The human startle reflex and alcohol cue reactivity: effects of early versus late abstinence

Discrimination, Stress and Reactivity to Alcohol Cues

Introduction: Our study investigated whether discrimination affects psychologi-cal/physiological stress and alcohol craving.

Method: Participants (N = 92) were asked to recall and write about (a) a neutral, (b) a negative, or (c) a discriminatory experience in the past and then completed a cue-reactivity procedure assessing their alcohol craving. In addition, we assessed levels of perceived stress before and after the discrimination manipulation, chronic substance use and craving, prior perceived discrimination, and strength of racial/ethnic identity.

Results: Results revealed a small effect in which the discrimination condition increased alcohol cue-elicited craving relative to the other conditions. Chronic craving moderated effects of discrimination on cortisol levels. Self-reported stress levels were increased in the discrimination and negative memory conditions relative to baseline. Strength of racial identity served as a protective factor for substance abuse in those who reported chronic high levels of discrimination.

Discussion: We discussed the direct link established between acute exposure to discrimination and craving, and experimental evidence for the relationship between discrimination and self-reported stress, but also addressed potential limitations of this work. It is further discussed how some individual differences factors (e.g., chronic craving) predict physiological stress in discriminatory settings. This work underscored the role of racial identity as a protective factor against alcohol abuse in individuals reporting high levels of discrimination.

Affective startle modulation and psychopathology: Implications for appetitive and defensive brain systems

Startle reflex potentiation versus startle attenuation to unpleasant versus pleasant stimuli likely reflect priming of the defensive versus appetitive motivational systems, respectively. This review summarizes and systemizes the literature on affective startle modulation related to psychopathologies with the aim to reveal underlying mechanisms across psychopathologies. We found evidence for psychopathologies characterized by increased startle potentiation to unpleasant stimuli (anxiety disorders), decreased startle potentiation to unpleasant stimuli (psychopathy), decreased startle attenuation to pleasant stimuli (ADHD), as well as a general hyporeactivity to affective stimuli (depression). Increased versus decreased startle responses to disorder-specific stimuli characterize specific phobia and drug dependence. No psychopathology is characterized by increased startle attenuation to standard pleasant stimuli or a general hyperreactivity to affective stimuli. This review indicates that the defensive and the appetitive systems operate independently mostly in accordance with the motivational priming hypothesis and that affective startle modulation is a highly valuable paradigm to unraveling dysfunctions of the defensive and appetitive systems in psychopathologies as requested by the Research Domain Criteria initiative.

The Modulation of the Startle Reflex as Predictor of Alcohol Use Disorders in a Sample of Heavy Drinkers: A 4-Year Follow-Up Study

BACKGROUND

Previous studies demonstrated that patients with alcohol use disorders (AUDs) show altered startle reflex responses to alcohol-related stimuli. However, there is little information about the role of these altered responses in the development of AUDs. This study examined the startle reflex response to different visual stimuli and the role of these patterns in the development of AUDs in a 4-year follow-up.

METHODS

Two hundred and thirty-nine (nondependent) heavy-drinking participants were selected. In the baseline period, the startle reflex responses to alcohol-related, aversive, appetitive, and neutral pictures were assessed. Startle reflex responses to these pictures were used as predictive variables. Status drinking (alcohol dependence and nondependence) assessed at 4-year follow-up was used as outcome measure.

RESULTS

At the 4-year follow-up assessment, 46% of participants fulfilled DSM-IV alcohol abuse or dependence criteria. Alcohol dependence status was predicted by an attenuated startle reflex response to alcohol-related and aversive pictures.

CONCLUSIONS

This study revealed that an attenuated modulation of startle reflex response to alcohol-related and aversive stimuli could be used as a clinical marker to predict the development of AUDs in participants with previous alcohol consumption.

New mechanisms and perspectives in nicotine withdrawal

Diseases associated with tobacco use constitute a major health problem worldwide. Upon cessation of tobacco use, an unpleasant withdrawal syndrome occurs in dependent individuals. Avoidance of the negative state produced by nicotine withdrawal represents a motivational component that promotes continued tobacco use and relapse after smoking cessation. With the modest success rate of currently available smoking cessation therapies, understanding mechanisms involved in the nicotine withdrawal syndrome are crucial for developing successful treatments. Animal models provide a useful tool for examining neuroadaptative mechanisms and factors influencing nicotine withdrawal, including sex, age, and genetic factors. Such research has also identified an important role for nicotinic receptor subtypes in different aspects of the nicotine withdrawal syndrome (e.g., physical vs. affective signs). In addition to nicotinic receptors, the opioid and endocannabinoid systems, various signal transduction pathways, neurotransmitters, and neuropeptides have been implicated in the nicotine withdrawal syndrome. Animal studies have informed human studies of genetic variants and potential targets for smoking cessation therapies. Overall, the available literature indicates that the nicotine withdrawal syndrome is complex, and involves a range of neurobiological mechanisms. As research in nicotine withdrawal progresses, new pharmacological options for smokers attempting to quit can be identified, and treatments with fewer side effects that are better tailored to the unique characteristics of patients may become available. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

Mediated substance cues: motivational reactivity and use influence responses to pictures of alcohol

This study examined how emotional and physiological responses to pictures of alcoholic or nonalcoholic beverages vary as a function of motivational type and alcohol use. The authors used the limited capacity model of motivated mediated message processing to guide predictions and the motivational activation measure to measure the reactivity of participants' appetitive and aversive motivational systems. Participants viewed and rated 9 pictures of alcoholic beverages and 9 pictures of nonalcoholic beverages. Facial electromyography data were collected during viewing. Overall results show that heavy users respond both more positively and more negatively to pictures of alcoholic beverages than to pictures of nonalcoholic beverages, whereas light users respond more positively overall and more positively to pictures of alcoholic beverages than to pictures of nonalcohol beverages. In addition, heavy use predictably reverses the response predicted by motivational type.

Craving, cue reactivity, and stimulus control among early-stage young smokers: effects of smoking intensity and gender

INTRODUCTION

Smoking initiation usually begins in adolescence, but how and for whom nicotine dependence emerges during this period is unclear. The cue-reactivity paradigm is well suited to examine one marker of dependence: craving-related stimulus control, i.e., the ability of environmental cues to elicit craving to smoke. This study examined the effects of both level of smoking involvement (daily vs. occasional smoking) and gender on reactivity to both smoking and alcohol cues.

METHODS

Young (age range 16-20; 42% female) daily (n = 55) and occasional (n = 52) smokers were exposed to each of three counterbalanced cues: (a) in vivo smoking (e.g., sight, smell, lighting of cigarette), (b) alcohol (e.g., opening, pouring, and smell of preferred beverage), and (c) neutral cue.

RESULTS

Daily smokers exhibited higher levels of tonic (i.e., noncue-elicited) craving than did occasional smokers. Both groups showed significant increases in craving in response to cues (i.e., cue-elicited craving), with little evidence that cue-elicited craving differed between groups. Females were more cue reactive to both the alcohol and smoking cues than males, particularly for the positively reinforced aspects of smoking (i.e., hedonic craving). There were no gender × group interaction effects in response to either the alcohol or the smoking cue.

CONCLUSIONS

Findings show the presence of cue-elicited craving even among occasional smokers and are consistent with literature demonstrating heightened sensitivity to environmental cues among females. Cue-elicited craving may be one mechanism that contributes to the maintenance of smoking behavior and perhaps to the development of nicotine dependence within early stage smokers.

Variables involved in the cue modulation of the startle reflex in alcohol-dependent patients

Cue modulation of the startle reflex is a paradigm that has been used to understand the emotional mechanisms involved in alcohol dependence. Attenuation of the startle reflex has been demonstrated when alcohol-dependent subjects are exposed to alcohol-related stimuli. However, the role of clinical variables on the magnitude of this response is unknown. The objective of this study was to determine the relationship between a number of clinical variables-severity of alcoholism, family history of alcoholism (FHA+), personality traits related to the sensitivity to reward-and the startle reflex response when subjects with alcohol dependence were viewing alcohol-related cues. After detoxification, 98 participants completed self-report instruments and had eye blink electromyograms measured to acoustic startle probes [100-millisecond burst of white noise at 95 dB(A)] while viewing alcohol-related pictures, and standardised appetitive, aversive and neutral control scenes. Ninety-eight healthy controls were also assessed with the same instruments. There were significant differences on alcohol-startle magnitude between patients and controls. Comparisons by gender showed that women perceived alcohol cues and appetitive cues more appetitive than men. Male and female patients showed more appetitive responses to alcohol cues when compared with their respective controls. Our patients showed an appetitive effect of alcohol cues that was positively related to severity of alcohol dependence, sensitivity to reward and a FHA+. The data confirmed that the pattern of the modulation of the acoustic startle reflex reveals appetitive effects of the alcohol cues and extended it to a variety of clinical variables.

The role of context in the processing of alcohol-relevant cues

In line with learning theories of drug addiction, drug-related cues may be viewed as important motivators of continued drug use. They may be differentially effective depending on the context and motivational significance. The present study aimed to test the significance of different contexts in modulating alcohol-related cue reactivity. Pictures depicting alcohol intake or its paraphernalia and pictures without any relation to alcohol intake were varied to depict physical and social contexts or different consumptive contexts associated with full/half-full/empty alcohol beverage containers. We obtained ratings of craving, valence and arousal of the cues as well as skin conductance responses (SCRs) and startle reflex modulation measures from 21 abstinent alcohol-dependent patients, recruited from an addiction treatment center, and 21 matched healthy controls. Social scenes and full glasses or bottles were rated as more pleasant and arousing compared with neutral drinking situations and empty glasses or bottles in patients. Furthermore, we found a decreased startle reflex magnitude to social compared with neutral drinking situations, and both higher SCRs and decreased startle reflex magnitude to full compared with empty glasses or bottles in patients versus controls. These results show that both physical and social and consumptive contexts differentially influence cue reactivity in abstinent alcohol-dependent patients with both social and pub-related physical contexts, and the initial consumptive context eliciting the most appetitive and arousing responses. These data have not only important implications for our understanding of the role of learning in drug dependence but also for treatment, which needs to take these factors into account.

N4 component responses to pre-pulse startle stimuli in young adults: relationship to alcohol dependence

Both physiological and behavioral studies provide evidence to suggest that deficits in frontal cortical control circuits may contribute to the risk for developing alcohol dependence. Event-related potential (ERP) and eye blink responses to startle and short delay prepulse-plus-startle stimuli, and psychiatric diagnoses were investigated in young adult (age 18-30 years) men (n=135) and women (n=205) Mexican Americans. Women displayed a significant increase in the amplitude of the eye blink response to both the startle and pre-pulse-plus-startle stimuli. None of the psychiatric diagnoses were associated with differences in eye blink responses. ERP responses to the startle and prepulse-plus startle stimuli included a negative polarity wave at approximately 400 ms that was of the highest amplitude in the frontal leads (N4S). Women were found to have significantly higher amplitude N4S responses than men. Participants with alcohol dependence demonstrated significantly less inhibition and more facilitation of the N4S component by the pre-pulse stimuli. This finding was not associated with a diagnosis of: any other drug dependence disorder (including nicotine), anxiety or affective disorder, or conduct/antisocial personality disorder. The present study suggests that gender and a lifetime diagnosis of alcohol dependence may selectively contribute to this frontal late wave electrophysiological response to prepulse-plus-startle stimuli.

Hidden Markov models for zero-inflated Poisson counts with an application to substance use

Paradigms for substance abuse cue-reactivity research involve pharmacological or stressful stimulation designed to elicit stress and craving responses in cocaine-dependent subjects. It is unclear as to whether stress induced from participation in such studies increases drug-seeking behavior. We propose a 2-state Hidden Markov model to model the number of cocaine abuses per week before and after participation in a stress-and cue-reactivity study. The hypothesized latent state corresponds to 'high' or 'low' use. To account for a preponderance of zeros, we assume a zero-inflated Poisson model for the count data. Transition probabilities depend on the prior week's state, fixed demographic variables, and time-varying covariates. We adopt a Bayesian approach to model fitting, and use the conditional predictive ordinate statistic to demonstrate that the zero-inflated Poisson hidden Markov model outperforms other models for longitudinal count data.

Heroin reduces startle and cortisol response in opioid-maintained heroin-dependent patients

Heroin dependence (HD) is a chronic relapsing brain disorder characterized by a compulsion to seek and use heroin. Stress is seen as a key factor for heroin use. Methadone maintenance and the prescription of pharmaceutical heroin [diacetylmorphine (DAM)] are established treatments for HD in several countries. The present study examined whether DAM-maintained patients and methadone-maintained patients differ from healthy controls in startle reflex and cortisol levels. Fifty-seven participants, 19 of each group matched for age, sex and smoking status, completed a startle session which included the presentation of 24 bursts of white noise while eye-blink responses to startling noises were recorded. Salivary cortisol was collected three times after awakening, before, during and after the startle session. DAM was administered before the experiment, while methadone was administered afterwards. Both heroin-dependent patient groups exhibited significantly smaller startle responses than healthy controls (P < 0.05). Whereas the cortisol levels after awakening did not differ across the three groups, the experimental cortisol levels were significantly lower in DAM-maintained patients, who received their opioid before the experiment, than in methadone-maintained patients and healthy controls (P < 0.0001). Opioid maintenance treatment for HD is associated with reduced startle responses. Acute DAM administration may suppress cortisol levels, and DAM maintenance treatment may represent an effective alternative to methadone in stress-sensitive, heroin-dependent patients.

Non-treatment laboratory stress- and cue-reactivity studies are associated with decreased substance use among drug-dependent individuals

INTRODUCTION

Human laboratory paradigms for examining stress- or cue-reactivity in substance-dependent individuals often involve exposure to pharmacological, psychosocial or physical laboratory procedures or drug paraphernalia. This study examines whether participation in such studies alters drug-seeking behavior and which patient attributes contribute to increased use.

METHODS

In two separate studies, the relationship between participation and drug use post-study were examined. Cocaine-dependent participants received 1 microg/kg of corticotropin releasing hormone intravenously, underwent the Trier Social Stress Task, and were exposed to drug cues and various measures obtained. Cocaine use for 90 days prior and 28 days following the study was assessed. Methamphetamine-dependent participants were exposed to drug cues and various measures obtained. Methamphetamine use for 90 days prior and 14 days following the study was assessed. Weekly drug use was modeled using a 2-state hidden Markov model assuming two possible underlying states at each week. Bayesian estimation was used. Results are presented as posterior mean odds ratios (OR) and 95% credible intervals (CI).

RESULTS

Participation decreased the odds of remaining in or transitioning to the high use state (cocaine study OR=0.04 [CI=0.01, 0.11]; methamphetamine study OR=0.39 [CI=0.07, 1.70]). In the cocaine study, older age increased the odds of remaining in or transitioning into the high use state (1.66 [CI=0.99, 2.96]). In the methamphetamine study, male gender increased the odds (2.70 [CI=1.10, 6.17]).

CONCLUSION

Stress and cue exposure paradigms were associated with a decreased odds of drug use following participation.

Potentiated startle as a measure of the negative affective consequences of repeated exposure to nicotine in rats

RATIONALE

Elevated acoustic startle amplitude has been used to measure anxiety-like effects of drug withdrawal in humans and animals. Withdrawal from a single opiate administration has been shown to produce robust elevations in startle amplitude ("withdrawal-potentiated startle") that escalate in severity with repeated exposure. Although anxiety is a clinical symptom of nicotine dependence, it is currently unknown whether anxiety-like behavior is elicited during the early stages of nicotine dependence in rodents.

OBJECTIVE

The objective of this study is to examine whether, as is the case with opiates, single or repeated exposure to nicotine can produce withdrawal-potentiated startle.

METHODS

Rats received daily nicotine injections for 14 days, and startle amplitude was tested during spontaneous withdrawal on injection days 1, 7, and 14.

RESULTS

Elevated startle responding was observed during nicotine withdrawal on days 7 and 14 but not on day 1, was greater at higher nicotine doses, and was reduced by a nicotine replacement injection given during an additional test session on day 15. Additional experiments demonstrated that nicotine withdrawal-potentiated startle was reduced by the alpha(2)-adrenergic agonist clonidine and that precipitated withdrawal-potentiated startle could not be induced by injection of the nicotinic acetylcholine receptor antagonist mecamylamine.

CONCLUSIONS

These results suggest that nicotine withdrawal escalates in severity across days, similar to the previously reported escalation of opiate withdrawal-potentiated startle. Potentiated startle may be a reliable measure of withdrawal from different classes of abused drugs and may be useful in the study of the early stages of drug dependence.

Alcohol expectancies and reactivity to alcohol-related and affective cues

Recent conceptualizations of alcohol expectancies relate cognitive schemas to their neurobiological underpinnings; cue reactivity paradigms lend themselves well to testing this broadened conceptual framework. In the present study, we examined the relationship between self-reported alcohol expectancies and responses to alcohol-related and affective picture cues among fifty-five young adults. In addition to traditional subjective and psychophysiological indices of cue reactivity, the startle eyeblink reflex was obtained during picture cue presentations to address both attention-arousal (early probes) and affective-motivational (late probes) aspects of cue processing. Analyses indicated that participants reporting greater positive, arousing, and social alcohol expectancies rated alcohol cues as more pleasant, arousing, and craving-inducing. In addition, participants displayed inhibited startle reactivity to late alcohol cue probes, indicative of an appetitive reaction. Finally, startle responding to early probes indicated that participants with greater alcohol expectancies displayed blunted attention to negative affect cues. Findings are discussed in terms of the utility of the startle reflex and cue reactivity paradigms for clarifying the relationship between alcohol expectancies and motivated attention to salient cues.

Cue-induced auditory evoked potentials in alcoholism

OBJECTIVE

Conditioning processes may convert neutral stimuli to drug-associated stimuli and create an implicit drug memory. Previous studies showed specific psychophysiological reactions to alcohol-associated stimuli differentiating alcohol-dependent subjects from healthy controls. This was shown in evoked potentials using visual and olfactory alcohol-related stimuli.

METHODS

Our study examined the effects of complex alcohol-associated sounds in comparison to complex neutral sounds on electrophysiological event-related potentials and the self-report of craving. We assessed 10 detoxified alcoholics and 10 healthy controls in a cue-reactivity paradigm.

RESULTS

Detoxified alcoholics demonstrated significantly higher alcohol stimulus-induced late P300 and late positive complexes. Subjective baseline craving and stimulus-induced craving only differed significantly between groups in terms of the craving dimension "relief of withdrawal symptoms".

CONCLUSIONS

The results show that auditory stimuli attach importance to stimulus-induced craving in alcoholics. Therapeutic consequences will be discussed.

SIGNIFICANCE

The study examined for the first time the effects of alcohol-associated auditory stimuli on alcohol craving and identifies learning processes as underlying neural mechanisms which support the assumption of an implicit addiction memory in alcoholics.

A preliminary report on the use of virtual reality technology to elicit craving and cue reactivity in cocaine dependent individuals

In the present feasibility study, we developed a 3-dimensional virtual "crack" cocaine environment and evaluated the environment's ability to elicit subjective craving and cue reactivity (i.e., subjective emotional responding, heart rate and skin conductance) in 11 crack cocaine dependent individuals. Each of the seven 3-D crack cocaine scenes in the cocaine environment depicted actors engaging in a range of using-related behaviors (i.e., smoking crack) whereas the neutral environment contained scenes depicted 3-D aquariums with active aquatic life (baseline measures were obtained following immersion in the neutral environment). Results indicated that craving was significantly elevated during the cocaine-related scenes as compared to baseline. Craving varied by scene content, with scenes depicting active cocaine use eliciting the highest levels of craving. Heart rate was significantly higher in four of the scenes with drug use content and positive affect (i.e., happiness) ratings were significantly lower during cocaine scenes as compared to baseline. Overall, the results suggest that a standardized and stimulus rich virtual reality environment effectively elicits craving and physiologic reactivity. Such technology has potential utility in the development and refinement of exposure-based behavioral and pharmacological interventions for substance use disorders.

Gender specific effects of a mild stressor on alcohol cue reactivity in heavy social drinkers

RATIONALE

Stress plays an important role in the development and maintenance of alcohol-abuse. Some of the effects of stress on alcohol-related behaviours, however, appear to be gender-dependent.

AIM

The present study set out to examine the effects of stress on feelings of desire for alcohol, skin conductance response and alcohol consumption in the presence of alcohol-related cues in relation to gender. Participants were heavy non-dependent alcohol drinkers.

METHODS

Thirty-two (16 males) participants drinking more than 21 units of alcohol per week were randomly allocated to undergo the experimental stress (based on the 'Trier Social Stress' Test) or the non-stress procedure before the alcohol cue exposure procedure, during which participants handled and smelled their preferred drink. Mood and saliva cortisol level changes were used as indices of the stress effects, while alcohol craving, skin conductance and alcohol consumption were the cue reactivity measures.

RESULTS

Self ratings of anxiety and tension increased and cortisol levels remained high in the stress compared to the non-stress condition; no gender differences were found. Stress induced gender-specific effects with regard to skin conductance response and alcohol consumption measurements. Stressed females did not show an increase from baseline in the skin conductance response during the alcohol cue-exposure session, which was observed in the non-stressed females; they also consumed less alcohol than males under stress.

CONCLUSION

Female participants respond less to alcohol-related cues when in a negative mood state. Such a finding suggests that females when in a negative mood may be less sensitive to positive incentive processes mediating cue reactivity compared to males.

Craving and startle modification during in vivo exposure to food cues

RATIONALE AND OBJECTIVES

Food craving and reactivity to food cues are related to food intake. Research has shown that both startle magnitude and prepulse inhibition of startle may be useful indices of cue reactivity and drug craving. The goal of this study was to assess the utility of these paradigms for the study of food craving in food-deprived participants.

METHODS

Twenty-nine non-smoking, food-deprived undergraduate participants were exposed to a counterbalanced series of food, cigarette, and neutral cues. During each 4.5-min cue, nine startle probes (102-dB white noise) were presented, and a prepulse (20-ms noise 8 dB above background) preceded 2/3 of the probes by 60 or 120 ms. Subjects were divided into those high and low in food-craving on the basis of subjective craving to food cues. Responses to food cues were compared to smoking cues to control for attention and arousal.

RESULTS

Both probe-alone startle magnitude and percent prepulse inhibition were significantly reduced during the food cue compared to the smoking cue among high food cravers, but not low food cravers. These processes seemed to be independent, as cue-induced changes in prepulse inhibition were uncorrelated with cue effects on probe-alone startle magnitude.

CONCLUSIONS

Both probe-alone startle magnitude and prepulse inhibition are sensitive to cue-induced craving for food, but appear to assess separate processes. Startle methodologies may prove useful in understanding basic processes that regulate food intake.

Assessment of substance cue reactivity: advances in reliability, specificity, and validity

An arousal-control and cross-over design was used to evaluate the reliability, specificity, and validity of the Normative Appetitive Picture System (NAPS), a cue exposure protocol with sets of visual alcohol, cigarette, and control cues. The authors also examined the utility of conceptualizing cue reactivity as a multidimensional phenomenon involving independent approach and avoidance dimensions. University student participants (n=369) rated multiple cue images in terms of arousing properties and capacity to elicit separate approach and avoidance inclinations. They also completed a battery of substance-related individual-difference measures. Results indicated that NAPS protocol reactivity profiles had good reliability and high specificity across cue types and individuals with different substance use histories. Avoidance reactivity independently predicted self-reports of substance-related behaviors, after controlling for approach reactivity.

Reactivity to Alcohol-Related Cues: Relationship Among Cue Type, Motivational Processes, and Personality

This study examined the relationship between personality traits implicated in the drinking literature (i.e., sensation seeking and anxiety) and reactivity to 2 different alcohol cues. The opportunity to consume alcohol was manipulated, and differences in urge and affective reactivity were assessed. Gray's (1987) model of impulsive sensation seeking and anxiety was adopted to investigate relationships between personality and responses to the appetitive (consumption) and aversive (no consumption, nonrewarding) alcohol cues in 40 regular social drinkers. The consumption cue produced increases in appetitive motivation and positive correlations with sensation-seeking traits. The no-consumption cue produced increases in aversive motivation and positive correlations with anxiety-related traits. It was concluded that Gray's model of impulsive sensation seeking and anxiety may provide a useful framework for examining the personality correlates of cue reactivity to different cues.

A review of the modulation of the startle reflex by affective states and its application in psychiatry

OBJECTIVE

To provide an overview of startle reflex methodologies applied to the examination of emotional and motivational states in humans and to review the findings in different forms of psychopathology.

METHODS

Pertinent articles were searched mostly via MEDLINE and PsycINFO.

RESULTS

The startle reflex is a non-invasive translational tool of research that bridges the gap between animal and human investigations. Startle is used to study fear and anxiety, affective disturbances, sensitization, motivational states, and homeostasis.

CONCLUSIONS

The startle reflex is highly sensitive to various factors that are of interest in the studies of emotional disorders and has promoted new areas of investigations in psychiatry. However, research in psychiatry is still in its infancy and most findings await replication. Future progress will benefit from the development of innovative and powerful designs tailored to investigate specific disorders.

SIGNIFICANCE

The startle reflex has utility as a research tool to examine trauma-related disorders, fear learning, drug addiction, and to contrast affective states and emotional processing across diagnostic groups, but its usefulness as a diagnostic tool is limited.