Comparison of response plasticity between the eyeblink and vertex potential in humans

Acquisition and retention of habituation as a function of intertrial interval duration during training in the blowfly

The influence of the duration of the interval between successive stimulations during habituation training on the dynamics of motor response decrement and its retention over time has been studied in the blowfly, Calliphora vomitoria . The intertrial interval (ITI) duration during training was either 7, 15, 30, 60 or 120 seconds. After a rest period of 30 minutes, a second session was given with the same ITI duration of 30 seconds for all groups. The response decrement observed during training is faster the longer the ITI duration. At the end of this session, the lower response level is reached with an ITI of 60 seconds. After the rest period, the lower responsiveness is observed in the animals which have been trained with the longer ITI. These results are discussed with reference to the dual-process theory of habituation, which can account for the results obtained during training, and memory-centered models to interpret the influence of ITI duration on retention performance.

Arousal and Habituation Effects (Excitability) on Startle Responses to the International Affective Picture Systems (IAPS)

The magnitude and habituation of startle reflex responses have been used to evaluate the excitability of the neural structures involved in this psychophysiological response. We analyzed the magnitude and habituation responses to startle reflex probes in 112 women. Results confirmed the modulation of eyeblink reflex by affective valence for arousing (F = 34.79, p < .001), but not for nonarousing pictures (F = 1.08, ns). Our results indicate that there is a linear adjustment for habituation in all picture groups, except for arousing unpleasant pictures where there is a quadratic adjustment that could be due to initial sensitization followed by the subsequent habituation. Multiple linear regression analysis revealed that the startle magnitude was partially determined by arousal and startle presentation order. In conclusion, our results emphasize the usefulness of arousing pictures to study startle reflex response and show evidence of different response mechanisms for pleasant and unpleasant pictures conditions.

Serotonergic hallucinogens as translational models relevant to schizophrenia

One of the oldest models of schizophrenia is based on the effects of serotonergic hallucinogens such as mescaline, psilocybin, and (+)-lysergic acid diethylamide (LSD), which act through the serotonin 5-HT(2A) receptor. These compounds produce a 'model psychosis' in normal individuals that resembles at least some of the positive symptoms of schizophrenia. Based on these similarities, and because evidence has emerged that the serotonergic system plays a role in the pathogenesis of schizophrenia in some patients, animal models relevant to schizophrenia have been developed based on hallucinogen effects. Here we review the behavioural effects of hallucinogens in four of those models, the receptor and neurochemical mechanisms for the effects and their translational relevance. Despite the difficulty of modelling hallucinogen effects in nonverbal species, animal models of schizophrenia based on hallucinogens have yielded important insights into the linkage between 5-HT and schizophrenia and have helped to identify receptor targets and interactions that could be exploited in the development of new therapeutic agents.

Mapping repetition suppression of the P50 evoked response to the human cerebral cortex

OBJECTIVE

The cerebral network subserving repetition suppression (RS) of the P50 auditory evoked response as observed using paired-identical-stimulus (S1-S2) paradigms is not well-described.

METHODS

We analyzed S1-S2 data from electrodes placed on the cortices of 64 epilepsy patients. We identified regions with maximal amplitude responses to S1 (i.e., stimulus registration), regions with maximal suppression of responses to S2 relative to S1 (i.e., RS), and regions with no or minimal RS 30-80 ms post stimulation.

RESULTS

Several temporal, parietal and cingulate area regions were shown to have significant initial registration activity (i.e., strong P50 response to S1). Moreover, prefrontal, cingulate, and parietal lobe regions not previously proposed to be part of the P50 habituation neural circuitry were found to exhibit significant RS.

CONCLUSIONS

The data suggest that the neural network underlying the initial phases of the RS process may include regions not previously thought to be involved like the parietal and cingulate cortexes. In addition, a significant role for the frontal lobe in mediating this function is supported.

SIGNIFICANCE

A number of regions of interest are identified through invasive recording that will allow further probing of the RS function using less invasive technology.

Mapping repetition suppression of the N100 evoked response to the human cerebral cortex

BACKGROUND

Repetition suppression (RS) phenomena, such as those observed using paired-identical-stimulus (S1-S2) paradigms, likely reflect adaptive functions such as habituation and, more specifically, sensory gating.

METHODS

To better characterize the neural networks underlying RS, we analyzed auditory S1-S2 data from electrodes placed on the cortices of 64 epilepsy patients who were being evaluated for surgical therapy. We identified regions with maximal amplitude responses to S1 (i.e., stimulus registration regions), regions with maximal suppression of responses to S2 relative to S1 (i.e., RS), and regions with no or minimal RS.

RESULTS

Auditory perceptual regions, such as the superior temporal gyri, were shown to have significant initial registration activity (i.e., strong response to S1). Several prefrontal, cingulate, and parietal lobe regions were found to exhibit stronger RS than those recorded from the auditory perceptual areas.

CONCLUSIONS

The data strongly suggest that the neural network underlying repetition suppression may include regions not previously thought to be involved, such as the parietal and cingulate cortexes. In addition, the data also support the notion that the initial response to stimuli and the ability to suppress the stimuli if repeated are two separate, but likely related, functions.

Considerations for the use of a startling acoustic stimulus in studies of motor preparation in humans

Recent studies have used a loud (> 120 dB) startle-eliciting acoustic stimulus as a probe to investigate early motor response preparation in humans. The use of a startle in these studies has provided insight into not only the neurophysiological substrates underlying motor preparation, but also into the behavioural response strategies associated with particular stimulus-response sets. However, as the use of startle as a probe for preparation is a relatively new technique, a standard protocol within the context of movement paradigms does not yet exist. Here we review the recent literature using startle as a probe during the preparation phase of movement tasks, with an emphasis on how the experimental parameters affect the results obtained. Additionally, an overview of the literature surrounding the startle stimulus parameters is provided, and factors affecting the startle response are considered. In particular, we provide a review of the factors that should be taken into consideration when using a startling stimulus in human research.

Habituation and sensitization of acoustic startle: opposite influences of dopamine D1 and D2-family receptors

The startle response evoked by repeated presentation of a loud acoustic stimulus is regulated by the independent processes of sensitization and habituation. While schizophrenia is associated with information processing impairments, there is conflicting evidence regarding the existence of habituation deficits in schizophrenic patients. Recent clinical evidence, however, indicates that patients with schizophrenia display exaggerated startle sensitization and diminished habituation. Given the linkage between dopaminergic abnormalities and schizophrenia, the goal of the present investigation was to examine the effect of deleting D1 and D2-like dopamine receptors on sensitization and habituation of the acoustic startle reflex in mice. For these experiments, the acoustic startle reflex was assessed in dopamine D1, D2, and D3 receptor wild-type (WT) and knockout (KO) mice on a C57BL/6J background, using a methodology that can measure both sensitization and habituation. Mice lacking the D1 receptor gene displayed enhanced sensitization, along with a decrease in the amount of habituation that occurs in response to repetitive presentations of a startling stimulus. Conversely, the loss of the dopamine D2 or D3 receptor gene produced a sensitization deficit and a significant increase in habituation. The behavioral phenotype exhibited by D1 receptor KO mice is clearly distinct from that of the D2 and D3 receptor KO mice. The findings in D1 receptor KO mice are reminiscent of the abnormalities observed in schizophrenic patients tested in comparable startle paradigms, and indicate that D1 agonists may possess therapeutic efficacy against the information processing deficits associated with schizophrenia.

Sensitization and habituation of the acoustic startle reflex in patients with schizophrenia

Assessments of prepulse inhibition and habituation of the acoustic startle response have proved to be valuable tools for assessing deficits of sensorimotor gating and information processing in schizophrenia patients. Recent studies, however, have reported inconsistent results regarding startle habituation deficits in schizophrenia using block-to-block analyses. Some of these inconsistencies may be due to abnormal initial sensitization effects to startle-eliciting stimuli. In a longitudinal study during the course of an acute psychotic episode, 34 medicated inpatients were examined with regard to sensitization and habituation effects in a trial-by-trial analysis and compared with 18 normal control subjects. On two examinations--10 days after admission and after psychopathological improvement 2-3 weeks later--schizophrenia patients exhibited an exaggerated magnitude increment across the first few startle-eliciting stimuli and habituation deficits that were evident when the effect of sensitization was removed from analysis. In the present study, both increased sensitization and reduced habituation appeared to be trait markers of schizophrenic psychoses. The enhanced sensitization effect--presumably due to an abnormal arousal modulation--reflects abnormal stimulus processing in schizophrenia, i.e. the diminished ability to learn the irrelevance of simple identical stimuli. In addition, the present data have important implications for designing startle studies to assess sensitization, habituation and prepulse inhibition in one session.

Modulation of startle and the startle-elicited P300 by the conditions of the cued continuous performance task in school-age boys

OBJECTIVES

This study compares the modulation of the startle response by conditions requiring response preparation, production, and inhibition during a cued continuous performance task (CPT) in children to the results of previous studies in adults and evaluates the modulation of the startle-elicited P300 under the same conditions. The latter variable, reflecting the cognitive processing of the startling stimulus (SS), has not been studied under these conditions.

METHODS

Normal boys completed a cued CPT in which the cue was the letter T, the go condition requiring a button press was an X following the T, and the no-go condition requiring response inhibition was a letter other than X following the T. SS were presented 450 ms following the letter of interest in each condition. The amplitudes of the startle-elicited P300 at Fz, Cz, and Pz and the startle blink were compared in the different CPT conditions.

RESULTS

The startle blink, measured by orbicularis oculi electromyography, was not inhibited by the no-go CPT condition as is the case in adults. The vertical electro-oculogram was actually largest in the no-go condition. The startle-elicited P300 showed a central predominance and was significantly larger in the no-go condition and in the cue condition than in the go condition.

CONCLUSIONS

The absence of inhibition of the startle response during the no-go condition probably reflects a relative inefficiency of prefrontal cortical mechanisms that mediate response inhibition in children compared to adults. The enhanced startle-elicited P300 in the no-go and cue conditions of the CPT reflects cognitive processing of the SS that has been influenced by response inhibition or its anticipation.

A primary acoustic startle pathway: obligatory role of cochlear root neurons and the nucleus reticularis pontis caudalis

Davis et al. (1982) proposed a primary acoustic startle circuit in rats consisting of the auditory nerve, posteroventral cochlear nucleus, an area near the ventrolateral lemniscus (VLL), nucleus reticularis pontis caudalis (PnC), and spinal motoneurons. Using fiber-sparing lesions, the present study reevaluated these and other structures together with the role of neurons embedded in the auditory nerve [cochlear root neurons (CRNs)], recently hypothesized to be involved in acoustic startle. Small electrolytic lesions of the VLL of ventrolateral tegmental nucleus (VLTg) failed to eliminate startle. Large electrolytic lesions including the rostral ventral nucleus of the trapezoid body (rVNTB) and ventrolateral parts of PnC or lesions of the entire PnC blocked startle. However, small NMDA-induced lesions of the rVNTB failed to block startle, making it unlikely that the rVNTB itself is part of the startle pathway. In contrast, NMDA lesions of the full extension of the ventrolateral part of the PnC blocked startle completely, suggesting that the ventrolateral part of the PnC is critically involved. Bilateral kainic acid lesions of CRNs also blocked the startle reflex completely, providing the first direct evidence for an involvement of CRNs in startle. This blockade probably was not caused by damage to the auditory nerve, because the lesioned animals showed intact compound action potentials recorded from the ventral cochlear nucleus. Hence, a primary acoustic startle pathway may involve three synapses onto (1) CRNs, (2) neurons in PnC, and (3) spinal motoneurons.

Habituation of P300 and reflex motor (startle blink) responses to repetitive startling stimuli in children

Positive EEG deflections with the latency and scalp distribution of the P300 accompany startle in response to loud auditory stimuli in a non-task context. The purpose of this investigation is to determine if habituation would have effects on the P300 similar to those on the startle blink. Thirty-four normal 7 to 11-year-old boys from a startle habituation study had EEG recordings of sufficient quality to provide data for the current study. Startle was measured both as orbicularis oculi EMG and vertical EOG and P300 was recorded at Pz in response to 40,104 dB bursts of white noise presented at 23-s intervals. Both the startle response and the P300 habituated toward asymptotic levels after the first 28 trials, suggesting that both startle and the subsequent cognitive evaluation of the startling stimulus, reflected in the P300 response, are modulated by a common neurophysiological mechanism extrinsic to the direct startle pathway. A modest significant correlation between the P300 and the vertical EOG peak latencies for the initial trials suggests that the cognitive evaluation of the startling stimulus may also include evaluation of the reflex response to that stimulus. Analyses of the within-subject associations between startle and P300 initial amplitudes and rates of habituation showed that these parameters varied independently within the individual subject, suggesting that the P300 is not a component of the startle response. Rather, it reflects an evaluation of the startling stimulus, decreasing in amplitude as the surprising value of the startling stimulus decreases with habituation.

Prestimulation-induced modulation of the P300 component of event related potentials accompanying startle in children

Positive EEG deflections with the latency and scalp distribution of the P300 accompany startle in response to loud auditory stimuli in a non-task context. The purpose of this investigation is to determine if inhibitory and facilitatory prestimulation would have effects on the P300 similar to those on the startle blink. Prestimulation conditions were chosen to induce startle amplitude facilitation (4000 msec sustained tone), startle amplitude inhibition (120 msec prestimulation interval), and startle onset latency facilitation (60 msec prestimulation interval). Ninety-three boys (including normals and those with ADHD and/or enuresis) from a startle modulation study had EEG recordings of sufficient quality to provide data for the current study. Repeated measures analyses of variance demonstrated startle amplitude and P300 amplitude facilitation following the 4000 msec tone, startle amplitude and P300 amplitude inhibition following the 120 msec prestimulation interval, and startle onset latency and P300 peak latency facilitation (shorter latencies) following the 60 msec prestimulation interval. Hence, the vertex-recorded P300 elicited by startling stimuli was modulated by non-startling prestimulation in a manner that paralleled that of modulation of the brain-stem generated startle blink. Startle inhibition by prestimulation is mediated by an inhibitory pathway in the mesopontine lateral tegmentum. This brain-stem circuitry has a similar effect on the P300 even though the latter may be generated in more rostral structures. Alternatively, this automatically elicited P300 may represent a limbic or cortical reflection of the sensory processing taking place in the brain-stem. Either interpretation suggests a "bottom-up" as contrasted with a "top-down" mode of sensory processing. This P300 obeys the rules of startle modulation by brain-stem mechanisms rather than indexing cortical evaluation of stimuli for task relevance, stimulus probability, and prior uncertainty.

Effects of stimulus repetition, duration, and rise time on startle blink and automatically elicited P300

Intense auditory stimuli of sudden onset evoke not only startle blinks but also an event-related potential component resembling classic P300, even when subjects have no assigned task. To more closely examine the relationship of this P300 to startle, event-related potentials and eyeblink were recorded from 16 young adults in three paradigms designed to produce wide variation in startle amplitude: an Habituation series of 30-ms, 105dBA white noise bursts, a Duration paradigm which presented 105dB noise bursts for 3, 10, 30, or 90 ms, and a Rise Time paradigm which varied the rise/fall times (3, 15, 30, and 45 ms) of 110dBA, 1000-Hz tone bursts. Subjects received two runs of each paradigm. Only on the final Duration and Rise Time runs were stimuli explicitly task relevant; on those runs subjects rated verbally, midway in each 8.4-s interstimulus interval, the disturbingness of the prior sound. Although even the briefest noise bursts evoked parietal P300 as well as startle blink, P300 did not behave like startle. P300 habituated more slowly than did blink amplitude, was more responsive to sustained noise than were blink, N110, and P190, and most importantly, did not show the sensitivity to stimulus rise time manifested by these measures. These findings suggest that the amplitude of automatically elicited P300 is not governed by the same mechanisms as startle amplitude, but behaves more like a defense response.

Effects of levonantradol on habituation of startle in rats

Levonantradol, a nonopioid analgetic related to cannabinoids, produced a dose-dependent impairment of the habituation of startle response in rats. Startle was elicited by air-puff stimuli and monitored in stabilimeters by a computer. Habituation was assessed by presenting the same tactile stimulus repeatedly at 15-second intervals. While a dose of 0.1 mg/kg reduced startle on all trials, doses ranging from 0.01 to 0.03 mg/kg had no effect on the initial level of reactivity to the first several stimuli but did impair the habituation of startle. This effect was not attributable to the time course of the drug's action and was also found with acoustic stimuli. The relatively inactive enantiomer of levonantradol was ineffective at 0.1 mg/kg. Thus, startle appears to be a sensitive measure of the effects of levonantradol in animals. Since comparable phenomena can be demonstrated in humans by measuring the blink reflex component of startle, direct comparisons can potentially be made across species.

The acoustic blink reflex: stimulus dependence, excitability and localizing value

The acoustic blink reflex was examined in 26 subjects with open eyes and 20 subjects with closed eyes by means of an electrooculogram. Amplitude and excitability are highly dependent on the loudness of the stimulus used and on the opening or closure of the eyelids. Particularly if the eyes are closed, it may be necessary to use a stimulus of high (105-110 dB SPL) intensity (hand-clapping is often not loud enough). If an acoustic blink reflex can be elicited, it can be assumed that certain pontine and mesencephalic structures are intact.

Neurochemical modulation of sensory-motor reactivity: acoustic and tactile startle reflexes

The present review argues that the startle reflex is particularly well suited as a model system to analyze how drugs alter stimulus reactivity and reflex excitability. It then reviews all the literature to date on how drugs or lesions that are thought to alter neurochemical transmitter systems affect acoustic and/or tactile startle. Hypotheses are presented to account for how serotonin, dopamine, norepinephrine, acetylcholine, and opiates modulate startle. Effects on startle plasticity such as habituation, sensitization, and potentiation resulting from prior associative learning are also included.