Amygdala central nucleus lesions attenuate acoustic startle stimulus-evoked heart rate changes in rats.

Amygdala central nucleus (CNA) lesions were used to test the hypothesis that stimulus-evoked heart rate changes can reflect the development of fear during acoustic startle testing A 120-dB white noise startle stimulus produced freezing as well as phasic heart rate accelerations and decelerations, and an abrupt decrease in tonic heart rate, in sham-operated rats. These responses were all significantly reduced in CNA-lesioned rats. In contrast, an 87-dB stimulus elicited only significant phasic decelerations that were similarly attenuated by the CNA lesions. In a follow-up experiment. the CNA lesions also attenuated phasic cardiac decelerations evoked by a conditioned stimulus-like, 85-dB pure tone. The results support the contention (B. J. Young & R. N. Leaton, see record 1995-12737-001) that heart rate changes can reflect fear conditioned during acoustic startle testing and, in addition, suggest that the amygdala mediates responses to nonsignal acoustic stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rearing experience differentially affects somatic and cardiac startle responses in rhesus monkeys (Macaca mulatta).

The present study reports, for the first time, somatic and cardiac responses to acoustic startle in 2 groups of rhesus monkeys (Macaca mulatta) with different rearing experiences. Both groups showed a significant direct relationship between startle amplitude and the intensity of the acoustic startle stimulus (80-120 dB) and rapid heart rate acceleration after a 120-dB stimulus. Monkeys reared with a same-age peer (PR) showed higher startle amplitudes than those reared with their mothers (MR), consistent with rearing effects in rodents. The MR monkeys, however, showed faster heart rate acceleration of greater overall magnitude than that of the PR group. The results are discussed with regard to a monkey model for neuropsychiatric disease. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physiologic responses to loud tones in Vietnam veterans with posttraumatic stress disorder.

The authors evaluated eyeblink and autonomic components of the acoustic startle response in combat-related posttraumatic stress disorder (PTSD). Thirty-seven Vietnam combat veterans with current PTSD and 19 combat veterans without PTSD were exposed to 15 consecutive 95-dB, 500-ms, 1000-Hz tones with 0-ms rise and fall times, while orbicularis oculi electromyogram, skin conductance, and heart rate responses were measured. PTSD veterans produced larger averaged electromyographic and heart rate responses, and a slower decline in skin conductance responses, across the 15 tone presentations compared to non-PTSD veterans. Results of this study provide laboratory support for an exaggerated startle response in PTSD and replicate and extend previous findings of increased autonomic responses to loud tone stimuli in this disorder. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotion, novelty, and the startle reflex: Habituation in humans.

Previous research with both animal and human Ss has shown that startle reflex magnitude is potentiated in an aversive stimulus context, relative to responses elicited in a neutral or appetitive context. In the present experiment, the same pleasant, unpleasant, and neutral picture stimuli were repeatedly presented to human Ss. Startle reflex habituation was assessed in each stimulus context and was compared with the habituation patterns of heart rate, electrodermal, and facial corrugator muscle responses. All systems showed initial differentiation among affective picture contents and general habituation over trials. The startle reflex alone, however, continued to differentiate among pleasant, neutral, and unpleasant pictures throughout the presentation series. These results suggest that (1) the startle probe reflex is relatively uninfluenced by stimulus novelty, (2) the startle modulatory circuit (identified with amygdala-reticular connections in animals) varies systematically with affective valence, and (3) the modulatory influence is less subject to habituation than is the obligatory startle pathway or responses in other somatic and autonomic systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Autonomic-somatic interaction and hippocampal theta activity.

In 2 experiments, a total of 16 New Zealand rabbits were given extended differential classical conditioning training in which tones served as conditioned stimuli (CS) and shock to the eye served as the unconditioned stimulus (UCS). Corneo-retinal potential (CRP), heart rate (HR), and hippocampal EEG conditioned responses were measured. Changes in general somatic activity were also assessed. HR decelerations were associated with early stages of CRP discrimination, whereas HR accelerations and relatively more somatomotor activity were associated with later acquisition. These findings suggest that HR accelerations, associated with asymptotic CRP responding, are mediated via somatomotor changes. Although relatively more hippocampal theta activity was associated with later stages of conditioning, when somatomotor increases occurred theta was also prominent throughout acquisition. This finding suggests that either arousal properties of the CR are instrumental in producing theta or it is correlated with the associative properties of CS-UCS contingencies. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic startle response and habituation in freezing and nonfreezing rats.

Divided rats according to their responses to startle-eliciting stimuli into 2 groups with different emotional states. About half of the 54 female Sprague-Dawley rats showed long-lasting freezing behavior after 1–8 stimuli (10 kHz, 110 dB spl). In freezing rats the startle amplitude was higher than in nonfreezing rats, even on the very first startle response. This finding demonstrates that the anxiety state of these animals before the 1st startle-eliciting stimulus, and not just the aversiveness of the stimulus, contributes to freezing behavior. In addition, in freezing rats there was no influence of spontaneous motor activity or of adaptation time on startle amplitude. Only in nonfreezing rats were high motor activities correlated with lowered startle amplitudes, and only in these rats did the course of startle habituation depend on adaptation time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Caudal pontine reticular formation of C57BL/6J mice: responses to startle stimuli, inhibition by tones, and plasticity

C57BL/6J (C57) mice were used to examine relationships between the behavioral acoustic startle response (ASR) and the responses of neurons in the caudal pontine reticular formation (PnC) in three contexts: 1) responses evoked by basic startle stimuli; 2) the prepulse inhibition (PPI) paradigm; and 3) the effects of high-frequency hearing loss and concomitant neural plasticity that occurs in middle-aged C57 mice. 1) Responses (evoked action potentials) of PnC neurons closely paralleled the ASR with respect to latency, threshold, and responses to rapidly presented stimuli. 2) "Neural PPI" (inhibition of responses evoked by a startle stimulus when preceded by a tone prepulse) was observed in all PnC neurons studied. 3) In PnC neurons of 6-mo-old mice with high-frequency (>20 kHz) hearing loss, neural PPI was enhanced with 12- and 4-kHz prepulses, as it is behaviorally. These are frequencies that have become "overrepresented" in the central auditory system of 6-mo-old C57 mice. Thus neural plasticity in the auditory system, induced by high-frequency hearing loss, is correlated with increased salience of the inhibiting tones in both behavioral and neural PPI paradigms.     

Cardiac response to acoustic playback experiments in the captive bottlenose dolphin (Tursiops truncatus).

Acoustic recordings were used to investigate the cardiac responses of a captive dolphin (Tursiops truncatus) to sound playback stimuli. A suction-cup hydrophone placed on the ventral midline of the dolphin produced a continuous heartbeat signal while the dolphin was submerged. Heartbeats were timed by applying a matched-filter to the phonocardiogram. Significant heart rate accelerations were observed in response to playback stimuli involving conspecific vocalizations compared with baseline rates or tank noise playbacks. This method documents that objective psychophysiological measures can be obtained for physically unrestrained cetaceans. In addition, the results are the 1st to show cardiac responses to acoustic stimuli from a cetacean at depth. Preliminary evidence suggests that the cardiac response patterns of dolphins are consistent with the physiological defense and startle responses in terrestrial mammals and birds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiated startle: Its relation to freezing and shock intensity in rats.

Two experiments with 47 albino rats measured acoustic startle response and freezing in a potentiated startle paradigm in which a startle stimulus was presented either alone or in the presence of a light conditioned stimulus/stimuli (CS) that had been paired previously with either 1-mA or 3-mA footshock. During the CS, the 1-mA group had higher startle amplitudes and a higher percentage of freezing than the 3-mA group. Startle amplitude was positively correlated with freezing under all conditions. The nonmonotonic relation between potentiated startle and shock intensity replicated the study of M. Davis and D. I. Astrachan (see record 1979-00353-001). However, rather than suppressing startle, as they suggested, freezing facilitated startle and, like startle amplitude, was nonmonotonically related to shock intensity. In Exp II, these results were replicated and showed a regularly decreasing monotonic extinction function or potentiated startle and shock-associated freezing for both shock-level groups. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delayed development of fear-potentiated startle in rats.

Examined the developmental emergence of fear-potentiated startle in rats ranging in age from 16 to 75 days. In Exp 1, a pure tone served as the CS and an acoustic startle pulse served as the unconditioned stimulus (UCS) for fear conditioning. Fear-potentiated startle by the tone CS was observed in rats 23 days of age and older but not in rats 16 days of age. In Exp 2, a light served as the CS. Rats 30 days of age and older showed fear-potentiated startle, whereas 23-day-old rats did not. The final experiment demonstrated that another behavioral index of fear, stimulus-elicited freezing, was observed earlier in development than fear-potentiated startle, confirming the effectiveness of the training procedure for conditioning fear. Results suggest that fear-potentiated startle is a relatively late-emerging response system, parallelling the development of conditioned autonomic changes (e.g., heart rate) rather than that of freezing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cardiac orienting and auditory discrimination in 6-wk-old infants.

A series of 3 experiments with 32 6-wk-old infants studied heart rate and sucking in response to changes in acoustic stimuli. Exp I used a conventional discrete trials paradigm to present trains of synthetic speech syllables, Exp II used a no-delay paradigm to present nonspeech stimuli (tone frequencies). Overall analysis of cardiac data indicated that discriminative capacities in 6-wk-olds can be revealed by changes in heart rate and that this discrimination is better demonstrated using a no-delay (rather than a discrete trials) paradigm. It is suggested that direction of this rate change may provide information about differences in processing, since cardiac responses to changes in synthetic speech syllables was accelerative (possibly a defensive or startle reaction) while responses to changes in tone frequency were decelerative (possibly an orienting index). Findings reveal a consistent absence of sucking responses, indicating that heart rate responses to changes in acoustic stimulation can occur independently of sucking in 6-wk-olds. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Immediate-startle stimulus presentation fails to condition freezing responses to contextual cues.

Placed 28 male Wistar rats in a novel and distinctive environment. 18 of these received an intense startle-eliciting white noise stimulus. Animals that experienced a 60-sec delay between placement and the startle stimulus demonstrated significant freezing in the context, both poststartle (Session 1) and on a later startle-free test (Session 2). Animals that received immediate startle, however, did not differ on either occasion from animals that did not experience the startle stimulus. The amplitude of the startle response was not affected by this manipulation, which indicates a dissociation between freezing and startle responses with immediate- vs delay-startle presentation. The findings are consistent with M. S. Fanselow's (1986) conditioned stimulus (CS)-based associative explanation of the immediate-shock freezing deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heart rate conditioning in newborn infants: Relationships among conditionability, heart rate variability, and sex.

Evaluated trace conditioning in 20 newborn infants by examining heart rate responses to the conditioned stimulus (CS), in anticipation of the unconditioned stimulus (UCS) and in the absence of the UCS. 2 sets of analyses were performed using subgroups based on preexperimental heart rate variability and sex. Preexperimental heart rate variability was related only to the response to the CS, with only the high-variance Ss showing a conditioned deceleration and exhibiting a change in response across trial blocks. Only the females exhibited conditioned decelerations in response to the CS and in anticipation of the UCS. In the absence of the UCS, only the experimental group as a whole responded with a deceleration. The relationship between sex and heart rate variability was also examined. Data suggest that females tend to have higher levels of heart rate variability which parallels their greater conditionability. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus modality and task condition on blink startle modification and on electrodermal responses

Participants in Experiments 1 and 2 performed a discrimination and counting task to assess the effect of lead stimulus modality on attentional modification of the acoustic startle reflex. Modality of the discrimination stimuli was changed across subjects. Electrodermal responses were larger during task-relevant stimuli than during task-irrelevant stimuli in all conditions. Larger blink magnitude facilitation was found during auditory and visual task-relevant stimuli, but not for tactile stimuli. Experiment 3 used acoustic, visual, and tactile conditioned stimuli (CSs) in differential conditioning with an aversive unconditioned stimulus (US). Startle magnitude facilitation and electrodermal responses were larger during a CS that preceded the US than during a CS that was presented alone regardless of lead stimulus modality. Although not unequivocal, the present data pose problems for attentional accounts of blink modification that emphasize the importance of lead stimulus modality.     

Cardiac and visual responses to stimuli presented both foveally and peripherally as a function of moving stimuli.

Measured heart rate (HR) and visual fixation responses as indices of attention getting (AG) and attention holding (AH) in 17 15-wk-old infants. The stimulus situation was one in which a brief central stimulus was followed by either a brief peripheral stimulus (AG trials) or a prolonged peripheral stimulus (AH trials). The stimuli for both central and peripheral presentations were moving black and white bar patterns. The speed for the central stimulus was constant over trials and groups (at 6.6°/sec), whereas the peripheral stimuli were either 6.6 or 26°/sec. Results suggest that much of the observed HR change can be accounted for by the AG phase, whereas the AH phase was reflected in the time it took for the cardiac responses to return to prestimulus baseline values. Stimulus speed also affected both attention behaviors; the faster speed produced the greatest HR change. Latency of 1st fixation and duration of looking measures did not show any discrimination between stimuli of different speeds. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CpG distribution patterns in methylated and non-methylated species

We evaluated eyeblink and autonomic reactivity to non-startling acoustic stimuli in a convenience sample of Vietnam combat veterans. Twenty veterans with current PTSD and 19 veterans who never had PTSD were exposed to 15 consecutive 86-dB, 500-ms, 100-Hz tones with 40-ms rise and fall times, while orbicularis oculi electromyogram (EMG), skin conductance (SC) and heart rate (HR) responses were measured. PTSD subjects had higher resting HR levels and produced larger averaged HR responses across the 15 tone presentations compared to non-PTSD subjects. Skin conductance and EMG responses did not differ between the groups. Results suggest that previous findings of larger HR responses to loud tones in PTSD extend to lower intensity, non-startling stimuli, but that the magnitude of the HR response appears smaller to the lower intensity stimuli. Previously observed differences in the magnitude of the eyeblink response and rate of decline of SC responses in PTSD to high intensity stimuli appear to disappear when using non-startling stimuli.     

Influence of long-term sensitization on long-term habituation of the acoustic startle response in rats: Central gray lesions, preexposure, and extinction.

The relation between long-term decrements of the acoustic startle response in rats and the development of freezing behavior during habituation training was examined. Freezing behavior developed over the initial trials of habituation training, and the rate of long-term response decrements was found to be inversely related to the development of freezing. Manipulations (neurological or behavioral) that either reduced the level of freezing or retarded its development promoted startle response decrements. In Experiment 1, rats receiving electrolytic lesions of the ventrolateral periaqueductal gray demonstrated both accelerated long-term startle response decrements and retarded development of freezing behavior. In Experiment 2, preexposure to the startle apparatus (i.e., latent inhibition) accelerated long-term startle decrements and inhibited development of freezing. In Experiment 3, exposure to the startle apparatus following initial habituation training (i.e., extinction) reduced both freezing behavior and startle response amplitudes. The results are discussed in terms of the influence of Pavlovian fear conditioning on long-term habituation of the acoustic startle response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Peripheral and central components of alerting: Habituation of acoustic startle, orienting responses, and elicited waveforms.

Behavioral orienting (OR), the acoustic startle reflex (ASR), pontogeniculooccipital (PGO) waves in the lateral geniculate body, and midlatency auditory evoked responses (MLR) represent components of alerting. The habituation rate for each was examined to test the hypothesis that OR, ASR, and PGO waves have related underlying neural mechanisms and determine the similarity in responsiveness between elicited PGO waves (PGOE) and elicited waves in the thalamic central lateral nucleus (CLE), a site that yields MLR. PGOE and CLE waves did not habituate in amplitude after 120 tones; however, the pattern of responses for each waveform was different. OR and ASR significantly decreased amplitude across trials with OR exhibiting a faster, more pronounced decrement. Some separation exists between the peripheral (OR and ASR) and central (PGOE and CLE) components of alerting. PGO and CL waves may have common underlying neural mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Startle amplitude and fear in an acoustic startle paradigm: Lesions to the brachium of the inferior colliculus or the lateral tegmental tract.

In 2 Experiments, startle amplitude and startle stimulus-induced freezing (an index of fear) were measured in an acoustic startle response (ASR) paradigm in rats. Lesions to lateral tegmental tract (LTG), a pathway medial to brachium of the inferior colllciulus (BIC), significantly decreased freezing and produced a persistent 5-fold increase in ASR amplitude compared with sham-operated controls. Lesions to BIC increased both ASR amplitude (2-fold) and freezing. Neither BIC not LTG lesions affected startle amplitude when startle was elicited by a brief footshock stimulus. Characteristics of the lesion effects were tested with manipulations of interstimulus interval, stimulus intensity, and prepulse inhibition. The data suggest (a) an ascending pathway medial to BIC that carries the fear-inducing dimensions of an acoustic stimulus and (b) a descending pathway that provides tonic inhibition of the sensory input to the ASR circuitry. (PsycINFO Database Record (c) 2010 APA, all rights reserved)