Abolition of latent inhibition by a single 5 mg dose of d-amphetamine in man

The Manic Idea Creator? A Review and Meta-Analysis of the Relationship between Bipolar Disorder and Creative Cognitive Potential

Even though a relationship between psychopathology and creativity has been postulated since the time of ancient Greece, systematic meta-analyses on this topic are still scarce. Thus, the meta-analysis described here can be considered the first to date that specifically focuses on the relationship between creative potential, as measured by divergent thinking, and bipolar disorder, as opposed to psychopathology in general. An extensive literature search of 4670 screened hits identified 13 suitable studies, including a total of 42 effect sizes and 1857 participants. The random-effects model showed an overall significant, positive, yet diminutively small effect (d = 0.11, 95% CI: [0.002, 0.209], p = 0.045) between divergent thinking and bipolar disorder. A handful of moderators were examined, which revealed a significant moderating effect for bipolar status, as either euthymic (d = 0.14, p = 0.043), subclinical (d = 0.17, p = 0.001), manic (d = 0.25, p = 0.097), or depressed (d = -0.51, p < 0.001). However, moderator analyses should be treated with caution because of the observed confounding of moderators. Finally, none of the employed methods for publication-bias detection revealed any evidence for publication bias. We discuss further results, especially regarding the differences between subclinical and clinical samples.

The orbitofrontal cortex is necessary for learning to ignore

Animals learn not only what is potentially useful but also what is meaningless and should be disregarded. How this is accomplished is a key but seldom explored question in psychology and neuroscience. Learning to ignore irrelevant cues is evident in latent inhibition-the ubiquitous phenomenon where presenting a cue several times without consequences leads to retardation of subsequent conditioning to that cue.1,2 Does learning to ignore these cues, because they predict nothing, involve the same neural circuits that are critical to learning to make predictions about other "real world" impending events? If so, the orbitofrontal cortex (OFC), as a key node in such networks, should be important.3 Specifically, the OFC has been hypothesized to participate in the recognition of hidden task states, which are not directly signaled by explicit outcomes.4 Evaluating its involvement in pre-exposure learning during latent inhibition would be an acid test for this hypothesis. Here, we report that selective chemogenetic inactivation of rat orbitofrontal cortex principal neurons during stimulus pre-exposure markedly reduces latent inhibition in subsequent conditioning. Inactivation only during pre-exposure ensured that the observed effects were due to an impact on the acquisition of information prior to its use in any sort of behavior, i.e., during latent learning. Further behavioral tests confirmed this, showing that the impact of OFC inactivation during pre-exposure was limited to the latent inhibition effect. These results demonstrate that the OFC is important for latent learning and the formation of associations even in the absence of explicit outcomes.

Personality, creativity and latent inhibition

The current study set out to investigate the relationship between creativity, multi‐dimensional schizotypy and personality more generally. This was achieved by analysing scores on a range of personality scales and measures of creativity, where it was found that the creativity measures were more closely related to asocial‐schizotypy than positive‐schizotypy. The study also sought to test Eysenck's prediction (1993, 1995) that, given the putative relationship between creativity and psychosis‐proneness, high psychosis‐prone scoring individuals and high creativity scoring individuals would demonstrate the same cognitive style of ‘overinclusiveness’ on latent inhibition. However, the results failed to demonstrate any evidence of a shared ‘widening of the associative horizon’ between high creativity and high psychosis‐prone scorers. The findings are discussed in relation to multi‐dimensional schizotypy. Copyright © 2006 John Wiley & Sons, Ltd.

The link between schizophrenia and substance use disorder: A unifying hypothesis

Substance use disorders occur commonly in patients with schizophrenia and dramatically worsen their overall clinical course. While the exact mechanisms contributing to substance use in schizophrenia are not known, a number of theories have been put forward to explain the basis of the co-occurrence of these disorders. We propose here a unifying hypothesis that combines recent evidence from epidemiological and genetic association studies with brain imaging and pre-clinical studies to provide an updated formulation regarding the basis of substance use in patients with schizophrenia. We suggest that the genetic determinants of risk for schizophrenia (especially within neural systems that contribute to the risk for both psychosis and addiction) make patients vulnerable to substance use. Since this vulnerability may arise prior to the appearance of psychotic symptoms, an increased use of substances in adolescence may both enhance the risk for developing a later substance use disorder, and also serve as an additional risk factor for the appearance of psychotic symptoms. Future studies that assess brain circuitry in a prospective longitudinal manner during adolescence prior to the appearance of psychotic symptoms could shed further light on the mechanistic underpinnings of these co-occurring disorders while identifying potential points of intervention for these difficult-to-treat co-occurring disorders.

Unmasking latent inhibition in humans

Presentations of a to-be-conditioned stimulus (CS) on its own impairs subsequent learning when that CS is paired with an unconditioned stimulus (US). Evidence for this latent inhibition (LI) effect in humans is said to require a "masking task" that diverts attention from the CS during preexposure. We present three experiments that demonstrate LI in humans without masking. Subjects performed a computerised task, making speeded responses to an imperative cue (the US) presented within a continuous stream of stimuli. During preexposure, a to-be-CS was presented 20 times among other stimuli, but excluding the US. Instructions ensured subjects actively monitored all stimuli at this time. This was immediately followed by the training phase, which included the US, the preexposed CS, and a novel CS. Both CSs were reliably followed by the US, but these associations were incidental to the instructed task. Nonetheless, some subjects learned the CS-US associations, responding faster when the US followed a CS than when it was unsignalled. All three experiments also found evidence for LI, in that subjects learned the novel CS-US association sooner than the preexposed CS-US association. We conclude that humans can show LI even when actively attending to the CS during preexposure.

Cognitive function in schizophrenia: conflicting findings and future directions

INTRODUCTION

Schizophrenia is a severe mental disorder with multiple psychopathological domains being affected. Several lines of evidence indicate that cognitive impairment serves as the key component of schizophrenia psychopathology. Although there have been a multitude of cognitive studies in schizophrenia, there are many conflicting results. We reasoned that this could be due to individual differences among the patients (i.e. variation in the severity of positive vs. negative symptoms), different task designs, and/or the administration of different antipsychotics.

METHODS

We thus review existing data concentrating on these dimensions, specifically in relation to dopamine function. We focus on most commonly used cognitive domains: learning, working memory, and attention.

RESULTS

We found that the type of cognitive domain under investigation, medication state and type, and severity of positive and negative symptoms can explain the conflicting results in the literature.

CONCLUSIONS

This review points to future studies investigating individual differences among schizophrenia patients in order to reveal the exact relationship between cognitive function, clinical features, and antipsychotic treatment.

Tcf4 transgenic female mice display delayed adaptation in an auditory latent inhibition paradigm

Schizophrenia (SZ) is a severe mental disorder affecting about 1 % of the human population. Patients show severe deficits in cognitive processing often characterized by an improper filtering of environmental stimuli. Independent genome-wide association studies confirmed a number of risk variants for SZ including several associated with the gene encoding the transcription factor 4 (TCF4). TCF4 is widely expressed in the central nervous system of mice and humans and seems to be important for brain development. Transgenic mice overexpressing murine Tcf4 (Tcf4tg) in the adult brain display cognitive impairments and sensorimotor gating disturbances. To address the question of whether increased Tcf4 gene dosage may affect cognitive flexibility in an auditory associative task, we tested latent inhibition (LI) in female Tcf4tg mice. LI is a widely accepted translational endophenotype of SZ and results from a maladaptive delay in switching a response to a previously unconditioned stimulus when this becomes conditioned. Using an Audiobox, we pre-exposed Tcf4tg mice and their wild-type littermates to either a 3- or a 12-kHz tone before conditioning them to a 12-kHz tone. Tcf4tg animals pre-exposed to a 12-kHz tone showed significantly delayed conditioning when the previously unconditioned tone became associated with an air puff. These results support findings that associate TCF4 dysfunction with cognitive inflexibility and improper filtering of sensory stimuli observed in SZ patients.

Latent learning in End Stage Renal Disease (ESRD)

Cognitive functions such as attention and memory are known to be impaired in End Stage Renal Disease (ESRD), but the sites of the neural changes underlying these impairments are uncertain. Patients and controls took part in a latent learning task, which had previously shown a dissociation between patients with Parkinson's disease and those with medial temporal damage. ESRD patients (n=24) and age and education-matched controls (n=24) were randomly assigned to either an exposed or unexposed condition. In Phase 1 of the task, participants learned that a cue (word) on the back of a schematic head predicted that the subsequently seen face would be smiling. For the exposed (but not unexposed) condition, an additional (irrelevant) colour cue was shown during presentation. In Phase 2, a different association, between colour and facial expression, was learned. Instructions were the same for each phase: participants had to predict whether the subsequently viewed face was going to be happy or sad. No difference in error rate between the groups was found in Phase 1, suggesting that patients and controls learned at a similar rate. However, in Phase 2, a significant interaction was found between group and condition, with exposed controls performing significantly worse than unexposed (therefore demonstrating learned irrelevance). In contrast, exposed patients made a similar number of errors to unexposed in Phase 2. The pattern of results in ESRD was different from that previously found in Parkinson's disease, suggesting a different neural origin.

Cognitive judgment bias in the psychostimulant-induced model of mania in rats

RATIONALE

Animal models of mania lack genuine cognitive parameters. The present gold standard of mania models, amphetamine-induced hyperlocomotion, is rather unspecific and does not necessarily target its cardinal symptoms. Therefore, alternative behavioral markers that are sensitive to stimulants are required.

OBJECTIVES

In the present study, by combining the psychostimulant-induced model of mania in rodents with the recently developed ambiguous-cue interpretation (ACI) tests, we investigated the effects of chronic administration of D-amphetamine and cocaine on the cognitive judgment bias of rats.

METHODS

To accomplish this goal, in two separate experiments, previously trained animals received chronic, daily injections of either D-amphetamine (2 mg/kg) or cocaine (10 mg/kg) for 2 weeks and were subsequently tested with the ACI procedure.

RESULTS

Chronic treatment with both psychostimulants did not make rats more "optimistic."

CONCLUSIONS

The results are discussed in terms of behavioral and pharmacological actions of the tested compounds and their implications for modeling mania in animals.

Latent inhibition in ADHD adults on and off medication: a preliminary study

OBJECTIVE

To determine the effects of stimulant medication on performance of ADHD adults on a selective attention task that assesses the processing of irrelevant stimuli.

METHOD

ADHD patients and matched controls were given two sessions of a two-stage visual search-latent inhibition (LI) task. In stage-1, they detected the location of a unique shape presented with homogeneous distractors. In stage- 2, target detection response time was examined as a function of the stage-1 experience with the target or distractor, or both, providing a within-subject measure of LI. In Session-1, the ADHD subjects were off their customary stimulant medication. In Session-2, they were on medication.

RESULTS

Off-medicated ADHD subjects exhibited similar LI to that of controls; medicated ADHD subjects exhibited less LI than controls. Group differences in LI were mediated by RTs to the previously task-irrelevant distractor stimulus.

CONCLUSION

The attenuated LI of the on-medication ADHD group is attributable to drug action that reduces attentional resources allocated to distractors.

Consequences at adulthood of transient inactivation of the parahippocampal and prefrontal regions during early development: new insights from a disconnection animal model for schizophrenia

The psychic disintegration characteristic of schizophrenia is thought to result from a defective connectivity, of neurodevelopmental origin, between several integrative brain regions. The parahippocampal region and the prefrontal cortex are described as the main regions affected in schizophrenia. Interestingly, latent inhibition (LI) has been found to be reduced in patients with schizophrenia, and the existence of a dopaminergic dysfunction is also generally well accepted in this disorder. In the present review, we have integrated behavioral and neurochemical data obtained in a LI protocol involving adult rats subjected to neonatal functional inactivation of the entorhinal cortex, the ventral subiculum or the prefrontal cortex. The data discussed suggest a subtle and transient functional blockade during early development of the aforementioned brain regions is sufficient to induce schizophrenia-related behavioral and dopaminergic abnormalities in adulthood. In summary, these results support the view that our conceptual and methodological approach, based on functional disconnections, is valid for modeling some aspects of the pathophysiology of schizophrenia from a neurodevelopmental perspective.

Negative priming in amphetamine psychosis

Amphetamine abuse may lead to a psychotic state, its symptomatology being very similar to what is seen in paranoid schizophrenia. Failure of attentional inhibition of irrelevant information is thought to be associated with the psychotic symptoms in schizophrenia. Negative priming (NP) paradigm is believed to measure this impairment. Several studies have shown impaired NP in schizophrenia. In the present study a spatial NP task was used to assess attentional inhibition in a group of amphetamine-induced psychosis patients. Nineteen patients with amphetamine-induced psychotic disorder and 20 healthy subjects participated in this study. Severity of psychotic symptoms was measured prior to testing using the Brief Psychiatric Rating Scale (BPRS). Patients showed no deficit in NP, and the amount of their NP effect was not significantly different from healthy subjects. Besides, we did not find any correlation between the amount of NP effect and severity of symptoms. Our results may indicate that cognitive mechanisms underlying NP might not be affected in amphetamine psychosis.

Memory reconsolidation in aversive and appetitive settings

Memory reconsolidation has been observed across species and in a number of behavioral paradigms. The majority of memory reconsolidation studies have been carried out in Pavlovian fear conditioning and other aversive memory settings, with potential implications for the treatment of post-traumatic stress disorder. However, there is a growing literature on memory reconsolidation in appetitive reward-related memory paradigms, including translational models of drug addiction. While there appears to be substantial similarity in the basic phenomenon and underlying mechanisms of memory reconsolidation across unconditioned stimulus valence, there are also notable discrepancies. These arise both when comparing aversive to appetitive paradigms and also across different paradigms within the same valence of memory. We review the demonstration of memory reconsolidation across different aversive and appetitive memory paradigms, the commonalities and differences in underlying mechanisms and the conditions under which each memory undergoes reconsolidation. We focus particularly on whether principles derived from the aversive literature are applicable to appetitive settings, and also whether the expanding literature in appetitive paradigms is informative for fear memory reconsolidation.

A conceptual and practical guide to the behavioural evaluation of animal models of the symptomatology and therapy of schizophrenia

Schizophrenia is a chronic debilitating brain disorder characterized by a complex set of perceptual and behavioural symptoms that severely disrupt and undermine the patient's psychological well-being and quality of life. Since the exact disease mechanisms remain essentially unknown, holistic animal models are indispensable tools for any serious investigation into the neurobiology of schizophrenia, including the search for remedies, prevention of the disease and possible biological markers. This review provides some practical advice to those confronted with the task of evaluating their animal models for relevance to schizophrenia, a task that inevitably involves behavioural tests with animals. To a novice, this challenge not only is a technical one but also entails attention to interpretative issues concerning validity and translational power. Here, we attempt to offer some guidance to help overcome these obstacles by drawing on our experience of diverse animal models of schizophrenia based on genetics, strain difference, brain lesions, pharmacological induction and early life developmental manipulations. The review pays equal emphasis to the general (theoretical) considerations of experimental design and the illustration of the problems related to critical test parameters and the data analysis of selected exemplar behavioural tests. Finally, the individual differences of behavioural expression in relevant tests observed in wild-type animals might offer an alternative approach in order to explore the mechanism of schizophrenia-related behavioural dysfunction at the molecular, cellular and structural levels, all of which are of more immediate relevance to cell and tissue research.

Paradoxical effects of low dose MDMA on latent inhibition in the rat

The cognitive effects of MDMA (‘Ecstasy’) are controversial, particularly in the case of acute administration of low doses. Latent inhibition (LI) refers to the reduction in conditioning to a stimulus that has received non-reinforced pre-exposure, an effect typically abolished by amphetamines and enhanced by antipsychotics. LI enhancement has also been shown using the 5-HT reuptake blocker sertraline. In the present study, the effects of MDMA (6 mg/kg, known to increase 5-HT release) were tested using 10 and 40 pre-exposures to produce weak and strong LI in controls, respectively. MDMA (injected twice, prior to pre-exposure and conditioning) significantly enhanced LI in that the effect was clearly demonstrated after only 10 pre-exposures, when it was absent in the saline controls. On its own such a profile of action would be consistent with a procognitive effect of MDMA mediated by increased availability of 5-HT. However, paradoxically the same MDMA treatment reduced LI in the 40 pre-exposures condition. This component of action is likely attributable to MDMA's actions on catecholaminergic systems and is consistent with other evidence of its adverse effects. Moreover, there were small but significant reductions in 5-HT in medial prefrontal cortex (mPFC) and amygdala assayed 7 days post MDMA administration (2 × 6 mg/kg, 24 h apart).

Effect of dopamine and serotonin receptor antagonists on fencamfamine-induced abolition of latent inhibition

The purpose of this investigation was to verify the role of dopamine and serotonin receptors in the effect of fencamfamine (FCF) on latent inhibition. FCF is a psychomotor stimulant with an indirect dopaminergic action. Latent inhibition is a model of attention. Latent inhibition is blocked by dopaminergic agents and facilitated by dopamine receptor agonists. FCF has been shown to abolish latent inhibition. The serotonergic system may also participate in the neurochemical mediation of latent inhibition. The selective dopamine D(1) receptor antagonist SCH 23390 (7-chloro-3-methyl-1-phenyl-1,2,4,5-tetrahydro-3-benzazepin-8-ol), D(2) receptor antagonists pimozide (PIM) and methoclopramide (METH), and serotonin 5-HT(2A/C) receptor antagonist ritanserin (RIT) were used in the present study. Latent inhibition was evaluated using a conditioned emotional response procedure. Male Wistar rats that were water-restricted were subjected to a three-phase procedure: preexposure to a tone, tone-shock conditioning, and a test of the effect of the tone on licking frequency. All of the drugs were administered before the preexposure and conditioning phases. The results showed that FCF abolished latent inhibition, and this effect was clearly antagonized by PIM and METH and moderately attenuated by SCH 23390. At the doses used in the present study, RIT pretreatment did not affect latent inhibition and did not eliminate the effect of FCF, suggesting that the FCF-induced abolition of latent inhibition is not mediated by serotonin 5-HT(2A/C) receptors. These results suggest that the effect of FCF on latent inhibition is predominantly related to dopamine D(2) receptors and that dopamine D(2) receptors participate in attention processes.

The positive symptoms of acute schizophrenia and latent inhibition in humans and animals: underpinned by the same process(es)?

INTRODUCTION

It has been suggested that the positive symptoms of acute schizophrenia are a consequence of a disruption of the process that produces latent inhibition (slower acquisition of conditioned responding after preexposure to the conditioned stimulus) and that this effect can be modelled by pro- and antipsychotic compounds in healthy participants and in nonhuman animals. This idea assumes that latent inhibition in humans and animals is underpinned by the same process(es).

METHOD

First, we question the equivalence of human and animal latent inhibition. Second, we review the studies that have examined latent inhibition in populations with schizophrenia and in healthy populations after administration of amphetamine or haloperidol.

RESULTS

Theoretical analysis of the similarities and differences in latent inhibition effects, and the procedures used to generate them, in humans and animals renders the suggested equivalence between them unconvincing. The studies examining latent inhibition in populations with schizophrenia and in healthy populations after administration of amphetamine or haloperidol are marked by a number of methodological shortcomings and reveal discrepant results.

CONCLUSIONS

The theoretical and empirical analyses provide little support for a common process underlying deficits of latent inhibition in patients exhibiting positive symptoms of acute schizophrenia, and such deficits in experimental models in healthy humans and infrahumans.

A preclinical assessment of d.l-govadine as a potential antipsychotic and cognitive enhancer

Tetrahydroprotoberberines (THPBs) are compounds derived from traditional Chinese medicine and increasing preclinical evidence suggests efficacy in treatment of a wide range of symptoms observed in schizophrenia. A receptor-binding profile of the THPB, d.l-govadine (d.l-Gov), reveals high affinity for dopamine and noradrenaline receptors, efficacy as a D2 receptor antagonist, brain penetrance in the 10-300 ng/g range, and thus motivated an assessment of the antipsychotic and pro-cognitive properties of this compound in the rat. Increased dopamine efflux in the prefrontal cortex and nucleus accumbens, measured by microdialysis, is observed following subcutaneous injection of the drug. d.l-Gov inhibits both conditioned avoidance responding (CAR) and amphetamine-induced locomotion (AIL) at lower doses than clozapine (CAR ED50: d.l-Gov 0.72 vs. clozapine 7.70 mg/kg; AIL ED50: d.l-Gov 1.70 vs. clozapine 4.27 mg/kg). Catalepsy is not detectable at low biologically relevant doses, but is observed at higher doses. Consistent with previous reports, acute d-amphetamine disrupts latent inhibition (LI) while a novel finding of enhanced LI is observed in sensitized animals. Treatment with d.l-Gov prior to conditioned stimulus (CS) pre-exposure restores LI to levels observed in controls in both sensitized animals and those treated acutely with d-amphetamine. Finally, possible pro-cognitive properties of d.l-Gov are assessed with the spatial delayed win-shift task. Subcutaneous injection of 1.0 mg/kg d.l-Gov failed to affect errors at a 30-min delay, but decreased errors observed at a 12-h delay. Collectively, these data provide the first evidence that d.l-Gov may have antipsychotic properties in conjunction with pro-cognitive effects, lending further support to the hypothesis that THPBs are a class of compounds which merit serious consideration as novel treatments for schizophrenia.

Opposing effects of 5,7-DHT lesions to the core and shell of the nucleus accumbens on the processing of irrelevant stimuli

There is good evidence that forebrain serotonergic systems modulate cognitive flexibility. Latent inhibition (LI) is a cross-species phenomenon which manifests as poor conditioning to a stimulus that has previously been experienced without consequence and is widely considered an index of the ability to ignore irrelevant stimuli. While much research has focused on dopaminergic mechanisms underlying LI, there is also considerable evidence of serotonergic modulation. However, the neuroanatomical locus of these effects remains poorly understood. Previous work has identified the nucleus accumbens (NAc) as a key component of the neural circuit underpinning LI and furthermore, this work has shown that the core and shell subregions of the NAc contribute differentially to the expression of LI. To examine the role of the serotonergic input to NAc in LI, we tested animals with 5,7-dihydroxytryptamine (5,7-DHT) lesions to the core and shell subregions on LI assessed under experimental conditions that produce LI in shams and subsequently with weak stimulus pre-exposure designed to prevent the emergence of LI in shams. We found that serotonergic deafferentation of the core disrupted LI whereas 5,7-DHT lesions to the shell produced the opposite effect and potentiated LI.

Disambiguating ventral striatum fMRI-related BOLD signal during reward prediction in schizophrenia

Reward detection, surprise detection and prediction-error signaling have all been proposed as roles for the ventral striatum (vStr). Previous neuroimaging studies of striatal function in schizophrenia have found attenuated neural responses to reward-related prediction errors; however, as prediction errors represent a discrepancy in mesolimbic neural activity between expected and actual events, it is critical to examine responses to both expected and unexpected rewards (URs) in conjunction with expected and UR omissions in order to clarify the nature of ventral striatal dysfunction in schizophrenia. In the present study, healthy adults and people with schizophrenia were tested with a reward-related prediction-error task during functional magnetic resonance imaging to determine whether schizophrenia is associated with altered neural responses in the vStr to rewards, surprise prediction errors or all three factors. In healthy adults, we found neural responses in the vStr were correlated more specifically with prediction errors than to surprising events or reward stimuli alone. People with schizophrenia did not display the normal differential activation between expected and URs, which was partially due to exaggerated ventral striatal responses to expected rewards (right vStr) but also included blunted responses to unexpected outcomes (left vStr). This finding shows that neural responses, which typically are elicited by surprise, can also occur to well-predicted events in schizophrenia and identifies aberrant activity in the vStr as a key node of dysfunction in the neural circuitry used to differentiate expected and unexpected feedback in schizophrenia.

High-frequency gamblers show increased resistance to extinction following partial reinforcement

Behaviours that have been rewarded intermittently persist for longer during periods of non-reward than behaviours that have been rewarded continuously. This classic phenomenon is known as the partial reinforcement extinction effect. For decades it has been generally understood that this phenomenon is fundamental to the persistence of gambling in the absence of winning. One obvious, yet untested hypothesis arising from this is that persistent (here, high-frequency) gamblers might be more sensitive to partial reinforcement contingencies. Therefore, our aim was to test the hypothesis that compared to low-frequency gamblers, high-frequency gamblers would show greater resistance to extinction following partial reinforcement in a computer based experiment. Participants were 19 high-frequency gamblers and 21 low-frequency gamblers, all healthy non-smokers aged between 18 and 52. Following partial or continuous reinforcement, persistence of responding in extinction was measured as the number of times a target response was made. After partial reinforcement, high-frequency gamblers made the target response a greater number of times in extinction (compared to low-frequency gamblers). Moreover, the partial reinforcement extinction effect was larger in high-frequency gamblers than in low-frequency gamblers. It remains to be seen whether increased sensitivity to partial reinforcement is a cause or effect of persistent gambling. Nevertheless, the present study represents an important first step in investigating the role of simple partial reinforcement contingencies in determining resistance to extinction in gamblers, the importance of which, whilst hitherto recognised, has never been demonstrated experimentally.

Dopamine in nucleus accumbens: salience modulation in latent inhibition and overshadowing

Latent inhibition (LI) is demonstrated when non-reinforced pre-exposure to a to-be-conditioned stimulus retards later learning. Learning is similarly retarded in overshadowing, in this case using the relative intensity of competing cues to manipulate associability. Electrolytic/excitotoxic lesions to shell accumbens (NAc) and systemic amphetamine both reliably abolish LI. Here a conditioned emotional response procedure was used to demonstrate LI and overshadowing and to examine the role of dopamine (DA) within NAc. Experiment 1 showed that LI but not overshadowing was abolished by systemic amphetamine (1.0 mg/kg i.p.). In Experiment 2, 6-hydroxydopamine (6-OHDA) was used to lesion DA terminals within NAc: both shell- and core- (plus shell-)lesioned rats showed normal LI and overshadowing. Experiment 3 compared the effects of amphetamine microinjected at shell and core coordinates prior to conditioning: LI, but not overshadowing, was abolished by 10.0 but not 5.0 µg/side amphetamine injected in core but not shell NAc. These results suggest that the abolition of LI produced by NAc shell lesions is not readily reproduced by regionally restricted DA depletion within NAc; core rather than shell NAc mediates amphetamine-induced abolition of LI; overshadowing is modulated by different neural substrates.

The M₁/M₄ preferring agonist xanomeline reverses amphetamine-, MK801- and scopolamine-induced abnormalities of latent inhibition: putative efficacy against positive, negative and cognitive symptoms in schizophrenia

A major challenge in developing schizophrenia pharmacotherapy is treating the different symptoms of this disorder, typically divided into positive, negative and cognitive symptoms. M₁/M₄ muscarinic acetylcholine receptor (mAChR) agonists have emerged as a promising therapeutic target, particularly for positive and cognitive symptoms. Here, we examined the activity of the M₁/M₄ mAChR-preferring agonist xanomeline in four pharmacological latent inhibition (LI) models. LI is the poorer conditioning to a stimulus previously experienced as irrelevant during repeated non-reinforced pre-exposure to that stimulus. No-drug controls displayed LI if non-reinforced pre-exposure to a tone was followed by weak, but not strong, conditioning (2 vs. 5 tone-shock pairings). Amphetamine (1 mg/kg)- or scopolamine (0.15 mg/kg)-treated rats failed to show LI with weak conditioning, whereas MK801 (0.05 mg/kg)- or scopolamine (1.5 mg/kg)-treated rats persisted in displaying LI with strong conditioning. Xanomeline (5 mg/kg, 15 mg/kg) reversed amphetamine- and scopolamine-induced LI disruption, effects considered predictive of activity against positive symptoms of schizophrenia. In addition, xanomeline alleviated MK801-induced abnormally persistent LI. Activity of xanomeline on NMDA antagonist-induced behaviour was demonstrated here for the first time and suggests that the drug is effective against negative/cognitive symptoms. Finally, xanomeline alleviated abnormally persistent LI induced by scopolamine, which was suggested to model antipsychotic drug-resistant cognitive impairments, providing further evidence for the cognition-enhancing capacity of xanomeline. Although the use of xanomeline in schizophrenia was discontinued due to cholinergic-related side-effects, our findings suggest that M₁/M₄ mAChR agonism should be an important target in drug development in schizophrenia, potentially beneficial for treatment of positive, negative and cognitive symptoms.

Learned irrelevance and associative learning is attenuated in individuals at risk for psychosis but not in asymptomatic first-degree relatives of schizophrenia patients: translational state markers of psychosis?

Learned irrelevance (LIrr) refers to a form of selective learning that develops as a result of prior noncorrelated exposures of the predicted and predictor stimuli. In learning situations that depend on the associative link between the predicted and predictor stimuli, LIrr is expressed as a retardation of learning. It represents a form of modulation of learning by selective attention. Given the relevance of selective attention impairment to both positive and cognitive schizophrenia symptoms, the question remains whether LIrr impairment represents a state (relating to symptom manifestation) or trait (relating to schizophrenia endophenotypes) marker of human psychosis. We examined this by evaluating the expression of LIrr in an associative learning paradigm in (1) asymptomatic first-degree relatives of schizophrenia patients (SZ-relatives) and in (2) individuals exhibiting prodromal signs of psychosis ("ultrahigh risk" [UHR] patients) in each case relative to demographically matched healthy control subjects. There was no evidence for aberrant LIrr in SZ-relatives, but LIrr as well as associative learning were attenuated in UHR patients. It is concluded that LIrr deficiency in conjunction with a learning impairment might be a useful state marker predictive of psychotic state but a relatively weak link to a potential schizophrenia endophenotype.

Creativity and psychopathology: a shared vulnerability model

Creativity is considered a positive personal trait. However, highly creative people have demonstrated elevated risk for certain forms of psychopathology, including mood disorders, schizophrenia spectrum disorders, and alcoholism. A model of shared vulnerability explains the relation between creativity and psychopathology. This model, supported by recent findings from neuroscience and molecular genetics, suggests that the biological determinants conferring risk for psychopathology interact with protective cognitive factors to enhance creative ideation. Elements of shared vulnerability include cognitive disinhibition (which allows more stimuli into conscious awareness), an attentional style driven by novelty salience, and neural hyperconnectivity that may increase associations among disparate stimuli. These vulnerabilities interact with superior meta-cognitive protective factors, such as high IQ, increased working memory capacity, and enhanced cognitive flexibility, to enlarge the range and depth of stimuli available in conscious awareness to be manipulated and combined to form novel and original ideas.

Transient exposure of neonatal mice to neuregulin-1 results in hyperdopaminergic states in adulthood: implication in neurodevelopmental hypothesis for schizophrenia

Neuregulin-1 (NRG1) is implicated in the etiology or pathology of schizophrenia, although its biological roles in this illness are not fully understood. Human midbrain dopaminergic neurons highly express NRG1 receptors (ErbB4). To test its neuropathological role in the neurodevelopmental hypothesis of schizophrenia, we administered type-1 NRG1 protein to neonatal mice and evaluated the immediate and subsequent effects on dopaminergic neurons and their associated behaviors. Peripheral NRG1 administration activated midbrain ErbB4 and elevated the expression, phosphorylation and enzyme activity of tyrosine hydroxylase (TH), which ultimately increased dopamine levels. The hyperdopaminergic state was sustained in the medial prefrontal cortex after puberty. There were marked increases in dopaminergic terminals and TH levels. In agreement, higher amounts of dopamine were released from this brain region of NRG1-treated mice following high potassium stimulation. Furthermore, NRG1-treated mice exhibited behavioral impairments in prepulse inhibition, latent inhibition, social behaviors and hypersensitivity to methamphetamine. However, there were no gross abnormalities in brain structures or other phenotypic features of neurons and glial cells. Collectively, our findings provide novel insights into neurotrophic contribution of NRG1 to dopaminergic maldevelopment and schizophrenia pathogenesis.

Reduced dopamine function within the medial shell of the nucleus accumbens enhances latent inhibition

Latent inhibition (LI) manifests as poorer conditioning to a CS that has previously been presented without consequence. There is some evidence that LI can be potentiated by reduced mesoaccumbal dopamine (DA) function but the locus within the nucleus accumbens of this effect is as yet not firmly established. Experiment 1 tested whether 6-hydroxydopamine (6-OHDA)-induced lesions of DA terminals within the core and medial shell subregions of the nucleus accumbens (NAc) would enhance LI under conditions that normally disrupt LI in controls (weak pre-exposure). LI was measured in a thirst motivated conditioned emotional response procedure with 10 pre-exposures (to a noise CS) and 2 conditioning trials. The vehicle-injected and core-lesioned animals did not show LI and conditioned to the pre-exposed CS at comparable levels to the non-pre-exposed controls. 6-OHDA lesions to the medial shell, however, produced potentiation of LI, demonstrated across two extinction tests. In a subsequent experiment, haloperidol microinjected into the medial shell prior to conditioning similarly enhanced LI. These results underscore the dissociable roles of core and shell subregions of the NAc in mediating the expression of LI and indicate that reduced DA function within the medial shell leads to enhanced LI.

Caffeine/nutrition interaction in the rat brain: Influence on latent inhibition and cortical spreading depression

Caffeine, like malnutrition, can produce behavioral and electrophysiological alterations. However, the interaction of both factors remains unclear. Here this interaction has been studied in male Wistar rats previously malnourished during the lactation period by feeding their dams the "regional basic diet" of Northeast Brazil, containing about 8% protein, predominantly from vegetable sources (RBD(8)). At 70-75days of life, a subset of the pups was treated intraperitoneally with 30mg/kg caffeine for 4days while being tested according to the behavioral model of latent inhibition. Another group was subjected to an electrophysiological recording of the phenomenon known as cortical spreading depression, and the effects of caffeine injected during the recording session were evaluated. Caffeine did not affect cortical spreading depression, but antagonized latent inhibition in both the RBD(8)-malnourished rats and in the well-nourished control group fed a chow diet with 22% protein. This effect of caffeine was not seen in malnourished rats fed a protein-supplemented RBD (protein increased to 22% by increasing the proportion of foodstuffs from vegetable origin; RBD(22) group), suggesting that the amino acid imbalance of this diet may modulate the caffeine effects on latent inhibition. The results indicate a differential effect of caffeine in the latent inhibition behavioral model, as compared to the cortical spreading depression phenomenon, and this effect is influenced by the early nutritional status of the animal. We suggest that caffeine may modulate dopaminergic subcortical receptors participating in attention processes, but does not interact at the cortical level, in a way that would affect cortical spreading depression.

Sex-dependent antipsychotic capacity of 17β-estradiol in the latent inhibition model: a typical antipsychotic drug in both sexes, atypical antipsychotic drug in males

The estrogen hypothesis of schizophrenia suggests that estrogen is a natural neuroprotector in women and that exogenous estrogen may have antipsychotic potential, but results of clinical studies have been inconsistent. We have recently shown using the latent inhibition (LI) model of schizophrenia that 17β-estradiol exerts antipsychotic activity in ovariectomized (OVX) rats. The present study sought to extend the characterization of the antipsychotic action of 17β-estradiol (10, 50 and 150 μg/kg) by testing its capacity to reverse amphetamine- and MK-801-induced LI aberrations in gonadally intact female and male rats. No-drug controls of both sexes showed LI, ie, reduced efficacy of a previously non-reinforced stimulus to gain behavioral control when paired with reinforcement, if conditioned with two but not five tone-shock pairings. In both sexes, amphetamine (1 mg/kg) and MK-801 (50 μg/kg) produced disruption (under weak conditioning) and persistence (under strong conditioning) of LI, modeling positive and negative/cognitive symptoms, respectively. 17β-estradiol at 50 and 150 μg/kg potentiated LI under strong conditioning and reversed amphetamine-induced LI disruption in both males and females, mimicking the action of typical and atypical antipsychotic drugs (APDs) in the LI model. 17β-estradiol also reversed MK-induced persistent LI, an effect mimicking atypical APDs and NMDA receptor enhancers, but this effect was observed in males and OVX females but not in intact females. These findings indicate that in the LI model, 17β-estradiol exerts a clear-cut antipsychotic activity in both sexes and, remarkably, is more efficacious in males and OVX females where it also exerts activity considered predictive of anti-negative/cognitive symptoms.

Catecholaminergic depletion within the prelimbic medial prefrontal cortex enhances latent inhibition

Latent inhibition (LI) refers to the reduction in conditioning to a stimulus that has received repeated non-reinforced pre-exposure. Investigations into the neural substrates of LI have focused on the nucleus accumbens (NAc) and its inputs from the hippocampal formation and adjacent cortical areas. Previous work has suggested that lesions to the medial prefrontal cortex (mPFC), another major source of input to the NAc, do not disrupt LI. However, a failure to observe disrupted LI does not preclude the possibility that a particular brain region is involved in the expression of LI. Moreover, the mPFC is a heterogeneous structure and there has been no investigation of a possible role of different regions within the mPFC in regulating LI under conditions that prevent LI in controls. Here, we tested whether 6-hydroxydopamine (6-OHDA)-induced lesions of dopamine (DA) terminals within the prelimbic (PL) and infralimbic (IL) mPFC would lead to the emergence of LI under conditions that do produce LI in controls (weak pre-exposure). LI was measured in a thirst motivated conditioned emotional response procedure with 10 pre-exposures to a noise conditioned stimulus (CS) and two conditioning trials. Sham-operated and IL-lesioned animals did not show LI and conditioned to the pre-exposed CS at comparable levels to the non-pre-exposed controls. 6-OHDA lesions to the PL, however, produced potentiation of LI. These results provide the first demonstration that the PL mPFC is a component of the neural circuitry underpinning LI.

Contrasting effects of increased and decreased dopamine transmission on latent inhibition in ovariectomized rats and their modulation by 17beta-estradiol: an animal model of menopausal psychosis?

Women with schizophrenia have later onset and better response to antipsychotic drugs (APDs) than men during reproductive years, but the menopausal period is associated with increased symptom severity and reduced treatment response. Estrogen replacement therapy has been suggested as beneficial but clinical data are inconsistent. Latent inhibition (LI), the capacity to ignore irrelevant stimuli, is a measure of selective attention that is disrupted in acute schizophrenia patients and in rats and humans treated with the psychosis-inducing drug amphetamine and can be reversed by typical and atypical APDs. Here we used amphetamine (1 mg/kg)-induced disrupted LI in ovariectomized rats to model low levels of estrogen along with hyperfunction of the dopaminergic system that may be occurring in menopausal psychosis, and tested the efficacy of APDs and estrogen in reversing disrupted LI. 17beta-Estradiol (50, 150 microg/kg), clozapine (atypical APD; 5, 10 mg/kg), and haloperidol (typical APD; 0.1, 0.3 mg/kg) effectively reversed amphetamine-induced LI disruption in sham rats, but were much less effective in ovariectomized rats; 17beta-estradiol and clozapine were effective only at high doses (150 microg/kg and 10 mg/kg, respectively), whereas haloperidol failed at both doses. Haloperidol and clozapine regained efficacy if coadministered with 17beta-estradiol (50 microg/kg, an ineffective dose). Reduced sensitivity to dopamine (DA) blockade coupled with spared/potentiated sensitivity to DA stimulation after ovariectomy may provide a novel model recapitulating the combination of increased vulnerability to psychosis with reduced response to APD treatment in female patients during menopause. In addition, our data show that 17beta-estradiol exerts antipsychotic activity.

Mouse behavioral endophenotypes for schizophrenia

An endophenotype is a heritable trait that is generally considered to be more highly, associated with a gene-based neurological deficit than a disease phenotype itself. Such, endophenotypic deficits may therefore be observed in the non-affected relatives of disease patients. Once endophenotypes have been established for a given illness, such as schizophrenia, mechanisms of, action may then be established and treatment options developed in order to target such measures. The, current paper describes and assesses the merits and limitations of utilizing behavioral and, electrophysiological endophenotypes of schizophrenia in mice. Such endophenotypic deficits include: decreased auditory event related potential (ERP) amplitude and gating (specifically, that of the P20, N40, P80 and P120); impaired mismatch negativity (MMN); changes in theta and gamma frequency, analyses; decreased pre-pulse inhibition (PPI); impaired working and episodic memories (for instance, novel object recognition [NOR], contextual and cued fear conditioning, latent inhibition, Morris and, radial arm maze identification and nose poke); sociability; and locomotor activity. A variety of, pharmacological treatments, including ketamine, MK-801 and phencyclidine (PCP) can be used to, induce some of the deficits described above, and numerous transgenic mouse strains have been, developed to address the mechanisms responsible for such endophenotypic differences. We also, address the viability and validity of using such measures regarding their potential clinical implications, and suggest several practices that could increase the translatability of preclinical data.

Can the role of genetic factors in schizophrenia be enlightened by studies of candidate gene mutant mice behaviour?

Schizophrenia is one of the most severe psychiatric disorders. Despite the knowledge accumulated over years, aetiology and pathophysiology remain uncertain. Research on families and twins suggests that genetic factors are largely responsible for the disease and implies specific genes as risk factors. Genetic epidemiology indicates a complex transmission mode, compatible with a multi-locus model, with single genes accounting for specific traits rather than for the entire phenotype. To better understand every single gene contribution to schizophrenia, the use of intermediate endophenotypes has been proposed. A straight communication between preclinical and clinical researchers could facilitate research on the association between genes and endophenotypes. Many behavioural tasks are available for humans and animals to measure endophenotypes. Here, firstly, we reviewed the most promising mouse behavioural tests modelling human behavioural tasks altered in schizophrenia. Secondly, we systematically reviewed animal models availability for a selection of candidate genes, derived from linkage and association studies. Thirdly, we systematically reviewed the studies which tested mutant mice in the above behavioural tasks. Results indicate a large mutant mice availability for schizophrenia candidate genes but they have been insufficiently tested in behavioural tasks. On the other hand, multivariate and translational approach should be implemented in several behavioural domains.

On giving a more active and selective role to consciousness

An active role for conscious processes in the production of behaviour is proposed, involving top level controls in a hierarchy of behavioural control. It is suggested that by inhibiting or sensitizing lower levels in the hierarchy conscious processes can play a role in the organization of ongoing behaviour. Conscious control can be more or less evident, according to prevailing circumstances.

The control of consciousness via a neuropsychological feedback loop

Gray's neuropsychological model of consciousness uses a hierarchical feedback loop framework that has been extensively discussed by many others in psychology. This commentary therefore urges Gray to integrate with, or at least acknowledge previous models. It also points out flaws in his feedback model and suggests directions for further theoretical work.

Don't leave the “un” off “consciousness”

Gray extrapolates from circuit models of psychopathology to propose neural substrates for the contents of consciousness. I raise three concerns: (1) knowledge of synaptic arrangements may be inadequate to fully support his model; (2) latent inhibition deficits in schizophrenia, a focus of this and related models, are complex and deserve replication; and (3) this conjecture omits discussion of the neuropsychological basis for the contents of the unconscious.

Consciousness is for other people

Gray has expanded his account of schizophrenia to explain consciousness as well. His theory explains neither phenomenon adequately because he treats individual minds (and brains) in isolation. The primary function of consciousness is to permit high level interactions with other conscious beings. The key symptoms of schizophrenia reflect a failure of this mechanism.

Comparators, functions, and experiences

The comparator model is insufficient for three reasons. First, consciousness is involved in the process of comparison as well as in the output. Second, we still do not have enough neurophysiological information to match the events of consciousness, although such knowledge is growing. Third, the anatomical localisation proposed can be damaged bilaterally but consciousness will persist.

Possible roles for a predictor plus comparator mechanism in human episodic recognition memory and imitative learning

This commentary is divided into two parts. The first considers a possible role for Gray's predictor plus comparator mechanism in human episodic recognition memory. It draws on the computational specifications of recognition outlined in Humphreys et al. (1994) to demonstrate how the logically necessary components of recognition tasks might be mapped onto the mechanism. The second part demonstrates how the mechanism outlined by Gray might be implicated in a form of imitative learning suitable for the acquisition of complex tasks.

Consciousness does not seem to be linked to a single neural mechanism

On the basis of neuropsychological evidence, it is clear that attention should be given a role in any model (or conjecture) of consciousness. What is known about the many instances of dissociation between explicit and implicit knowledge after brain damage suggests that conscious experience might not be linked to a restricted area of the brain. Even if it were true that there is a single brain area devoted to consciousness, the subicular area would seem to be an unlikely possibility.

Segmentalized consciousness in schizophrenia

Segmentalized consciousness in schizophrenia reflects a loss of the normal Gestalt organization and contextualization of perception. Grays model explains such segmentalization in terms of septohippocampal dysfunction, which is consistent with known neuropsychological impairment in schizophrenia. However, other considerations suggest that everyday perception and its failure in schizophrenia also involve prefrontal executive mechanisms, which are only minimally elaborated by Gray.

Unitary consciousness requires distributed comparators and global mappings

Gray, like other recent authors, seeks a scientific approach to consciousness, but fails to provide a biologically convincing description, partly because he implicitly bases his model on a computationalist foundation that embeds the contents of thought in irreducible symbolic representations. When patterns of neural activity instantiating conscious thought are shorn of homuncular observers, it appears most likely that these patterns and the circuitry that compares them with memories and plans should be found distributed over large regions of neocortex.

On seeking the mythical fountain of consciousness

Because consciousness has an organizational, or functional, center, Gray supposes that there must be a corresponding physical center in the brain. He proposes further that since this center generates consciousness, ablating it would eliminate consciousness, while leaving behavior intact. But the center of consciousness is simply the product of the functional linkages among sensory input, memory, inner speech, and so on, and behavior.

Prospects for a cognitive neuroscience of consciousness

In this commentary, I point out some weaknesses in Gray's target article and, in the light of that discussion, I attempt to delineate the kinds of problem a cognitive neuroscience of consciousness faces on its way to a scientific understanding of subjective experience.

Septohippocampal comparator: Consciousness generator or attention feedback loop?

As Gray insists, his comparator model proposes a brute correlation only – of consciousness with septohippocampal output. I suggest that the comparator straddles a feedback loop that boosts the activation ofnovelrepresentations, thus helping them feature in present or recollected experience. Such a role in organizing conscious contents would transcend correlation and help explain how consciousness emerges from brain function.