Responses to Aversive Acoustic Stimuli in Posttraumatic Stress Disorder: Moderation by the Presence of a Service Dog

Responses to Aversive Acoustic Stimuli in Posttraumatic Stress Disorder: Moderation by the Presence of a Service Dog | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 24 September 2025 V1 Latest version Share on Responses to Aversive Acoustic Stimuli in Posttraumatic Stress Disorder: Moderation by the Presence of a Service Dog Authors : Steven Woodward [email protected] , Andrea L. Jamison , Sasha Gala , Diana Villasenor 0000-0001-7927-305X , Gisselle C. Tamayo , and Ned J. Arsenault Authors Info & Affiliations https://doi.org/10.22541/au.175870451.17512199/v1 198 views 125 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Abstract Background: Psychophysiologic responses to series of aversively loud tones have discriminated persons with from those without PTSD in multiple studies. Using a within-subjects design, we examined whether such responses were moderated by repeated presentation, by the severity of PTSD-related hyperarousal, and by the custody of a service dog. Methods: U.S. military Veterans engaged in residential treatment for posttraumatic stress disorder and concurrently participating in a service animal training intervention were administered a loud tones protocol over four to six weekly sessions. During approximately one-half of sessions, participants were accompanied by their assigned service dog-in-training. Skin conductance and heart rate responses to the tones were quantified and modeled. Results: Skin conductance responses to aversive tones exhibited main effects and interactions involving trial, session, hyperarousal, and service dog presence. Service dog presence was associated with smaller responses and moderation of effects of hyperarousal. Pre-stimulus inter-beat intervals exhibited effects closely aligned with those on skin conductance, including main effects of hyperarousal and service dog presence, and moderation of an increase in heart rate over sessions by service dog presence. Furthermore, post-stimulus decreases in inter-beat interval were strongly inversely correlated with pre-stimulus values. After cardiac responses were adjusted for pre-stimulus ”baseline” values, service dog presence was associated with smaller responses and moderation of effects of hyperarousal, paralleling skin conductance. Discussion: Moderation of skin conductance and cardiac responses by service dog presence may offer insight into reports of “calming” provided by posttraumatic stress disorder patients when queried about benefits received from service dogs. Objective psychophysiological measures may inform studies of the health benefits associated with dog and pet companionship. The loud tones protocol may provide a platform for examining anticipation of threat, a behavior which appears to recruit amygdala and bed nucleus of the stria terminalis, core components of central fear systems implicated in posttraumatic stress disorder. Introduction Exaggerated psychophysiological responses to aversively loud tones are among the most replicable objective correlates of posttraumatic stress disorder (PTSD). They have been demonstrated in male military combat veterans (Orr, Lasko, Metzger, & Pitman, 1997; Orr, Lasko, Shalev, & Pitman, 1995; Orr, Solomon, Peri, Pitman, & Shalev, 1997), female military veterans (Carson, et al., 2007), female survivors of sexual abuse (Metzger, et al., 1999), and civilian survivors of mixed traumas (See review in Mueller-Pfeiffer, et al., 2014; Shalev, Orr, Peri, Schreiber, & Pitman, 1992) Studies comparing responses to aversive tones in homozygotic versus dizygotic twins discordant for PTSD have concluded that such responses are an acquired trait rather than inherited (Orr, et al., 2003; Pitman, et al., 2006). Griffin et al found that responses to aversive tones were attenuated in responders to PTSD treatment (Griffin, Resick, & Galovski, 2012). In light of these results, it is reasonable to ask whether responses to aversively loud tones are modified by additional candidate factors alleged to impact PTSD. One such candidate is service dog companionship. Several small, open-label trials of service dog interventions have reported improved mood status in persons with PTSD (Bergen-Cico, et al., 2018; Lass-Hennemann, et al., 2018; Whitworth, Scotland-Coogan, & Wharton, 2019). Service dog interventions have been instituted at a number of U.S. Military and Department of Veterans Affairs medical centers (Chumley, 2012; Yount, Olmert, & Lee, 2012). One of these is the VA Palo Alto Health Care System (VAPAHCS) where the Men’s Trauma Recovery Program (MTRP) includes an optional Service Animal Training Intervention (SATI), the structure of which made possible a series of within-subjects tests of the effects of service dog custody (Miller, Jamison, Gala, & Woodward, 2018; Woodward, Jamison, Gala, & Holmes, 2017; Woodward, et al., 2021; Woodward, et al., 2023; Woodward, et al., 2024; Woodward, et al., submitted), In the current study, participants were administered a loud tones protocol on four to six occasions with and without their assigned service dog present. In light of Rodriguez’ (Rodriguez, LaFollette, Hediger, Ogata, & O’Haire, 2020) finding that “calming” was the leading benefit of canine companionship reported by Veterans with PTSD, the hyperarousal (Criterion D) score from the Clinician-Administered PTSD Scale was also included when modeling response amplitudes. Pre-stimulus cardiac responses were analyzed in the same manner as post-stimulus responses in light of evidence provided by Brinkman and colleagues (Brinkmann, et al., 2017) that core components of the central fear system implicated in PTSD, the amygdala and bed nucleus of the stria terminalis, are activated during anticipation of aversive auditory stimuli in persons with PTSD. Methods and Materials Participants and Procedures The participants in this study were male U.S. Military veterans, primarily of the Iraq and Afghanistan wars, engaged in residential treatment for PTSD, who elected to participate in the SATI. Participants in the SATI were supervised by professionals in the provision of early socialization and training to young service dogs provided by a non-profit organization (Paws for Purple Hearts). The dogs involved in the study were Labrador Retrievers bred to achieve the highest level of service animal employment as future aides to mobility-challenged veterans11The final stages of training were supplied by professional trainers and occurred after the dogs’ assignments to the VA setting. Not all dogs were expected to achieve full certification. For patients, the criteria for acceptance into the SATI included relative behavioral stability, low fall risk, and consistent engagement with the therapeutic milieu. Patients admitted to the SATI typically waited two to three weeks for a service-dog-in-training to become available during which time the patients engaged in one-hour group training sessions three to four times per week. Veterans continuing with the SATI were then assigned in pairs to a specific dog, alternating custody of that dog on a weekly basis. The custodial trainer maintained nearly continuous contact with the dog, including during treatment groups, meals, off-campus outings, and at night. The non-custodial trainer had little contact with the dog. Room assignments were arranged to support this contrast. SATI participants did not work with their dogs on weekends. SATI participation typically continued for five or more weeks. SATI participants who enrolled in this study came each Thursday or Friday to the psychophysiology laboratory located on the same campus as the MTRP. The first laboratory session began with a brief audiologic screening to exclude participants with pure-tone hearing loss greater than 40 dB at 1000 Hz. No participants were excluded on this basis. Electrodermal and electrocardiogram (ECG) electrodes were applied and participants seated in a comfortable chair in the testing chamber. If present, the dog was located on the floor near the participant. The loud tones task involved listening passively to a series of fifteen computer-generated 1000 Hz pure tones, each 500 milliseconds in duration with one millisecond rise-times. The tones were presented binaurally at 95 dB using Telephonics TDH-50P headphones embedded in AuralDome ambient sound attenuators. Inter-stimulus intervals were 40 +/10 seconds. The task required approximately 10 minutes to complete. Participants were instructed to move as little as possible. The tones task was delivered as the fourth of five tasks and followed a version of the Reading the Mind in the Eyes Test (Baron-Cohen, Wheelwright, Hill, Raste, & Plumb, 2001) and two attentional bias tasks (Woodward, Jamison, Gala, & Holmes, 2017). It preceded a final serial subtraction task. The first three tasks were all well-tolerated by participants and required approximately 40 minutes including set up. The entire session required approximately one hour. Three participants declined to complete the loud tones task on one or more occasions and were excluded on that basis. Psychometric Assessments Psychiatric diagnoses were made using the Clinician-Administered PTSD Scale for DSM-5 (Weathers, et al., 2013) and the Structured Clinical Interview for DSM-5 (First, Williams, Karg, & Spitzer, 2015). These assessments were performed by B.A. and Masters-level staff who had undergone extensive training using materials provided by the Veterans Administration, the National Center for PTSD, and the American Psychiatric Association. These materials included both didactics and videotaped interviews of simulated patients. In addition, assessment staff regularly met with the doctoral-level study coordinator (ALJ) to co-score training interviews and audiotaped particpant assessments. Collection and Pre-processing of Psychophysiological Data Skin conductance responses (SCRs) were obtained using 1 cm 2 Ag/AgCl electrodes (In Vivo Metric) filled with isotonic NaCl-amended (0.05 molar) Unibase electrolyte (Boucsein, et al., 2012) and located on the distal phalanges of 2 nd and 3 rd fingers of non-dominant hand. These electrodes were connected to a Coulbourn Instruments S71-22 isolated skin conductance coupler (constant 0.5V DC excitation, AC-coupled output). All responses were quantified with “non-responses” scored as zeroes. ECG signals were obtained using pre-gelled, foam-backed electrodes applied in the V1 - Lead II derivation and amplified using a Coulbourn Instruments S75-01 bioamplifier. ECG signals were analog pre-filtered to 1 - 250 Hz bandwidth. Both biosignals signals were digitized at 1000 Hz with 16 bits of amplitude resolution via an IOTech digitizer and QuikDaq software. Synchronization of stimuli and data was achieved by imposing a square-wave signal coincident with stimulus onset on a separate data channel. A combination of automated trial-wise and manual session-wise artifact exclusion was executed blind to service dog presence. SCR amplitude was operationalized as the signal maximum within the three-second, post-stimulus window minus the median of the whole-session baseline. Use of the session baseline in this manner, which attenuated the impact of pre-stimulus movement artifacts on SCR amplitude measurements, was made possible by the AC-coupling of the electrodermal signal. R-waves in the ECG were detected and inter-beat-intervals (IBIs) resampled to an equal-interval time series. The cardiac response was operationalized as the minimum IBI within a window beginning one second and ending nine seconds post-stimulus minus the median of the two second window ending 0.5 seconds pre-stimulus. Separating the windows by 1.5 seconds prevented any blurring of pre- and post-stimulus values due to resampling. As noted, pre-stimulus IBI values were analyzed as a potential index of anticipation of aversive stimulation. Statistics Thirty-four participants completed the loud tone task a minimum of four times and contributed at least one session with and one session without the presence of their service dog. Twenty-six participants enrolled in the parent study did not meet these criteria. The most common reason for this was discharge from the MTRP. After exclusion of sessions contaminated by excess signal artifact, the re-application of the above criteria led to the retention of 26 participants for the analysis of SCR responses and 32 participants for the analysis of IBI responses, with 71% overlap across the subsamples. For each subsample, responses for missing sessions and any automatically-excluded individual trials were multi-level imputed using the MICE package (van Buuren & Groothuis-Oudshoorn, 2011). Imputation predictors were obtained by application of the quickpred procedure using default settings. Prior to imputation, SCR response outliers were excluded by winsorising at the 2.5 and 97.5 percentiles (Ruppert, 2006). Winsorization of SCRs was imposed within trials, as outliers were more common and larger in earlier trials. After imputation, negative values of SCR amplitude were set to zero and winsorization reapplied. Winsorization was judged unnecessary for pre- and post-stimulus IBI responses. Linear mixed effects modeling (Pinheiro, Bates, DebRoy, Sarkar, & Team, 2016) was performed including trial, session, hyperarousal score, and service dog presence as predictors. A random intercept was estimated to account for within-participant clustering of observations and adjust for otherwise unmeasured participant-level traits. Trial and session were treated as interval variables and centered. This strategy simplified modeling, advantageous in light of the small sample, but precluded consideration of specific trials or sessions. Dog presence was treated as a factor. Based upon prior between-subjects results, was predicted that PTSD-related hyperarousal would be associated with larger amplitude post-stimulus SCR and IBI responses, and that repetition (both trial and session) and service dog presence would be associated with smaller amplitude responses. Pre-stimulus IBI responses were expected to follow a similar pattern based upon Brinkman et al. Sample The following psychometrics describe the 34 participants originally included after application of the session number and service dog contrast criteria.11Psychometrics of the EDA subsample are provided in Supplemental Materials. As 32 of 34 participants provided IBI data, no separate subsample results are provided. Mean age was 39.1 (sd = 11.6) years. Thirty of 34 participants (88.2%) met criterion for PTSD. Three failed to meet Criterion C and one fell below a total severity score of 26. Mean CAPS-5 total severity score was 40.3 (sd = 7.6). Sixty-five percent of the sample self-identified as White, non-Hispanic, 2.9% as African-American, 14.7% as White, Hispanic, 5.8% as American Indian/Alaskan, 8.8% as Hawaiin/Pacific Islander, and 2.9% as Multi-racial. Sevent-seven percent of the sample met criteria for current Major Depressive Disorder (MDD) and 88.2% for lifetime MDD. Fifty-three percent met criteria for current (past 12 months) Alcohol Use Disorder (AUD) and 94% for lifetime AUD. Twenty-nine percent met criteria for a current (past 12 months) non-alcohol Substance Use Disorder (SUD) and 58.8% for lifetime SUD. Eight participants excluded on the basis of EDA signal artifact did not differ from those retained on CAPS total severity scores (excluded vs retained, 39.5 vs 40.5), CAPS hyperarousal scores (excluded vs retained, 15.4 vs 16.5), the frequency of current or lifetime MDD, AUD, or SUD (all p’s > 0.32), or in age (EDA excluded vs retained, 43.8 vs 37.6, t = 1.18, p = 0.27). Participants’ assigned service dogs were present during 56% of laboratory sessions; however, dog presence, which was not under the control of the experimenters, was not uniformly distributed over sessions (See Supplementary Table S1); nevertheless, the mean session values were similar across the dog presence contrast (SCR: dog present, 3.4, dog absent, 3.5; IBI: dog present, 3.5, dog absent, 3.4) and so unlikely to have introduced bias. Insert Figure 1 about here. SCRs to Aversive Tones Figures 1a and b plot the grand mean SCRs and IBI responses to the 15 aversively loud tones, excluding variable inter-stimulus times, averaged over participants and sessions. SCR amplitude exhibited expected effects of trial (effect = -0.20 υmho/ sd Trial, SE = 0.02, t(356) = -12.20, p < 0.0001, CI95%: -0.24 – -0.17), session (effect = -0.11 υmho/ sd Session, SE = 0.02, t(319) = -6.15, p < 0.0001, CI95%: -0.14 – -0.07), and their interaction (estimate = 0.06 υmho/ sd Trial/ sd Session, SE = 0.02, t(176) = 3.72, p = 0.0003, CI95%: 0.03 – 0.10; See Supplemental Figure S1). SCR amplitude exhibited an interaction of trial and CAPS hyperarousal score (effect = -0.06 υmho/ sd Trial/ sd Hyperarousal, SE = 0.02, t(513) = -3.49, p = 0.0005, CI95%: -0.09 – -0.02). related to the fact that higher hyperarousal scores were associated with larger SCRs on early trials after which mean SCR amplitude converged on zero by trial 15 across levels of hyperarousal (See Figure Supplemental S2). As plotted in Figure 2, hyperarousal score and service dog presence interacted as the slope of the relationship between hyperarousal and SCR amplitude was flatter with service dog presence (effect = -0.10 υmho/ sd Hyperarousal/DogPresence, SE = 0.02, t(231) = -4.19, p < 0.0001, CI95%: -0.15 – 0.06). SCR amplitude exhibited a main effect of hyperarousal score (effect = 0.11 υmho/ sd Hyperarousal, SE = 0.04, t(1799) = 3.05, p = 0.002, CI95%: 0.04 – 0.18; See Supplemental Figure S3) and a trend inverse effect of service dog presence (effect = -0.04 υmho/DogPresence, SE = 0.02, t(279) = -1.73, p = 0.086, CI95%: -0.09 – 0.01). Insert Figure 2 about here Cardiac Responses in Anticipation of Aversive Tones Mean pre-stimulus IBI was 877.53 msec (SE = 17.81 msec) or 68.37 BPM (SE = 1.36 BPM). Plotted in Figure 3, pre-stimulus IBI was influenced by a three-way interaction of session, hyperarousal, and service dog presence (effect = 31.12 msec/ sd Session/ sd Hyperarousal/DogPresence, SE = 4.48, t(399) = 6.94, p < 0.0001, CI95%: 22.30 – 39.94). There was session-to-session evolution in the relations between hyperarousal and dog presence as they influenced pre-stimulus IBI. Among participants endorsing increasingly higher levels of hyperarousal, dog presence was associated with lengthening of IBI over sessions, while the opposite was true in dog absence. Lower levels of hyperarousal did not show this effect. Employing a median split of CAPS hyperarousal scores at 17, it was determined that the two-way interaction of service dog presence and session was significant when hyperarousal was relatively high (effect = 32.76 msec/ sd Session/DogPresence, SE = 4.77, t(1222) = 6.87, p < 0.0001, CI95%: 23.40 – 42.12), but not when when it was relatively low (effect = -8.12 msec/ sd Session/DogPresence, SE = 6.10, t(97) = -1.33, p = 0.19, CI95%: -20.23 – 4.00). The two-way interaction of session and service dog presence was also significant (effect = 11.95 msec/ sd Session/DogPresence, SE = 3.76, t(119) = 3.18, p = 0.002, CI95%: 4.51 – 19.38 ; See Figure 4) as pre-stimulus IBI decreased by 32 msec (2.50 BPM) over sessions absent service dogs but was relatively flat over sessions with dog presence. Dog presence moderated the effect of hyperarousal on pre-stimulus IBI (effect = 10.02 msec/ sd Hyperarousal/DogPresence, SE = 3.92, t(874) = 2.55, p < 0.01, CI95%: 2.32 – 17.7; See Figure 5). The interaction of session and hyperarousal was significant (effect = -12.50 msec/ sd Session/ sd Hyperarousal, SE = 3.08, t(308) = -4.06, p = 0.0006, CI95%: -18.57 – -6.44) as lower hyperarousal was associated with longer pre-stimulus IBI in early sessions which then decreased more rapidly as sessions progressed (See Supplemental Figure S4). Finally, pre-stimulus IBI exhibited main effects of session (effect = -10.75 msec/ sd Session, SE = 2.72, t(315) = -3.94, p < 0.0001, CI95%: -16.10 – -5.39) and service dog presence (effect = 12.23 msec/DogPresence, SE = 3.78, t(285) = 3.23, p = 0.001, CI95%: 4.79 – 19.67; See Supplementary Figures 5a and b), as well as a trend toward shorter IBIs as hyperaroual increased (effect = -29.49 msec/ sd Hyperarousal, SE = 17.46.72, t(2694) = -1.69, p = 0.091, CI95%: -63.72 – 4.73). A similar pattern of results was obtained when ten-seconds of pre-stimulus were quantified (See Supplemental Table S2). All these results were in the direction predicted by a framework in which anticipation of an aversive stimulus is subserved by brain systems dysregulated in PTSD. Insert Figures 4 - 5 about here Cardiac Responses to Aversive Tones Mean cardioacceleratory response to tones was -77.44 msec (SE = 6.41 msec) or 6.62 BPM (SE = 2.66 BPM). A trading relationship was observed in which higher pre-stimulus heart rates were associated with smaller post-stimulus responses to the tones. This is evident in the bivariate plot in Figure 6. Pre-stimulus IBI was therefore entered in the model of the IBI response. A three-way interaction of session, hyperarousal, and service dog presence influenced adjusted cardioacceleratory (effect = -6.17 msec/ sd Session/ sd Hyperarousal/DogPresence, SE = 2.92, t(68) = -2.12, p = 0.038, CI95%: -11.99 – -0.35; See Supplemental Figure S6). As shown in Figure 7, adjusted IBI responses to aversive tones decreased over sessions with dog presence, but increased with dog absence (effect = 5.46 msec/ sd Session/DogPresence, SE = 2.43, t(75) = -2.25, p = 0.027, CI95%: 0.53 – 10.29). Service dog presence also moderated increases in the cardioacceleratory response associated with higher levels of hyperarousal (effect = 6.06 msec/ sd Hyperarousal/DogPresence, SE = 2.44, t(170) = 2.48, p = 0.014, CI95%: 1.24 – 10.88; See Figure 8). Adjusted IBI responses declined slightly over trials (effect = 3.23 msec/ sd Trial, SE = 1.51, t(633) = 2.13, p = 0.033, CI95%: 0.26 – 6.20), and a three-way interaction of trial, session, and hyperarousal was nominally significant (effect = -4.72 msec/ sd Trial/ sd Session/ sd Hyperarousal, SE = 2.07, t(2495) = -2.07, p = 0.04, CI95%: -8.32 – -0.222. See Supplemental Figure S7). In it, low and high leves of hyperarousal were associated with divergent trajectories of trial effects over sessions, with the former participants exhibiting increasing trial-wise habituation, and the latter, decreasing trial-wise habituation, as sessions progressed. Finally, service dog presence was associated with smaller adjusted cardioacceleratory responses to aversive tones (effect = 5.05 msec/DogPresence, SE = 2.15, t(1415) = 2.35, p = 0.018, CI95%: 0.84 – 9.27). Insert Figures 6 - 8 about here. Discussion The amplitudes of SCRs and IBI responses to aversive tones were influenced by repetition, hyperarousal, and service dog presence in this sample of male Veterans with deployment-related PTSD. As summarized in Table 1, all three outcomes exhibited moderation of effects hyperarousal by service dog presence. This result appears consistent with Rodriguez’ (Rodriguez, LaFollette, Hediger, Ogata, & O’Haire, 2020) finding that “calming” is the leading self-reported benefit of canine companionship endorsed by Veterans with PTSD, both in the coherence of the two constructs, calming and reduced hyperarousal, and in the enlarged effect in more hyper-aroused participants among whom the signal value of reduced arousal would be more detectable. All three outcomes demonstrated attenuation in the presence of participants’ service dogs. The effects were small, however, and in the case of SCR, only a trend. Their directionality and modest size align with other service dog effects observed in this male Veteran sample in basal heart rate (Woodward, et al., 2023; Woodward, et al., 2024), affect (Woodward, et al., 2021), and attentional bias (Woodward, Jamison, Gala, & Holmes, 2017). Nevertheless, these small effects should also be understood in the context of limited and discontinuous exposures, approximately 15 days spread over four to six weeks, to service dogs whose companionship was understood to be temporary. This intervention may thus be a weak proxy for dog ownership which has, in epidemiological studies, been associated with substantial reductions in cardiac disease risk and all-cause mortality (Friedmann & Thomas, 1995; Kramer, Mehmood, & Suen, 2019; Mubanga, Byberg, Egenvall, Ingelsson, & Fall, 2019; Mubanga, et al., 2017; Woodward, Baldassarri, & Pietrzak, 2023). Extended clinical trials can begin to address the chasm between these two classes of studies and their results (O’Haire & Rodriguez, 2018) and can, with ingenuity, incorporate randomization (O’Haire, NCT03245814). Adding objective biomarkers such as responses to aversive tones may provide further insight into mechanisms. Insert Table 1 about here. SCRs and pre-stimulus IBIs both varied systematically over sessions spaced one week apart, but in opposite directions. SCRs became smaller, while pre-stimulus IBI/heart rate responses increased. It is possible that the subjective aversiveness of the loud tones protocol increased over repeated sessions, but that this increase was captured by a basal cardiac index and not by phasic responses to stimuli. Alternatively, it may be that session was confounded with days in study (or days in treatment) which has been associated with basal heart rate increases in both this sample and in a similar but independent sample (Ong, Ramirez, & Woodward, 2025; Woodward, et al., 2023; See also ), an effect attributed to deconditioning. The study design does not allow us to discriminate between these two possibilities. This study analyzed pre-stimulus IBI values more intensively than prior studies, inspired by the results of Brinkman et al suggesting that anticipation of aversive stimulation activates core fear system components whose dysregulation is thought to be central to PTSD (Etkin & Wager, 2007; Pitman, et al., 2012; Pitman, Shin, & Rauch, 2001). When analyzed, elevated pre-stimulus heart rate in persons with PTSD versus controls is a common finding in this literature (Carson et al 2007; Orr et al, 1997; Shalev et al, 1992). An advantage of pre-stimulus IBI/heart rate as an outcome is that it is based upon more data and so will be more reliable than peak estimates. It is also less vulnerable to movement artifact than electrodermal measures as was demonstrated, here. The current results suggest the familiar loud tones protocol may be a useful probe of fear system activation in anticipation of threat. It is interesting to compare the results Brinkman et al, which were specific to anticipation, with those of Mueller-Pfeiffer et al., which focused on the response phase. Both studies observed activation of anterior insula, pregenual anterior and mid-cingulate cortex, and lateral pre-frontal cortex; however, only the former found activation of amygdala and bed nucleus of the stria terminalis. As a construct, anticipation of threat would seem to closely overlap hypervigilance, one component of the CAPS hyperarousal (D-criterion) score. Future studies of service dog impacts on persons with PTSD might productively employ focused psychometrics (Kimble, Fleming, & Bennion, 2013) and/or objective measures of hypervigilance (Kimble, Cappello, & Fleming, 2023; Kimble & Hyatt, 2019). Simultaneous measurement of skin conduct level may provide a second measure of anticipation of the aversive tones. In addition to limitations noted above, it is important to consider that the generalizability of these effects beyond male US military Veterans remains to be established. As well, the design of the study could not distinguish between effects associated with the presence of the service dog in the test setting from possible carryover effects of having spent time with the dog during the days and hours prior to testing. Conclusion Service dog presence/custody was associated with smaller skin conductance and cardi-acceleratory responses to aversively loud tones in U.S. military Veterans with deployment-related PTSD tested in a within-subjects design. The results are consistent with patient reports of the subjective benefits of service dogs. They are consistent with mild reduction in sympathetic tone when a familiar service dog is present and so are aligned with the risk reductions observed in epidemiological studies in direction if not in magnitude. Building an empirical bridge between the two classes of studies, in Veterans with PTSD and in the general population, will require temporally extended randomized trials. Acknowledgements This research was supported by Contract W81XWH-15-2-0005 (Log #13046055) to Steven H. Woodward, PhD, from the Defense Health Program, Military Operational Medical Research Program, U.S. Army Medical Research and Materiel Command, U.S. Department of Defense. This research would not have been possible without the additional support of the National Center for PTSD, Dissemination and Training Division, the Palo Alto Veterans Institute for Research, the Research Service and Men’s Trauma Recovery Program, VA Palo Alto Health Care System, Paws for Purple Hearts, and the Veterans who participated. The authors also wish to thank Drs. Sarah Righi, Catherine Lawlor, Chloe Bhowmick, Dustin Kiesnick, and Meghan Goulet for their contributions to testing and assessing participants. 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Dog presence was associated with milder increases in SCR amplitudes over groups endorsing higher levels of hyperarousal. Figure 3: Plot of the interaction of session, CAPS hyperarousal, and service dog presence on pre-stimulus IBI. The contrast of dog presence versus absence on habituation over sessions was strongest in participants endorsing the highest levels of hyperarousal. Figure 4: Plot of the interaction of session and service dog presence on pre-stimulus IBI indicating that the collapsing the effects in Figure 3 over hyperarousal groups revealed a strong relationship between service-dog presence and session-wise habituation to the anticipation of aversive stimuli. Figure 5: Plot of the interaction of CAPS hyperarousal score and service dog presence on pre-stimulus IBI. Collapsing the forgoing three-way interaction over sessions revealed that service dog presence flattened the slope relating increased hyperarousal to shorter pre-stimulus IBIs/higher heart rates. Figure 6: Bi-variate plot of pre-stimulus mean IBI (x-axis) and post-stimulus peak IBI (y-axis) suggesting that high pre-stimulus heart rates limited subsequent cardio-acceleratory responses. Figure 7: Plot of the interaction of session and service dog presence on adjusted IBI response to aversive tones. Cardiac response amplitudes diverged over sessions, increasing with dog absence and decreasing with dog presence. Figure 8: Plot of the interaction of CAPS hyperarousal score and service dog presence on adjusted IBI response to aversive tones. As with pre-stimulus IBIs, service dog presence flattened the slope relating increased hyperarousal to larger post-stimulus peak responses. . Tables Table 1 A table summarizing the observed effects on study outcomes with “1” indicating and effect, “0.5” a trend, and “0”, no effect. Supplementary Material File (main figures 9_23_25.pptx) Download 239.01 KB Information & Authors Information Version history V1 Version 1 24 September 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Authors Affiliations Steven Woodward [email protected] VA Palo Alto Health Care System View all articles by this author Andrea L. Jamison VA Palo Alto Health Care System View all articles by this author Sasha Gala VA Palo Alto Health Care System View all articles by this author Diana Villasenor 0000-0001-7927-305X VA Palo Alto Health Care System View all articles by this author Gisselle C. Tamayo VA Palo Alto Health Care System View all articles by this author Ned J. Arsenault VA Palo Alto Health Care System View all articles by this author Metrics & Citations Metrics Article Usage 198 views 125 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Steven Woodward, Andrea L. Jamison, Sasha Gala, et al. 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