Examining habituation of the startle reflex with the reinforcement sensitivity theory of personality

The habituation of the acoustic startle reflex (ASR) was examined concerning individual differences in sensitivity to punishment (PUN) and sensitivity to reward (REW), within the general framework of the reinforcement sensitivity theory (RST) of personality. Two hypotheses derived from the RST were evaluated: the separable subsystems hypothesis and the joint subsystems hypothesis. In addition, we examined the direction of the relationship of PUN and REW with the habituation of the ASR. A habituation segment of electromyography recordings of the orbicularis oculi was assessed with an unconditional latent curve model. In accordance with the RST hypotheses, the relationship of PUN and REW on the habituation process was assessed with two conditional latent curve models. There was higher support for the separable subsystems hypothesis. In addition, PUN and REW related with the habituation trajectory of the ASR in the expected directions. Higher levels of PUN and lower levels of REW related with a slower habituation of the ASR, whereas lower levels of PUN and higher levels of REW related with a faster habituation of the ASR.     

Habituation and sensitization in the modulation of reflex amplitude.

The interaction of decrement due to repeated presentation of an auditory eliciting stimulus with an ancillary visual stimulus that itself increased reflex amplitude was studied in 4 separate experiments. This interaction produced a multiplicity of complex reflex changes that cannot readily be accounted for by current conceptualizations of the processes of habituation (underlying reflex decrement) and sensitization (underlying reflex increment) that presumably modulate reflex change.     

Habituation and prestimulus inhibition of the auditory startle reflex in decerebrate rats

Integrated emgs, recorded from muscles of the neck, have been used to study the auditory startle reflex in the decerebrate rat. The reflex had a mean onset latency of 11.6 msec and a mean duration of 90 msec; it was abolished by lesions in the inferior colliculus and, in some animals, lesions in the pontine or caudal mesencephalic reticular formation. It was found that the startle response, in the decerebrate animal, was habituated in a way comparable with that described in the intact animal. The size of the response was also reduced by a single preceding auditory stimulus, whether or not that stimulus was above threshold for eliciting a startle response. It therefore appears that short term habituation and prestimulus inhibition of the startle reflex are not dependent on higher regions of the central nervous system.     

Habituation of the startle response in adrenalectomized rats

In a series of three experiments adrenalectomized, sham-operated and non-operated rats (N = 15) were presented with 27 tones at each of three intensities on two successive days or 60 tones at a 60 sec interstimulus interval with each tone being followed by another tone either 2, 4, 8 or 16 sec later, or 50 tones at a 30 sec interstimulus interval on each of five successive days. All groups had equivalent initial startle amplitudes and showed equivalent rates of response decrement at each test intensity and each interstimulus interval as well as over successive days of exposure. The results indicate that the adrenal glands are not crucial for habituation of the acoustic startle response and suggest that those aspects of stress adaptation that require an intact adrenal-pituitary system are not important for habituation of the startle.     

Habituation of the Blink Reflex in Normals and Schizophrenic Patients

The present study demonstrates an impairment of habituation in schizophrenic patients on a measure of defensive responding to startling stimuli. The blink reflex component of human startle in response to 116dB(A) tones (40 msec, 1000 Hz) was monitored and distinguished from voluntary eyeblinks by a computer. With a background noise level of 70dB(A), 121 tones were given at varied intervals averaging 15 sec. All three groups tested, 25 presumed normals, 20 psychiatric patient controls and 22 schizophrenic patients, exhibited similar responses to the first several stimuli. However, while normals and patient controls exhibited roughly 70% decrements in response amplitudes across trials, schizophrenic patients habituated by less than 50%. An unexpected finding was that the latency-to-peak values for normals and controls were non-monotonically related to both trial number and response amplitudes. That is, latencies first increased and then decreased as the same stimulus was repeated. As with amplitude habituation, this phenomenon was also delayed in the schizophrenic patients. The results indicate that schizophrenic patients have abnormal habituation of defensive responses to exteroceptive stimuli. Possible links between abnormal habituation and symptom formation in schizophrenia are discussed.     

Influence of individual differences in Behavioral Inhibition System on the magnitude and time course of the fear-potentiated startle

Previous research has shown that the startle reflex is potentiated during experimentally induced anxiety (fear-potentiated startle). In the present study, the magnitude and time course of the startle blink reflex were examined among 35 undergraduates scoring one standard deviation above (n = 14) or below (n = 21) the mean in a self-report measure of sensitivity to punishment (SP) in a paradigm involving the anticipation of electric shocks. Contrary to our predictions, SP did not relate to differences in the magnitude or in the time course of fear-potentiated startle. Our data do not support an association between this individual differences variable and the fear-potentiated startle.     

Chemosensory anxiety signals augment the startle reflex in humans

The aim of the present study was to investigate whether chemosensory anxiety signals can activate behavioral withdrawal systems in humans. Twelve male university students donated their axillary sweat in two situations: right before an oral academic examination (anxiety condition) and during ergometric training (exercise condition). Subjective ratings revealed that the odor donors experienced significantly more anxiety and less pleasure during the anxiety condition than during the exercise condition. Seven subjects (three females) participated in the psychophysiological experiment. The chemosensory stimuli from pooled sweat samples of the donors, and from unused cotton pads (pad condition) were presented via a constant-flow olfactometer. Acoustic startle probes (100 dB (A)) were delivered during and between the presentations of the chemosensory stimuli. Only three subjects were able to discriminate the chemosensory stimuli of the human sweat samples from room air. However, the startle reflex amplitude (EMG of the eyeblink response) recorded in the context of chemosensory anxiety signals was increased, as compared to the amplitude recorded in the context of chemosensory stimuli from either exercise (p = 0.018) or cotton pad (p = 0.012). It is concluded that chemosensory anxiety signals may pre-attentively prime defensive behavior.     

Habituation and conditioning of the human long latency stretch reflex

Summary The effects of stretch repetition rate, prior warning stimuli and self administered stretch were examined on the size of the short and long latency components of the stretch reflex electromyographic EMG response in flexor pollicis longus and the flexor muscles of the wrist and fingers. Stretches of constant velocity and extent were given every 10 s, 5 s, 2 s, or 1 s to either the wrist or thumb during a small background contraction of the flexor muscles. The size of the long latency component of the stretch reflex (measured as the area under the averaged rectified EMG responses) declined dramatically at faster repetition rates, especially in the wrist and finger flexors. The size of the short latency component was relatively unaffected. The size of the electrically elicited H-reflex in forearm muscles also failed to habituate under the same conditions. If each individual trial of a series was examined, the long latency component of the stretch reflex EMG could be seen to decrease in size over the first three to six stretches if stretches were given every 1 s, but not if stretches were given every 10 s. When stretches were given every 5 s to either wrist or thumb, an electrical stimulus applied to the digital nerves of the opposite hand 1 s before stretch reduced the size of the long latency component of the reflex EMG response. The short latency component was unaffected. Self triggering of wrist or thumb stretch by the subject pressing the stimulator button himself with his opposite hand, also decreased the size of the long latency component of the reflex EMG response without affecting the short latency component. It is concluded that factors other than stretch size or velocity can have marked effects on the size of the long latency component of the stretch reflex. These factors must be taken into account when comparing values of reflex size obtained with different stretching techniques and in different disease states in man.     

Habituation and sensitization of the rat startle response: effects of raphe lesions

In the first experiment raphe lesioned, sham operated and nonoperated rats were presented with 150 tones (50 at each of 3 intensities) a day for 5 days. No differences were found among the groups in the rate of startle response habituation either within or between sessions. However, overall levels of startle were much greater following raphe lesions and a tone by tone analysis indicated that this was caused by heightened tone-elicited sensitization in the raphe group. Further tests of startle sensitization in Experiment 2 found the raphe group to be more sensitized than the other groups by loud tones and footshocks but not by different levels of background white noise. The results support the theory that repetitive stimulus exposure produces both habituation and sensitization and that different neural systems may underly these two processes.     

Influence of individual differences in the Behavioral Inhibition System and stimulus content (fear versus blood-disgust) on affective startle reflex modulation

Inconsistencies among affective startle reflex modulation studies may be due to differences in the startle potentiation produced by the specific content of the images used, to individual differences in sensitivity to negative stimuli, or to the interaction of both factors. To explore this interaction, 52 undergraduates obtaining extreme scores on a self-report measure of the Behavioral Inhibition System (BIS) participated in an affective startle reflex modulation paradigm. A significant interaction between BIS group (high versus low) and image content emerged from the MANOVA. Comparing startle magnitude between fear and pleasant images, low BIS participants did not seem to show startle potentiation, whereas high BIS participants did. Both groups displayed potentiated startle during blood-disgust images. The present results suggest the importance of considering personality variables and their interaction with image content in the affective startle modulation paradigm.     

Facilitation and habituation of the startle reflex over the tonically active biceps brachii muscle contralateral to electrical stimuli

The aim of the present investigation was to explore the impact of muscle contraction on startle reflex responses after electrical stimuli (single or trains of 3) and to study startle reflex habituation. The electromyogram was recorded over the tonically active biceps brachii muscle in 19 healthy subjects contralateral to electrical stimuli (9–12 mA) that were delivered at 1.0 and 0.4 Hz over the superficial radial nerve. The muscle contraction level was varied by loading weight on the subject's bent arm (0.0, 1.0 or 1.5 kg). Furthermore, short term reflex habituation was investigated using 30 blocks of 5 subsequent stimuli. Startle response amplitudes gained significantly (p < 0.05) after (i) train stimuli as compared with single stimuli, during (ii) high versus low levels of muscle contraction, and at (iii) 0.4 Hz versus 1.0 Hz stimuli. Startle reflex amplitudes decreased significantly by the influence of preceding stimuli (p < 0.05). This study provides evidence that the startle reflex can be significantly influenced by weight load, i.e. by volitional influences. Startle reflex investigation over a contracted limb muscle results in a high probability of startle release and thereby improved detection of SR habituation following preceding stimuli.     

Emotional qualities of odors and their influence on the startle reflex in humans

Recent human and animal research suggests that the startle reflex might serve as a psychophysiological indicator of the emotional valence of foreground stimulation. The present experiment was designed to evaluate the emotional effects of positive and negative odorant stimuli. We examined the effects of continuous hydrogen sulphide (H2S) and vanillin stimulation on the magnitude of the acoustic startle reflex (measured at the M. orbicularis oculi) and on ratings of subjective valence in 16 healthy subjects. In accordance with the view that odors have emotional qualities, we found that H2S, a presumed negative foreground stimulus, significantly enhanced the startle-reflex amplitude relative to neutral air stimulation, whereas vanillin, a positive foreground stimulus, tended to reduce the reflex amplitude compared with neutral air stimulation. Both odorant stimuli were rated as equally intense by the subjects, and heart rate and electrodermal activity were not affected differentially by the two odorants.     

Differences in startle reflex and prepulse inhibition in European-Americans and African-Americans

The acoustic startle reflex and its modulation by a prepulse are psychophysiological phenomena that are commonly studied to evaluate various aspects of information processing. Recent reports in human populations suggest that subjects from disparate racial backgrounds may have significant differences in the startle response. To determine if this pattern could be observed in our subject population and whether it extended to prepulse inhibition (PPI), we evaluated baseline startle parameters and PPI in 53 African-Americans (AA) and 38 European-Americans (EA). In AA compared to EA, mean startle magnitude and probability of blink response were lower, with no difference in habituation. PPI was greater in AA than EA when groups were matched on baseline startle magnitude. These findings support the idea of racial differences in startle response. Implications for study design are highlighted, and possible environmental and genetic influences are considered.     

Genetic and environmental influences on emotion-modulated startle reflex: a twin study

Emotion-modulated startle reflex is an important indicator of traitlike differences in affective processing implicated in the biological basis of personality and psychopathology. This study examined heritability of startle modulation by affective pictures in 66 pairs of monozygotic and 57 pairs of dizygotic female twins. Consistent with previous studies, startle magnitude was significantly influenced by emotional valence of the picture (positive < neutral < negative). Absolute response magnitude showed high heritability in all three valence conditions (59-61%); however, there were no significant genetic influences on the amount of startle modulation. Thus, our data do not support the hypothesis that emotion-modulated startle can serve as an indicator of genetically transmitted individual differences in affective processing.     

Not just noise: Individual differences in general startle reactivity predict startle response to uncertain and certain threat

General startle reactivity reflects defensive reactivity independent of affective foreground. We examined the relationship between general startle reactivity and startle response to threat in three tasks with distinct manipulations of threat uncertainty. General startle reactivity was a stronger predictor of startle response during threat (vs. no threat) and uncertain (vs. certain threat). These results confirm that including general startle reactivity in our analyses can increase the power and/or precision to test effects of other focal experimental manipulations or grouping variables. Moreover, this suggests that individual differences in defensive reactivity moderate responding to threats of various types in our environment. As such, individual differences in general startle reactivity may index important psychological attributes related to trait affectivity, premorbid vulnerability for psychopathology, and manifest psychopathology.     

Resting heart rate variability and the startle reflex to briefly presented affective pictures

We have previously shown that persons with low HRV showed potentiated startle responses to neutral stimuli. In the present study we replicated our prior findings and extended them to examine the effects of HRV on the startle magnitude to pictures that were presented outside of conscious awareness. A total of 85 male and female students were stratified via median split on their resting HRV. They were presented pictures for 6 s or for 30 ms. Results indicated that the high HRV group showed the context appropriate startle magnitude increase to unpleasant foreground. The low HRV group showed startle magnitude increase from pleasant to neutral pictures but no difference between the neutral and unpleasant pictures. This pattern of results was similar for the 30 ms and the 6 s conditions. These results suggest that having high HRV may allow persons to more efficiently process emotional stimuli and to better recognize threat and safety signals.     

Habituation of the acoustic startle response following lesion of the medial septal nucleus

Adult male rats were subjected to one of three surgical procedures: total lesions of the medial septal nuclei (TMS), partial lesions of the medial septal nuclei (PMS), and lesions of the dorsal fimbria (FM), as an attempt to determine the role of the septo-hippocampal relationship in habituation of the acoustic startle response. The initial startle amplitude of the TMS group was approximately three times that of the other groups, but rapidly decreased to the level of the other experimental groups and thereafter habituated at similar slow rates. Unlike animals with hippocampal lesions, all animals with hippocampal afferent damage displayed overdays savings of habituation. Following nine days without startle stimulation, startle amplitudes of the TMS groups had returned to their initial level while the PMS, FM and Control groups exhibited nonsignificant recovery. Differences in rates of habituation and amplitude of startle responses were attributed to loss of hippocampal input, and increased hippocampal output over intact pathways, respectively.     

Reaction time facilitation by acoustic task-irrelevant stimuli is not related to startle

Previous research has been interpreted to suggest that the startle reflex mediates the RT facilitation observed if intense, accessory acoustic stimuli are presented coinciding with the onset of a visual imperative stimulus in a forewarned simple RT task. The present research replicated this finding as well as the facilitation of startle observed during the imperative stimulus. It failed, however, to find any relationship between the size of the blink startle reflex elicited by the accessory acoustic stimuli, which differed in intensity and rise time, and RT or RT facilitation observed on trials with accessory acoustic stimuli. This finding suggests that the RT facilitation is not mediated by the startle reflex elicited by the accessory acoustic stimuli.     

The psychophysiology of social anxiety: Emotional modulation of the startle reflex during socially-relevant and -irrelevant pictures

The present study examined affective processes of social anxiety (SA) through emotional modulation of the startle reflex. Eighty-four high and low trait socially anxious undergraduates viewed socially-relevant and socially-irrelevant pleasant, neutral, and unpleasant pictures, and acoustic startle probes were presented during pictures and the inter-trial interval. Startle was potentiated during unpleasant compared to pleasant stimuli, but this valence modulation did not reliably vary between groups or socially-relevant and -irrelevant stimuli. However, when participants were categorized based on public-speaking fears rather than general SA symptoms, the high fear group demonstrated reliable valence modulation, whereas the low fear group did not. These findings are interpreted within the context of the broader literature suggesting that the specificity of fear in SA may influence psychophysiological reactivity.     

Effects of background noise on the human startle reflex and prepulse inhibition

Three experiments investigated whether background noise modified the startle blink reflex and prepulse inhibition (PPI). In Experiment 1 background noise was about 28 (ambient), 40, and 60 dB; in Experiments 2 and 3 background noise was ambient and 60 dB. Prepulses were 70-dB tones (Experiments 1 and 3) or a tactile stimulus (Experiment 2). Startle-eliciting stimuli were 94-dB noise (Experiments 1 and 2) or an airpuff to the face (Experiment 3). Prepulses were presented at stimulus onset asynchronies of 30, 60, 120, 240, and 2000 ms relative to the startle-eliciting stimulus. Background noise of 60 dB had no effect on control reflexes, whereas 40-dB background noise increased control reflexes. Background noise decreased PPI, but only when an acoustic stimulus was used as prepulse. In sum, the findings show that background noise reduces the signal-to-noise ratio of acoustic prepulses and decreases their modulatory effect on the startle reflex.