interactions.
Baseline Acoustic Startle Response During the Experimental Session
In order to examine initial startle reactivity in more detail, we compared abuse groups on startle magnitude to the first six trails of the pre-conditioning habituation block. Here we also found a significant effect of perceived physical abuse (F (1,57)=4.97,p<0.05) and perceived sexual abuse (F (1,57)=7.28,p<0.01) on startle magnitude. Even in these early trials, there was no effect of perceived emotional abuse. However, startle magnitude in all three types of abuse decreased over the 6 trials (physical abuse linear F(1,57)=7.91, p<0.01; sexual abuse linear F(1,57)=6.50, p=0.01; emotional abuse linear F(1,57)=9.76,p<0.01), again showing habituation. There were no trial-by-group interactions.
ANCOVAs of startle reactivity with demographic and clinical covariates did not eliminate the effect of abuse. Subjects reporting high levels of physical abuse had higher startle than those with low abuse after co-varying for sex, age, PTSD and depression (F(1,47)=4.33, p<0.05). Furthermore, subjects reporting high levels of sexual abuse had higher levels of startle than those with low abuse after co-varying for sex, age, PTSD and depression (F(1,47)=4.04, p<0.05).
A hierarchical regression analysis was performed by entering emotional, physical, and sexual abuse as independent variables in a stepwise procedure. The dependent variable was the average startle magnitude to all the noise alone trials in the session. The overall final model was significant, F(3,59)=3.39, p<0.05, accounting for 15.4% of the variance in startle magnitude, see . Adding physical abuse resulted in an R2 change of 0.058, p=0.07. Adding sexual abuse resulted in a significant R2 change of 0.081, p=0.02.
The table displays the statistics for the hierarchical regression analyses examining the contributions of each abuse type on baseline startle.
Fear acquisition (see ) was tested comparing startle magnitude trial types (2 levels: NA, CS+) on the last block of conditioning with the between groups factor of child abuse group (2 levels: high, low) for each of the three types of abuse. There was a significant effect of group for perceived physical abuse (F(1,58)=4.58, p<0.05) and perceived sexual abuse (F(1,58)=6.78, p<0.05), but not for physical or emotional abuse ().
Acoustic Startle Response During Fear Acquisition
In all three types of child abuse there was an overall significant main effect of trial type. Startle magnitude to the CS+ trials was significantly higher than NA for physical (F(1,58)=24.39, p<0.001), sexual (F(1,58)=22.60, p<0.001), and emotional abuse (F(1,58)=17.24, p<0.001), see . However, there were no trial-type-by-group interactions.
Differential conditioning to CS+ and CS−, and fear inhibition on transfer trials was assessed with a RM ANOVA comparing the groups on percent startle potentiation to AX+, BX−, and AB (see ). There were no significant between-groups effects. However, this analysis showed a significant within-subjects main effect of trial type in all three abuse categories: physical abuse, F(2,116)=4.78, p<0.05), sexual abuse, F(2,116)=3.63, p<0.05), and emotional abuse, F(2,116)=3.73, p<0.05), see . Within-subjects contrasts showed that fear-potentiated startle was greater on the AX+ trials than the BX− trials in all three categories: physical abuse, F(1,58)=11.36, p<0.01), sexual abuse, F(1,58)=7.02, p<0.01), and emotional abuse, F(1,58)=8.30, p<0.01). Finally, fear-potentiated startle was inhibited on the AB transfer test relative to AX+ in all three categories: physical abuse, F(1,58)=7.09, p<0.01), sexual abuse, F(1,58)=5.42, p<0.01), and emotional abuse, F(1,58)=5.58, p<0.05). There were no significant trial-type-by-group interactions on either the main effects or either of the two contrasts.
The results of the response keypad data showed that, across all three abuse types, subjects reporting high and low levels of abuse understood the experimental contingencies. There was a main effect of CS type, with higher US expectancy for the AX+ than the BX−: physical abuse (F(1, 57)=25.82, p<0.001), sexual abuse (F(1, 57)=22.25, p<0.001), and emotional abuse (F(1, 57)=25.25, p<0.001). There was no main effect of group; as in the startle analyses, there were no trial-type-by-group interactions. We used the response keypad data to categorize individuals as to their awareness of the reinforcement contingencies in the experiment using criteria described in our previous study [17
]. The distribution of aware and unaware subjects did not vary in the high and low abuse groups for physical abuse (high abuse: 15 aware and 5 unaware, low abuse: 24 aware and 13 unaware, χ2
(57)=0.62, p>0.1), sexual abuse (high abuse: 9 aware and 6 unaware, low abuse: 30 aware and 12 unaware, χ2
(57)=0.67, p>0.1), or emotional abuse (high abuse: 9 aware and 4 unaware, low abuse: 30 aware and 14 unaware, χ2
When we examined the effect of awareness on baseline startle magnitude to NA, fear acquisition, differential conditioning and conditioned inhibition we found no significant differences between aware and unaware subjects. However, due to the small number of unaware subjects there was not enough power to compare aware and unaware individuals in each group. Given the possibility that unaware subjects were occluding the results of the conditioning trials, we ran additional analyses of the fear-potentiated startle data by restricting the dataset to aware subjects. These analyses replicated the first set of analyses which included all subjects, in that there were no significant between-group differences on the AX+, BX−, or AB trials: physical abuse F(1, 37)=0.01, p>0.1), sexual abuse, F(1, 37)=2.09, p>0.1), or emotional abuse, F(1, 37)=0.01, p>0.1). Furthermore, there were no significant interactions between group and trial type: physical abuse F(2, 74)=1.17, p>0.1), sexual abuse, F(2, 74)=0.28, p>0.1), or emotional abuse, F(2, 74)=0.98, p>0.1).