Terry D. Blumenthal

Inhibition of the human startle response is affected by both prepulse intensity and eliciting stimulus intensity

The present study evaluated the effects of the intensity of prepulses and eliciting stimuli on the modification of the adult human acoustic startle eyeblink. Eyeblinks were elicited by 85, 95, and 105 dB(A) noise bursts, preceded a some trials by 60 or 70 dB(A) tones at a 120 ms stimulus onset asynchrony. Prepulse intensity was a within-subject variable in Experiment 1 (N = 19) and a between-groups variable in Experiment 2 (N = 38). For no-prepulse trials, as startle stimulus intensity decreased, startle amplitude, probability, and magnitude decreased, and startle latency increased. As startle stimulus intensity decreased from 105 to 95 dB, the amount of inhibition of response amplitude and magnitude remained stable for 70 dB prepulses in Experiment 1 and for both 60 and 70 dB prepulses in Experiment 2, whereas inhibition of response probability became more pronounced. As startle stimulus intensity decreased from 95 to 85 dB, prepulse inhibition of response amplitude and magnitude lessened and inhibition of response probability became still more pronounced in both experiments. These data show that the inhibition of startle can be affected by eliciting stimulus intensity, and that startle response amplitude and probability are affected by stimulus intensity changes in different ways.

A relationship between inhibition of the acoustic startle response and the protection of prepulse processing

The relationship between prepulse inhibition of the startle eyeblink reflex and the processing of the prepulse was tested by measuring both the startle eyeblink response and the accuracy of identification of the prepulse in college students. In Experiment 1 (N = 26), startle stimuli were 100-dB(A), 50-msec-duration noise pulses, preceded on some trials by low- or high-frequency 65-dB(A) tone pre-pulses at stimulus onset asynchronies (SOAs) of 30–800 msec; in Experiment 2 (N = 21), prepulses were 50- or 200-Hz vibrotactile pulses to the hand, at SOAs of 50–800 msec. Average prepulse identification accuracy was significantly higher on trials during which startle magnitude was inhibited than on trials during which startle magnitude was not inhibited, at all SOAs. This simultaneous occurrence of prepulse inhibition and higher prepulse identification accuracy shows that the inhibition of the startle response by the prepulse coexists with a decrease in degree to which the startle stimulus (or response) interrupts the preattentive processing of the prepulse.

Caffeine-associated stimuli elicit conditioned responses : an experimental model of the placebo effect

Rationale: A neutral stimulus repeatedly paired with administration of a drug may elicit a conditioned response. This process, termed pharmacological classical conditioning, may be important in the understanding of placebo effects. Objective: The unconditioned response to caffeine is increased physiological and psychological arousal. The present study investigated whether stimuli associated with the use of caffeine, i.e. the smell and taste of coffee, elicited a conditioned increase in arousal. It was also investigated whether conditioned arousal modulated the unconditioned arousal induced by caffeine. Methods: Twenty subjects who drank at least two cups of coffee per day were exposed to four conditions in a within-subjects design, where the subjects received coffee or orange juice crossed with placebo or 2 mg/kg caffeine. Dependent variables were skin conductance responses and startle reflexes to 85 dB noise bursts, skin conductance levels, blood pressure, heart rate, and subjective measures of arousal. Results: Both caffeine (caffeinated juice) and caffeine-associated stimuli (decaffeinated coffee) increased subjective and physiological arousal. When caffeine and caffeine-associated stimuli were presented together (caffeinated coffee), a non-significant tendency towards an additive effect of the conditioned arousal on the unconditioned arousal to caffeine was seen in some dependent variables. Conclusions: Presentation of caffeine-associated stimuli to caffeine-users elicited conditioned responses similar to the unconditioned drug response. Thus, presentation of caffeine-associated stimuli could be used as an experimental model of placebo effects.

For whom the bell (curve) tolls: Cortisol rapidly affects memory retrieval by an inverted U-shaped dose–response relationship

Stress and cortisol are generally considered to impair declarative memory retrieval, although opposite results have also been reported. Dose-dependent effects and differences between genomic and non-genomic cortisol effects are possible reasons for these discrepancies. The aim of the current experiment was to assess the non-genomic effects of escalating doses of intravenous cortisol on cued recall of socially relevant information in humans. 40 participants (age range 20-30 years; 20 females) learned associations between male faces with a neutral facial expression and descriptions of either positive or negative social behaviors and were tested one week later in a cued recall paradigm. Escalating doses of cortisol (0, 3, 6, 12, 24 mg) were administered 8 min before testing according to a between-subjects design. An inverted U-shaped dose-response relationship between salivary cortisol levels and recall performance was observed, with moderate elevation of salivary cortisol resulting in the best recall performance. This is the first study in humans demonstrating that cortisol rapidly modulates declarative memory retrieval via a dose-dependent, non-genomic mechanism that follows an inverted U-shaped curve. Our result further emphasizes the importance of fast cortisol effects for human cognition.

Prepulse inhibition of the startle eyeblink as an indicator of temporal summation

The inhibition of the human startle eyeblink response was assessed in three experiments in which the duration of the prepulse was manipulated. In all cases, inhibition of startle was more pronounced as prepulse duration increased from 6 to 50 msec. Inhibition of startle amplitude for single prepulses was not significantly different from that for paired prepulses (Experiment 1), but inhibition was more pronounced as prepulse intensity increased (Experiment 3). Varying the interval between prepulse offset and startle-stimulus onset had no significant effect on inhibition (Experiment 2). These data demonstrate the sensitivity of startle inhibition to prepulse duration, and suggest that this response system can be used to evaluate early temporal summation in the auditory system.

PREPULSE EFFECTS ON MAGNITUDE ESTIMATION OF STARTLE-ELICITING STIMULI AND STARTLE RESPONSES

The present studies investigated the relationship between prepulse effects on the modification of the brainstem startle reflex and magnitude estimates of startle-eliciting stimuli. In Experiment 1, startle eyeblink responses were elicited in 24 students, half of whom were instructed to estimate the loudness of the startle stimulus (actual intensities of 80, 90, and 100 dB) and half of whom were instructed to estimate the magnitude of their eyeblink. When weak acoustic prepulses preceded the startle-eliciting stimulus, eyeblink amplitude was inhibited, and estimates of response magnitude decreased, but estimates of startle stimulus magnitude decreased only when 100-dB startle stimuli were presented. In Experiment 2, the same startle stimuli were preceded on some trials by a vibrotactile prepulse to the hand. In conditions in which startle amplitude was inhibited, startle stimulus magnitude estimates were not affected. This suggests that the effect of acoustic prepulses on 100-dB startle stimuli in Experiment 1 may have been due to loudness assimilation, an effect independent of the prepulse inhibition of startle responding.

The startle response as an indicator of temporal summation

The present study assessed temporal summation of transient and sustained stimuli in the startle eyeblink response system. In two experiments, adult subjects received 95-dB(A), fast-rising broadband noise bursts of two types: (1) single stimuli varying in duration from 20 to 100 msec (Experiment 1) or 30 to 55 msec (Experiment 2) and (2) pairs of 3-msec bursts presented at interpulse intervals corresponding to the single stimulus durations. In addition, a single 3-msec pulse was used as an anchor point for both stimulus types. Though the temporal functions depended on whether startle amplitude or probability was assessed, both measures showed that temporal summation was similar for sustained stimuli and pulse pairs up to about 40 to 50 msec. Beyond this point, single stimuli maintained responding to 100 msec, whereas the second pulse of the pair quickly lost its effect. The results indicate that, although startle is influenced by summation of the sustained aspects of a stimulus, summation of transients produces an equivalent effect and does so with more acoustic efficiency (requires less energy). Response latency measures showed no significant summation with paired pulses, and only a narrow summation window for single stimuli. Thus, differential summation of sustained and transient information is demonstrated by all three response measures, but in different ways.

Emotional reactivity in nonsuicidal self-injury: divergence between self-report and startle measures.

The current study examined emotional reactivity in nonsuicidal self-injurers and noninjuring controls using self-report (the Emotional Reactivity Scale: ERS) and psychophysiological measures (the startle reflex was measured during and after the presentation of IAPS images). Self-injurers reported greater emotional reactivity on the ERS, but did not exhibit differences in startle modulation during or after picture viewing compared to controls. Results suggest a divergence between self-report and psychophysiological measures of emotion in NSSI.

The effects of caffeine and directed attention on acoustic startle habituation.

The present experiment tested the effects of caffeine on acoustic startle habituation during different attention tasks in which subjects either (a) attended to the acoustic startle stimulus (auditory attention; n = 9) (b) attended to a visual search task during presentation of acoustic startle stimuli (visual attention; n = 10), or (c) were given no specific instructions during acoustic startle testing (no attention; n = 9). Startle eyeblink responses were measured after subjects received either caffeine (1 mg/kg) or placebo. Caffeine significantly delayed response habituation in the no attention group and in the auditory attention group, but had no effect on habituation in the visual attention group. These data show that startle habituation can occur with minimal attention being directed to the acoustic startle stimulus, and that visual attention cancels the effects of caffeine on startle habituation.

Effects of Caffeine and Caffeine-Associated Stimuli on the Human Startle Eyeblink Reflex

An experiment was performed (n = 19) that investigated the effect of caffeine and expectancy of caffeine on the eyeblink component of the startle reflex. Nineteen habitual caffeine users received caffeinated coffee, caffeinated juice, decaffeinated coffee, or decaffeinated juice in four sessions spaced 1 week apart. Twenty-five to 30 min after ingestion of the liquid, 30 acoustic startle stimuli were presented. The results showed that caffeine increased startle eyeblink amplitude. Startle reflex onset latency was significantly longer in the decaffeinated coffee condition than in the other three conditions. This may have been due to the activation of a compensatory slowing of the reflex by the anticipation of caffeine, a slowing that was then overridden by caffeine speeding the response.