Effects of experimental context and explicit threat cues on acoustic startle in Vietnam veterans with posttraumatic stress disorder

BACKGROUND: The hypothesis that exaggerated startle in Vietnam veterans with posttraumatic stress disorder (PTSD) reflects an anxiogenic response to stressful contexts was tested. METHODS: Thirty-four nonmedicated Vietnam veterans with PTSD, and 17 combat and 14 civilian non-PTSD controls participated in two testing sessions over separate days. Acoustic startle stimuli were delivered alone or in a test of prepulse inhibition. In the first session, startle was assessed without experimental stress. In the second session, startle was investigated during a stressful "threat of shock" experiment, when subjects anticipated the administration of shocks during threat periods and during safe periods when no shocks were anticipated. RESULTS: The magnitude of startle did not differ significantly among the three groups in the first session, but was increased throughout the threat of shock experiment in the PTSD veterans in the second session. The actual increase in startle in the threat compared to the safe condition did not significantly differ among the three groups. Prepulse inhibition was reduced in the PTSD veterans, compared to the non-PTSD civilians, but not compared to the non-PTSD veterans. CONCLUSION: Exaggerated startle in Vietnam veterans with PTSD reflects an anxiogenic response to an environment that is experienced as stressful.     

Olfactory bulbectomy enhances sensitization of the acoustic startle reflex produced by acute or repeated stress.

The effects of olfactory bulbectomy on the acoustic startle reflex and shock-induced sensitization of the startle reflex were examined in 3 experiments. In Experiment 1, bulbectomized animals showed a modest increase in baseline startle responding following surgery, and normal acquisition of fear-potentiated startle, but a pronounced increase in baseline startle responding during the course of conditioning relative to sham-operated controls. In Experiments 2 and 3, bulbectomized animals showed shock-induced sensitization of the startle reflex to shock intensities that did not produce sensitization in sham and unoperated controls. These data suggest that olfactory bulbectomy results in an increased vulnerability to stressors, which may be mediated by a disinhibition of the amygdala or other structures involved in mediating stress and anxiety. Thus, the olfactory bulbectomy model of depression may share some similarities with other stress-induced models of depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fear-potentiated startle conditioning to explicit and contextual cues in Gulf War veterans with posttraumatic stress disorder.

Aversive conditioning to explicit and contextual cues was examined in Gulf War veterans with and without posttraumatic stress disorder (PTSD) by use of the startle reflex methodology. Veterans participated in a differential aversive conditioning experiment consisting of 2 sessions separated by 4 or 5 days. Each session comprised two startle habituation periods, a preconditioning phase, a conditioning phase, and a postconditioning extinction test. In contrast to the non-PTSD group, the PTSD group showed a lack of differential startle response in the presence of a conditioned stimulus with or without an unconditioned stimulus in Session 1 and an increase in the baseline startle response during Session 2. The PTSD group also exhibited normal differential conditioning following reconditioning in Session 2. These data suggest that individuals with PTSD tend to generalize fear across stimuli and are sensitized by stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An inference system based on fuzzy logic

While psychophysiologic studies of posttraumatic stress disorder (PTSD) have investigated the effects of trauma-related stimuli on arousal, none have explored the development of intrusive imagery and affect states in the absence of such specific cues. The present study compares autonomic arousal during PTSD-related Rorschach responses in PTSD veterans vs. combat controls and noncombat controls. It was found that Rorshach responses containing traumatic content were found only in the PTSD group, and that these responses showed elevations in skin conductance (SC) and heart rate (HR). Our data also suggest that PTSD patients are more easily hyperaroused, especially under conditions of experienced stress and helplessness. Finally, combat control subjects exhibited lower baseline SC and HR than their counterparts, as well as decelerated HR during trauma- and stress-related Rorschach responses, suggesting a physiologic resilience in this group.     

Self-rated health among cardiovascular drug users in a study of Swedish twins

Fear can be elicited by physically-presented explicit threat stimuli or by more static contextual stimuli that are not an immediate source of danger. Research in both humans and animals suggest that fear produced by these two types of stimuli represents separate processes mediated by different brain structures. The present study used the startle reflex methodology to examine affective responses elicited by an explicit threat cue signalling a period of shock anticipation and by two types of contextual stimuli; darkness and attaching the shock electrodes. As expected, shock anticipation potentiated startle (fear-potentiated startle). Startle was also facilitated by darkness and by the placement of shock electrodes. Further, darkness increased fear-potentiated startle to an explicit threat cue, but did not affect the facilitation of startle produced by attaching the shock electrodes. It is suggested that affective responses to contextual stimuli should be considered when investigating both normal and pathological fear.     

Lesions of the bed nucleus of the stria terminalis block sensitization of the acoustic startle reflex produced by repeated stress, but not fear-potentiated startle

1. The effects of lesions of the bed nucleus of the stria terminalis (BST) on the acquisition of conditioned fear were examined. In Experiment 1, BST lesions did not block acquisition of fear-potentiated startle to an explicit visual conditioned stimulus (CS) over 20 days of training. However, BST lesions blocked a gradual elevation in baseline startle also seen over the course of training. 2. The gradual increase in baseline startle was replicated in Experiment 2 without the presence of an explicit CS, using unoperated subjects. Experiment 2 showed that the elevation was due to repetitive exposure to shock, because unshocked control subjects did not show any elevation over sessions. 3. In Experiment 3, lesions of the BST did not disrupt rapid sensitization of the startle reflex by footshock, showing that different neural substrates underlie sensitization of startle by acute and chronic exposure to footshock. 4. These data indicate that the BST, despite its anatomical continuity with the amygdala, is not critically involved in the acquisition of conditioned fear to an explicit CS. Nevertheless, the BST is involved in mediating a stress-induced elevation in the startle reflex. This suggests that the BST and the CeA, which constitute part of the "extended amygdala" have complementary roles in responses to stress.     

Emotional-Processing in Posttraumatic Stress Disorder II: Startle Reflex Modulation During Picture Processing.

This study examined the impact of a trauma-related stressor on subsequent emotional behavior in veterans with (n = 35) and without (n = 24) posttraumatic stress disorder (PTSD). Self-report and physiological responses, including acoustic startle, were recorded during viewing of emotionally evocative photographs at baseline and following exposure to trauma-related and non-trauma-related stressors. The 2 groups exhibited equivalent patterns of emotional response across self-report and physiological measures at baseline. In contrast, following the trauma challenge, participants with PTSD showed a pattern of startle modulation suggestive of greater defensive reactivity and reduced visual perceptual engagement. These findings, along with augmented corrugator EMG reactivity during the same interval, suggest that trauma-related reexperiencing primes subsequent negative emotional responding in individuals with PTSD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensitization of the acoustic startle reflex by footshock.

Administration of footshock (500-ms duration, 0.2–2.4 mA) increased the amplitude of the startle reflex for a long time after its presentation. The effect occurred with a single footshock, although its magnitude and consistency across animals were greater with 5 or 10 footshocks presented 1/s. The facilitatory effect came on within 2–4 min with a 0.6-mA shock, peaking in about 10 min and then dissipating over the next 40 min. Stronger shocks also increased startle, but with a more delayed onset of facilitation (8–20 min). Footshocks increased startle in rats not previously given startle-eliciting stimuli, indicating sensitization rather than dishabituation. The facilitatory effect may not be attributable to a rapid conditioning to the experimental context, because a change in lighting conditions from shock presentation to testing did not attenuate shock sensitization. This excitatory effect of shock on startle may represent the unconditioned effect of shock that can become associated with a neutral stimulus to support classical fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Greater sustained anxiety but not phasic fear in women compared to men.

Startle reflex studies in rodents indicate that female are more reactive than rats in experimental models of sustained anxiety but not in models of phasic fear (Toufexis, 2007). This study examined evidence for a similar effect in humans. Participants were exposed to three conditions, (1) predictable aversive shocks signaled by a cue, (2) unpredictable shocks, and (3) no shocks. Acoustic startle stimuli were delivered regularly across conditions. Phasic startle potential to the threat cue in the predictable condition was not affected by sex. In contrast, and consistent with basic research, the sustained increase in startle in the predictable and unpredictable conditions was greater in women compared to men. Animal studies suggest that such an effect may be mediated by the effects of sexual dimorphism in limbic structures, including the bed nucleus of the stria terminalis. However, psychosocial factors may also contribute to this effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alcohol selectively reduces anxiety but not fear: Startle response during unpredictable versus predictable threat.

Recent theory and empirical research have suggested that fear and anxiety are distinct processes with separable neurobiological substrates. Furthermore, a laboratory procedure has been developed to manipulate fear versus anxiety independently via administration of predictable or unpredictable electric shock, respectively. Benzodiazepines appear to selectively reduce anxiety but not fear in this procedure. The primary aim of this experiment was to determine if alcohol produced a similar selective reduction in anxiety. Intoxicated (target blood alcohol concentration of .08%) and nonintoxicated participants viewed a series of colored squares separated by variable intertrial intervals (ITIs) in 3 conditions. In the predictable shock condition, shocks were administered contingently during every square. In the unpredictable shock condition, shocks were administered noncontingently during both squares and ITIs. In the no-shock condition, no shocks were administered at any time. Alcohol significantly reduced startle potentiation during cues signaling unpredictable but not predictable shock, consistent with the thesis that alcohol selectively reduces anxiety but not fear. In addition, alcohol’s effect on startle potentiation during unpredictable shock was mediated by vigilance. This anxiolytic effect may clarify the nature of alcohol’s reinforcing effects in social and problem drinkers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrast-enhanced MR angiography

These studies investigated appraisal and coping strategies of tension-type headache sufferers and headache-free controls. In study 1, 60 women engaged in an interpersonal stressor. They completed measures that assessed subjective stress and coping strategies. Headache sufferers reported greater levels of stress at baseline than did controls but were not more reactive to a stressful interpersonal situation. All participants reported greater use of disengagement coping during the interpersonal interaction, while the amount of engagement coping strategies did not differ. Participants (30 women) in Study 2 engaged in progressive muscle relaxation. Headache participants again reported higher levels of subjective stress at baseline, this difference was nearly gone following relaxation. Together, the results suggest that individuals with tension-type headache report higher levels of subjective stress than headache-free controls when they make baseline ratings of stress and that this elevation cannot be attributed to the anticipation of a future stressful event.     

The psychophysiology of posttraumatic stress disorder: A meta-analysis.

This meta-analysis of 58 resting baseline studies, 25 startle studies, 17 standardized trauma cue studies, and 22 idiographic trauma cue studies compared adults with and without posttraumatic stress disorder (PTSD) on psychophysiological variables: facial electromyography (EMG), heart rate (HR), skin conductance (SC), and blood pressure. Significant weighted mean effects of PTSD were observed for HR (r = .18) and SC (r = .08) in resting baseline studies; eyeblink EMG (r = .13), HR (r = .23), and SC habituation slope (r = .21) in startle studies; HR (r = .27) in standardized trauma cue studies; and frontalis EMG (r = .21), corrugator EMG (r = .34), HR (r = .22), and SC (r = .19) in idiographic trauma cue studies. The most robust correlates of PTSD were SC habituation slope, facial EMG during idiographic trauma cues, and HR during all study types. Overall, the results support the view that PTSD is associated with elevated psychophysiology. However, the generalizability of these findings is limited by characteristics of the published literature, including its disproportionate focus on male veterans and neglect of potential PTSD subtypes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Footshock-induced sensitization of electrically elicited startle reflexes.

Acoustic startle is a short-latency reflex mediated by a neural circuit consisting of the ventral cochlear nucleus (VCN), ventral nucleus of the lateral lemniscus (VLL), the nucleus reticularis pontis caudalis (RPC), and the spinal cord. The present study sought to determine the point along this pathway where footshocks might ultimately alter neural transmission to affect startle response. Rats were implanted bilaterally with stimulating electrodes in either the VCN, VLL, or RPC. Startle could be elicited acoustically with a noise burst or electrically with a single-pulse stimulus to either the VCN, VLL, or RPC before and after a train of ten 0.6-mA, 500-ms shocks presented at a rate of 1 shock/s. Startle elicited acoustically or electrically in the VCN or VLL was significantly elevated following shocks. Data suggest that footshock sensitization ultimately alters transmission in the startle circuit at the RPC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensitization of the startle reflex by footshock: Blockade by lesions of the central nucleus of the amygdala or its efferent pathway to the brainstem.

Bilateral electrolytic lesions of the central, but not the lateral, nucleus of the amgydala blocked shock sensitization of startle (the increase in startle produced by presentation of ten 0.6-mA footshocks in rapid succession). Lesions of the central nucleus also decreased reactivity to shock (jumping and flinching) during shock presentation. However, this decrease in reactivity cannot account for the blockade of shock sensitization, because when a higher shock intensity (1.0 mA) was used, producing equivalent reactivity to that of controls at 0.6 mA, central nucleus lesions still blocked shock sensitization. Moreover, lesions of the caudal part of the ventral amygdalofugal pathway, which carries central nucleus efferents to the startle reflex pathway, also blocked shock sensitization. It is hypothesized that shock activates the central nucleus of the amygdala, which increases startle through modulation of the startle pathway. Activation of the amygdala by shock may be the unconditioned response relevant for fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electroconvulsive shocks exacerbate the heightened acoustic startle response in stressed rats.

Electroconvulsive therapy (ECT) has been successfully used in the treatment of depression, particularly when the illness is refractory to pharmacological therapy. A recent study has shown that ECT is also effective in reducing both depressive and posttraumatic stress disorder (PTSD) symptoms in patients with major depression (MDD) and co-occurring PTSD. This raises the possibility that ECT might be effective in the treatment of PTSD, a disease whose prevalence has increased substantially in recent years. A characteristic symptom of PTSD is an exaggerated reactivity to startling sounds (acoustic startle response; ASR). In the present study, we investigated the effects of electroconvulsive shocks (ECS) on the ASR, in a rat model of traumatic stress. The animals were subjected to a restraint/tailshock paradigm and then administered ECS. ASR measurements were obtained at several time points following ECS administration. Although ECS had no effect in control rats, it significantly exacerbated the already potentiated ASR in the stressed group. While ECT may prove to be an effective treatment for certain symptoms of co-occurring MDD/PTSD or PTSD alone, it may exacerbate heightened arousal associated with PTSD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in vulnerability to inescapable shock in rats.

The present study determined whether individual differences in neophobia during an open-field pretest predict vulnerability to inescapable electric shock, as measured by 2 tests of learned helplessness in rats. Shuttle-escape latencies and saccharin finickiness increased across groups that had received increasing numbers of inescapable shocks 24 hr earlier. Dispersion in the test measure as well as the percentage of variance explained by pretest neophobia were greater when no or few shocks were delivered in the interpolated stress phase. Pretest neophobia was positively related to stress vulnerability in both tests under these conditions. Further increments in stressor severity overwhelmed even the most stress-resistant rats, thereby decreasing dispersion in the test measure and eliminating the predictive value of pretest neophobia. This pattern of outcomes was more robust for the shuttle-escape measure of helplessness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention, Heart Rate, and Startle Response During Exposure to Trauma-Relevant Pictures: A Comparison of Recent Trauma Victims and Patients With Posttraumatic Stress Disorder.

Victims of a recent trauma were compared with posttraumatic stress disorder (PTSD) patients and healthy controls to assess whether a specific anxiety response and an attentional bias were evident initially or only in chronic PTSD. Heart rate (HR) and startle response were measured, and a dot-probe task was carried out using trauma-relevant pictures. Severely affected recent trauma victims and chronic PTSD patients showed HR acceleration to trauma-related material, which was the only significant group difference. A bias away from trauma-related material was related to severity of intrusions in recent trauma victims, and the bias toward trauma-related material increased with amplitude of the HR response in PTSD patients. A specific anxiety reaction is present initially in severely affected trauma victims. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A sensory-enhanced context facilitates learning and multiple measures of unconditioned stimulus processing in the preweanling rat.

This study tested the hypothesis that increased processing or efficacy of the unconditioned stimulus (US) contributes to the facilitation of trace conditioning that occurs when preweanling rats are conditioned in a novel sensory-rich context. Experiment 1 extended previous findings (D. L. McKinzie & N. E. Spear, 1995) of facilitated acoustic trace conditioning in the 17-day-old rat in a sensory-enhanced versus a home odor context. In the enhanced or more familiar context, Experiment 2 tested rats of this age for degree of spontaneous locomotor activity and ultrasonic vocalizations, activity and ultrasounding in response to shock, and the acoustic startle reflex. The enhanced context resulted in a greater overall activity response to shock, increased ultrasounding to discrete shocks, and a sensitized latency to startle. The results suggest that enhanced US processing in a sensory-rich context is a likely contributor to its facilitative effect on infant learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suppression of an inhibitory jaw reflex by the anticipation of pain in man

Electromyographic recordings (EMGs) were made from the active masseter muscle, of the inhibitory reflex evoked by application of electrical stimuli to the skin of the upper lip in 15 human subjects. In control sequences, the reflex had a mean latency and duration (+/- S.E.M.) of 45.4 +/- 1.3 msec and 47.9 +/- 2.8 msec, respectively. Significant decreases in the reflex as well as increases in heart rate and anxiety levels assessed by a visual analogue scale, occurred when the subjects were stressed by the anticipation of receiving painful electrical stimuli above the ankle (P < 0.00005; Student's t-tests). During such sequences, the magnitude of the reflex measured by integration of the EMG, was reduced by 47.7 +/- 5.6%. This effect involved a reduction in both the duration and depth of the inhibitory wave. It occurred regardless of whether the painful stimuli were applied during or after the recording of the reflex and of whether the baseline activity in the muscle was inadvertently raised or lowered during the stressful sequences. It is concluded that stress induced by the anticipation of pain, can markedly reduce an inhibitory jaw reflex in man by exerting an influence on the reflex pathway prior to the motoneurones.     

Human blink startle during aversive and nonaversive Pavlovian conditioning.

Potentiation of blink startle during aversive and nonaversive Pavlovian single-cue conditioning was assessed in human Ss. In Exp 1 (N?=?89), the conditioning group received paired presentations of a visual CS and an unconditioned stimulus/stimuli (UCS), whereas the control group was presented with a random sequence. The UCS was an electric shock for half the Ss and a nonaversive reaction time (RT) task for the other half. Electrodermal conditioning was evident regardless of the nature of the UCS, but blink potentiation was found only in the conditioning group that had been trained with the aversive UCS. These results were replicated in Exp 2 (N?=?65), in which a nonaversive UCS of increased motivational significance was used. Thus, only aversive conditioning seems to affect the affective valence of the CS, at least as reflected by changes in a skeletal reflex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)