Startle reflex modulation during exposure to pleasant and unpleasant odors

Myoclonus and other jerky movement disorders

Myoclonus and other jerky movements form a large heterogeneous group of disorders. Clinical neurophysiology studies can have an important contribution to support diagnosis but also to gain insight in the pathophysiology of different kind of jerks. This review focuses on myoclonus, tics, startle disorders, restless legs syndrome, and periodic leg movements during sleep. Myoclonus is defined as brief, shock-like movements, and subtypes can be classified based the anatomical origin. Both the clinical phenotype and the neurophysiological tests support this classification: cortical, cortical-subcortical, subcortical/non-segmental, segmental, peripheral, and functional jerks. The most important techniques used are polymyography and the combination of electromyography-electroencephalography focused on jerk-locked back-averaging, cortico-muscular coherence, and the Bereitschaftspotential. Clinically, the differential diagnosis of myoclonus includes tics, and this diagnosis is mainly based on the history with premonitory urges and the ability to suppress the tic. Electrophysiological tests are mainly applied in a research setting and include the Bereitschaftspotential, local field potentials, transcranial magnetic stimulation, and pre-pulse inhibition. Jerks due to a startling stimulus form the group of startle syndromes. This group includes disorders with an exaggerated startle reflex, such as hyperekplexia and stiff person syndrome, but also neuropsychiatric and stimulus-induced disorders. For these disorders polymyography combined with a startling stimulus can be useful to determine the pattern of muscle activation and thus the diagnosis. Assessment of symptoms in restless legs syndrome and periodic leg movements during sleep can be performed with different validated scoring criteria with the help of electromyography.

The origin of smiling, laughing, and crying: The defensive mimic theory

Why do we leak lubricant from the eyes to solicit comfort from others? Why do we bare our teeth and crinkle our faces to express non-aggression? The defensive mimic theory proposes that a broad range of human emotional expressions evolved originally as exaggerated, temporally extended mimics of the fast, defensive reflexes that normally protect the body surface. Defensive reflexes are so important to survival that they cannot be safely suppressed; yet they also broadcast information about an animal's internal state, information that can potentially be exploited by other animals. Once others can observe and exploit an animal's defensive reflexes, it may be advantageous to the animal to run interference by creating mimic defensive actions, thereby manipulating the behaviour of others. Through this interaction over millions of years, many human emotional expressions may have evolved. Here, human social signals including smiling, laughing and crying, are compared component-by-component with the known, well-studied features of primate defensive reflexes. It is suggested that the defensive mimic theory can adequately account for the physical form of not all, but a large range of, human emotional expression.

Identification of new behavioral parameters to assess odorant hedonic value in humans: A naturalistic approach

BACKGROUND

When you smell an odorant, your first reaction will certainly be either I like it or I dislike it. This primary reaction is a reflection of what is called the "hedonic value" of the odor. Very often, this hedonic value dominates the olfactory percept, more than olfactory identification or intensity. This component of olfactory perception is of primary importance for guiding behavior: avoiding danger (the smell of smoke, gas, etc.), consuming food, or seduction. Olfactory hedonics can be assessed using a large number of methods in humans, including psychophysical measures, autonomic responses, measurement of facial expressions or peripheral nervous activity. All of these techniques have their limitations: subjectivity, invasiveness, need for expertise, etc. A NEW METHOD: The olfactory system is closely linked to the reward system, the role of which is to mediate motivated behavior. In this context, we propose that the capacity odorants have of recruiting the reward system and thus inducing motivated behavior can be used to identify new behavioral parameters to assess odor hedonic value in humans.

RESULTS

We recorded freely moving human participants exploring odors emanating from flasks, and showed that five parameters linked to motivated behavior were closely linked to odor hedonics: speed of approach to the nose and withdrawal of the flask containing the odorant, distance between flask and nose, number of samplings, and withdrawal distance (maximal distance between nose and flask after odor sampling).

CONCLUSIONS

We highlighted new non-verbal and non-invasive parameters to evaluate olfactory hedonics in humans based on the assessment of odor-motivated behavior.

Disgusting odours affect the characteristics of the Adaptive Force in contrast to neutral and pleasant odours

The olfactomotor system is especially investigated by examining the sniffing in reaction to olfactory stimuli. The motor output of respiratory-independent muscles was seldomly considered regarding possible influences of smells. The Adaptive Force (AF) characterizes the capability of the neuromuscular system to adapt to external forces in a holding manner and was suggested to be more vulnerable to possible interfering stimuli due to the underlying complex control processes. The aim of this pilot study was to measure the effects of olfactory inputs on the AF of the hip and elbow flexors, respectively. The AF of 10 subjects was examined manually by experienced testers while smelling at sniffing sticks with neutral, pleasant or disgusting odours. The reaction force and the limb position were recorded by a handheld device. The results show, inter alia, a significantly lower maximal isometric AF and a significantly higher AF at the onset of oscillations by perceiving disgusting odours compared to pleasant or neutral odours (p < 0.001). The adaptive holding capacity seems to reflect the functionality of the neuromuscular control, which can be impaired by disgusting olfactory inputs. An undisturbed functioning neuromuscular system appears to be characterized by a proper length tension control and by an earlier onset of mutual oscillations during an external force increase. This highlights the strong connection of olfaction and motor control also regarding respiratory-independent muscles.

A network model of affective odor perception

The affective appraisal of odors is known to depend on their intensity (I), familiarity (F), detection threshold (T), and on the baseline affective state of the observer. However, the exact nature of these relations is still largely unknown. We therefore performed an observer experiment in which participants (N = 52) smelled 40 different odors (varying widely in hedonic valence) and reported the intensity, familiarity and their affective appraisal (valence and arousal: V and A) for each odor. Also, we measured the baseline affective state (valence and arousal: BV and BA) and odor detection threshold of the participants. Analyzing the results for pleasant and unpleasant odors separately, we obtained two models through network analysis. Several relations that have previously been reported in the literature also emerge in both models (the relations between F and I, F and V, I and A; I and V, BV and T). However, there are also relations that do not emerge (between BA and V, BV and I, and T and I) or that appear with a different polarity (the relation between F and A for pleasant odors). Intensity (I) has the largest impact on the affective appraisal of unpleasant odors, while F significantly contributes to the appraisal of pleasant odors. T is only affected by BV and has no effect on other variables. This study is a first step towards an integral study of the affective appraisal of odors through network analysis. Future studies should also include other factors that are known to influence odor appraisal, such as age, gender, personality, and culture.

Alteration of the affective modulation of the startle reflex during antidepressant treatment

Whereas the amplitude of the startle reflex varies with stimulus valence in the normal population, a lack of this affective modulation has been reported in patients with major depressive disorder. The present study sought to clarify blunted startle modulation as a feature of depression by comparing 16 patients diagnosed with major depression prior to and after 2 weeks of SSRI treatment, and 16 healthy controls. The affect-modulated startle reflex paradigm and the Self-Assessment Manikin were used to probe affective reactivity. In addition, a preliminary analysis of change in affective reactivity pattern was performed with depressed patients who could be assessed in the eighth week of treatment (n = 13). The control group showed a linear trend in response across valence categories, which was stable over sessions. Blunted affective reactivity was observed only in the patients and persisted after 2 weeks of treatment. Nevertheless, a linear trend could be detected in the eighth week of treatment. These findings confirm that the affective reactivity is blunted in depression and provide initial evidence for the lack of change in the early phase of SSRI antidepressant treatment. Nevertheless, in a small group, the emergence of a linear trend in response was evident later with treatment. Large-scale studies are required to assess the relation between the treatment response and the change in affective modulation of the startle reflex, as a potential biomarker.

Odours and incontinence: What does the nose know?

The fear of producing malodours that can be detected by others is a daily cause of anxiety for millions of people with incontinence. For many, the risk-whether real or imagined-that leaked waste products will be detectable by odour is sufficiently concerning to result in limitations on many types of activities. However, worry about personal odours can sensitise our olfactory system and cause us to be more aware of odours that may otherwise not be perceptible. In addition, heightened olfactory attention can often lead to odour misattributions, such as when we erroneously identify our body as the source of an odour that may simply be present in the environment. Odours produced by our bodies (endogenous odours) do enjoy a greater access to emotional brain centers and are processed faster than general odours. Here we provide examples from both everyday life and laboratory studies to explain how and why the olfactory system is unique among our sensory systems and how this knowledge can provide insights to our concerns about smell and incontinence and inform the development of products and solutions for incontinence.

Defensive reflexes in people with pain – a biomarker of the need to protect? A meta-analytical systematic review

Upregulation of defensive reflexes such as the nociceptive flexion reflex (NFR) has been attributed to sensitisation of peripheral and spinal nociceptors and is often considered biomarkers of pain. Experimental modulation of defensive reflexes raises the possibility that they might be better conceptualised as markers of descending cognitive control. Despite strongly held views on both sides and several narrative reviews, there has been no attempt to evaluate the evidence in a systematic manner. We undertook a meta-analytical systematic review of the extant English-language literature from inception. Thirty-six studies satisfied our a priori criteria. Seventeen were included in the meta-analysis. Reflexive threshold was lower in people with clinical pain than it was in pain-free controls, but reflex size, latency, and duration were unaffected. The pattern of difference was not consistent with sensitisation of nociceptive neurones, as these changes were not isolated to the affected body part but was more consistent with top-down cognitive control reflective of heightened protection of body tissue. The pattern of modulation is dependent on potentially complex evaluative mechanisms. We offer recommendations for future investigations and suggest that defensive reflex threshold may reflect a biomarker of a broader psychological construct related to bodily protection, rather than sensitisation of primary nociceptors, spinal nociceptors, or pain.

Effect of stress and attention on startle response and prepulse inhibition

The startle reflex magnitude can be modulated when a weak stimulus is presented before the onset of the startle stimulus, a phenomenon termed prepulse inhibition (PPI). Previous research has demonstrated that emotional processes can modulate PPI and startle intensity, but the available evidence is inconclusive. In order to obtain additional evidence in this domain, we conducted two experiments intended to analyze the effect of induced stress and attentional load on PPI and startle magnitude. Specifically, in Experiment 1 we used a between subject strategy to evaluate the effect on startle response and PPI magnitude of performing a difficult task intended to induce stress in the participants, as compared to a group exposed to a control task. In Experiment 2 we evaluated the effect of diverting attention from the acoustic stimulus on startle and PPI intensity. The results seem to indicate that induced stress can reduce PPI, and that startle reflex intensity is reduced when attention is directed away from the auditory stimulus that induces the reflex.

The blink reflex magnitude is continuously adjusted according to both current and predicted stimulus position with respect to the face

The magnitude of the hand-blink reflex (HBR), a subcortical defensive reflex elicited by the electrical stimulation of the median nerve, is increased when the stimulated hand is close to the face (‘far–near effect’). This enhancement occurs through a cortico-bulbar facilitation of the polysynaptic medullary pathways subserving the reflex. Here, in two experiments, we investigated the temporal characteristics of this facilitation, and its adjustment during voluntary movement of the stimulated hand. Given that individuals navigate in a fast changing environment, one would expect the cortico-bulbar modulation of this response to adjust rapidly, and as a function of the predicted spatial position of external threats. We observed two main results. First, the HBR modulation occurs without a temporal delay between when the hand has reached the stimulation position and when the stimulus happens (Experiments 1 and 2). Second, the voluntary movement of the hand interacts with the ‘far–near effect’: stimuli delivered when the hand is far from the face elicit an enhanced HBR if the hand is being moved towards the face, whereas stimuli delivered when the hand is near the face elicit an enhanced HBR regardless of the direction of the hand movement (Experiment 2). These results indicate that the top-down modulation of this subcortical defensive reflex occurs continuously, and takes into account both the current and the predicted position of potential threats with respect to the body. The continuous control of the excitability of subcortical reflex circuits ensures appropriate adjustment of defensive responses in a rapidly-changing sensory environment.

The Scent of Blood: A Driver of Human Behavior?

The scent of blood is potentially one of the most fundamental and survival-relevant olfactory cues in humans. This experiment tests the first human parameters of perceptual threshold and emotional ratings in men and women of an artificially simulated smell of fresh blood in contact with the skin. We hypothesize that this scent of blood, with its association with injury, danger, death, and nutrition will be a critical cue activating fundamental motivational systems relating to either predatory approach behavior or prey-like withdrawal behavior, or both. The results show that perceptual thresholds are unimodally distributed for both sexes, with women being more sensitive. Furthermore, both women and men’s emotional responses to simulated blood scent divide strongly into positive and negative valence ratings, with negative ratings in women having a strong arousal component. For women, this split is related to the phase of their menstrual cycle and oral contraception (OC). Future research will investigate whether this split in both genders is context-dependent or trait-like.

Is there a negative interpretation bias in depressed patients? An affective startle modulation study

BACKGROUND/AIMS

Scientists proposed that patients with depression favour negative interpretations when appraising ambiguity. As self-report measures seem prone to response bias, implicit measures of emotional valence should be additionally used.

METHODS

A total of 16 patients with depression and 19 controls underwent an acoustic imagery task comprising neutral and negative words, as well as ambiguous words that could be understood either way. Affective startle modulation and direct interrogation were used to assess implicit and explicit emotional valence, respectively. We expected a negative bias for ambiguous words in the patient group, resulting in augmented startle magnitudes and preference for negative interpretations of the ambiguous words in the interrogation.

RESULTS

Surprisingly, both groups preferred neutral interpretations and showed augmented startle magnitudes to ambiguous words. Furthermore, both groups displayed an emotional startle potentiation for negative words.

CONCLUSION

In summary, our results do not confirm a negative interpretation bias or a blunted emotional response in patients with major depression. The mismatch between self-report and affective startle reaction to ambiguous targets might reflect defensive mobilization or attention effects.

Hedonic appreciation and verbal description of pleasant and unpleasant odors in untrained, trainee cooks, flavorists, and perfumers

Olfaction is characterized by a salient hedonic dimension. Previous studies have shown that these affective responses to odors are modulated by physicochemical, physiological, and cognitive factors. The present study examined expertise influenced processing of pleasant and unpleasant odors on both perceptual and verbal levels. For this, performance on two olfactory tasks was compared between novices, trainee cooks, and experts (perfumers and flavorists): Members of all groups rated the intensity and pleasantness of pleasant and unpleasant odors (perceptual tasks). They were also asked to describe each of the 20 odorants as precisely as possible (verbal description task). On a perceptual level, results revealed that there were no group-related differences in hedonic ratings for unpleasant and pleasant odors. On a verbal level, descriptions of smells were richer (e.g., chemical, olfactory qualities, and olfactory sources terms) and did not refer to pleasantness in experts compared to untrained subjects who used terms referring to odor sources (e.g., candy) accompanied by terms referring to odor hedonics. In conclusion, the present study suggests that as novices, experts are able to perceptually discriminate odors on the basis of their pleasantness. However, on a semantic level, they conceptualize odors differently, being inclined to avoid any reference to odor hedonics.

A psychophysiological investigation of laterality in human emotion elicited by pleasant and unpleasant film clips

BACKGROUND

Research on laterality in emotion suggests a dichotomy between the brain hemispheres. The present study aimed to investigate this further using a modulated startle reflex paradigm.

METHODS

We examined the effects of left and the right ear stimulation on the modulated startle reflex (as indexed by eyeblink magnitude, measured from the right eye) employing short (2 min) film clips to elicit emotions in 16 right-handed healthy participants. The experiment consisted of two consecutive sessions on a single occasion. The acoustic startle probes were presented monaurally to one of the ears in each session, counterbalanced across order, during the viewing of film clips.

RESULTS

The findings showed that eyeblink amplitude in relation to acoustic startle probes varied linearly, as expected, from pleasant through neutral to unpleasant film clips, but there was no interaction between monaural probe side and foreground valence.

CONCLUSIONS

Our data indicate the involvement of both hemispheres when affective states, and associated startle modulations, are produced, using materials with both audio and visual properties. From a methodological viewpoint, the robustness of film clip material including audio properties might compensate for the insufficient information reaching the ipsilateral hemisphere when using static pictures. From a theoretical viewpoint, a right ear advantage for verbal processing may account for the failure to detect the expected hemispheric difference. The verbal component of the clips would have activated the left hemisphere, possibly resulting in an increased role for the left hemisphere in both positive and negative affect generation.

The Use of Semantic Differential Scaling to Define the Multi-Dimensional Representation of Odors

The mental representation elicited by smelling an odor often consists of multiple sensory and affective dimensions, yet, the richness of this elaboration is difficult to capture using methods to rate the intensity of these factors in isolation. Attempts to use language descriptors for olfactory experience have also been shown to be rather limited; among non-specialists, there is no universally accepted system for describing odors, leading to greater reliance on specific item associations. In this study we explored the utility of semantic differential scaling for illustrating the various dimensions of olfactory experience. 300 volunteers rated thirty distinct odorants using 50 SDS adjectives. Three factors emerged from the analysis (based on 17 adjective-pairs) accounting for 53% of the variance, and corresponding to the evaluation, potency and activity dimensions identified for other stimulus types. SD scaling appears to be a viable method for identifying the multiple dimensions of mental representation evoked when smelling an odorant and may prove a useful tool for both consumer and basic research alike. PRACTICAL APPLICATIONS: Although numerous methods of classifying odors have been developed, little agreement has been achieved on the dimensions that are useful to both basic and consumer research. The identification of a set of Semantic Differential adjectives which are relevant to olfactory experience can become a useful tool for classifying the qualitative and affective basis on which odorants differ.. In particular, the degree to which odorants evokes multi-dimensional representations from other sensory modalities (visual, auditory, somatosensory or gustatory), can be usefully applied in the arena of product development both within and across cultures.

Appetitive odor-cue conditioning attenuates the acoustic startle response in rats

We here show that a neutral odor previously paired with a positive emotional context is an effective stimulus for attenuating the acoustic startle response (ASR) in rats. Olfactory cues can, therefore, be effectively used in the startle probe procedure for appetitive conditioning. This cue-induced reduction in ASR is not related to attentional alterations or a more general arousal by odor presentation, the conditioned olfactory cue rather elicits a pleasant emotional state during which the ASR is inhibited. This odor conditioned "pleasure" attenuation of the startle response might, therefore, provide a new effective operational measure for the hedonic aspects of reward.

Olfactory Event-Related Potentials Reflect Individual Differences in Odor Valence Perception

Investigating the neural substrates of perceived quality in olfaction using different odorants is intrinsically difficult. By utilizing individual differences in perceived quality of the odor of androstenone, we obtained a continuum of individual differences in rated valence of the same stimulus allowing investigations of its manifestation in the olfactory event-related potentials (ERPs). In an initial group consisting of 43 individuals that were screened for their verbal descriptors and sensitivity for the odor of androstenone, 22 normosmic volunteers were chosen forming 2 distinct groups with regard to verbal labels ("body odor" and "nonbody odor") for androstenone while maintaining chemical structure, concentration, and intensity constant. In the main experiment, these participants rated both intensity and pleasantness of androstenone during the recording of olfactory ERPs. There was a significant difference in rated valence between the groups but not in intensity. Participants in the body odor label group had larger amplitudes of the late positive ERP component than those in the nonbody odor label group. A negative correlation between valence and amplitudes of the late positive component for androstenone indicated that these differences were mediated by the difference in odor valence between the 2 groups. This was further supported by a comparison of ERP peaks in response to stimulation with androstenone and the invariably unpleasant hydrogen sulfide that had been used as a control. Altogether, the results suggest that the late positive component reflects the processing of odor valence. Future olfactory studies with the aim of assessing the dimension of pleasantness would benefit from the use of these interindividual differences in the perception of a specific odor.

Lateralization of the startle reflex circuit in humans: An examination with monaural probes following unilateral temporal lobe resection

Startle reflex (SR) modulation elicited by monaural probes during affective picture viewing was investigated in patients following left temporal lobectomy (LTL; n = 8) and right temporal lobectomy (RTL; n = 10) and in controls (n = 18). All patients had undergone anteromedial temporal lobe (ATL) resection. LTL participants exhibited attenuated overall SR magnitude. Affective SR modulation in controls was significant for left ear probes, at both eyes, but not for right ear probes. RTL but not LTL participants displayed significant startle attenuation during pleasant picture viewing. Results suggest that monaural startle probes primarily activate structures in the ipsilateral ATL and that the ATLs are interconnected, with the left ATL more critical in perceiving arousing properties of affective stimuli, necessary for affective SR modulation.

Emotion, motivation, and the brain: Reflex foundations in animal and human research

This review will focus on a motivational circuit in the brain, centered on the amygdala, that underlies human emotion. This neural circuitry of appetitive/approach and defensive/avoidance was laid down early in our evolutionary history in primitive cortex, sub-cortex, and mid-brain, to mediate behaviors basic to the survival of individuals and the propagation of genes to coming generations. Thus, events associated with appetitive rewards, or that threaten danger or pain, engage attention and prompt information gathering more so than other input. Motive cues also occasion metabolic arousal, anticipatory responses, and mobilize the organism to prepare for action. Findings are presented from research with animals, elucidating these psychophysiological (e.g., cardiovascular, neuro-humoral) and behavioral (e.g., startle potentiation, "freezing") patterns in emotion, and defining their mediating brain circuits. Parallel results are described from experiments with humans, showing similar activation patterns in brain and body in response to emotion cues, co-varying with participants' reports of affective valence and increasing emotional arousal.

Affective modulation of somatosensory-evoked potentials elicited by tactile stimulation

The present investigation was aimed to evaluate the influence of emotional valence on brain correlates of non-painful somatosensory processing. For this purpose, we examined changes on the somatosensory-evoked potentials (SEP) elicited by frequent and deviant tactile stimuli (probability 14%) when subjects were viewing affective pictures. Twenty healthy volunteers aged between 19 and 47 years old participated in the study. The P50, N80, and P200 components of the SEP, as well as the P200 component of the visual-evoked potentials (VEP) elicited by the affective pictures were analyzed. Overall, a significant P50 amplitude reduction was observed when subjects were viewing unpleasant pictures, in comparison to pleasant pictures. Furthermore, larger SEP amplitudes were obtained in response to the deviant than to the frequent stimuli. In addition, unpleasant pictures elicited larger P200 amplitudes of the VEP than pleasant. Data suggest that affective stimuli may modulate the early processing of somatosensory information in the brain, probably reflecting the existence of an adaptive perceptual/attentional mechanism to motivationally relevant stimuli.

Apomorphine effects on emotional modulation of the startle reflex in rats

RATIONALE

Emotional modulation of the startle reflex in the rat may be used to assess whether activation of dopamine receptors specifically increases hedonia, incentive, fear or arousal.

OBJECTIVES

The objective of the study is to determine the effects of apomorphine (0.8 mg/kg s.c.) on the startle reflex of rats (72 male Sprague-Dawley rats) exposed to one of three affective conditions. These conditions were negative affective stimulus (exposure to cat smell), positive affective stimulus (availability of a 20% sucrose solution), neutral stimulus (no additional affective stimulus) and one of two appetitive "drive" states (food deprived or non-food deprived).

METHODS

The startle response (whole-body flinch response) was measured after presentation of a range of intensities of acoustic stimuli (65-120 dB, 40-ms duration white noise). The resulting sigmoidal stimulus intensity-response magnitude (SIRM) curves were fitted using a logistic regression procedure, and features of these functions were abstracted for analysis.

RESULTS

Maximal startle amplitudes were increased by the negative affect (fear) stimulus in non-food-deprived rats and decreased by the positive affect stimulus in food-deprived rats. Apomorphine mimicked the effects of food deprivation under both affect conditions, but also produced an effect in food-deprived rats similar to that of the positive affect condition.

CONCLUSIONS

The results are consistent with both a positive incentive effect and a direct hedonic action of apomorphine, but inconsistent with a role in general arousal. In addition, a method of analysing SIRM functions with logistic regressions is introduced as a useful means of standardising startle reflex measurements.

Information processing in the mammalian olfactory system

Recently, modern neuroscience has made considerable progress in understanding how the brain perceives, discriminates, and recognizes odorant molecules. This growing knowledge took over when the sense of smell was no longer considered only as a matter for poetry or the perfume industry. Over the last decades, chemical senses captured the attention of scientists who started to investigate the different stages of olfactory pathways. Distinct fields such as genetic, biochemistry, cellular biology, neurophysiology, and behavior have contributed to provide a picture of how odor information is processed in the olfactory system as it moves from the periphery to higher areas of the brain. So far, the combination of these approaches has been most effective at the cellular level, but there are already signs, and even greater hope, that the same is gradually happening at the systems level. This review summarizes the current ideas concerning the cellular mechanisms and organizational strategies used by the olfactory system to process olfactory information. We present findings that exemplified the high degree of olfactory plasticity, with special emphasis on the first central relay of the olfactory system. Recent observations supporting the necessity of such plasticity for adult brain functions are also discussed. Due to space constraints, this review focuses mainly on the olfactory systems of vertebrates, and primarily those of mammals.

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.

Temporal course of emotional startle modulation in schizophrenia patients

The temporal course of startle reflex modulation to emotional pictures was investigated in 49 relatively asymptomatic schizophrenia outpatients and 46 normal controls. Participants viewed pleasant, neutral and unpleasant pictures, which were presented for 6 s and acoustic startle probes were delivered at five different times after picture onset. Replicating previous findings schizophrenia patients showed the same affective modulation of the startle reflex as healthy controls when probes were presented later during the picture-viewing period (3800 ms). For the early probe times (300 and 800 ms), affective pictures proved to be the effective prepulse stimuli resulting in a clear Prepulse inhibition (PPI) effect in both groups. In contrast to previous findings, the PPI of startle response was not stronger during processing emotional stimuli relative to neutral stimuli. For control subjects, blink reflexes were larger for unpleasant pictures compared with neutral and pleasant pictures, representing an early activation of motivational systems. Schizophrenia patients on the other hand, did not show this early affective modulation of the acoustic startle reflex.

The defense system of fear: behavior and neurocircuitry

Fear can be conceived as a functional defense behavior system representing a part of the innate species-specific behavioral repertoire (ethogram), basic to the survival of individuals and species. Its function is to protect living beings against dangerous, threatening and aversive situations. A distinction is made between anticipatory defense behaviors released by potential dangers and those elicited by effective dangers, especially predators. The neural mechanisms serving the defense system constitute a hierarchical network with the amygdala as point of convergence of the various threatening stimuli. The central nucleus of the amygdala projects to the midbrain periaqueductal gray (PAG), the hypothalamus and the brainstem which coordinate various defensive responses such as flight, defensive fight, freezing, avoidance reactions, submissive postures, tonic immobilization, hypoalgesia and autonomic arousal. These circuits may be activated either by unconditioned or conditioned stimuli.

Perceptual, affective, and cognitive judgments of odors: pleasantness and handedness effects

The present study sought to examine the differential processing of pleasant, neutral, and unpleasant odors. The effects of the nostril stimulated (left or right) and the type of judgment (perceptual, affective, or cognitive) performed on the olfactory stimuli were also studied. To this end, 64 subjects were asked to smell pleasant, neutral, and unpleasant odors under four conditions (detection, intensity, pleasantness, and familiarity tasks). The participants were to perform these tasks as quickly as possible, while response times were recorded. The results showed that (i) unpleasant odors were assessed more rapidly than neutral or pleasant odors, and that this was specifically true (ii) during right nostril stimulation, and (iii) during pleasantness assessment, suggesting possible differential cerebral hemisphere involvement, with a right-side advantage for processing of unpleasant affect in olfaction. A handedness effect on familiarity judgment is also discussed.

Affective modulation and prepulse inhibition of startle among undergraduates high and low in behavioral inhibition and approach

Valence modulation and prepulse inhibition of startle were examined among 80 undergraduates scoring in the upper and lower quartiles of self-report measures of behavioral inhibition (BIS) and behavioral approach (BAS). Participants viewed a series of pleasant, neutral, and unpleasant pictures. Acoustic startle probes (102 dB) were presented during most pictures and during intertrial intervals, and a prepulse (120-ms SOA) preceded half of the probes. Valence modulation on no-prepulse trials was greater among high-BAS than low-BAS participants. Consistent with theory regarding behavioral approach, post hoc tests demonstrated robust inhibition during pleasant versus neutral pictures among high-BAS participants, but not low-BAS participants. Valence modulation was reliable among high-BIS but not low-BIS participants, but the group difference was not significant. Contrary to our prediction, prepulse inhibition tended to be greater among high-BAS than low-BAS participants. The present data call attention to the role of individual differences in pleasant affective experience in startle modification.

Asymmetry of pleasant vs. unpleasant odor processing during affective judgment in humans

The objective of the present study was to investigate interactions between odor hedonic tone, perceived odor intensity, olfactory judgments and stimulated nostril laterality. Subjects were stimulated in the right and the left nostril separately, with two odors: vanillin (pleasant); and indole (unpleasant). They had two tasks to perform: an intensity judgment; and an affective judgment. Two concentrations (one strong and one weak) of each odor were presented. Odors were presented for a short period corresponding to one inhalation (about 1 s). The inter-stimulus interval was always 30 s. The nostril stimulated and task presentation order were counterbalanced according to a Latin square. Odor presentation order was randomized for each subject. Results indicated that response times for unpleasant odors were significantly shorter than for pleasant odors during affective judgment and right nostril stimulation, indicating greater right hemisphere efficiency for the decoding of unpleasant affects induced by odors.

Psychophysiological and subjective indicators of aversive pavlovian conditioning in generalized social phobia

Aversive conditioning has been proposed as an important etiologic mechanism in social phobia; however, empirical evidence is scarce and has not relied on a detailed analysis of the acquisition and extinction of the conditioned emotional response. Fourteen men sustaining generalized social phobia and 19 healthy control subjects participated in differential aversive conditioning with two neutral faces as conditioned stimuli and an aversive odor as unconditioned stimulus. Subjective and peripheral physiological responses were obtained. Both groups were successfully conditioned as reflected by differential subjective (valence, arousal, subjective unconditioned stimulus expectancy) and peripheral physiological responses (skin conductance, startle response). There was no evidence for an enhanced conditionability in the social phobics; however, they showed an enhanced unconditioned stimulus expectancy, especially for the nonreinforced conditioned stimuli during acquisition, and a delayed extinction of the conditioned skin conductance response as well as a certain dissociation between subjective and physiological responses.The enhanced unconditioned stimulus expectancy during acquisition and the overall elevated subjective arousal suggest that, under threat, subjects with generalized social phobia may be more prone to associate neutral social cues and an aversive outcome. Furthermore, delayed extinction of the conditioned response seems to contribute to the etiology and maintenance of generalized social phobia.

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

This study investigated the human eyeblink startle reflex as a measure of alcohol cue reactivity. Alcohol-dependent participants early (n = 36) and late (n = 34) in abstinence received presentations of alcohol and water cues. Consistent with previous research, greater salivation and higher ratings of urge to drink occurred in response to the alcohol cues. Differential salivary and urge responding to alcohol versus water cues did not vary as a function of abstinence duration. Of special interest was the finding that startle response magnitudes were relatively elevated to alcohol cues, but only in individuals early in abstinence. Affective ratings of alcohol cues suggested that alcohol cues were perceived as aversive. Methodological and theoretical implications of the findings are discussed.

Influence of affective and cognitive judgments on autonomic parameters during inhalation of pleasant and unpleasant odors in humans

Hedonic tone is so salient in odor perception that several authors have used odors to induce affective states. Various studies have shown that the electrophysiological and psychophysiological response patterns induced by olfactory stimuli are different for pleasant and unpleasant odors, and that these types of odor activate brain structures differentially. These results suggest that odors are first categorized according to pleasantness. The objective of the present work was to study the possible existence of an involuntary affective categorization in olfaction. Given that certain variations in the autonomic system, such as skin conductance amplitude and heart rate, are not under the voluntary control of human subjects, we used such psychophysiological methods for this investigation. Our results indicate that unpleasant odors provoke heart-rate acceleration during both a smelling task (control condition: a task in which subjects had only to inhale odors) and a pleasantness judgment, but not during a familiarity judgment. These results suggest that subjects involuntarily categorize odors by their pleasantness.

Olfactory-mediated fear-potentiated startle

Recently, R. Richardson, A. Vishney, and J. Lee (1999) reported that ambient odor cues that were previously paired with footshock potentiate the acoustic startle response in rats. The authors of the present study extend those findings by using a discrete 4-s amyl acetate odor paired with footshock to address several parametric issues that might be important for using odorants as conditioned stimuli (CSs) in this paradigm. Amyl acetate (5%) had no significant effect on startle in untrained rats but did potentiate startle in rats that received 1, 2, 5, or 10 odor-shock pairings. Fear-potentiated startle decreased but was still significant up to 40 days after conditioning and could be measured in test trials separated by as little as 30 s. The magnitude of potentiated startle decreased with decreasing concentrations of amyl acetate (5%-5 x 10-9%). The anxiolytic compound buspirone (10 mg/kg) significantly attenuated olfactory-mediated fear-potentiated startle.

The specificity of infant emotional expression for emotion perception

Attachment theory emphasizes the role of negative emotional expression in infancy for establishing proximity to and care of the caregiver. According to Lang's biphasic model of emotions protective reflexes (e.g. startle response) are primed if a defensive motivational set is activated. The aim of the study was to examine whether the perception of an infant emotional expression can prime such defensive behavior. The sample consisted of 48 university students. Startle reflex, corrugator and zygomatic EMG activity and subjective ratings of valence and arousal were assessed as a response to presentation of pictures of different emotional valence. Affective startle modulation was obtained when probes were presented during pictures of the International Affective Pictures System replicating previous findings. By contrast, negative infant emotion pictures did not prompt an augmentation of the startle response, although both the subjective ratings and the mimic EMG activity indicated a clear differentiation between negative and positive infant pictures. This pattern of findings was found only in a between-subject design, but not when the two picture sets were presented in the same session, indicating an interference of contrasting content of pictures.

Similar patterns of cardiovascular response during emotional activation as a function of affective valence and arousal and gender

OBJECTIVE

Laboratory studies of emotion-induced cardiovascular responses have been conducted predominantly with a specific affects approach rather than a dimensional approach. The purpose of this study was to apply the principles of the Circumplex Model of Affect (i.e., valence and arousal) to investigate cardiovascular reactivity during emotional activation in men and women.

METHODS

Forty-two healthy university students (mean age = 19.45, 52% women, 58% Caucasian) engaged in personally relevant recall tasks that varied as a function of valence and arousal. Self-reported valence and arousal, systolic and diastolic blood pressure (SBP and DBP, respectively), heart rate (HR), preejection period (PEP), stroke index (SI), cardiac index (CI), and total peripheral resistance (TPR) were measured during baseline and task periods.

RESULTS

Cardiovascular responses were found to be largely comparable across the recall tasks and were characterized by significant increases in blood pressure, HR, and TPR, and decreases in SI (Ps < .001). In addition, SBP during negative valence tasks was significantly higher than during positive valence tasks (P < .03), and PEP lengthened more during low as compared to high arousal tasks (P < .03).

CONCLUSIONS

These results highlight the similarity of hemodynamic adjustments during the verbal expression of emotion across gender and the dimensions of valence and arousal. The overall response pattern suggests alpha-adrenergically mediated sympathetic activation and vagal withdrawal.

Anterior electroencephalographic asymmetry changes in elderly women in response to a pleasant and an unpleasant odor

Greater left than right frontal EEG activation has been associated with increased positive and/or decreased negative affect, whereas greater right than left frontal activation has been associated with the opposite pattern. Substantial research has documented the trait properties of asymmetry, as well as responses to pleasant and unpleasant stimuli. The present study examined changes in anterior alpha asymmetries in response to pleasant (vanilla), unpleasant (valerian), and neutral (water) odors. As predicted, vanilla produced relative left frontal activation compared to valerian and water. Frontal asymmetry did not differ in response to valerian compared to water. The results are consistent with the hypothesis that the left frontal region of the brain is involved in positive/approach-related emotion, and extend previous results into the olfactory realm.

Geruchs- und emotionale Reiz-Bewertung bei Patienten mit Major Depression

Zusammenfassung. Die Untersuchung der affektiven Reaktion auf olfaktorische und visuelle Reize bei Patienten mit Major Depression (MD) hatte zum Ziel, aufzuklären, ob eine abweichende Reizbewertung bei MD-Patienten modalitätsspezifisch ist und/oder von der Reiz-Valenz abhängig ist. Es wurden 26 MD-Patienten untersucht und mit einer nach Alter und Geschlecht parallelisierten Kontroll- Stichprobe verglichen. Die Teilnehmer hatten zur Aufgabe, ihre emotionale Reaktion auf 10 Gerüche und 20 Bilder aus dem International Affective Picture System (IAPS) auf drei Dimensionen (Valenz, Arousal, Dominanz) zu beschreiben. Alle Reize wurden entsprechend ihrer Valenz in positive, neutrale und negative klassifiziert. Depressive Patienten reagierten mit stärkerer Erregung auf negative Reize als die nicht-depressiven Kontrollen. Dieser Effekt war unabhängig von der Reizmodalität. Außerdem fühlten sich MD-Patienten bei beiden Reizqualitäten und unabhängig von der Valenz-Klasse submissiver als die Kontrollen. Auf der Valenz-Dimension ergaben sich keine Gruppen-Unterschiede.

The neurobiology of startle

Startle is a fast response to sudden, intense stimuli and probably protects the organism from injury by a predator or by a blow. The acoustic startle response (ASR) of mammals is mediated by a relatively simple neuronal circuit located in the lower brainstem. Neurons of the caudal pontine reticular nucleus (PnC) are key elements of this primary ASR pathway. The ASR in humans and animals has a non-zero baseline, that is, the response magnitude can be increased or decreased by a variety of pathological conditions and experimental manipulations. Therefore, the ASR has been used as a behavioral tool to assess the neuronal basis of behavioral plasticity and to model neuropathological dysfunctions of sensorimotor information processing. Cross-species examples for the increase of the ASR magnitude are sensitization, fear-potentiation and drug-induced enhancement. Examples for the reduction of the ASR magnitude are habituation, prepulse inhibition, drug-induced inhibition and the attenuation by positive affect. This review describes the neuronal basis underlying the mediation of the ASR, as well as the neuronal and neurochemical substrates of different phenomena of enhancement and attenuation of the ASR. It also attempts to elucidate the biological background of these forms of behavioral plasticity. Special emphasis is put on the potential relevance of ASR modulations for the understanding of human psychiatric and neurological diseases.

Affective startle modulation in clinical depression: preliminary findings

BACKGROUND

Modulation of the startle reflex by affective foreground stimuli was investigated in a group receiving inpatient treatment for major depressive episodes (n = 14) and an age and gender matched nondepressed group (n = 14).

METHODS

Participants viewed 27 pleasant, neutral, and unpleasant pictures chosen from the International Affective Picture System. Acoustic startle probes were presented during picture viewing, and participants also rated the affective qualities of the pictures.

RESULTS

While ratings of the pictures were largely similar between the depressed and nondepressed groups, they displayed dissimilar patterns of startle modulation. In the nondepressed group, blinks elicited during unpleasant pictures were significantly larger than during pleasant pictures, whereas the depressed group failed to show this effect. Analyses, which separated the depressed participants into moderate and severe groups based on Beck Depression Inventory scores, revealed that while the moderately depressed group also showed a normal pattern of startle modulation, the severely depressed showed potentiated startles during the pleasant pictures.

CONCLUSIONS

These preliminary results suggest that severely depressed patients may respond to some pleasant stimuli as if they are aversive, possibly because such stimuli are seen as signals of frustrative nonreward.

A demonstration of classical conditioning of the human eyeblink to an olfactory stimulus

While acquisition of the eyeblink conditioned response to a variety of stimuli has been widely studied, it has yet to be established that humans will demonstrate a conditioned response to an olfactory stimulus. In this study we present data to show that humans will demonstrate a classically conditioned eyeblink response to an olfactory stimulus. Ten participants were tested in a delay conditioning procedure with an olfactory stimulus presented in a heated, humidified stream of air via an olfactometer, allowing the precise control over stimulus duration necessary for delay conditioning. Trials on which odor alone was presented were administered to four additional participants. Establishing that humans will demonstrate an eyeblink conditioned response to an olfactory stimulus will allow further exploration of the pathways involved in classical conditioning and associative learning, as well as an analysis of conditioning pathways across sensory modalities.

Emotion, motivation, and anxiety: brain mechanisms and psychophysiology

The organization of response systems in emotion is founded on two basic motive systems, appetitive and defensive. The subcortical and deep cortical structures that determine primary motivated behavior are similar across mammalian species. Animal research has illuminated these neural systems and defined their reflex outputs. Although motivated behavior is more complex and varied in humans, the simpler underlying response patterns persist in affective expression. These basic phenomena are elucidated here in the context of affective perception. Thus, the research examines human beings watching uniquely human stimuli--primarily picture media (but also words and sounds) that prompt emotional arousal--showing how the underlying motivational structure is apparent in the organization of visceral and behavioral responses, in the priming of simple reflexes, and in the reentrant processing of these symbolic representations in the sensory cortex. Implications of the work for understanding pathological emotional states are discussed, emphasizing research on psychopathy and the anxiety disorders.

Effects of home-nest odors on the startle response in preweanling rats

The present study examined the effects of a highly preferred, biologically relevant olfactory stimulus (i.e., home-nest odors) on the startle response in preweanling rats. Although the rats detected the odor (as revealed by reductions in ultrasound vocalizations) it had no effect on either the initial magnitude of the startle response or habituation of this response across 80 test trials. These results are discussed in relation to recent studies on modulation of the startle response in developing rats, the effects of olfactory stimuli on the startle response, and the pleasure-attenuation of startle in nonhuman subjects.