Repeated testing of prepulse inhibition and habituation of the startle reflex: a study in healthy human controls

Testing Prepulse Inhibition of Acoustic Startle in Rodents

Prepulse inhibition (PPI) is a measure of sensorimotor gating which is widely used in rodents to study information processing and attention dysfunction. PPI is commonly measured in rats and mice using automated equipment. Here, we present details of a PPI testing protocol extensively used in previous studies. The protocol includes a set pulse-alone startle level and prepulse-pulse combinations with varying interval and intensity. Variations of this protocol can be used depending on the experimental aim or equipment and software version.

Negative emotion-conditioned prepulse induces the attentional enhancement of prepulse inhibition in humans

Prepulse inhibition (PPI) is a reduction of the acoustic startle reflex (ASR) when the startling stimulus is preceded by a weaker and non-startling stimulus (i.e., prepulse). Previous studies have revealed that PPI can be top-down modulated by selective attention to the fear-conditioned prepulse in animals. However, few researchers have tested this assumption in humans. Thus, in this study, the negative emotional-conditioned prepulse (CS+) was used to explore whether it could improve participants' attention, and further improve the PPI. The results showed that the CS+ prepulse increased the PPI only in females, PPI produced by CS+ prepulse was larger in females than in males, and the perceptual spatial attention further improved the PPI in both females and males. The results suggested that the PPI was affected by emotional, perceptual spatial attention, and sex. These findings highlight an additional method to measure top-down attentional regulation of PPI in humans. Which may offer a useful route to enhance the diagnosis of affective disorders, such as anxiety, depression, and post-traumatic stress disorder.

Prospective longitudinal assessment of sensorimotor gating as a risk/resiliency factor for posttraumatic stress disorder

Little is understood about cognitive mechanisms that confer risk and resiliency for posttraumatic stress disorder (PTSD). Prepulse Inhibition (PPI) is a measure of pre-attentional response inhibition that is a stable cognitive trait disrupted in many neuropsychiatric disorders characterized by poor behavioral or cognitive inhibition, including PTSD. Differentiating between PTSD-related phenotypes that are pre-existing factors vs. those that emerge specifically after trauma is critical to understanding PTSD etiology and can only be addressed by prospective studies. This study tested the hypothesis that sensorimotor gating performance is associated with risk/resiliency for combat-related PTSD. As part of a prospective, longitudinal study, 1226 active duty Marines and Navy Corpsman completed a PPI test as well as a clinical interview to assess PTSD symptoms both before,  and 3 and 6 months after a combat deployment. Participants that developed PTSD 6 months following deployment (N=46)  showed lower PPI across pre and post-deployment time points compared to participants who did not develop PTSD (N=1182) . Examination of the distribution of PTSD across PPI performance revealed a lower than expected number of cases in the highest performing quartile compared to the rest of the distribution (p < 0.04). When controlling for other factors that predict PTSD in this population, those in the top 25% of PPI performance showed a >50% reduction in chance to develop PTSD (OR = 0.32). Baseline startle reactivity and startle habituation were not significantly different between PTSD risk and control groups. These findings suggest that robust sensorimotor gating may represent a resiliency factor for development of PTSD following trauma.

Test-retest reliability of prepulse inhibition (PPI) and PPI correlation with working memory

OBJECTIVE

Sensorimotor gating is experimentally operationalized by the prepulse inhibition (PPI) of the startle response (SR). Previous studies suggest high test-retest reliability of PPI and potential correlation with working memory (WM). Here, we aimed to validate and extend the test-retest reliability of PPI in healthy humans and its correlation with WM performance.

METHODS

We applied an acoustic startle PPI paradigm with four different prepulse intensities (64, 68, 72 and 76 dB) and two different WM tasks [n-back, change detection task (CDT)] in a group of 26 healthy adults (final sample size n = 23). To assess test-retest reliability, we performed all tests on two separate days ~27 days (range: 21-32 days) apart.

RESULTS

We were able to confirm high test-retest reliability of the PPI with a mean intraclass correlation (ICC) of > 0.80 and significant positive correlation of PPI with n-back but not with CDT performance. Detailed analysis showed that PPI across all prepulse intensities significantly correlated with both the 2-back and 0-back conditions, suggesting regulation by cross-conditional processes (e.g. attention). However, when removing the 0-back component from the 2-back data, we found a specific and significant correlation with WM for the 76-dB PPI condition.

CONCLUSION

With the present study, we were able to confirm the high test-retest reliability of the PPI in humans and could validate and expand on its correlation with WM performance.

The influence of stimulus onset asynchrony, task order, sex and hormonal contraception on prepulse inhibition and prepulse facilitation: Methodological considerations for drug and imaging research

BACKGROUND

Prepulse-induced startle modulation occurs when a weak sensory stimulus ('prepulse') is presented before a startling sensory stimulus ('pulse'), producing an inhibited (Prepulse Inhibition, PPI) or facilitated (Prepulse Facilitation, PPF) startle response. We recently identified several gaps and outlined future lines of enquiry to enable a fuller understanding of the neurobiology of PPI and PPF in healthy and clinical populations. However, before embarking on these studies, it is important to consider how task and population characteristics affect these phenomena in healthy humans.

METHODS

We examined PPI and PPF in separate tasks, with counterbalanced task order across participants in one session, using a range of stimulus onset asynchronies (SOAs), in 48 healthy adults (23 men, 25 women; 10 hormonal contraceptive users) to determine which SOAs produce the strongest PPI and PPF and also explored how sex and hormonal contraception might influence PPI and PPF under these experimental conditions.

RESULTS

Both PPI and PPF were affected by SOA, with greatest PPI observed at 60 and 120 ms, and greatest PPF at 4500 and 6000 ms. PPI was influenced by sex (more PPI in men than women) and hormonal contraception, whereas PPF was affected by task order (greater PPF when the PPF task followed, rather than preceded, the PPI task).

CONCLUSIONS

Our findings indicate that studies of PPI and PPF need to consider, not only sex and hormonal status of study participants, but also task characteristics and presentation order to reduce variance and increase replicability across studies.

Receptor-Mediated AKT/PI3K Signalling and Behavioural Alterations in Zebrafish Larvae Reveal Association between Schizophrenia and Opioid Use Disorder

The link between substance abuse and the development of schizophrenia remains elusive. In this study, we assessed the molecular and behavioural alterations associated with schizophrenia, opioid addiction, and opioid withdrawal using zebrafish as a biological model. Larvae of 2 days post fertilization (dpf) were exposed to domperidone (DMP), a dopamine-D2 dopamine D2 receptor antagonist, and morphine for 3 days and 10 days, respectively. MK801, an N-methyl-D-aspartate (NMDA) receptor antagonist, served as a positive control to mimic schizophrenia-like behaviour. The withdrawal syndrome was assessed 5 days after the termination of morphine treatment. The expressions of schizophrenia susceptibility genes, i.e., pi3k, akt1, slc6a4, creb1 and adamts2, in brains were quantified, and the levels of whole-body cyclic adenosine monophosphate (cAMP), serotonin and cortisol were measured. The aggressiveness of larvae was observed using the mirror biting test. After the short-term treatment with DMP and morphine, all studied genes were not differentially expressed. As for the long-term exposure, akt1 was downregulated by DMP and morphine. Downregulation of pi3k and slc6a4 was observed in the morphine-treated larvae, whereas creb1 and adamts2 were upregulated by DMP. The levels of cAMP and cortisol were elevated after 3 days, whereas significant increases were observed in all of the biochemical tests after 10 days. Compared to controls, increased aggression was observed in the DMP-, but not morphine-, treated group. These two groups showed reduction in aggressiveness when drug exposure was prolonged. Both the short- and long-term morphine withdrawal groups showed downregulation in all genes examined except creb1, suggesting dysregulated reward circuitry function. These results suggest that biochemical and behavioural alterations in schizophrenia-like symptoms and opioid dependence could be controlled by common mechanisms.

Evaluating the Modulation of the Acoustic Startle Reflex in Children and Adolescents via Vertical EOG and EEG: Sex, Age, and Behavioral Effects

Acoustic startle reflex (ASR) constitutes a reliable, cross-species indicator of sensorimotor and inhibitory mechanisms, showing distinct signature in cognitive aging, sex, and psychopathological characterization. ASR can be modulated by the prepulse inhibition (PPI) paradigm, which comprises the suppression of reactivity to a startling stimulus (pulse) following a weak prepulse (30- to 500-ms time difference), being widely linked to inhibitory capabilities of the sensorimotor system. If the prepulse–pulse tones are more clearly separated (500–2,000 ms), ASR amplitude is enhanced, termed as prepulse facilitation (PPF), reflecting sustained or selective attention. Our study aimed to investigate early-life sensorimotor sex/age differences using Electroencephalographic recordings to measure muscular and neural ASR in a healthy young population. Sixty-three children and adolescents aged 6.2–16.7 years (31 females) took part in the experiment. Neural ASR was assessed by two different analyses, namely, event-related potentials (ERPs) and first-derivative potentials (FDPs). As expected, PPF showed enhanced responses compared with PPI, as indicated by eyeblink, ERP and FDP measures, confirming the gating effect hypothesis. Sex-related differences were reflected in FDPs, with females showing higher ASR than males, suggesting increased levels of poststartle excitability. Intragroup age effects were evaluated via multipredictor regression models, noticing positive correlation between age versus eyeblink and ERP responses. Attention-related ERPs (N100 and P200) showed distinct patterns in PPI versus PPF, potentially indicative for alternative attentional allocation and block-out of sensory overload. Screening measures of participants’ neurodevelopmental (assessed by Wechsler Intelligence Scale for Children) and behavioral (assessed by Child Behavior Checklist) markers were also associated with increased N100/P200 responses, presumably indexing synergy between perceptual consistency, personality profiling, and inhibitory performance. Conclusively, modulation of ASR by PPI and PPF is associated with biological sex and internal/external personality traits in childhood and adolescence, potentially useful to guide symptomatology and prevention of psychopathology.

Neural mapping of prepulse-induced startle reflex modulation as indices of sensory information processing in healthy and clinical populations: A systematic review

Startle reflex is modulated when a weaker sensory stimulus ("prepulse") precedes a startling stimulus ("pulse"). Prepulse Inhibition (PPI) is the attenuation of the startle reflex (prepulse precedes pulse by 30-500 ms), whereas Prepulse Facilitation (PPF) is the enhancement of the startle reflex (prepulse precedes pulse by 500-6000 ms). Here, we critically appraise human studies using functional neuroimaging to establish brain regions associated with PPI and PPF. Of 10 studies, nine studies revealed thalamic, striatal and frontal lobe activation during PPI in healthy groups, and activation deficits in the cortico-striato-pallido-thalamic circuitry in schizophrenia (three studies) and Tourette Syndrome (two studies). One study revealed a shared network for PPI and PPF in frontal regions and cerebellum, with PPF networks recruiting superior medial gyrus and cingulate cortex. The main gaps in the literature are (i) limited PPF research and whether PPI and PPF operate on separate/shared networks, (ii) no data on sex differences in neural underpinnings of PPI and PPF, and (iii) no data on neural underpinnings of PPI and PPF in other clinical disorders.

Early auditory-evoked potentials in body dysmorphic disorder: An ERP/sLORETA study

Body dysmorphic disorder (BDD) is characterized by excessive preoccupation with imagined or slight physical defects in appearance. BDD is associated with cognitive impairments (attention, visual processing). Our study aims to evaluate the early neural responses (N100, P200) to prepulse inhibition (PPI) and prepulse facilitation (PPF), to investigate attentional processing of BDD in the auditory domain. Fifty-five adults took part: 30 BDD patients and 25 healthy controls. We compared their brain responses to PPI and PPF by analyzing global field power (GFP), event-related potentials (ERPs) and their respective sources. BDD exhibited reduced N100 amplitudes compared to healthy controls in response to the startle tone elicited by both PPI and PPF, potentially suggesting impaired allocation of attention. Interestingly, the lower the GFP at the N100, the higher the BDD severity. Source reconstruction analysis showed reduced activation for BDD during the N100 time window in PPI. Scalp responses and source activations in PPI were decreased overall compared to PPF, confirming the gating effect of PPI. We provided evidence that the N100 may serve as an electrophysiological marker of BDD, predicting its severity. Our study demonstrated the potential of using ERPs combined with behavioural PPI and PPF protocols to advance our understanding of BDD pathophysiology.

Life-Course Contribution of Prenatal Stress in Regulating the Neural Modulation Network Underlying the Prepulse Inhibition of the Acoustic Startle Reflex in Male Alzheimer's Disease Mice

The prepulse inhibition (PPI) of the acoustic startle reflex (ASR), as an index of sensorimotor gating, is one of the most extensively used paradigms in the field of neuropsychiatric disorders. Few studies have examined how prenatal stress (PS) regulates the sensorimotor gating during the lifespan and how PS modifies the development of amyloid-beta (Aβ) pathology in brain areas underlying the PPI formation. We followed alternations in corticosterone levels, learning and memory, and the PPI of the ASR measures in APPNL-G-F/NL-G-F offspring of dams exposed to gestational noise stress. In-depth quantifications of the Aβ plaque accumulation were also performed at 6 months. The results indicated an age-dependent deterioration of sensorimotor gating, long-lasting PS-induced abnormalities in PPI magnitudes, as well as deficits in spatial memory. The PS also resulted in a higher Aβ aggregation predominantly in brain areas associated with the PPI modulation network. The findings suggest the contribution of a PS-induced hypothalamic-pituitary-adrenal (HPA) axis hyperactivity in regulating the PPI modulation substrates leading to the abnormal development of the neural protection system in response to disruptive stimuli. The long-lasting HPA axis dysregulation appears to be the major underlying mechanism in precipitating the Aβ deposition, especially in brain areas contributed to the PPI modulation network.

Disrupted sensorimotor gating in first-episode psychosis patients is not affected by short-term antipsychotic treatment

BACKGROUND

Impaired sensorimotor gating, commonly measured as disrupted prepulse inhibition (PPI) of the acoustic startle response, has been widely observed in psychotic diseases. However, most PPI studies published so far involve patients with long illness duration and different drug treatments. Few studies have investigated untreated patients at their first episode of psychotic symptoms.

METHOD

PPI is an acoustic startle paradigm (30, 60-, 120-ms interstimulus intervals). Startle reactivity and habituation were succesfully assessed in 49 antipsychotic-naïve first-episode psychosis (FEP) patients and compared with 35 age- and gender-matched healthy control subjects. Mean age of patients was 28 years and 27 for controls. Patients treated with antipsychotics more than 30 days were not included in the study and twenty-three out of forty-nine patients received antipsychotic treatment with a mean treatment time of 13 days.

RESULTS

PPI was significantly lower in FEP patients, compared to healthy controls. The PPI deficiency found in these patients was not due to antipsychotic treatment since PPI did not differ between treated (n=23) and untreated patients n=(26). By using the latent curve modeling we identified a delayed habituation in patients treated with antipsychotics, suggesting that antipsychotic treatment should be considered as a confound when investigating habituation in schizophrenia.

CONCLUSIONS

Our results suggest that acute pharmacological treatment does not normalize PPI in FEP patients but should be considered as a confound when investigating habituation in these patients.

Meta-Analysis of Sensorimotor Gating Deficits in Patients With Schizophrenia Evaluated by Prepulse Inhibition Test

Prepulse inhibition (PPI) of startle is an operational measure of sensorimotor gating that is often impaired in patients with schizophrenia. Despite the large number of studies, there is considerable variation in PPI outcomes reported. We conducted a systematic review and meta-analysis investigating PPI impairment in patients with schizophrenia compared with healthy control subjects, and examined possible explanations for the variation in results between studies. Major databases were screened for observational studies comparing healthy subjects and patients with schizophrenia for the prepulse and pulse intervals of 60 and 120 ms as primary outcomes, ie, PPI-60 and PPI-120. Standardized mean difference (SMD) and 95% confidence intervals (CI) were extracted and pooled using random effects models. We then estimated the mean effect size of these measures with random effects meta-analyses and evaluated potential PPI heterogeneity moderators, using sensitivity analysis and meta-regressions. Sixty-seven primary studies were identified, with 3685 healthy and 4290 patients with schizophrenia. The schizophrenia group showed reduction in sensorimotor gating for both PPI-60 (SMD = -0.50, 95% CI = [-0.61, -0.39]) and PPI-120 (SMD = -0.44, 95% CI = [-0.54, -0.33]). The sensitivity and meta-regression analysis showed that sample size, gender proportion, imbalance for gender, source of control group, and study continent were sources of heterogeneity (P < .05) for both PPI-60 and PPI-120 outcomes. Our findings confirm a global sensorimotor gating deficit in schizophrenia patients, with overall moderate effect size for PPI-60 and PPI-120. Methodological consistency should decrease the high level of heterogeneity of PPI results between studies.

Auditory cognitive training improves prepulse inhibition in serine racemase mutant mice

Evidence indicates that neuroplasticity-based cognitive training can improve cognition in patients with schizophrenia, but the individual response to training varies greatly between subjects. Hence, there is a need to understand the neurological underpinnings of cognitive training to reveal predictors of treatment response. D-serine is a crucial modulator of neuroplasticity, and decreased levels of D-serine may contribute to deficits in neuroplasticity in schizophrenia. Interestingly, we observed that training mice to identify auditory oddballs increased extracellular levels of D-serine in the hippocampus during training. Serine racemase (Srr) is the only source of brain D-serine; thus, it is possible that Srr may mediate the response to training. To test this hypothesis, we trained mice that have a mutated version of Srr (SrrY269*/SrrY269*) and reduced levels of D-serine in the same auditory training. SrrY269*/SrrY269* mice showed decreased performance during auditory training (defined as the capacity to discriminate an oddball during a sequence of tones). Importantly, auditory training improved prepulse inhibition (PPI) in SrrY269*/SrrY269* but not in wild-type mice. Finally, D-serine (100 mg/kg i.p.) given 30 min before training sessions to SrrY269*/SrrY269* mice improved training performance, but it did not enhance PPI. Taken together, our results show that D-serine is involved in the response to neuroplasticity-based auditory training and that PPI deficits can be improved by auditory oddball training even in the presence of neuroplasticity deficits.

Prepulse inhibition of the acoustic startle reflex and P50 gating in aging and alzheimer's disease

Inhibition plays a crucial role in many functional domains, such as cognition, emotion, and actions. Studies on cognitive aging demonstrate changes in inhibitory mechanisms are age- and pathology-related. Prepulse inhibition (PPI) is the suppression of an acoustic startle reflex (ASR) to an intense stimulus when a weak prepulse stimulus precedes the startle stimulus. A reduction of PPI is thought to reflect dysfunction of sensorimotor gating which normally suppresses excessive behavioral responses to disruptive stimuli. Both human and rodent studies show age-dependent alterations of PPI of the ASR that are further compromised in Alzheimer's disease (AD). The auditory P50 gating, an index of repetition suppression, also is characterized as a putative electrophysiological biomarker of prodromal AD. This review provides the latest evidence of age- and AD-associated impairment of sensorimotor gating based upon both human and rodent studies, as well as the AD-related disruption of P50 gating in humans. It begins with a concise review of neural networks underlying PPI regulation. Then, evidence of age- and AD-related dysfunction of both PPI and P50 gating is discussed. The attentional/ emotional aspects of sensorimotor gating and the neurotransmitter mechanisms underpinning PPI and P50 gating are also reviewed. The review ends with conclusions and research directions.

Prepulse inhibition and “psychosis-proneness” in healthy individuals: An fMRI study

Objective

Prepulse inhibition (PPI) of the startle response provides an operational index of sensorimotor gating that is reliably demonstrable in both human and animal subjects. Patients with schizophrenia, first-degree relatives of patients with schizophrenia, patients with schizotypal personality disorder and healthy individuals scoring high on psychometric measures of psychosis-proneness display reduced PPI. This study examined associations between individual differences in “psychosis-proneness” and brain activity during a tactile prepulse inhibition paradigm previously found to reveal activation in controls and deficient activation in schizophrenia patients in the striatum, thalamus, insula, hippocampal, temporal, inferior frontal, and inferior parietal regions.

Methods

Fourteen right-handed healthy men underwent psychophysiological testing and functional magnetic resonance imaging (fMRI) during a 15-min tactile PPI paradigm involving the use of tactile stimuli as both the pulse (a 40-ms presentation of 30 psi air-puff) and the prepulse (a 20-ms presentation of 6 psi air-puff presented 30-ms or 120-ms before the pulse). Individual differences in “psychosis-proneness” were assessed with Psychoticism scale of the Eysenck Personality Questionnaire-Revised (EPQ-R).

Results

High psychosis-proneness was associated with lower PPI and reduced activity in the inferior frontal gyrus, insula extending to putamen and thalamus, parahippocampal gyrus, and inferior parietal and middle temporal regions. No regional activity correlated positively with psychosis-proneness.

Conclusions

The present observations extend the findings observed previously in people with schizophrenia to people with high psychosis-proneness, providing support to continuum theories of psychosis with implications for understanding trait-related neural deficits in schizophrenia.

The Impact of Removal of Ovarian Hormones on Cholinergic Muscarinic Receptors: Examining Prepulse Inhibition and Receptor Binding

Ovarian hormones, such as estrogens and progesterone, are known to exert beneficial effects on cognition and some psychiatric disorders. The basis of these effects is not fully understood, but may involve altered cholinergic neurotransmission. This study aimed to investigate how a lack of ovarian hormones would impact muscarinic receptor-induced deficits in prepulse inhibition (PPI) and muscarinic receptor density in several brain regions. Adult female rats were either ovariectomized, to remove the source of ovarian hormones, or left intact (sham-operated). PPI is a measure of sensorimotor gating that is typically impaired in schizophrenia patients, and similar deficits can be induced in rats by administering scopolamine, a muscarinic receptor antagonist. Our results revealed no significant effects of ovariectomy on PPI after saline or scopolamine treatment. Autoradiography was performed to measure cholinergic muscarinic receptor binding density using [³H]-pirenzepine, [³H]-AF-DX, and [³H]-4-DAMP, to label M₁, M₂/M₄, and M₃ receptors, respectively. We examined the amygdala, caudate putamen, dorsal hippocampus, motor cortex, retrosplenial cortex, and ventromedial hypothalamus. There were no significant group differences in any region for any muscarinic receptor type. These results suggest that removing peripheral ovarian hormones does not influence the cholinergic muscarinic receptor system in the context of PPI or receptor binding density.

Evidence of Slow Neural Processing, Developmental Differences and Sensitivity to Cannabis Effects in a Sample at Clinical High Risk for Psychosis From the NAPLS Consortium Assessed With the Human Startle Paradigm

ABSTRACT

Biomarkers are important in the study of the prodromal period of psychosis because they can help to identify individuals at greatest risk for future psychotic illness and provide insights into disease mechanism underlying neurodevelopmental abnormalities. The biomarker abnormalities can then be targeted with treatment, with an aim toward prevention or mitigation of disease. The human startle paradigm has been used in translational studies of psychopathology including psychotic illness to assess preattentive information processing for over 50 years. In one of the largest studies to date in clinical high risk (CHR) for psychosis participants, we aimed to evaluate startle indices as biomarkers of risk along with the role of age, sex, treatment, and substance use in this population of high risk individuals.

METHODS

Startle response reactivity, latency, and prepulse inhibition (PPI) were assessed in 543 CHR and 218 Normal Comparison (NC) participants between the ages of 12 and 35.

RESULTS

At 1 year follow-up, 58 CHR participants had converted to psychosis. CHR and NC groups did not differ across any of the startle measures but those CHR participants who later converted to psychosis had significantly slower startle latency than did those who did not convert to psychosis, and this effect was driven by female CHR participants. PPI was significantly associated with age in the CHR, but not the NC, participants with the greatest positive age correlations present in those CHR participants who later converted to psychosis, consistent with a prior report. Finally, there was a significant group by cannabis use interaction due to greater PPI in cannabis users and opposite PPI group effects in users (CHR>NC) and non-users (NC>CHR).

DISCUSSION

This is the first study to demonstrate a relationship of startle response latency to psychotic conversion in a CHR population. PPI is an important biomarker that may be sensitive to the neurodevelopmental abnormalities thought to be present in psychosis prone individuals and the effects of cannabis. The significant correlations with age in this sample as well as the finding of greater PPI in CHR cannabis users replicate findings from another large sample of CHR participants.

Investigating the effect of anticipating a startling acoustic stimulus on preparatory inhibition

OBJECTIVES

Motor-evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) show a profound suppression when elicited during the instructed-delay of reaction time (RT) tasks. One predominant hypothesis is that this phenomenon, called "preparatory inhibition", reflects the operation of processes that suppress motor activity to withhold prepared (but delayed) responses, a form of impulse control. In addition, a startling acoustic stimulus (SAS) - a loud and narrow sound - can trigger the release of prepared responses in RT tasks. We predicted that, if such premature release is clearly forbidden, then anticipating a SAS during delay periods may be associated with increased preparatory inhibition for greater impulse control.

METHODS

Subjects performed a behavioural (n=16) and TMS (n=11) experiment. Both used a choice RT task that required subjects to choose a response based on a preparatory cue but to only release it after an imperative signal. SAS and TMS pulses were elicited at the end of the delay period and subjects were asked to do their best to only release their response after the imperative signal, even in the presence of SAS. SAS could be either rare or frequent, in separate blocks.

RESULTS

Consistent with the literature, SAS shortened RTs, especially when they occurred frequently. Moreover, MEPs were suppressed when subjects delayed prepared responses but this preparatory inhibition did not depend on whether SAS were frequent or rare.

DISCUSSION

The stronger RT shortening with frequent rather than rare SAS may be due to increased attention and/or reduced reactive inhibition to SAS, leaving preparatory inhibition unaffected.

Startling Differences: Using the Acoustic Startle Response to Study Sex Differences and Neurosteroids in Affective Disorders

PURPOSE OF REVIEW

Neuroactive steroid hormones, such as estradiol and progesterone, likely play a role in the pathophysiology of female-specific psychiatric disorders such as premenstrual dysphoric disorder (PMDD) and postpartum depression and may contribute to the marked sex differences observed in the incidence and presentation of affective disorders. However, few tools are available to study the precise contributions of these neuroactive steroids (NSs). In this review, we propose that the acoustic startle response (ASR), an objective measure of an organism's response to an emotional context or stressor, is sensitive to NSs. As such, the ASR represents a unique translational tool that may help to elucidate the contribution of NSs to sex differences in psychiatric disorders.

RECENT FINDINGS

Findings suggest that anxiety-potentiated startle (APS) and prepulse inhibition of startle (PPI) are the most robust ASR paradigms for assessing contribution of NSs to affective disorders, while affective startle response modulation (ASRM) appears less diagnostic of sex or menstrual cycle (MC) effects. However, few studies have appropriately used ASR to test a priori hypotheses about sex or MC differences. We recommend that ASR studies account for sex as a biological variable (SABV) and hormonal status to further knowledge of NS contribution to affective disorders.

Sensorimotor Gating in Depressed and Euthymic Patients with Bipolar Disorder: Analysis on Prepulse Inhibition of Acoustic Startle Response Stratified by Gender and State

BACKGROUND

Prepulse inhibition (PPI) of the acoustic startle reflex is an operational measure of sensorimotor gating. The findings on PPI deficits in bipolar disorder (BD) are inconsistent among studies due to various confounding factors such as gender. This study aimed to assess sensorimotor gating deficits in patients with BD stratified by gender and state (depressed/euthymic), and to explore related clinical variables.

METHODS

Subjects were 106 non-manic BD patients (26 BD I and 80 BD II; 63 with depression and 43 euthymic) and 232 age-, gender-, and ethnicity-matched (Japanese) healthy controls. Depression severity was assessed using the Hamilton Depression Rating Scale-21. The electromyographic activity of the orbicularis oculi muscle was measured by a computerized startle reflex test unit. Startle magnitude, habituation, and PPI were compared among the three clinical groups: depressed BD, euthymic BD, and healthy controls. In a second analysis, patients were divided into four groups using the quartile PPI levels of controls of each gender, and a ratio of the low-PPI group (<1st quartile of controls) was compared. Effects of psychosis and medication status were examined by the Mann-Whitney U test. Clinical correlates such as medication dosage and depression severity with startle measurements were examined by Spearman's correlation.

RESULTS

Male patients with depression, but not euthymic male patients, showed significantly lower PPI at a prepulse of 86 dB and 120 ms lead interval than did male controls. More than half of the male patients with depression showed low-PPI. In contrast, PPI in female patients did not differ from that in female controls in either the depressed or euthymic state. Female patients with active psychosis showed significantly lower PPI than those without psychosis. Female patients on typical antipsychotics had significantly lower PPI, than those without such medication. PPI showed a significant positive correlation with lamotrigine dosage in male patients and lithium dosage in female patients.

CONCLUSION

These findings suggest that sensorimotor gating is impaired in male BD patients with depression. However, we obtained no evidence for such abnormalities in female BD patients except for those with current psychosis. The observed associations between medication and startle measurements warrant further investigation.

Pubertal development and anxiety risk independently relate to startle habituation during fear conditioning in 8-14 year-old females

Reduced habituation to aversive stimuli has been observed during adolescence and may reflect an underlying mechanism of vulnerability for anxiety disorders. This study examined the startle reflex during a fear-learning task in 54 8-14-year-old girls. We examined the relationship between mean startle, startle habituation, pubertal development, and two measures linked to risk for anxiety: behavioral inhibition system (BIS) and the error-related negativity (ERN). Puberty, BIS, and the ERN were unrelated to mean startle; however, each measure modulated startle habituation. Greater pubertal development was associated with reduced startle habituation across the CS+ and CS-. Higher BIS related to a larger ERN, and both were associated with reduced startle habituation specifically to the CS+. All effects were independent of each other. Findings suggest that puberty alters habituation of defense system activation to both threat and safety cues, and this is independent of risk for anxiety, which uniquely impacts habituation to threat cues.

Sexually dimorphic deficits of prepulse inhibition in patients with major depressive disorder and their relationship to symptoms: A large single ethnicity study

BACKGROUND

Sensorimotor gating deficits as measured by prepulse inhibition (PPI) of acoustic startle reflex have been repeatedly observed in patients with schizophrenia. However, studies investigating PPI in patients with major depressive disorder (MDD) are scarce, and this issue remains to be elucidated.

METHODS

Subjects were 221 patients with MDD and 250 age-matched healthy comparison subjects. Depressive symptoms were assessed by the 21-item version of the Hamilton Depression Rating Scale (HAM-D21), and the scores were divided into six factors. Thirty-five trials of startle reflex to pulse alone and pulse with prepulse were measured by electromyography. Startle magnitude, habituation, and PPI were compared between patients and comparisons stratified by sex. Relationships of startle measures to symptoms and antidepressant medication were assessed.

RESULTS

Male patients showed significantly reduced PPI compared to male comparisons, while no significant PPI difference was found between female patients and comparisons. HAM-D21 total score and several subscales were significantly correlated with PPI only in male patients. The effect of antidepressant medication was not significant for either male or female patients.

LIMITATIONS

Possible effects of the menstrual cycle could not be excluded among female subjects.

CONCLUSIONS

These findings suggest that male patients with MDD show sensorimotor gating deficits in a state-dependent manner. However, we obtained no evidence for such abnormalities in female patients with MDD.

Low startle magnitude may be a behavioral marker of vulnerability to cocaine addiction

Cocaine addicted men have low startle magnitude persisting during prolonged abstinence. Low startle rats show greater cocaine self-administration than high startle rats. Low startle may be a marker of a vulnerability to heightened cocaine-related behaviors in rats and similarly may be a marker of vulnerability to cocaine addiction in humans.

A large single ethnicity study of prepulse inhibition in schizophrenia: Separate analysis by sex focusing on effect of symptoms

Deficits in sensorimotor gating, as measured with prepulse inhibition (PPI), have been considered an endophenotype of schizophrenia. However, the question remains whether these deficits are related to current symptoms. This single site study aimed to explore clinical features related to the modulation of startle reflex in a large sample of Japanese patients with schizophrenia (DSM-IV). The subjects comprised 181 patients and 250 healthy controls matched for age and sex. Schizophrenia symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS). Startle reflex to acoustic stimuli was recorded using a startle stimulus of 115 dB and a prepulse of four different conditions (intensity: 86 dB or 90 dB; lead interval: 60 ms or 120 ms). Patients exhibited significantly reduced startle magnitude (p < 0.001), habituation (p = 0.001), and PPI (90 dB, 60 ms, p = 0.016; 90 dB, 120 ms, p = 0.001) compared with controls. Patients of both sexes exhibited significantly lower habituation and PPI (90 dB, 120 ms) compared with the same sex controls. We could not detect a significant correlation with any clinical variable in the entire patients, however, when men and women were examined separately, there was a negative correlation with the PANSS cognitive domain (ρ = -0.33, p = 0.008) in men, but not in women. Moreover, when patients were subdivided into four clusters, two clusters with high positive symptoms showed significant PPI deficits in men. Our results suggest that sensorimotor gating is impaired in schizophrenia of both sexes, and PPI deficits may be related to thought disturbance and disorganization in male patients with schizophrenia.

Reduced Prepulse Inhibition as a Biomarker of Schizophrenia

The startle response is composed by a set of reflex behaviors intended to prepare the organism to face a potentially relevant stimulus. This response can be modulated by several factors as, for example, repeated presentations of the stimulus (startle habituation), or by previous presentation of a weak stimulus (Prepulse Inhibition [PPI]). Both phenomena appear disrupted in schizophrenia that is thought to reflect an alteration in dopaminergic and glutamatergic neurotransmission. In this paper we analyze whether the reported deficits are indicating a transient effect restricted to the acute phase of the disease, or if it reflects a more general biomarker or endophenotype of the disorder. To this end, we measured startle responses in the same set of thirteen schizophrenia patients with a cross-sectional design at two periods: 5 days after hospital admission and 3 months after discharge. The results showed that both startle habituation and PPI were impaired in the schizophrenia patients at the acute stage as compared to a control group composed by 13 healthy participants, and that PPI but not startle habituation remained disrupted when registered 3 months after the discharge. These data point to the consideration of PPI, but not startle habituation, as a schizophrenia biomarker.

Foreknowledge of an impending startling stimulus does not affect the proportion of startle reflexes or latency of StartReact responses

During a simple reaction time (RT) task, movements can be initiated early and involuntarily through presentation of a loud startling acoustic stimulus (SAS), a phenomenon termed the StartReact effect. In order to infer that activity in startle-related structures led to the early response triggering, it is important to observe a concurrent startle reflex in sternocleidomastoid. It is generally accepted that to consistently elicit a startle reflex, the SAS must be both intense and unpredictable. However, it remains unclear what effect explicit foreknowledge of an impending SAS has on the effectiveness of a SAS to elicit a startle reflex when preparing a motor response. To test this, participants completed two separate blocks of a simple RT task (counterbalanced order), where the control auditory go-signal was replaced with a SAS on 20 % of trials. In an unwarned block, knowledge of the trial type (SAS vs. control) was not provided in advance, while in a warned block, the trial type was forewarned. Results revealed that while foreknowledge of an impending SAS reduced the magnitude of the startle reflex, it did not affect the proportion of startle reflexes elicited or the magnitude of the StartReact effect. An increase in control trial RT was observed during the unwarned block, but only when it was performed first. These results indicate that preparation of a motor response leads to sufficiently increased activation in startle-related neural structures such that even with explicit knowledge of an upcoming SAS, participants are unable to proactively gate the upcoming sensory input.

Progression of temporal processing deficits in the HIV-1 transgenic rat

The HIV-1 transgenic (Tg) rat, which expresses 7 of the 9 HIV-1 genes, was used to investigate the effect(s) of long-term HIV-1 viral protein exposure on chronic neurocognitive deficits observed in pediatric HIV-1 (PHIV). A longitudinal experimental design was used to assess the progression of temporal processing deficits, a potential underlying dimension of neurocognitive impairment in HIV-1. Gap prepulse inhibition (gap-PPI), a translational experimental paradigm, was conducted every thirty days from postnatal day (PD) 30 to PD 180. HIV-1 Tg animals, regardless of sex, displayed profound alterations in the development of temporal processing, assessed using prepulse inhibition. A differential sensitivity to the manipulation of interstimulus interval was observed in HIV-1 Tg animals in comparison to control animals. Moreover, presence of the HIV-1 transgene was diagnosed with 90.8% accuracy using measures of prepulse inhibition and temporal sensitivity. Progression of temporal processing deficits in the HIV-1 Tg rat affords a relatively untapped opportunity to increase our mechanistic understanding of the role of long-term exposure to HIV-1 viral proteins, observed in pediatric HIV-1, in the development of chronic neurological impairment, as well as suggesting an innovative clinical diagnostic screening tool.

Startle reveals decreased response preparatory activation during a stop-signal task

In a stop-signal task participants are instructed to initiate a movement in response to a go signal, but to inhibit this movement if an infrequent stop signal is presented after the go. Reaction time (RT) in a stop-signal task is typically longer compared with that in a simple RT task, which may be attributed to a reduced readiness to initiate the response caused by the possibility of having to inhibit the response. The purpose of this experiment was to probe the preparatory activation level of the motor response during a stop-signal task using a startling acoustic stimulus (SAS), which has been shown to involuntarily trigger sufficiently prepared responses at a short latency. Participants completed two separate tasks: a simple RT task, followed by a stop-signal RT task. During both tasks, an SAS (120 dB) was pseudorandomly presented concurrently with the go signal. As expected, RT during the simple RT task was significantly shorter than during the stop-signal task. A significant reduction in RT was noted when an SAS was presented during the simple RT task; however, during the stop-signal task, an SAS resulted in either a significant speeding or a moderate delay in RT. Additionally, the subset of SAS trial responses with the shortest RT latencies produced during the stop-signal task were also delayed compared with the short-latency SAS trial responses observed during the simple RT task. Despite evidence that a response was prepared in advance of the go signal during a stop-signal task, it appears that the amount of preparatory activation was reduced compared with that achieved during a simple RT task.

Individual difference in prepulse inhibition does not predict spatial learning and memory performance in C57BL/6 mice

The startle reflex to an intense acoustic pulse stimulus is attenuated if the pulse stimulus is shortly preceded by a weak non-startling prepulse stimulus. This attenuation of the startle reflex represents a form of pre-attentional sensory gating known as prepulse inhibition (PPI). Although PPI does not require learning, its expression is regulated by higher cognitive processes. PPI deficits have been detected in several psychiatric conditions including schizophrenia where they co-exist with cognitive deficits. A potential link between PPI expression and cognitive performance has therefore been suggested such that poor PPI may predict, or may be mechanistically linked to, overt cognitive impairments. A positive relationship between PPI and strategy formation, planning efficiency, and execution speed has been observed in healthy humans. However, parallel studies in healthy animals are rare. It thus remains unclear what cognitive domains may be associated with, or orthogonal to, sensory gating in the form of PPI in healthy animals. The present study evaluated a potential link between the magnitude of PPI and spatial memory performance by comparing two subgroups of animals differing substantially in baseline PPI expression (low-PPI vs high-PPI) within a homogenous cohort of 100 male adult C57BL/6 mice. Assessment of spatial reference memory in the Morris water maze and spatial recognition memory in the Y-maze failed to reveal any difference between low-PPI and high-PPI subjects. These negative findings contrast with our previous reports that individual difference in PPI correlated with sustained attention and working memory performance in C57BL/6 mice.

Effects of sleep deprivation on inhibitory biomarkers of schizophrenia: implications for drug development

Development of drugs for the treatment of the clinical symptoms and cognitive deficits of schizophrenia is unsatisfactory, with many initially promising compounds not showing beneficial effects in clinical studies. Experimental model systems of schizophrenia combined with well-validated biomarkers are urgently needed to provide early indicators of effectiveness. Herein, we argue that experimentally controlled sleep deprivation represents a translational model system that can be studied in combination with neurocognitive biomarkers. Specifically, we review data on the psychotomimetic effects of sleep deprivation in healthy human beings and provide evidence of the psychosis-like deficits in translational inhibitory biomarkers-prepulse inhibition and antisaccades-that occur after sleep deprivation. These data support the use of the sleep deprivation model in combination with biomarkers with excellent psychometric properties and well-characterised neural mechanisms, such as prepulse inhibition and antisaccades, to substantially advance development of drugs with antipsychotic or pro-cognitive effects.

The role of ephrin-A2 and ephrin-A5 in sensorimotor control and gating

Many factors influence neurodevelopment. However, their contribution to adult neural function is often unclear. This is often due to complex expression profiles, cell signalling, neuroanatomy, and a lack of effective tests to assess the function of neural circuits in vivo. Ephrin-A2 and ephrin-A5 are cell surface proteins implicated in multiple aspects of neurodevelopment. While the role of ephrin-As in visual, auditory and learning behaviours has been explored, little is known about their role in dopaminergic and neuromotor pathways, despite expression in associated brain regions. Here we probe the function of ephrin-A2 and ephrin-A5 in the development of the dopaminergic and neuromotor pathways using counts of tyrosine hydroxylase (TH) positive cells in the substantia nigra pars compacta (SNpc) and the ventral tegmental area (VTA), the acoustic startle reflex (ASR), and a measure of sensorimotor gating, prepulse inhibition (PPI). Analysis of the ASR and PPI in ephrin-A2 and/or ephrin-A5 knock-out mice revealed that both genes play distinct roles in mediating ASR circuits, but are unlikely to play a role in PPI. Knock-out of either gene resulted in robust changes in startle response magnitude and measures of startle onset and peak latencies. However, ephrin-A2 and ephrin-A5 regulate aspects of the ASR differently: ephrin-A2 KO mice have increased startle amplitude, increased sensitivity and reduced latency to startle, whilst ephrin-A5 KO mice show opposite effects. Neither of the gene knock outs affected PPI, despite ephrin-A5 KO mice showing changes in dopamine cell numbers in nuclei thought to regulate PPI. We propose that majority of the changes observed ephrin-A2 and ephrin-A5 KO mice appear to be mediated by the effects on motor neurons and their muscle targets, rather than changes in auditory sensitivity.

Pre-pulse inhibition and striatal dopamine in subjects at an ultra-high risk for psychosis

Reduced prepulse inhibition (PPI) of the acoustic startle response is thought to represent a robust biomarker in schizophrenia. Reduced PPI has been demonstrated in subjects at ultra high risk (UHR) for developing psychosis. Imaging studies report disruption of striatal dopaminergic neurotransmission in patients with schizophrenia. First, we compared the PPI of the acoustic startle response in UHR subjects versus healthy controls, to see if we could replicate previous findings of reduced PPI; secondly, we investigated our hypothesis that PPI would be negatively correlated with striatal synaptic dopamine (DA) concentration. We measured the startle reactivity and PPI of the acoustic startle response in 14 UHR subjects, and 14 age- and gender-matched healthy controls. Imaging of 11 UHR subjects and 11 healthy controls was completed by an [(123)I]-IBZM (radiotracer for dopamine D2/3 receptors) SPECT, at baseline and again after DA depletion with alpha-methyl-para-tyrosine (AMPT). The percentage change in striatal [(123)I]-IBZM radiotracer binding potential is a proxy of striatal synaptic DA concentration. UHR subjects showed reduced PPI, compared to control subjects. In both UHR and control subjects, there were no significant correlations between striatal synaptic DA concentration and PPI. We provide further evidence for the hypothesis that these two biomarkers are measuring different aspects of pathophysiology.

Between-site reliability of startle prepulse inhibition across two early psychosis consortia

Prepulse inhibition (PPI) and reactivity of the acoustic startle response are widely used biobehavioral markers in psychopathology research. Previous studies have demonstrated that PPI and startle reactivity exhibit substantial within-site stability; however, between-site stability has not been established. In two separate consortia investigating biomarkers of early psychosis, traveling participants studies were carried out as a part of quality assurance procedures to assess the fidelity of data across sites. In the North American Prodromal Longitudinal Studies (NAPLS) consortium, eight normal participants traveled to each of the eight NAPLS sites and were tested twice at each site on the startle PPI paradigm. In preparation for a binational study, 10 healthy participants were assessed twice in both San Diego and Mexico City. Intraclass correlations between and within sites were significant for PPI and startle response parameters, confirming the reliability of startle measures across sites in both consortia. There were between-site differences in startle magnitude in the NAPLS study that did not appear to be related to methods or equipment. In planning multisite studies, it is essential to institute quality assurance procedures early and establish between-site reliability to assure comparable data across sites.

Trigeminal high-frequency stimulation produces short- and long-term modification of reflex blink gain

Reflex blinks provide a model system for investigating motor learning in normal and pathological states. We investigated whether high-frequency stimulation (HFS) of the supraorbital branch of the trigeminal nerve before the R2 blink component (HFS-B) decreases reflex blink gain in alert rats. As with humans (Mao JB, Evinger C. J Neurosci 21: RC151, 2001), HFS-B significantly reduced blink size in the first hour after treatment for rats. Repeated days of HFS-B treatment produced long-term depression of blink circuits. Blink gain decreased exponentially across days, indicating a long-term depression of blink circuits. Additionally, the HFS-B protocol became more effective at depressing blink amplitude across days of treatment. This depression was not habituation, because neither long- nor short-term blink changes occurred when HFS was presented after the R2. To investigate whether gain modifications produced by HFS-B involved cerebellar networks, we trained rats in a delay eyelid conditioning paradigm using HFS-B as the unconditioned stimulus and a tone as the conditioned stimulus. As HFS-B depresses blink circuits and delay conditioning enhances blink circuit activity, occlusion should occur if they share neural networks. Rats acquiring robust eyelid conditioning did not exhibit decreases in blink gain, whereas rats developing low levels of eyelid conditioning exhibited weak, short-term reductions in blink gain. These results suggested that delay eyelid conditioning and long-term HFS-B utilize some of the same cerebellar circuits. The ability of repeated HFS-B treatment to depress trigeminal blink circuit activity long term implied that it may be a useful protocol to reduce hyperexcitable blink circuits that underlie diseases like benign essential blepharospasm.

Clonidine normalizes sensorimotor gating deficits in patients with schizophrenia on stable medication

BACKGROUND

Cognitive deficits form core features in schizophrenia. Several studies have shown improvements in prefrontal cognitive function by α 2 -agonists in schizophrenia. In the present study, it was investigated whether clonidine (an α 2 -adrenoceptor agonist) could normalize sensorimotor gating deficits in schizophrenia.

METHODS

In a double blind, placebo controlled, randomized, yet balanced, cross-over experiment, 20 male schizophrenia patients on stable medication were assessed in an auditory prepulse inhibition (PPI), sensitization, and habituation of the startle reflex paradigm on 5 occasions: once after oral administration of placebo and after a single dose of 25, 50, 75, and 150 µg of clonidine. Their results were compared with 20 age- and gender-matched healthy volunteers, who received no treatment.

RESULTS

In the placebo treatment, patients showed deficient PPI and sensitization, yet normal habituation compared with the controls. Except the highest dose, all dosages of clonidine significantly increased percentage PPI in the patients compared with placebo, to such levels that it no longer differed significantly from the healthy controls. However, none of the dosages increased sensitization or influenced habituation.

CONCLUSIONS

This is the first study to show that even a single low dose of clonidine added to the medical treatment of patients with schizophrenia who are clinically stable on their antipsychotic medication not only significantly ameliorates their PPI deficits, but also normalizes them. The results have a potentially high clinical relevance for the medical treatment of schizophrenia.

Exploring the role of 5-HT1A receptors in the regulation of prepulse inhibition in mice: implications for cross-species comparisons

Prepulse inhibition (PPI) is a model of sensorimotor gating, a sensory filtering mechanism which is disrupted in schizophrenia. Here, investigation of the role of the serotonin-1A (5-HT(1A)) receptor in the regulation of PPI in two mouse strains, C57Bl/6 and Balb/c, was used to address findings in the PPI literature on species and mouse strain differences that question the usefulness of PPI as a cross-species preclinical test. Although the full 5-HT(1A) receptor agonist, 8-OH-DPAT, induced markedly different strain-specific responses in PPI, other selective 5-HT(1A) receptor ligands with partial agonist or antagonist activity elicited similar effects across strains. Pretreatment with the serotonin precursor, 5-HTP, to increase serotonergic activity in the brain, unmasked a decrease in PPI caused by 8-OH-DPAT in C57Bl/6 mice. Pretreatment with the serotonin synthesis inhibitor, PCPA, to decrease serotonergic activity in the brain, unmasked an 8-OH-DPAT-induced increase in PPI in this strain. These studies show that the strain-dependent involvement of 5-HT(1A) receptors in PPI can be modulated by the type of 5-HT(1A) ligand used, or increasing or decreasing serotonin levels in the brain. These results help to clarify some of the mouse strain and species differences in PPI regulation and strengthen its usefulness as a cross-species measure of sensorimotor gating.

Startle reactivity and prepulse inhibition of the acoustic startle response are modulated by catechol-O-methyl-transferase Val(158) Met polymorphism in adults with 22q11 deletion syndrome

22q11 deletion syndrome (22q11DS) is a genetic disorder caused by a microdeletion on chromosome 22, which includes the gene coding for catechol-O-methyl-transferase (COMT). High dopamine (DA) levels due to COMT haplo-insufficiency may be associated with the increased risk of developing schizophrenia in adults with 22q11DS. Reduced prepulse inhibition (PPI) of the acoustic startle response has been associated with schizophrenia and with disrupted DAergic transmission in the prefrontal cortex (PFC). COMT Val(158)Met polymorphism has been shown to influence PPI. We report the first study in adults with 22q11DS to examine PPI of the acoustic startle response and its modulation by COMT Val(158)Met polymorphism. Startle reactivity (SR) and PPI of the acoustic startle response were measured in 23 adults with 22q11DS and 21 healthy controls. 22q11DS subjects were genotyped for the functional COMT Val(158)Met polymorphism. 22q11DS Met hemizygotes showed reduced SR and PPI compared with 22q11DS Val hemizygotes. The effect of COMT Val(158)Met polymorphism on PPI was no longer significant when controlling for baseline SR. Met hemizygosity in 22q11DS is associated with reduced SR and influences PPI indirectly. Decreased PFC functioning following excessive PFC DA levels may be one of the mechanisms by which the Met genotype in 22q11DS disrupts SR.

Prepulse inhibition of auditory change-related cortical responses

Background

Prepulse inhibition (PPI) of the startle response is an important tool to investigate the biology of schizophrenia. PPI is usually observed by use of a startle reflex such as blinking following an intense sound. A similar phenomenon has not been reported for cortical responses.

Results

In 12 healthy subjects, change-related cortical activity in response to an abrupt increase of sound pressure by 5 dB above the background of 65 dB SPL (test stimulus) was measured using magnetoencephalography. The test stimulus evoked a clear cortical response peaking at around 130 ms (Change-N1m). In Experiment 1, effects of the intensity of a prepulse (0.5 ~ 5 dB) on the test response were examined using a paired stimulation paradigm. In Experiment 2, effects of the interval between the prepulse and test stimulus were examined using interstimulus intervals (ISIs) of 50 ~ 350 ms. When the test stimulus was preceded by the prepulse, the Change-N1m was more strongly inhibited by a stronger prepulse (Experiment 1) and a shorter ISI prepulse (Experiment 2). In addition, the amplitude of the test Change-N1m correlated positively with both the amplitude of the prepulse-evoked response and the degree of inhibition, suggesting that subjects who are more sensitive to the auditory change are more strongly inhibited by the prepulse.

Conclusions

Since Change-N1m is easy to measure and control, it would be a valuable tool to investigate mechanisms of sensory gating or the biology of certain mental diseases such as schizophrenia.

Prepulse inhibition of startle response: recent advances in human studies of psychiatric disease

Prepulse inhibition (PPI) is considered to be one of the most promising neurophysiological indexes for translational research in psychiatry. Impairment of PPI has been reported in several psychiatric diseases, particularly schizophrenia, where PPI is considered a candidate intermediate phenotype (endophenotype) of the disease. Recent findings from a variety of research areas have provided important evidence regarding PPI impairment. Human brain imaging studies have demonstrated the involvement of the striatum, hippocampus, thalamus and frontal and parietal cortical regions in PPI. In addition, several genetic polymorphisms, including variations in the genes coding for Catechol O-methyltransferase, Neuregulin 1, nuclear factor kappa-B subunit 3 and serotonin-2A receptor were related to PPI; and these findings support PPI as a polygenetic trait that involves several neurotransmitter pathways. Early psychosis studies suggest that PPI disruption is present before the onset of psychosis. Also, discrepancy of PPI impairment between children and adults can be found in other psychiatric diseases, such as autistic spectrum disorders and posttraumatic stress disorder, and comprehensive investigation of startle response might contribute to understand the impairment of the neural circuitry in psychiatric diseases. Finally, recent studies with both Asian and Caucasian subjects indicate that patients with schizophrenia exhibit impaired PPI, and impaired sensorimotor gating might be a global common psychophysiological feature of schizophrenia. In conclusion, studies of PPI have successfully contributed to a better understanding of the fundamental neural mechanisms underlying sensorimotor gating and will certainly be most valuable in devising future approaches that aim to investigate the complex pathogenesis of psychiatric diseases.

Startle reactivity and prepulse inhibition in prodromal and early psychosis: effects of age, antipsychotics, tobacco and cannabis in a vulnerable population

The use of biomarkers in the study of the prodrome and first episode of psychosis provides a means of not only identifying individuals at greatest risk for psychosis but also understanding neurodevelopmental abnormalities early in the course of illness. Prepulse inhibition (PPI), a marker that is deficient in schizophrenia and after developmental manipulations in animal models, was assessed in 75 early psychosis (EP), 89 at risk (AR) for psychosis and 85 comparison subjects (CS) at baseline and 6 months. Consistent with findings in chronic schizophrenia, PPI was stable with repeated assessment and EP subjects had reduced PPI but this was most evident in tobacco smokers. A significant positive PPI and age association in AR and EP samples, but not CS, demonstrated potential neurodevelopmental differences in early psychosis. Unexpected findings included the fact that medication naive EP subjects, as well as AR subjects who later developed psychosis, had greater PPI, introducing the possibility of early compensatory changes that diverge from findings in chronic patients. In addition, subjects with a history of cannabis use had greater startle reactivity while EP and AR subjects who used cannabis and were also taking an antipsychotic had greater PPI, again highlighting the potentially important cannabis/psychosis association.

The association of schizophrenia risk D-amino acid oxidase polymorphisms with sensorimotor gating, working memory and personality in healthy males

There is evidence supporting a role for the D-amino acid oxidase (DAO) locus in schizophrenia. This study aimed to determine the relationship of five single-nucleotide polymorphisms (SNPs) within the DAO gene identified as promising schizophrenia risk genes (rs4623951, rs2111902, rs3918346, rs3741775, and rs3825251) to acoustic startle, prepulse inhibition (PPI), working memory, and personality dimensions. A highly homogeneous study entry cohort (n = 530) of healthy, young male army conscripts (n = 703) originating from the Greek LOGOS project (Learning On Genetics Of Schizophrenia Spectrum) underwent PPI of the acoustic startle reflex, working memory, and personality assessment. The QTPHASE from the UNPHASED package was used for the association analysis of each SNP or haplotype data, with p-values corrected for multiple testing by running 10,000 permutations of the data. The rs4623951_T-rs3741775_G and rs4623951_T-rs2111902_T diplotypes were associated with reduced PPI and worse performance in working memory tasks and a personality pattern characterized by attenuated anxiety. Median stratification analysis of the risk diplotype group (ie, those individuals homozygous for the T and G alleles (TG+)) showed reduced PPI and working memory performance only in TG+ individuals with high trait anxiety. The rs4623951_T allele, which is the DAO polymorphism most strongly associated with schizophrenia, might tag a haplotype that affects PPI, cognition, and personality traits in general population. Our findings suggest an influence of the gene in the neural substrate mediating sensorimotor gating and working memory, especially when combined with high anxiety and further validate DAO as a candidate gene for schizophrenia and spectrum disorders.

The influence of schizophrenia-related neuregulin-1 polymorphisms on sensorimotor gating in healthy males

BACKGROUND

Neuregulin-1 (NRG1) variations have been shown to modulate schizophrenia candidate endophenotypes related to brain structure and function. The objective of this cross-sectional genetic association study was to determine the relationship of six core single-nucleotide polymorphisms within the NRG1 gene identified as promising schizophrenia risk genes (rs6994992, SNP8NRG221132, SNP8NRG241930, rs3924999, rs2439272 and rs10503929) to prepulse inhibition (PPI) of the acoustic startle reflex, a well validated schizophrenia endophenotype.

METHODS

PPI was tested in a highly homogeneous study entry cohort (n = 445) of carefully screened healthy, young male army conscripts originating from the Greek LOGOS project (Learning on Genetics of Schizophrenia Spectrum). The QTPHASE from the UNPHASED package was used for the association analysis of each single-nucleotide polymorphisms or haplotype data.

RESULTS

Reduced PPI, particularly at 75-dB_120-msec and 85-dB_60-msec trials, was related to the SNP8NRG241930 G allele and especially the rs6994992 T allele and rs2439272 C allele. Haplotype analysis followed up by risk versus no-risk groups Analysis of variance confirmed that the rs10503929 and rs3924999 SNPs were also associated with PPI reductions, when combined with rs2439272.

CONCLUSIONS

We provide solid evidence for a role of NRG1 risk genotype variations in PPI reductions in a large and demographically and genetically highly homogeneous cohort of healthy young males. These results further validate NRG1 as a candidate gene for the schizophrenia and spectrum disorders and improve our understanding of its functional mechanisms within the human brain because they suggest an influence of the gene in the neural substrate mediating sensorimotor gating.

Sex differences and hormonal influences in human sensorimotor gating: implications for schizophrenia

Prepulse inhibition (PPI) of the startle response serves to prevent the interruption of ongoing perceptual and early sensory analysis and provides a simple operational measure of sensorimotor gating. In line with postulated deficits in early stages of information processing, PPI is disrupted in schizophrenia. PPI is considered a valid candidate for an endophenotypic marker in genetic studies of schizophrenia and has also been extensively used in translational research. Importantly, there are well-replicated sex differences and menstrual phase effects in prepulse-elicited startle modulation of nonclinical young populations. Lack of knowledge about the precise roles of sex differences and hormonal effects in prepulse-elicited startle modulation and in the schizophrenia disease process presents a stumbling block to continuous progress in this field. This chapter reviews a wealth of data demonstrating sex and hormonal influences in prepulse-elicited startle modulation and considers their implications for our understanding of the pathophysiology, genetics, and potential treatments of schizophrenia.

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.