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

Auditory Sensory Gating: Effects of Noise

Cortical auditory evoked potentials (CAEPs) indicate that noise degrades auditory neural encoding, causing decreased peak amplitude and increased peak latency. Different types of noise affect CAEP responses, with greater informational masking causing additional degradation. In noisy conditions, attention can improve target signals' neural encoding, reflected by an increased CAEP amplitude, which may be facilitated through various inhibitory mechanisms at both pre-attentive and attentive levels. While previous research has mainly focused on inhibition effects during attentive auditory processing in noise, the impact of noise on the neural response during the pre-attentive phase remains unclear. Therefore, this preliminary study aimed to assess the auditory gating response, reflective of the sensory inhibitory stage, to repeated vowel pairs presented in background noise. CAEPs were recorded via high-density EEG in fifteen normal-hearing adults in quiet and noise conditions with low and high informational masking. The difference between the average CAEP peak amplitude evoked by each vowel in the pair was compared across conditions. Scalp maps were generated to observe general cortical inhibitory networks in each condition. Significant gating occurred in quiet, while noise conditions resulted in a significantly decreased gating response. The gating function was significantly degraded in noise with less informational masking content, coinciding with a reduced activation of inhibitory gating networks. These findings illustrate the adverse effect of noise on pre-attentive inhibition related to speech perception.

Sensory Gating Networks in Normal-Hearing Adults With Minimal Tinnitus

PURPOSE

The goal of this study was to observe sensory gating-related networks underlying cortical auditory evoked potential (CAEP) peak components in individuals with and without minimal tinnitus, as measured using the Tinnitus Handicap Inventory (THI). This analysis was performed on previously published sensory gating responses in normal-hearing adults with and without minimal tinnitus.

METHOD

Independent component analysis was performed for each individual CAEP gating component (Pa, P50, N1, and P2). Significant components were retained for source localization analyses within the following groups: no tinnitus, tinnitus with a THI score ≤ 6, and tinnitus with a THI score > 6. Brain source localization was performed on the gating difference wave for each component using standardized low-resolution brain electromagnetic tomography.

RESULTS

Gating-related networks were identified within each group. Different regional sources were observed between groups, with parietal sources underlying the Pa and P50 components as tinnitus severity increased. A larger prefrontal regional activation was also shown for the N1 gating component as tinnitus severity increased. These results expand upon the functional gating responses via CAEP waveforms in a previously published study.

CONCLUSIONS

The auditory gating response, as measured via CAEPs, has previously been shown to significantly correlate with an increase in tinnitus severity in adults with normal hearing. The corresponding changes in the gating response appear to be supported by different cortical regions in those without tinnitus, those with a THI score ≤ 6, and those with a THI score > 6. Next, functional differences between localized cortical regions should be tested.

Cholinergic modulation of sensory perception and plasticity

Sensory systems are highly plastic, but the mechanisms of sensory plasticity remain unclear. People with vision or hearing loss demonstrate significant neural network reorganization that promotes adaptive changes in other sensory modalities as well as in their ability to combine information across the different senses (i.e., multisensory integration. Furthermore, sensory network remodeling is necessary for sensory restoration after a period of sensory deprivation. Acetylcholine is a powerful regulator of sensory plasticity, and studies suggest that cholinergic medications may improve visual and auditory abilities by facilitating sensory network plasticity. There are currently no approved therapeutics for sensory loss that target neuroplasticity. This review explores the systems-level effects of cholinergic signaling on human visual and auditory perception, with a focus on functional performance, sensory disorders, and neural activity. Understanding the role of acetylcholine in sensory plasticity will be essential for developing targeted treatments for sensory restoration.

Sensory Inhibition and Speech Perception-in-Noise Performance in Children With Normal Hearing

PURPOSE

This study investigated whether sensory inhibition in children may be associated with speech perception-in-noise performance. Additionally, gating networks associated with sensory inhibition were identified via standardized low-resolution brain electromagnetic tomography (sLORETA), and the detectability of the cortical auditory evoked potential (CAEP) N1 response was enhanced using a 4- to 30-Hz bandpass filter.

METHOD

CAEP gating responses, reflective of inhibition, were evoked via click pairs and recorded using high-density electroencephalography in neurotypical 5- to 8-year-olds and 22- to 24-year-olds. Amplitude gating indices were calculated and correlated with speech perception in noise. Gating generators were estimated using sLORETA. A 4- to 30-Hz filter was applied to detect the N1 gating component.

RESULTS

Preliminary findings indicate children showed reduced gating, but there was a correlational trend between better speech perception and decreased N2 gating. Commensurate with decreased gating, children presented with incomplete compensatory gating networks. The 4- to 30-Hz filter identified the N1 response in a subset of children.

CONCLUSIONS

There was a tenuous relationship between children's speech perception and sensory inhibition. This may suggest that sensory inhibition is only implicated in atypically poor speech perception. Finally, the 4- to 30-Hz filter settings are critical in N1 detectability.

SIGNIFICANCE

Gating may help evaluate reduced sensory inhibition in children with clinically poor speech perception using the appropriate methodology. Cortical gating generators in typically developing children are also newly identified.

N-methyl-D-aspartate receptor antagonism impairs sensory gating in the auditory cortex in response to speech stimuli

Deficits in early auditory sensory processing in schizophrenia have been linked to N-methyl-D-aspartate receptor (NMDAR) hypofunction, but the role of NMDARs in aberrant auditory sensory gating (SG) in this disorder is unclear. This study, conducted in 22 healthy humans, examined the acute effects of a subanesthetic dose of the NMDAR antagonist ketamine on SG as measured electrophysiologically by suppression of the P50 event-related potential (ERP) to the second (S2) relative to the first (S1) of two closely paired (500 ms) identical speech stimuli. Ketamine induced impairment in SG indices at sensor (scalp)-level and at source-level in the auditory cortex (as assessed with eLORETA). Together with preliminary evidence of modest positive associations between impaired gating and dissociative symptoms elicited by ketamine, tentatively support a model of NMDAR hypofunction underlying disturbances in auditory SG in schizophrenia.

Sensory gating in tobacco-naïve cannabis users is unaffected by acute nicotine administration

OBJECTIVES

Long-term cannabis use has been associated with the appearance of psychotic symptoms and schizophrenia-like cognitive impairments; however these studies may be confounded by concomitant use of tobacco by cannabis users. We aimed to determine if previously observed cannabis-associated deficits in sensory gating would be seen in cannabis users with no history of tobacco use, as evidenced by changes in the P50, N100, and P200 event-related potentials. A secondary objective of this study was to examine the effects of acute nicotine administration on cannabis users with no tobacco use history.

METHODS

Three components (P50, N100, P200) of the mid-latency auditory-evoked response (MLAER) were elicited by a paired-stimulus paradigm in 43 healthy, non-tobacco smoking male volunteers between the ages of 18-30. Cannabis users (CU, n = 20) were administered nicotine (6 mg) and placebo gum within a randomized, double-blind design. Non-cannabis users (NU, n = 23) did not receive nicotine.

RESULTS

Between-group sensory gating effects were only observed for the N100, with CUs exhibiting a smaller N100 to S1 of the paired stimulus paradigm, in addition to reduced dN100 (indicating poorer gating). Results revealed no significant sensory gating differences with acute administration of nicotine compared to placebo cannabis conditions.

CONCLUSIONS

These findings suggest a relationship between gating impairment and cannabis use; however, acute nicotine administration nicotine does not appear to impact sensory gating function.

Reduced coupling of somatosensory gating and gamma oscillation in panic disorder

Previous studies have reported that patients with panic disorder (PD) exhibited an aberrant level of GABA concentration, an inhibitory neurotransmitter in the human brain. However, it remains substantially unclear whether the inhibitory function regarding the neurophysiological characteristics is altered in this disease. Sensory gating (SG) is considered as an automatic inhibitory function in the sensory cortex. In addition, brain's gamma oscillation within the sensory cortex is another index to reflect inhibitory function. Here we aimed to investigate whether the patients with PD showed altered inhibitory function in the somatosensory system, including the primary (SI) and secondary (SII) somatosensory cortices. A total of 20 healthy controls and 21 patients with PD underwent magnetoencephalographic recordings. Paired-pulse and single-pulse paradigms were used to study SG and gamma oscillations, respectively. There were no significant between-group differences in the SG function in the SI and SII. However, patients with PD demonstrated a reduced gamma power in the SI. Among the healthy individuals, strong associations between SG ratios and gamma frequency values were observed in the SI. However, such a functional relationship disappeared among the patients with PD. We suggested the reduced coupling of SG and gamma oscillation as one of the neural signatures in PD.

CDP-choline and galantamine, a personalized α7 nicotinic acetylcholine receptor targeted treatment for the modulation of speech MMN indexed deviance detection in healthy volunteers: a pilot study

RATIONALE

The combination of CDP-choline, an α7 nicotinic acetylcholine receptor (α7 nAChR) agonist, with galantamine, a positive allosteric modulator of nAChRs, is believed to counter the fast desensitization rate of the α7 nAChRs and may be of interest for schizophrenia (SCZ) patients. Beyond the positive and negative clinical symptoms, deficits in early auditory prediction-error processes are also observed in SCZ. Regularity violations activate these mechanisms that are indexed by electroencephalography-derived mismatch negativity (MMN) event-related potentials (ERPs) in response to auditory deviance.

OBJECTIVES/METHODS

This pilot study in thirty-three healthy humans assessed the effects of an optimized α7 nAChR strategy combining CDP-choline (500 mg) with galantamine (16 mg) on speech-elicited MMN amplitude and latency measures. The randomized, double-blinded, placebo-controlled, and counterbalanced design with a baseline stratification method allowed for assessment of individual response differences.

RESULTS

Increases in MMN generation mediated by the acute CDP-choline/galantamine treatment in individuals with low baseline MMN amplitude for frequency, intensity, duration, and vowel deviants were revealed.

CONCLUSIONS

These results, observed primarily at temporal recording sites overlying the auditory cortex, implicate α7 nAChRs in the enhancement of speech deviance detection and warrant further examination with respect to dysfunctional auditory deviance processing in individuals with SCZ.

Sensory Inhibition Is Related to Variable Speech Perception in Noise in Adults With Normal Hearing

Purpose Speech perception in noise (SPiN) varies widely in individuals with normal hearing, which may be attributed to factors that are not reflected in the audiogram, such as inhibition. However, inhibition is involved at both sensory and cognitive stages of auditory perception, and while inhibition at the cognitive level has been shown to be a significant factor in SPiN processes, it is unknown whether sensory inhibition may also contribute to SPiN variability. Therefore, the goal of this study was to evaluate sensory inhibition in adults with normal hearing and mild SPiN impairment. Method Cortical auditory evoked potentials (CAEPs) were recorded in 49 adults via high-density electroencephalography using an auditory gating paradigm. Participants were categorized according to a median signal-to-noise ratio (SNR) loss of 1.5 dB: typical SNR loss ≤ 1.5 dB (n = 32), mild SNR loss > 1.5 dB (n = 17). CAEP gating responses were compared and correlated with SNR loss and extended high-frequency thresholds. Current density reconstructions were performed to qualitatively observe underlying cortical inhibitory networks in each group. Results In comparison to adults with typical SPiN ability, adults with mild SPiN impairment showed an absence of the gating response. A CAEP gating component (P2) reflected decreased sensory inhibition and correlated with increased SNR loss. Extended high-frequency thresholds were also found to correlate with SNR loss, but not gating function. An atypical cortical inhibitory network was observed in the mild SNR loss group, with reduced frontal and absent prefrontal activation. Conclusion Sensory inhibition appears to be atypical and related to SPiN deficits in adults with mild impairment. In addition, cortical inhibitory networks appear to be incomplete, with a possible compensatory parietal network. Further research is needed to delineate between types or levels of central inhibitory mechanisms and their contribution to SPiN processes.

Auditory Gating in Hearing Loss

BACKGROUND

Sensory gating is a measure used to evaluate inhibitory deficits underlying neurological disorders. However, the effects of hearing loss (HL), thought to decrease inhibition, remain unknown on gating function.

PURPOSE

The goal of this study was to investigate gating performance in HL.

RESEARCH DESIGN

This was a prospective, cross-sectional study with independent group comparison and correlational design.

STUDY SAMPLE

Eleven adults (mean age/standard deviation = 47.546 ± 7.967 years) with normal hearing (NH) and 11 adults (mean age/standard deviation = 56.273 ± 13.871 years) with mild-moderate high-frequency HL.

DATA COLLECTION AND ANALYSIS

Cortical auditory evoked potentials (CAEPs) were recorded in response to tonal pairs via high-density electroencephalography. The CAEP response to the second tone in the pair (S2) was compared with the response to the first tone in the pair (S1) within groups. Amplitude gating indices were compared between groups and correlated with auditory behavioral measures. Current density reconstructions were performed to estimate cortical gating generators.

RESULTS

Amplitude gating indices were decreased and correlated with elevated auditory thresholds. Gating generators in temporal, frontal, and prefrontal regions were localized in the NH group, while HL gating was localized in mainly temporal and parietal areas.

CONCLUSIONS

Reduced inhibition may be associated with compensatory cortical gating networks in HL and should be considered when utilizing gating in clinical populations.

Biomarkers and neuromodulation techniques in substance use disorders

Addictive disorders are a severe health concern. Conventional therapies have just moderate success and the probability of relapse after treatment remains high. Brain stimulation techniques, such as transcranial Direct Current Stimulation (tDCS) and Deep Brain Stimulation (DBS), have been shown to be effective in reducing subjectively rated substance craving. However, there are few objective and measurable parameters that reflect neural mechanisms of addictive disorders and relapse. Key electrophysiological features that characterize substance related changes in neural processing are Event-Related Potentials (ERP). These high temporal resolution measurements of brain activity are able to identify neurocognitive correlates of addictive behaviours. Moreover, ERP have shown utility as biomarkers to predict treatment outcome and relapse probability. A future direction for the treatment of addiction might include neural interfaces able to detect addiction-related neurophysiological parameters and deploy neuromodulation adapted to the identified pathological features in a closed-loop fashion. Such systems may go beyond electrical recording and stimulation to employ sensing and neuromodulation in the pharmacological domain as well as advanced signal analysis and machine learning algorithms. In this review, we describe the state-of-the-art in the treatment of addictive disorders with electrical brain stimulation and its effect on addiction-related neurophysiological markers. We discuss advanced signal processing approaches and multi-modal neural interfaces as building blocks in future bioelectronics systems for treatment of addictive disorders.

Auditory Sensory Gating and the Big Five Personality Factors

Abstract. Sensory gating allows an individual to filter out irrelevant sensory information from the environment, potentially freeing attentional resources for more complex tasks. Some work has demonstrated a relationship between auditory sensory gating and cognitive skills such as executive function, although the functional significance is not well understood. The relationship between sensory gating and personality dimensions has not been adequately explored. Participants completed a paired-tone sensory gating event-related potential (ERP) paradigm and the Big Five Inventory to assess personality characteristics. Participants with more robust P50 sensory gating reported a significantly greater degree of conscientiousness; conscientiousness (but not the other Big Five factors) predicted sensory gating ability. Longer ERP latencies were associated with participants being more conscientious (P50 component), more agreeable, and less neurotic (N100 component). A better understanding of the behavioral correlates of sensory gating will help elucidate the functional consequences of reduced sensory gating both in typical adults and clinical groups.

Combining CDP-choline and galantamine: Effects of a selective α7 nicotinic acetylcholine receptor agonist strategy on P50 sensory gating of speech sounds in healthy volunteers

BACKGROUND

Schizophrenia (SCZ) patients and relatives have deficits in early cortical sensory gating (SG) typically measured by suppression of electroencephalography-derived P50 event-related potentials (ERPs) in a conditioning-testing (S₁-S₂) paradigm. Associated with alpha 7 nicotinic acetylcholine receptor (α7 nAChR) dysfunction and shown to be improved with nicotine and α7 nAChR agonists, SG has recently been shown to be improved in low P50 suppressing SCZ patients following acute CDP-choline treatment.

AIMS

This pilot study in healthy humans assessed the SG effects of an α7 nAChR strategy combining CDP-choline with galantamine, a positive allosteric modulator (PAM) of nAChRs, aimed at increasing and prolonging nicotinic receptor activity.

METHODS

The combined effect of CDP-choline (500 mg) and galantamine (16 mg) on speech P50 gating indices rP50 (S₂/S₁) and dP50 (S₁-S₂) was examined in 30 healthy participants stratified into low and high baseline P50 suppressors in a randomized, double-blind, placebo-controlled and counterbalanced design.

RESULTS

In low suppressors, CDP-choline/galantamine (vs. placebo) improved rP50 and dP50 gating, and reduced S₂P50 amplitudes. No P50 gating effects were observed in high suppressors; however, CDP-choline/galantamine (vs. placebo) increased their S₂P50 amplitudes.

CONCLUSION

Findings from this pilot study with CDP-choline/galantamine in a healthy, SCZ-like surrogate deficient gating sample are consistent with the association of α7 nAChR mechanisms in SG impairment in SCZ and support further research trials with CDP-choline and galantamine targeting sensory processes.

Auditory Gating and Extended High-Frequency Thresholds in Normal-Hearing Adults With Minimal Tinnitus

Purpose The goal of this study was to assess whether peripheral auditory sensitivity in frequency regions above 8 kHz is related to central inhibitory function, as measured through a sensory gating paradigm, in normal-hearing adults with tinnitus (TINN) and without tinnitus (NTINN). The contribution of gating processes and peripheral sensitivity in extended high frequencies to tinnitus severity was evaluated via a hierarchical multiple regression method. Method Cortical auditory evoked potentials (CAEPs) were recorded in response to pairs of tones in normal-hearing adults without tinnitus, NTINN ( n = 45), and adults with tinnitus, TINN ( n = 21). CAEP peak component amplitude, latency, and gating indices were compared and correlated with extended high-frequency (EHF) pure-tone averages (PTAs) across groups and with tinnitus severity. An exploratory analysis was performed to investigate gating variability within the TINN group. Based on Tinnitus Handicap Inventory (Newman, Jacobson, & Spitzer, 1996) median scores, the TINN group was categorized into low- and high-median subgroups, and gating indices were compared between these subgroups. A hierarchical multiple regression analysis was performed to determine the amount of variance accounted for in the TINN group. Results Decreased gating via the CAEP Pa component and increased gating via the N1 component correlated with increased tinnitus severity, even in individuals who would traditionally be classified as having no tinnitus handicap. In the TINN group, lower EHF PTA thresholds correlated with tinnitus severity and decreased Pa gating. Individuals with a greater severity of tinnitus demonstrated atypical gating function reflected in both Pa and N1 components. Gating function and EHF PTA accounted for significant variance regarding tinnitus severity. Conclusions A trade-off between lower and higher level gating function was observed in adults with normal hearing and tinnitus, indicative of higher order compensatory mechanisms. Better cochlear sensitivity in extended high frequencies was related to decreased lower level gating processes and increased tinnitus THI scores, suggestive of an interaction between decreased gating and heightened auditory awareness. We are currently exploring whether gating processes in this population are compensatory, and the role of gating in auditory awareness.

Combining CDP-choline and galantamine, an optimized α7 nicotinic strategy, to ameliorate sensory gating to speech stimuli in schizophrenia

Neural α7 nicotinic acetylcholine receptor (nAChR) expression and functioning deficits have been extensively associated with cognitive and early sensory gating (SG) impairments in schizophrenia (SCZ) patients and their relatives. SG, the suppression of irrelevant and redundant stimuli, is measured in a conditioning-testing (S₁-S₂) paradigm eliciting electroencephalography-derived P50 event-related potentials (ERPs), the S₂ amplitudes of which are typically suppressed relative to S₁. Despite extensive reports of nicotine-related improvements and several decades of research, an efficient nicotinic treatment has yet to be approved for SCZ. Following reports of SG improvements in low P50 suppressing SCZ patients and healthy participants with the α7 agonist, CDP-choline, this pilot study examined the combined modulatory effect of CDP-choline (500 mg) and galantamine (16 mg), a nAChR positive allosteric modulator and acetylcholinesterase inhibitor, on SG to speech stimuli in twenty-four SCZ patients in a randomized, double-blind and placebo-controlled design. As expected, in low P50 suppressors CDP-choline/galantamine (vs. Placebo) improved rP50 and dP50 scores by increasing inhibitory mechanisms as reflected by S₂P50 amplitude reductions. Results also suggest a moderating role for auditory verbal hallucinations in treatment response. These preliminary findings provide supportive evidence for the involvement of α7 nAChR activity in speech gating in SCZ and support additional trials, examining different dose combinations and repeated doses of this optimized and personalized targeted α7 cholinergic treatment for SG dysfunction in subgroups of SCZ patients.

Assessing the acute effects of CDP-choline on sensory gating in schizophrenia: A pilot study

Deficient sensory gating (SG) in schizophrenia is associated with functional outcome and offers a therapeutic target as it is linked to the altered function/expression of the α7 nicotinic acetylcholine receptors (nAChRs). This study analyzed the effects of citicoline (CDP-choline), a supplement with α7 nAChRs agonist properties, on SG in a sample of schizophrenia (SZ) patients. Using a randomized, placebo-controlled, double-blind design the dose-dependent (500 mg, 1000 mg, 2000 mg) and baseline-dependent (deficient versus normal suppressors) effects of CDP-choline on SG were examined using the P50 event-related potential (ERP) index of SG. Overall analysis failed to demonstrate treatment effects but CDP-choline improved SG (500 mg) in the deficient SZ subgroup by increasing suppression of the S2 P50 amplitude. These findings tentatively support α7 nAChR dysfunction in the expression of SG deficits and suggest further trials to assess the effects of sustained α7 nAChR activation on SG with low doses of CDP-choline.

Neuronal effects of nicotine during auditory selective attention in schizophrenia

Although nicotine has been shown to improve attention deficits in schizophrenia, the neurobiological mechanisms underlying this effect are poorly understood. We hypothesized that nicotine would modulate attention-associated neuronal response in schizophrenia patients in the ventral parietal cortex (VPC), hippocampus, and anterior cingulate based on previous findings in control subjects. To test this hypothesis, the present study examined response in these regions in a cohort of nonsmoking patients and healthy control subjects using an auditory selective attention task with environmental noise distractors during placebo and nicotine administration. In agreement with our hypothesis, significant diagnosis (Control vs. Patient) X drug (Placebo vs. Nicotine) interactions were observed in the VPC and hippocampus. The interaction was driven by task-associated hyperactivity in patients (relative to healthy controls) during placebo administration, and decreased hyperactivity in patients after nicotine administration (relative to placebo). No significant interaction was observed in the anterior cingulate. Task-associated hyperactivity of the VPC predicted poor task performance in patients during placebo. Poor task performance also predicted symptoms in patients as measured by the Brief Psychiatric Rating Scale. These results are the first to suggest that nicotine may modulate brain activity in a selective attention-dependent manner in schizophrenia.

The separate and combined effects of monoamine oxidase A inhibition and nicotine on the mismatch negativity event related potential

The mismatch negativity (MMN) auditory event-related potential (ERP) has been extensively studied as a potential biomarker for abnormal auditory processing in schizophrenia (SZ), a population which exhibits abnormally high smoking rates. The relationship between nicotinic activation and cognition in SZ may be related to underlying nicotinic and NMDA receptor dysfunction within the disease. However, transient cognitive improvements via smoking in patients may also result from monoamine oxidase (MAO) inhibition, achieved through tobacco smoke. In 24 healthy non-smoking males, we investigated the separate and combined effects of nicotine and MAO-A inhibition via moclobemide (75mg) on the optimal-5 variation of the MMN paradigm. No significant drug effects were observed in our total sample, however, stratification of individuals into low (N=12) and high (N=12) baseline MMN amplitude groups revealed increases in duration MMN amplitude relative to placebo by nicotine, as well as moclobemide, but not after the combination of the two. Because previous research has shown there was no effect of monoamine modulation on MMN, this study shows an unexpected effect of moclobemide on duration MMN.

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.

Spatio-temporal dynamics of adaptation in the human visual system: a high-density electrical mapping study

When sensory inputs are presented serially, response amplitudes to stimulus repetitions generally decrease as a function of presentation rate, diminishing rapidly as inter-stimulus intervals (ISIs) fall below 1 s. This 'adaptation' is believed to represent mechanisms by which sensory systems reduce responsivity to consistent environmental inputs, freeing resources to respond to potentially more relevant inputs. While auditory adaptation functions have been relatively well characterized, considerably less is known about visual adaptation in humans. Here, high-density visual-evoked potentials (VEPs) were recorded while two paradigms were used to interrogate visual adaptation. The first presented stimulus pairs with varying ISIs, comparing VEP amplitude to the second stimulus with that of the first (paired-presentation). The second involved blocks of stimulation (N = 100) at various ISIs and comparison of VEP amplitude between blocks of differing ISIs (block-presentation). Robust VEP modulations were evident as a function of presentation rate in the block-paradigm, with strongest modulations in the 130-150 ms and 160-180 ms visual processing phases. In paired-presentations, with ISIs of just 200-300 ms, an enhancement of VEP was evident when comparing S2 with S1, with no significant effect of presentation rate. Importantly, in block-presentations, adaptation effects were statistically robust at the individual participant level. These data suggest that a more taxing block-presentation paradigm is better suited to engage visual adaptation mechanisms than a paired-presentation design. The increased sensitivity of the visual processing metric obtained in the block-paradigm has implications for the examination of visual processing deficits in clinical populations.

Neurocognitive effects of acute choline supplementation in low, medium and high performer healthy volunteers

Novel pharmacological treatments targeting alpha 7 nicotinic acetylcholine receptor (α7 nAChR) hypofunction in schizophrenia have shown mixed success in ameliorating cognitive impairments associated with this disorder. Choline, a selective agonist at α7 receptors is increased with oral administration of cytidine 5'-diphosphocholine (CDP-choline), the cognitive effects of which were assessed in healthy volunteers. Using the CogState test battery, behavioral performance in schizophrenia-relevant cognitive domains was assessed in 24 male participants following a single low (500mg) and moderate (1000mg) dose of CDP-choline. Relative to placebo, CDP-choline improved processing speed, working memory, verbal learning, verbal memory, and executive function in low baseline performers, while exerting no effects in medium baseline performers, and diminishing cognition in high baseline performers. Dose effects varied with cognitive domain but were evident with both the 500mg and 1000mg doses. These preliminary findings of cognitive enhancement in relatively impaired performers are consistent with the α7 receptor mechanism and support further trials with CDP-choline as a potential pro-cognitive strategy for cognitive impairment in schizophrenia.

Nicotinic receptors and attention

Facilitation of different attentional functions by nicotinic acetylcholine receptor (nAChR) agonists may be of therapeutic potential in disease conditions such as Alzheimer's disease or schizophrenia. For this reason, the neuronal mechanisms underlying these effects have been the focus of research in humans and in preclinical models. Attention-enhancing effects of the nonselective nAChR agonist nicotine can be observed in human nonsmokers and in laboratory animals, suggesting that benefits go beyond a reversal of withdrawal deficits in smokers. The ultimate aim is to develop compounds acting with greater selectivity than nicotine at a subset of nAChRs, with an effects profile narrowly matching the targeted cognitive deficits and minimizing unwanted effects. To date, compounds tested clinically target the nAChR subtypes most abundant in the brain. To help pinpoint more selectively expressed subtypes critical for attention, studies have aimed at identifying the secondary neurotransmitter systems whose stimulation mediates the attention-enhancing properties of nicotine. Evidence indicates that noradrenaline and glutamate, but not dopamine release, are critical mediators. Thus, attention-enhancing nAChR agents could spare the system central to nicotine dependence. Neuroimaging studies suggest that nAChR agonists act on a variety of brain systems by enhancing activation, reducing activation, and enhancing deactivation by attention tasks. This supports the notion that effects on different attentional functions may be mediated by distinct central mechanisms, consistent with the fact that nAChRs interact with a multitude of brain sites and neurotransmitter systems. The challenge will be to achieve the optimal tone at the right subset of nAChR subtypes to modulate specific attentional functions, employing not just direct agonist properties, but also positive allosteric modulation and low-dose antagonism.

CDP-choline: effects of the procholine supplement on sensory gating and executive function in healthy volunteers stratified for low, medium and high P50 suppression

Diminished auditory sensory gating and associated neurocognitive deficits in schizophrenia have been linked to altered expression and function of the alpha-7 nicotinic acetycholinergic receptor (α7 nAChR), the targeting of which may have treatment potential. Choline is a selective α7 nAChR agonist and the aim of this study was to determine whether cytidine 5'-diphosphocholine (CDP-choline), or citicoline, a dietary source of choline, increases sensory gating and cognition in healthy volunteers stratified for gating level. In a randomized, placebo-controlled, double-blind design involving acute administration of low, moderate doses (500 mg, 1000 mg) of CDP-choline, 24 healthy volunteers were assessed for auditory gating as indexed by suppression of the P50 event-related potential (ERP) in a paired-stimulus (S1, S2) paradigm, and for executive function as measured by the Groton Maze Learning Task (GMLT) of the CogState Schizophrenia Battery. CDP-choline improved gating (1000 mg) and suppression of the S2 P50 response (500 mg, 1000 mg), with the effects being selective for individuals with low gating (suppression) levels. Tentative support was also shown for increased GMLT performance (500 mg) in low suppressors. These preliminary findings with CDP-choline in a healthy, schizophrenia-like surrogate sample are consistent with a α7 nAChR mechanism and support further trials with choline as a pro-cognitive strategy.

Modulation of auditory deviance detection by acute nicotine is baseline and deviant dependent in healthy nonsmokers: a mismatch negativity study

OBJECTIVE

Cognitive enhancement resulting from nicotinic acetylcholine receptor stimulation may be evidenced by increased efficiency of the auditory-frontal cortex network of auditory discrimination, which is impaired in schizophrenia, a cognitive disorder associated with excessive tobacco use. Investigating automatic (preattentive) detection of acoustic change with the mismatch negativity (MMN) brain event-related potential in response to nicotine in individuals with varying baseline levels of auditory discrimination may provide useful insight into the cholinergic regulation of this neural network and its potential amelioration with novel nicotinic agents.

METHODS

Sixty healthy, non-smoking male volunteers were presented with an 'optimal' multi-feature MMN paradigm in a randomized, placebo controlled double-blind design with 6 mg of nicotine gum.

RESULTS

Participants with low, medium, and high baseline amplitudes responded differently to nicotine (vs. placebo), and nicotine response was feature specific. Whereas MMN in individuals with high amplitudes was diminished by nicotine, MMN increased in those with low amplitudes. Nicotine effects were not shown in medium amplitude participants.

CONCLUSIONS

These findings provide preliminary support for the role of nicotinic neurotransmission in sensory memory processing of auditory change and suggest that nicotinic receptor modulation can both enhance and diminish change detection, depending on baseline MMN and its eliciting stimulus feature.

Neurocognitive endophenotypes in schizophrenia: modulation by nicotinic receptor systems

Cigarette smoking is the leading preventable cause of death in the Western world, with a considerably higher prevalence observed in schizophrenia compared to the general population. Despite the negative health consequences of smoking heavily, it has been proposed that individuals with schizophrenia may maintain smoking behaviors to remediate symptoms associated with the disorder. Neurocognitive deficits are a core feature of schizophrenia and are present in approximately 80% of patients. Further, these deficits constitute an endophenotype of schizophrenia, as they are stable across disease phases, and are heritable. The neurocognitive deficits that are present in schizophrenia are especially debilitating, since they are associated with poor clinical and functional outcomes and community integration. Interestingly, these deficits may also constitute a vulnerability factor towards the initiation and maintenance of tobacco use. Contributing to the potential shared vulnerability between schizophrenia and tobacco dependence is a dysregulation of the nicotinic acetylcholine receptor (nAChR) system. Pre-clinical evidence has shown that nicotine affects several neurotransmitter systems, including dopamine (DA), glutamate, and γ-aminobutyric acid (GABA), and certain neuropsychological deficits associated with these neurotransmitters (reaction time, spatial working memory, sustained attention, and sensory gating) are improved after nicotine administration in patients with schizophrenia. These positive effects on neurocognition appear to be more pronounced in smokers with schizophrenia, and may be an important mechanism that explains the co-morbidity of schizophrenia and tobacco dependence.

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.

Effects of nicotine on visuospatial attentional orienting in non-smokers

Nicotine is a highly addictive substance, suggested to be in part due to its cognitive enhancing effects in the attentional domain. Improvements in stimulus selection with nicotine have been reported but its effects on visual-spatial selective attention are unclear. This study utilized event-related potentials (ERPs) to examine the acute effects of nicotine on selective attention in non-smokers performing a Posner-type visuo-spatial task. The attentional processing of visual-spatial locations is reflected in the P1 ERP component, which represents earlier stages of visual analysis. 24 non-smokers received nicotine gum (6 mg) in a randomized, double-blind, placebo-controlled, repeated measures design. Behavioral performance and ERPs were assessed in response to target locations preceded by valid, invalid and neutral cues. Nicotine did not affect behavioral performance indices. P1 amplitudes were greater in valid and neutral cue trials compared to invalid cue trials and acute nicotine administration (vs. placebo) was found to increase P1 amplitudes in the right hemisphere, particularly in valid cue trials. In addition, in high symptomatic subjects (as indexed by greater increases in heart rate post-administration), nicotine (vs. placebo) produced greater P1 amplitudes in valid cue trials. The study concludes that nicotine enhanced visuospatial selective attention with regards to early visual encoding and analysis. These results demonstrate support in general for the attentional effects of nicotine and nicotinic agonists and they specifically extend these effects to include orienting of visual-spatial attention.

Effects of acute nicotine on auditory change-related cortical responses

RATIONALE AND OBJECTIVE

Nicotine is known to have enhancing effects on some aspects of attention and cognition. The purpose of the present study was to elucidate the effects of nicotine on pre-attentive change-related cortical activity.

METHODS

Change-related cortical activity in response to an abrupt increase (3 dB) and decrease (6 dB) in sound pressure in a continuous sound was recorded by using magnetoencephalography. Nicotine was administered with a nicotine gum (4 mg of nicotine). Eleven healthy nonsmokers were tested with a double-blind and placebo-controlled design. Effects of nicotine on the main component of the onset response peaking at around 50 ms (P50m) and the main component of the change-related response at around 120 ms (Change-N1m) were investigated.

RESULTS

Nicotine failed to affect P50m, while it significantly increased the amplitude of Change-N1m evoked by both auditory changes. The magnitude of the amplitude increase was similar among subjects regardless of the magnitude of the baseline response, which resulted in the percent increase of Change-N1m being greater for subjects with Change-N1m of smaller amplitude.

CONCLUSIONS

Since Change-N1m represents a pre-attentive automatic process to encode new auditory events, the present results suggest that nicotine can exert beneficial cognitive effects without a direct impact on attention.

Nicotine differentially modulates antisaccade performance in healthy male non-smoking volunteers stratified for low and high accuracy

RATIONALE

Nicotinergic agents are currently examined as possible pro-cognitive drugs for a variety of clinical conditions marked by cognitive deficits, such as attention deficit hyperactivity disorder (ADHD) or schizophrenia. The response to acute nicotine is heterogeneous across subjects and samples; however, only a few reliable predictors of response have been identified.

OBJECTIVES

We tested the hypothesis that baseline performance level in cognitive control may be a predictor of the cognitive effects of nicotine.

METHODS

We tested 28 healthy Caucasian, male, non-smoking volunteers with the antisaccade task, an oculomotor measure of cognitive control. Participants were given a 7-mg nicotine patch in a double-blind, placebo-controlled, counterbalanced, within-subjects design. Subjects were stratified into high and low performers based on their antisaccade error rate in the placebo condition (median split).

RESULTS

Nicotine tended to reduce response time variability of prosaccade latency (p = 0.06). There was no main effect of nicotine on antisaccade error rate (p = 0.31). However, nicotine significantly reduced antisaccade error rate in the low-accuracy probands while leaving performance of the high-accuracy probands unaffected (interaction, p < 0.05). Furthermore, we found a nicotine-induced reduction of response time variability of antisaccade latency at one target location in the low-performing group (interaction, p < 0.05).

CONCLUSIONS

The present results demonstrate the importance of baseline performance differences for the effectiveness of pharmacological enhancement of cognitive control. More generally, the results suggest that stimulation of the nicotinic acetylcholine receptor system might be an effective way of improving cognition in people with poor cognitive performance, such as patients with ADHD or schizophrenia.

The moderating role of the dopamine transporter 1 gene on P50 sensory gating and its modulation by nicotine

Although schizophrenia has been considered primarily a disease of dopaminergic neurotransmission, the role of dopamine in auditory sensory gating deficits in this disorder and their amelioration by smoking/nicotine is unclear. Hypothesizing that individual differences in striatal dopamine levels may moderate auditory gating and its modulation by nicotine, this preliminary study used the mid-latency (P50) auditory event-related potential (ERP) to examine the single dose (6 mg) effects of nicotine (vs. placebo) gum on sensory gating in 24 healthy nonsmokers varying in the genetic expression of the dopamine transporter (DAT). Consistent with an inverted-U relationship between dopamine level and the drug effects, individuals carrying the 9R (lower gene expression) allele, which is related to greater striatal dopamine levels, tended to evidence increased baseline gating compared to 10R (higher gene expression) allele carriers and showed a reduction in gating with acute nicotine. The present results may help to understand the link between excessive smoking and sensory gating deficits in schizophrenia and to explain the potential functional implications of genetic disposition on nicotinic treatment in schizophrenia.