Sensory gating deficits in schizophrenia: can we parse the effects of medication, nicotine use, and changes in clinical status?

Exploring causal mechanisms of psychosis risk

Robust epidemiological evidence of risk and protective factors for psychosis is essential to inform preventive interventions. Previous evidence syntheses have classified these risk and protective factors according to their strength of association with psychosis. In this critical review we appraise the distinct and overlapping mechanisms of 25 key environmental risk factors for psychosis, and link these to mechanistic pathways that may contribute to neurochemical alterations hypothesised to underlie psychotic symptoms. We then discuss the implications of our findings for future research, specifically considering interactions between factors, exploring universal and subgroup-specific factors, improving understanding of temporality and risk dynamics, standardising operationalisation and measurement of risk and protective factors, and developing preventive interventions targeting risk and protective factors.

Sensory Gating in Neurodevelopmental Disorders: A Scoping Review

This review aimed to explore the current understanding of sensory gating in neurodevelopmental disorders as a possible transdiagnostic mechanism. We applied methods according to the Joanna Briggs Institute Manual for Evidence Synthesis, following the population, concept, and context scoping review eligibility criteria. Using a comprehensive search strategy in five relevant research databases (Medline, EMBASE, CINAHL, PsychInfo, and Scopus), we searched for relevant peer-reviewed, primary research articles and unpublished data. Two independent reviewers screened the titles and abstracts, full-texts, and completed data extraction. We identified a total of 81 relevant articles and used descriptive analyses to summarize the characteristics and outcomes of all identified studies. Literature regarding sensory gating was most common in autistic populations with relatively fewer studies examining attention-deficit/hyperactivity disorder, tic disorders, and childhood-onset fluency disorder (COFD). The methods to assess sensory gating varied widely both within and between groups and included measures such as habituation, prepulse inhibition, affect-modulated inhibition, medication and other intervention trials. Most consistently, when participants complete questionnaires about their sensory experiences, those who have neurodevelopmental disorders report differences in their sensory gating. Affect-modulated inhibition appears to be discrepant between samples with and without neurodevelopmental disorder diagnoses. Habituation was the most commonly reported phenomenon and many differences in habituation have been found in autistic individuals and individuals with tic disorders whereas concerns with inhibition seemed more common in COFD. Overall, the evidence is inconsistent within and between disorders suggesting there is still much to learn about sensory gating in neurodevelopmental disorders.

Mechanisms of Short- and Long-Latency Sensory Suppression: Magnetoencephalography Study

Prepulse inhibition (PPI) is sensory suppression whose mechanism (i.e., whether PPI originates from specific inhibitory mechanisms) remains unclear. In this study, we applied the combination of short-latency PPI and long-latency paired pulse suppression in 17 healthy subjects using magnetoencephalography to investigate the mechanisms of sensory suppression. Repeats of a 25-ms pure tone without a blank at 800 Hz and 70 dB were used for a total duration of 1600 ms. To elicit change-related cortical responses, the sound pressure of two consecutive tones in this series at 1300 ms was increased to 80 dB (Test). For the conditioning stimuli, the sound pressure was increased to 73 dB at 1250 ms (Pre 1) and 80 dB at 700 ms (Pre 2). Six stimuli were randomly presented as follows: (1) Test alone, (2) Pre 1 alone, (3) Pre 1 + Test, (4) Pre 2 + Test, (5) Pre 2 + Pre 1, and (6) Pre 2 + Pre 1 + Test. The inhibitory effects of the conditioning stimuli were evaluated using N100m/P200m components. The results showed that both Pre 1 and Pre 2 significantly suppressed the Test response. Moreover, the inhibitory effects of Pre 1 and Pre 2 were additive. However, when both prepulses were present, Pre 2 significantly suppressed the Pre 1 response, suggesting that the Pre 1 response amplitude was not a determining factor for the degree of suppression. These results suggested that the suppression originated from a specific inhibitory circuit independent of the excitatory pathway.

Impaired Sensorimotor Gating Using the Acoustic Prepulse Inhibition Paradigm in Individuals at a Clinical High Risk for Psychosis

Many robust studies have investigated prepulse inhibition (PPI) in patients with schizophrenia. Recent evidence indicates that PPI may help identify individuals who are at clinical high risk for psychosis (CHR). Selective attention to prepulse stimulus can specifically enhance PPI in healthy subjects; however, this enhancement effect is not observed in patients with schizophrenia. Modified PPI measurement with selective attentional modulation using perceived spatial separation (PSS) condition may be a more robust and sensitive index of PPI impairment in CHR individuals. The current study investigated an improved PSSPPI condition in CHR individuals compared with patients with first-episode schizophrenia (FES) and healthy controls (HC) and evaluated the accuracy of PPI in predicting CHR from HC. We included 53 FESs, 55 CHR individuals, and 53 HCs. CHRs were rated on the Structured Interview for Prodromal Syndromes. The measures of perceived spatial co-location PPI (PSCPPI) and PSSPPI conditions were applied using 60- and 120-ms lead intervals. Compared with HC, the CHR group had lower PSSPPI level (Inter-stimulus interval [ISI] = 60 ms, P < .001; ISI = 120 ms, P < .001). PSSPPI showed an effect size (ES) between CHR and HC (ISI = 60 ms, Cohen's d = 0.91; ISI = 120 ms, Cohen's d = 0.98); on PSSPPI using 60-ms lead interval, ES grade increased from CHR to FES. The area under the receiver operating characteristic curve for PSSPPI was greater than that for PSCPPI. CHR individuals showed a PSSPPI deficit similar to FES, with greater ES and sensitivity. PSSPPI appears a promising objective approach for preliminary identification of CHR individuals.

Urbanicity: The need for new avenues to explore the link between urban living and psychosis

AIM

A growing body of evidence suggests that urban living contributes to the development of psychosis. However, the mechanisms underlying this phenomenon remain unclear. This paper aims to explore the best available knowledge on the matter, identify research gaps and outline future prospects for research strategies.

METHOD

A comprehensive literature survey on the main computerized medical research databases, with a time limit up to August 2017 on the issue of urbanicity and psychosis has been conducted.

RESULTS

The impact of urbanicity may result from a wide range of factors (from urban material features to stressful impact of social life) leading to "urban stress." The latter may link urban upbringing to the development of psychosis through overlapping neuro- and socio-developmental pathways, possibly unified by dopaminergic hyperactivity in mesocorticolimbic system. However, "urban stress" is poorly defined and research based on patients' experience of the urban environment is scarce.

CONCLUSIONS

Despite accumulated data, the majority of studies conducted so far failed to explain how specific factors of urban environment combine in patients' daily life to create protective or disruptive milieus. This undermines the translation of a vast epidemiological knowledge into effective therapeutic and urbanistic developments. New studies on urbanicity should therefore be more interdisciplinary, bridging knowledge from different disciplines (psychiatry, epidemiology, human geography, urbanism, etc.) in order to enrich research methods, ensure the development of effective treatment and preventive strategies as well as create urban environments that will contribute to mental well-being.

Pharmacological Mechanisms Involved in Sensory Gating Disruption Induced by (±)-3,4-Methylene- Dioxymethamphetamine (MDMA): Relevance to Schizophrenia

Sensory gating deficits have been demonstrated in schizophrenia, but the mechanisms involved remain unclear. In the present study, we used disruption of paired-pulse gating of evoked potentials in rats by the administration of (±)-3,4-methylene-dioxymethamphetamine (MDMA) to study serotonergic and dopaminergic mechanisms involved in auditory sensory gating deficits. Male Sprague-Dawley rats were instrumented with cortical surface electrodes to record evoked potential changes in response to pairs of 85dB tones (S1 and S2), 500msec apart. Administration of MDMA eliminated the normal reduction in the amplitude of S2 compared to S1, representing disruption of auditory sensory gating. Pretreatment of the animals with the dopamine D1 receptor antagonist, SCH23390, the dopamine D2 receptor antagonist, haloperidol, the serotonin (5-HT)1A receptor antagonist, WAY100635, or the 5-HT2A receptor antagonist, ketanserin, all blocked the effect of MDMA, although the drugs differentially affected the individual S1 and S2 amplitudes. These data show involvement of both dopaminergic and serotonergic mechanisms in disruption of auditory sensory gating by MDMA. These and previous results suggest that MDMA targets serotonergic pathways, involving both 5-HT1A and 5-HT2A receptors, leading to dopaminergic activation, involving both D1 and D2 receptors, and ultimately sensory gating deficits. It is speculated that similar interactive mechanisms are affected in schizophrenia.

Sensory Gating Capacity and Attentional Function in Adults With ADHD: A Preliminary Neurophysiological and Neuropsychological Study

Objective: The inability to filter sensory input correctly may impair higher cognitive function in ADHD. However, this relationship remains largely elusive. The objectives of the present study is to investigate the relationship between sensory input processing and cognitive function in adult patients with ADHD. Method: This study investigated the relationship between deficit in sensory gating capacity (P50 amplitude changes in a double-click conditioning-testing paradigm and perceptual abnormalities related to sensory gating deficit with the Sensory Gating Inventory [SGI]) and attentional and executive function (P300 amplitude in an oddball paradigm and attentional and executive performances with a neuropsychological test) in 24 adult patients with ADHD. Results: The lower the sensory gating capacity of the brain and the higher the distractibility related to sensory gating inability that the patients reported, the lower the P300 amplitude. Conclusion: The capacity of the brain to gate the response to irrelevant incoming sensory input may be a fundamental protective mechanism that prevents the flooding of higher brain structures with irrelevant information in adult patients with ADHD.

Multisensory cortical processing and dysfunction across the neuropsychiatric spectrum

Sensory processing is affected in multiple neuropsychiatric disorders like schizophrenia and autism spectrum disorders. Genetic and environmental factors guide the formation and fine-tuning of brain circuitry necessary to receive, organize, and respond to sensory input in order to behave in a meaningful and consistent manner. During certain developmental stages the brain is sensitive to intrinsic and external factors. For example, disturbed expression levels of certain risk genes during critical neurodevelopmental periods may lead to exaggerated brain plasticity processes within the sensory circuits, and sensory stimulation immediately after birth contributes to fine-tuning of these circuits. Here, the neurodevelopmental trajectory of sensory circuit development will be described and related to some example risk gene mutations that are found in neuropsychiatric disorders. Subsequently, the flow of sensory information through these circuits and the relationship to synaptic plasticity will be described. Research focusing on the combined analyses of neural circuit development and functioning are necessary to expand our understanding of sensory processing and behavioral deficits that are relevant across the neuropsychiatric spectrum.

Association of metabolic syndrome with sensory gating deficits in patients with chronic schizophrenia

Metabolic syndrome is more prevalent in schizophrenia than in the general population and is associated with an increased rate of morbidity. It has been associated with cognitive impairments in schizophrenia, which are a core deficit in patients with chronic schizophrenia. Sensory gating deficit is also a core deficit in schizophrenia. The principal objective of this study was to investigate the relationship between sensory gating deficit and metabolic syndrome in patients with schizophrenia, after adjusting for key confounding factors. We hypothesized that patients with metabolic syndrome exhibit a higher rate of sensory gating deficit compared to those without metabolic syndrome. This study investigated sensory gating with the auditory event-related potential method by measuring P50 amplitude changes in a double click conditioning-testing procedure in 51 patients with schizophrenia. Patients with metabolic syndrome (n = 14) had a higher rate of sensory gating deficit (P50 suppression <50%) (p < 0.001) compared to those without metabolic syndrome (n = 37). This result remained significant (B = 2.94, Wald = 8.32, p = 0.004) after taking into account 5 potential confounding factors (age, gender, duration of disorder, Fagerström test, presence of clozapine or olanzapine). In patients without metabolic syndrome, sensory gating deficit was linked to a poorer attentional performance (rho = -0.371, p = 0.05). In patients with metabolic syndrome, sensory gating deficit was linked to poorer memory performance (rho = -0.635, p = 0.02). These findings suggest that metabolic syndrome may be linked to sensory gating deficit in patients with schizophrenia and that the relationship between neurocognitive function and sensory gating deficit could be affected by the metabolic status of the patients. Further studies are needed to address the causal relationship between sensory gating deficit related to schizophrenia, cognitive impairments and metabolic syndrome.

The separate and combined effects of monoamine oxidase inhibition and nicotine on P50 sensory gating

INTRODUCTION

The cognitive effects of nicotine in humans remain a topic of great interest, due to the continued prevalence of cigarette smoking in society as well as the hypothesis that cognitively impaired populations such as schizophrenia patients use nicotine as a means of self-medicating against deficits of sensory gating. However, chronic smoking can predispose individuals to robust monoamine oxidase (MAO) inhibition, and thus far, the effect of MAO inhibition on human sensory gating is unknown.

METHODS

In this study, we investigated the effects of both nicotine (6-mg gum) and pharmacologically induced MAO-A inhibition via moclobemide (75 mg) on P50 event-related potential-indexed sensory gating in a sample of 24 healthy non-smoking males.

RESULTS

Ratio score (rP50) measured gating revealed significant improvement in auditory stimulus suppression after combined nicotine and MAO-A inhibition compared to placebo and to the nicotine-alone condition. This nicotine + MAO-A inhibition-induced efficient gating was consistent regardless of participants' baseline (placebo) gating efficiency, despite the observation that nicotine in the absence of MAO-A inhibition exhibited a detrimental effect on gating in participants with high baseline suppression ratios.

CONCLUSION

Nicotine and monoamine oxidase-inhibiting agents in tobacco smoke appear to exert a synergistic effect on sensory gating, which may contribute to the elevated dependence rates seen in populations with cognitive deficits such as schizophrenia.

On the correlation between perceptual inundation caused by realistic immersive environmental auditory scenes and the sensory gating inventory in schizophrenia

BACKGROUND

In schizophrenia, perceptual inundation related to sensory gating deficit can be evaluated "off-line" with the sensory gating inventory (SGI) and "on-line" during listening tests. However, no study investigated the relation between "off-line evaluation" and "on-line evaluation". The present study investigates this relationship.

METHODS

A sound corpus of 36 realistic environmental auditory scenes was obtained from a 3D immersive synthesizer. Twenty schizophrenic patients and twenty healthy subjects completed the SGI and evaluated the feeling of "inundation" from 1 ("null") to 5 ("maximum") for each auditory scene. Sensory gating deficit was evaluated in half of each population group with P50 suppression electrophysiological measure.

RESULTS

Evaluation of inundation during sound listening was significantly higher in schizophrenia (3.25) compared to the control group (2.40, P<.001). The evaluation of inundation during the listening test correlated significantly with the perceptual modulation (n=20, rho=.52, P=.029) and the over-inclusion dimensions (n=20, rho=.59, P=.01) of the SGI in schizophrenic patients and with the P50 suppression for the entire group of controls and patients who performed ERP recordings (n=20, rho=-.49, P=.027).

CONCLUSION

An evaluation of the external validity of the SGI was obtained through listening tests. The ability to control acoustic parameters of each of the realistic immersive environmental auditory scenes might in future research make it possible to identify acoustic triggers related to perceptual inundation in schizophrenia.

Greater general startle reflex is associated with greater anxiety levels: a correlational study on 111 young women

Startle eyeblink reflex is a valid non-invasive tool for studying attention, emotion and psychiatric disorders. In the absence of any experimental manipulation, the general (or baseline) startle reflex shows a high inter-individual variability, which is often considered task-irrelevant and therefore normalized across participants. Unlike the above view, we hypothesized that greater general startle magnitude is related to participants’ higher anxiety level. 111 healthy young women, after completing the State-Trait Anxiety Inventory (STAI), were randomly administered 10 acoustic white noise probes (50 ms, 100 dBA acoustic level) while integrated EMG from left and right orbicularis oculi was recorded. Results showed that participants with greater state anxiety levels exhibited larger startle reflex magnitude from the left eye (r₁₀₉ = 0.23, p < 0.05). Furthermore, individuals who perceived the acoustic probe as more aversive reported the largest anxiety scores (r₁₀₉ = 0.28, p < 0.05) and had the largest eyeblinks, especially in the left eye (r₁₀₉ = 0.34, p < 0.001). Results suggest that general startle may represent a valid tool for studying the neural excitability underlying anxiety and emotional dysfunction in neurological and mental disorders.

Validation of the French sensory gating inventory: a confirmatory factor analysis

The Sensory Gating Inventory (SGI) is an instrument investigating daily experiences of sensory gating deficit developed for English speaking schizophrenia patients. The purpose of this study is to design and validate a French version of the SGI. A forward-backward translation of the SGI was performed. The psychometric properties of the French SGI version were analyzed. A confirmatory factor analysis (CFA) was carried out to determine whether factor structure of the French version is similar to the original English version. In a sample of 363 healthy subjects (mean age=31.8 years, S.D.=12.2 years) the validation process revealed satisfactory psychometric properties: the internal consistency reliability was confirmed for each dimension; each item achieved the 0.40 standard threshold for item-internal consistency; each item was more highly correlated with its contributive dimension than with the other dimensions; and based on a CFA, we found a 4-factor structure for the French version of the SGI similar to the original instrument. Test-retest reliability was not determined. The French version of the SGI is a psychometrically sound self-report for measuring phenomenological sensory gating experiences.

Do schizophrenia patients with low P50-suppression report more perceptual anomalies with the sensory gating inventory?

BACKGROUND

P50 amplitude changes in dual click conditioning-testing procedure might be a neurophysiological marker of deficient sensory gating in schizophrenia. However, the relationship between abnormalities in the neurophysiological and phenomenological dimensions of sensory gating in schizophrenia remains unclear. The aim of the present study was to determine if patients with low P50-suppression (below 50%) report more perceptual anomalies.

METHODS

Three groups were compared: twenty-nine schizophrenia patients with high P50-suppression (above 50% amplitude suppression), twenty-three schizophrenia patients with low P50-suppression (below 50%) and twenty-six healthy subjects. The Sensory Gating Inventory (SGI), a four-factor self-report questionnaire, was used to measure perceptual anomalies related to sensory gating. A comparison of demographic and clinical data was also carried out.

RESULTS

Patients with low P50-suppression presented: i) significantly higher scores on the SGI (for the overall SGI score and for each of the 4 factors) and ii) significantly larger P50 amplitude at the second click, than both patients with high P50-suppression and healthy subjects. There were no group differences in the most of demographic and clinical data.

DISCUSSION

The finding offers support for conceptual models wherein abnormal neurophysiologic responses to repetitive stimuli give rise to clinically relevant perceptions of being inundated and overwhelmed by external sensory stimuli. Further studies are needed to explore the contributions of clinical symptoms, medication and neuropsychological functions to the relationship between P50-suppression and the SGI, and the role of sensory "gating in" versus "gating out".

Baseline dependency of nicotine's sensory gating actions: similarities and differences in low, medium and high P50 suppressors

Reduced suppression of the P50 auditory event-related potential in schizophrenia patients relative to normal controls is indicative of a sensory gating deficit and is one of the most robust findings reported for functional brain abnormalities in this disorder. However, there is considerable gating variability in patients and controls and there is little understanding as to how inter-individual differences moderate gating responses to drugs and nicotinic agonists in particular, which have shown potential to reverse gating deficits. In this study the effects of acutely administered nicotine (gum, 6 mg) on sensory gating in a paired (S₁-S₂) auditory stimulus paradigm were investigated in 57 healthy, non-smoking volunteers stratified as low (n = 19), medium (n = 19) and high (n = 19) P50 suppressors on the basis of three separate baseline derived gating indices, P50 ratios, P50 difference scores, and gating difference waveforms. Relative to placebo, nicotine consistently improved gating in low suppressors as stratified with all three gating indices, exerted no effects in medium suppressors and reduced gating in high suppressors. Analysis of individual stimulus (S₂, S₂) amplitudes showed distinctly different mechanisms of action underlying nicotine effects in individuals with low and high baseline suppression. The results parallel similar findings of baseline-dependency in the gating effects of several antipsychotic drugs in healthy volunteers and support the use of group segmentation as a translational model in novel cognitive drug development for schizophrenia.

Effects of COMT genotype on sensory gating and its modulation by nicotine: Differences in low and high P50 suppressors

Elevated smoking rates seen in schizophrenia populations may be an attempt to correct neuropathologies associated with deficient nicotinic acetylcholine receptors and/or dopaminergic systems using exogenous nicotine. However, nicotine's effects on cognitive processing and sensory gating have been shown to be baseline-dependent. Evidence of a restorative effect on sensory gating deficits by nicotine-like agonists has been demonstrated, however, its underlying mechanisms in the context of dopamine dysregulation are unclear. Catechol-O-methyltransferase (COMT), a key dopamine regulator in the brain, contains a co-dominant allele in which a valine-to-methionine substitution causes variations in enzymatic activity leading to reduced synaptic dopamine levels in the Val/Val genotype. Using a randomized, double-blind, placebo-controlled design with 57 non-smokers, this study examined the effects of COMT genotype on sensory gating and its modulation by nicotine in low vs. high suppressors. The results were consistent with the hypothesis that increased dopamine resulting from nicotine stimulation or Met allelic activity would benefit gating in low suppressors and impair gating in high suppressors, and that this gating improvement with nicotine would be more evident in Val carriers who were low suppressors, while the gating impairment would be more evident in Met carriers who were high suppressors. These findings reaffirm the importance of baseline-dependency and suggest a subtle relationship between COMT genotype and baseline-stratified levels of sensory gating, which may help to explain the variability of cognitive abilities in schizophrenia populations.

[Neurophysiological endophenotypes and schizophrenic disorder: emergence and evolution of a clinical concept]

It is proposed an historical approach to concepts leading to the development of operational paradigms for measuring objectives neurophysiological endophenotypes. It is hypothesized that psychiatric interest for paradigms measuring Event-Related Potential (ERP) come from Bleuler (1911) and McGhie and Chapman (1961) phenomenological and clinical descriptions. They noted, first that patients with schizophrenia generally feel as if they are being flooded by an overwhelming mass of sensory input combined with a heightened sensory perception, second that they were distractible to irrelevant sensory stimuli. These subjective abnormalities may be related, first to inability to filter incongruent information measured in a double click paradigm by a deficit in P50 amplitude gating, and second to an inability to select a stimulus of interest measured in the oddball paradigm by a deficit in P300 amplitude. The analysis of these P50 and P300 ERP in cohorts of patients with schizophrenia found most of Gottesman endophenotype criteria. P50 and P300 ERP are therefore relevant neurophysiological endophenotypes. However, from a clinical point of view, these endophenotypes lack specificity. The hypothesis of this article leads us to formulate ways of research. It is shown the value of combining objective neurophysiological measures with subjective measures using self-administered questionnaires ("offline") or psychophysiological tests ("online") to develop rigorous neurophysiological experimental paradigms especially as clinical observations of their origins are not forgotten.

Functional imaging of the hemodynamic sensory gating response in schizophrenia

The cortical (auditory and prefrontal) and/or subcortical (thalamic and hippocampal) generators of abnormal electrophysiological responses during sensory gating remain actively debated in the schizophrenia literature. Functional magnetic resonance imaging has the spatial resolution for disambiguating deep or simultaneous sources but has been relatively under-utilized to investigate generators of the gating response. Thirty patients with chronic schizophrenia (SP) and 30 matched controls participated in the current experiment. Hemodynamic response functions (HRFs) for single (S1) and pairs (S1 + S2) of identical ("gating-out" redundant information) or nonidentical ("gating-in" novel information) tones were generated through deconvolution. Increased or prolonged activation for patients in conjunction with deactivation for controls was observed within auditory cortex, prefrontal cortex, and thalamus in response to single tones during the late hemodynamic response, and these group differences were not associated with clinical or cognitive symptomatology. Although patient hyperactivation to paired-tones conditions was present in several regions of interest, the effects were not statistically significant for either the gating-out or gating-in conditions. Finally, abnormalities in the postundershoot of the auditory HRF were also observed for both single and paired-tones conditions in patients. In conclusion, the amalgamation of the entire electrophysiological response to both S1 and S2 stimuli may limit hemodynamic sensitivity to paired tones during sensory gating, which may be more readily overcome by paradigms that use multiple stimuli rather than pairs. Patient hyperactivation following single tones is suggestive of deficits in basic inhibition, neurovascular abnormalities, or a combination of both factors.

Differential sensory gating functions between smokers and non-smokers among drug-naive first episode schizophrenic patients

Although an acute effect of cigarette smoking and nicotine on sensory gating of schizophrenias has been investigated in published papers, the chronic effect of cigarette smoking on this phenomenon has not yet been reported. We report the effects of chronic cigarette smoking, without new acute exposure before testing, on sensory gating using the P50 auditory evoked potential in a group of drug-naive first episode schizophrenic smokers and healthy smokers. Sensory gating was evaluated using auditory P50 suppression elicited using the conditioning (S1)-testing (S2) paradigm. Fifty six male drug-naive first episode schizophrenic patients were compared to 41 healthy male controls. Patients were classified into subgroups of current smokers (n=18) and non-smokers (n=38) to explore the effects of smoking on sensory gating. All subjects did not smoke a cigarette for at least 1h prior to testing. Schizophrenic patients showed an increased S2 amplitude and a poorer sensory gating as measured by both S2/S1 ratio and S1-S2 difference of P50 amplitude, as compared to healthy controls. However, smokers showed an increased S1 amplitude and better sensory gating than did non-smokers both in schizophrenia patients and healthy controls. Our findings support a sensory gating deficit among first episode schizophrenic patients. However, it was less pronounced among schizophrenic patients who were current cigarette smokers, suggesting a positive effect of chronic cigarette smoking on ameliorating this sensory gating deficit in schizophrenia. Our findings of the present study present new evidence supporting the self-medication hypothesis of self-medication by cigarette smoking in schizophrenia to possibly ameliorate pre-existing functional deficits.

Differential effects of nicotine on P50 amplitude, its gating, and their neural sources in low and high suppressors

Sensory gating impairment in schizophrenia has been documented in the form of aberrant middle latency P50 event-related brain potential responses to S(1) and/or S(2) stimuli in a paired (S(1)-S(2)) auditory stimulus paradigm. Evidenced by a failure to suppress S(2) P50 or by attenuated S(1) P50s, these sensory deficits have been associated with increased smoking behaviour in this disorder, and may be related to the putative ameliorating effects of smoke-inhaled nicotine on neural mechanisms regulating gating. Comparison of healthy controls with low versus high gating efficiency has been forwarded as a model for investigating the actions of antipsychotic agents on aberrant gating functions. In the current study, the effect of a single dose (6 mg) of nicotine gum on P50, gating indices, and their cortical sources indexed with sLORETA (standardized low resolution electromagnetic tomography), was examined in healthy non-smokers (n=24) stratified for low and high gating levels. Scalp surface recordings revealed nicotine modulation of P50 and its gating to be differentially exhibited in high (decreasing gating) and low (increasing gating) suppressors while the underlying cortical sources influenced by nicotine (middle frontal gyrus, inferior/superior parietal lobules, pre- and post-central gyri) were seen only in low suppressors. These findings suggest that nicotine impacts sensory gating in healthy volunteers and as the gating enhancing effects were dependent on low baseline gating efficiency, nicotinic receptor agonists may be associated with unique P50 modulating actions in schizophrenia.

Perceptual/attentional anomalies in schizophrenia: a family study

Endophenotypes have emerged as an important concept in the study of schizophrenia. Perceptual/attentional anomalies were examined as potential endophenotypes in a family study using a strategy for "multiplex/simplex schizophrenia". The sample was comprised of 797 subjects: 206 schizophrenia patients, 302 first-degree relatives and 289 controls. The Spanish versions of the Structured Interview for Assessing Perceptual/attentional Anomalies (SIAPA) and Positive and Negative Symptoms Scale (PANSS) were applied to measure the presence of perceptual/attentional anomalies, and positive and negative subscale respectively. An ANCOVA was carried out for global comparisons between groups. The multiplex schizophrenic group had significantly more frequent auditory and visual perceptual/attentional anomalies than Simplex schizophrenic and control groups. The most interesting finding was that the severity of auditory and visual perceptual/attentional anomalies and negative symptoms was significantly higher in the relatives of the multiplex schizophrenia group than in those relatives from the simplex schizophrenia and control groups. The existence of perceptual/attentional anomalies in nonaffected relatives suggests the presence of familial association for these symptoms which may therefore be a potential endophenotype suitable for genetic studies.

Association of the 5'-upstream regulatory region of the alpha7 nicotinic acetylcholine receptor subunit gene (CHRNA7) with schizophrenia

BACKGROUND

The alpha7 neuronal nicotinic acetylcholine receptor subunit gene (CHRNA7) is localized in a chromosomal region (15q14) linked to schizophrenia in multiple independent studies. CHRNA7 was selected as the best candidate gene in the region for a well-documented endophenotype of schizophrenia, the P50 sensory processing deficit, by genetic linkage and biochemical studies.

METHODS

Subjects included Caucasian-Non Hispanic and African-American case-control subjects collected in Denver, and schizophrenic subjects from families in the NIMH Genetics Initiative on Schizophrenia. Thirty-five single nucleotide polymorphisms (SNPs) in the 5'-upstream regulatory region of CHRNA7 were genotyped for association with schizophrenia, and for smoking in schizophrenia.

RESULTS

The rs3087454 SNP, located at position -1831 bp in the upstream regulatory region of CHRNA7, was significantly associated with schizophrenia in the case-control samples after multiple-testing correction (P=0.0009, African American; P=0.013, Caucasian-Non Hispanic); the association was supported in family members. There was nominal association of this SNP with smoking in schizophrenia.

CONCLUSIONS

The data support association of regulatory region polymorphisms in the CHRNA7 gene with schizophrenia.

Auditory gating in rat hippocampus and medial prefrontal cortex: effect of the cannabinoid agonist WIN55,212-2

Sensory gating can be assessed in rodents and humans using an auditory conditioning (C)-test (T) paradigm, with schizophrenic patients exhibiting a loss of gating. Dysregulation of the endocannabinoid system has been proposed to be involved in the pathogenesis of schizophrenia. We studied auditory gating and the effects of the cannabinoid agonist WIN55,212-22 on gating in CA3 and dentate gyrus (DG) of the hippocampus and medial prefrontal cortex (mPFC) in male Lister hooded rats using in vivo electrophysiology. The effects of a single dose of WIN55,212-2 on the N2 local field potential (LFP) test/conditioning amplitude ratios (T/C ratio) and response latencies were examined. In rats that demonstrated gating of N2, mPFC showed higher T/C ratios and shorter conditioning response latencies compared to DG and CA3. WIN55,212-2 disrupted auditory gating in all three areas with a significant increase in test amplitudes in the gating rats. A group of non-gating rats demonstrated higher test amplitudes and higher T/C ratios compared to gating rats. WIN55,212-2 had no effect on T/C ratios in the non-gating rats. The cannabinoid receptor (CB1) antagonist SR141716A prevented WIN55,212-2 induced disruption of gating. This study demonstrates gated auditory-evoked responses in CA3, DG and mPFC. The mPFC showed an early phase of gating which may later be modulated by CA3 and DG activity. Furthermore, cannabinoid receptor activation disrupted auditory gating in CA3, DG and mPFC, an effect which was prevented by CB1 receptor antagonism. The results further demonstrate the presence of a non-gating rat population which responded differently to cannabinoid agonists.

P50 auditory evoked potential suppression in bipolar disorder patients with psychotic features and their unaffected relatives

BACKGROUND

Diminished suppression of the P50 response, a consistent finding in schizophrenia, has also been reported in patients with psychotic bipolar disorder. It is a promising endophenotype for schizophrenia, but its relationship to genetic liability in bipolar disorder is unknown. We therefore assessed whether diminished P50 suppression is associated with familial risk for psychotic bipolar disorder.

METHODS

The P50 response was collected in a conditioning (C)--testing (T) paradigm from 42 outpatients with bipolar 1 disorder who had experienced psychotic symptoms and 44 of their unaffected first-degree relatives, all from families multiply affected with bipolar disorder or another non-organic psychotic disorder; 48 healthy control subjects were also studied. The T/C ratio was compared between the groups, with linear regression analyses and robust variance estimators for clustered data.

RESULTS

Both patients (estimated mean difference in T/C ratio to control subjects, 32, 95% confidence interval [CI] 15-48, p=.001) and unaffected relatives (20, 95% CI 7-32, p=.002) demonstrated higher T/C ratio, thus indicating diminished P50 suppression compared with control subjects.

CONCLUSIONS

To our knowledge, this is the first report of diminished P50 gating in unaffected relatives of psychotic bipolar disorder patients from multiply affected families. Our results suggest that impaired P50 gating is a putative endophenotype for psychotic bipolar disorder and thus might reflect the impact of susceptibility genes across psychosis.

Sensory Gating Deficit Assessed by P50/Pb Middle Latency Event Related Potential in Alzheimer’s Disease

Sensory gating is defined as the brain's ability to inhibit repetitive and irrelevant incoming sensory stimuli and is supposed to be related to cholinergic transmission. Indeed, Alzheimer's disease (AD) is characterized by a cholinergic deficit that is believed to be involved in cerebral cortex hyperexcitability and short latency afferent inhibition deficit. Therefore, a sensory gating deficit may be supposed present in AD within the frame of cortex hyperexcitability and loss of cortex modulation of sensory inputs. The authors investigated whether a sensory gating deficit may be present in AD and whether this deficit may be related to the presence of neuropsychiatric symptoms (NPS) and reversed by donepezil treatment. Sensory gating was evaluated using a paired-stimulus auditory P50 event-related potential paradigm. Eighteen drug-naïve probable AD patients (mean age 76.1 years; SD 5.6 years; 13 females and 5 males) and 15 healthy elderly controls (mean age 74.2 years; SD 5.4 years; 10 females and 5 males) were recruited. Sensory gating was evaluated in AD patients before starting therapy and after 1 and 3 months of donepezil treatment. Auditory P50 sensory gating was impaired in AD patients but no correlation was found between gating deficit and NPS. Moreover, AD patients displayed increased P50 amplitude when compared with healthy elderly subjects. Donepezil treatment did not improve P50 sensory gating in AD patients but decreased P50 amplitude. Patients with AD displayed an augmented P50 amplitude, in accordance with previous studies, suggesting increased cortex excitability. Donepezil does not affect P50 sensory gating but reduces P50 amplitude. Donepezil may induce P50 amplitude reduction by means of enhanced dopamine release. Indeed, it has been demonstrated that donepezil induces dopamine release "in vitro." The findings suggest that AD patients have a sensory gating impairment but the link with both NPS and the cholinergic deficit is doubtful.

The use of neurophysiological endophenotypes to understand the genetic basis of schizophrenia

Specifying the complex genetic architecture of the “fuzzy” clinical phenotype of schizophrenia is an imposing problem. Utilizing metabolic, neurocognitive, and neurophysiological “intermediate” endophenotypic measures offers significant advantages from a statistical genetics stand-point. Endophenotypic measures are amenable to quantitative genetic analyses, conferring upon them a major methodological advantage compared with largely qualitative diagnoses using the Diagnostic and Statistical Manual of Mental Health, 4th Edition (DSM-IV). Endophenotypic deficits occur across the schizophrenia spectrum in schizophrenia patients, schizotypal patients, and clinically unaffected relatives of schizophrenia patients, Neurophysiological measures, such as P50 event-related suppression and the prepulse inhibition (PPI) of the startle response, are endophenotypes that can be conceptualized as being impaired because of a single genetic abnormality in the functional cascade of DNA to RNA to protein. The “endophenotype approach” is also being used to understand other medical disorders, such as colon cancer, hemochromatosis, and hypertension, where there is interplay between genetically conferred vulnerability and nongenetic stressors. The power and utility of utilizing endophenotypes to understand the genetics of schizophrenia is discussed in detail in this article.