Deviation from expected cognitive ability is a core cognitive feature of schizophrenia related to neurophysiologic, clinical and psychosocial functioning

Cognitive functioning in schizophrenia is characterized by a generalized impairment in current cognitive ability based on traditional population-based norms. However, these norms assume a normal cognitive trajectory and do not directly account for illness-related declines from expected cognitive potential. Indeed, schizophrenia patients exhibit even greater deviation between their observed and expected cognitive functioning based on expanded norms that leverage premorbid variables resistant to illness-related features. The current study further quantified the extent to which illness-related features account for this deviation from expectation and assessed its relationship to neurophysiologic (mismatch negativity, P3a, theta oscillations), clinical, and psychosocial functioning in schizophrenia patients. Expected cognitive ability (PENN-CNB global cognition) in patients (n = 684) was calculated using healthy comparison subject (n = 660) weighted regression based on premorbid variables resistant to illness-related decline (demographics, single-word reading, parental education). The magnitude of any deviation between current (observed) and regression-predicted (expected) cognitive ability was calculated. Results indicated that 24% (n = 164) of the total patient population exhibited significant (≥-1.96 SD) deviation between observed and expected global cognitive ability. Interestingly, 20% of the total patient population (n = 136) had "normal" range cognitive performance when using traditional population-based norms, but also had significant deviation from expected cognitive ability. The magnitude of this deviation was associated with more severe neurophysiologic abnormalities, longer illness duration, higher levels of negative symptoms, and worse psychosocial functioning. Assessment of cognitive deviation is thus a complementary metric for characterizing the severity of illness-related cognitive declines in patients, while also reflecting the expression and severity of key endophenotypes of schizophrenia.

Decomposing the constituent oscillatory dynamics underlying mismatch negativity generation in schizophrenia: Distinct relationships to clinical and cognitive functioning

Abnormalities in early auditory information processing (EAIP) contribute to higher-order deficits in cognition and psychosocial functioning in schizophrenia. A passive auditory oddball paradigm is commonly used to evoke event-related potential (ERP) measures of EAIP reflecting auditory sensory registration and deviance detection, including mismatch negativity (MMN) and P3a responses. MMN and P3a have been extensively studied in healthy subjects and neuropsychiatric patient populations and are increasingly used as translational biomarkers in the development of novel therapeutics. Despite widespread use, relatively few studies have examined the constituent oscillatory elements and the extent to which sensory registration and deviance detection represent distinct or intercorrelated processes. This study aimed to determine the factor structure and clinical correlates of these oscillatory measures in schizophrenia patients (n = 706) and healthy comparison subjects (n = 615) who underwent clinical, cognitive, and functional characterization and EEG testing via their participation in the Consortium of Genomics in Schizophrenia (COGS-2) study. Results revealed significant deficits in theta-band (4-7 Hz) evoked power and phase locking in patients. Exploratory factor analyses of both ERP and oscillatory measures revealed two dissociable factors reflecting sensory registration and deviance detection. While each factor shared a significant correlation with social cognition, the deviance detection factor had a unique relationship to multiple cognitive and clinical domains. Results support the continued advancement of functionally relevant oscillatory measures underlying EAIP in the development of precognitive therapeutics.

Measuring P50 suppression and prepulse inhibition in a single recording session

OBJECTIVE

Two distinct measures have been used to assess inhibitory gating deficits in schizophrenia patients: P50 suppression and prepulse inhibition of the startle response. It remains unclear whether both measures can be assessed in a single testing session.

METHOD

Twelve normal subjects underwent testing in a carefully designed combined P50/prepulse inhibition session using stimulus characteristics similar to those described in the existing literature.

RESULTS

The levels of both P50 suppression and prepulse inhibition obtained in the combined session were highly similar to those obtained in independent testing of previous cohorts of normal subjects. As in previous experiments, P50 suppression and prepulse inhibition were not significantly correlated.

CONCLUSIONS

Measuring P50 suppression and prepulse inhibition in a single session is feasible and offers a unique opportunity to assess these two distinct gating measures contemporaneously in cohorts of normal comparison subjects and schizophrenia patients, so that temporal shifts in one or both measures are minimized.

Sensorimotor gating deficits in bipolar disorder patients with acute psychotic mania

BACKGROUND

Deficits in sensorimotor gating as assessed by prepulse inhibition (PPI) and habituation of the human startle response have been noted in schizophrenia and other patients with known dysfunction in the brain substrates that regulate PPI. During acute mania, bipolar disorder (BD) and schizophrenia patients present with symptoms that are similar. To determine if these clinical similarities extend to neurophysiologic domains, PPI and startle habituation were assessed in BD patients with acute psychotic mania and compared with a sample of acutely psychotic schizophrenia patients and a normal comparison group.

METHODS

Fifteen BD patients, 16 schizophrenia patients, and 17 control subjects were assessed on PPI and startle habituation.

RESULTS

The BD patients had significantly lower PPI than did the control subjects in two of the three PPI conditions (60- and 120-msec interstimulus intervals) as well as less startle habituation. The BD patients did not statistically differ from the schizophrenia patients in PPI or habituation.

CONCLUSIONS

These findings of sensorimotor gating deficits among bipolar disorder patients are consistent with other findings using different measures of information processing and suggest that the neurobiological substrates underlying sensorimotor gating may be dysregulated during acute manic and psychotic states.

Neural circuit regulation of prepulse inhibition of startle in the rat: current knowledge and future challenges

RATIONALE

Sensorimotor gating of the startle reflex can be assessed across species, using similar stimuli to elicit similar responses. Prepulse inhibition (PPI), a measure of sensorimotor gating, is reduced in patients with some neuropsychiatric disorders, and in rats after manipulations of limbic cortex, striatum, pallidum or pontine tegmentum ("CSPP" circuitry).

OBJECTIVE

To review the current knowledge of the neural circuit regulation of PPI in rats, and to anticipate the future challenges facing this line of inquiry.

METHODS

The published literature was reviewed and critically evaluated.

RESULTS

Limbic CSPP circuitry has been studied in rats to reveal the neurochemical and neuroanatomical substrates regulating PPI at a high level of resolution. In translational cross-species research, this detailed circuit information is used as a "blueprint" to identify substrates that may lead to PPI deficits in psychiatrically disordered humans. Some human disorders with identifiable, localized lesions in CSPP circuitry may provide direct validation for the contribution of CSPP circuitry to this cross-species model. The rapid collection of experimental data supporting this cross-species PPI circuit "blueprint" has supported continuing advances in the development of theoretical models for understanding how this circuitry normally functions to regulate PPI. Such models are needed for building a conceptual framework for understanding the role of this circuitry in the regulation of sensorimotor gating in normal humans, and in the relative loss of sensorimotor gating, and the resulting clinical consequences, in individuals with particular neuropsychiatric disorders.

CONCLUSIONS

Our understanding of the neural regulation of PPI has increased tremendously over the past 15 years. Progress has come in "broad strokes", and a number of important details and complex questions remain to be addressed. It is anticipated that this is a "work in progress", and that the precise models for the neural regulation of PPI will evolve substantially in the coming years.

Pharmacological studies of prepulse inhibition models of sensorimotor gating deficits in schizophrenia: a decade in review

RATIONALE

Patients with schizophrenia exhibit deficits in an operational measure of sensorimotor gating: prepulse inhibition (PPI) of startle. Similar deficits in PPI are produced in rats by pharmacological or developmental manipulations. These experimentally induced PPI deficits in rats are clearly not animal models of schizophrenia per se, but appear to provide models of sensorimotor gating deficits in schizophrenia patients that have face, predictive, and construct validity. In rodents, disruptions in PPI of startle are produced by: stimulation of D2 dopamine (DA) receptors, produced by amphetamine or apomorphine; activation of serotonergic systems, produced by serotonin (5-HT) releasers or direct agonists at multiple serotonin receptors; and blockade of N-methyl-D-aspartate (NMDA) receptors, produced by drugs such as phencyclidine (PCP). Accordingly, dopaminergic, serotonergic, and glutamatergic models of disrupted PPI have evolved and have been applied to the identification of potential antipsychotic treatments. In addition, some developmental manipulations, such as isolation rearing, have provided non-pharmacological animal models of the PPI deficits seen in schizophrenia.

OBJECTIVE

This review summarizes and evaluates studies assessing the effects of systemic drug administrations on PPI in rats.

METHODS

Studies examining systemic drug effects on PPI in rats prior to January 15, 2001 were compiled and organized into six annotated appendices. Based on this catalog of studies, the specific advantages and disadvantages of each of the four main PPI models used in the study of antipsychotic drugs were critically evaluated.

RESULTS

Despite some notable inconsistencies, the literature provides strong support for significant disruptions in PPI in rats produced by DA agonists, 5-HT2 agonists, NMDA antagonists, and isolation rearing. Each of these models exhibits sensitivity to at least some antipsychotic medications. While the PPI model based on the effects of direct DA agonists is the most well-validated for the identification of known antipsychotics, the isolation rearing model also appears to be sensitive to both typical and atypical antipsychotics. The 5-HT PPI model is less generally sensitive to antipsychotic medications, but can provide insight into the contribution of serotonergic systems to the actions of newer antipsychotics that act upon multiple receptors. The deficits in PPI produced by NMDA antagonists appear to be more sensitive to clozapine-like atypical antipsychotics than to typical antipsychotics. Hence, despite some exceptions to this generalization, the NMDA PPI model might aid in the identification of novel or atypical antipsychotic medications.

CONCLUSIONS

Studies of drug effects on PPI in rats have generated four distinctive models that have utility in the identification of antipsychotic medications. Because each of these models has specific advantages and disadvantages, the choice of model to be used depends upon the question being addressed. This review should help to guide such decisions.

Human studies of prepulse inhibition of startle: normal subjects, patient groups, and pharmacological studies

RATIONALE

Since the mid-1970s, cross-species translational studies of prepulse inhibition (PPI) have increased at an astounding pace as the value of this neurobiologically informative measure has been optimized. PPI occurs when a relatively weak sensory event (the prepulse) is presented 30-500 ms before a strong startle-inducing stimulus, and reduces the magnitude of the startle response. In humans, PPI occurs in a robust, predictable manner when the prepulse and startling stimuli occur in either the same or different modalities (acoustic, visual, or cutaneous).

OBJECTIVE

This review covers three areas of interest in human PPI studies. First, we review the normal influences on PPI related to the underlying construct of sensori- (prepulse) motor (startle reflex) gating. Second, we review PPI studies in psychopathological disorders that form a family of gating disorders. Third, we review the relatively limited but interesting and rapidly expanding literature on pharmacological influences on PPI in humans.

METHODS

All studies identified by a computerized literature search that addressed the three topics of this review were compiled and evaluated. The principal studies were summarized in appropriate tables.

RESULTS

The major influences on PPI as a measure of sensorimotor gating can be grouped into 11 domains. Most of these domains are similar across species, supporting the value of PPI studies in translational comparisons across species. The most prominent literature describing deficits in PPI in psychiatrically defined groups features schizophrenia-spectrum patients and their clinically unaffected relatives. These findings support the use of PPI as an endophenotype in genetic studies. Additional groups of psychopathologically disordered patients with neuropathology involving cortico-striato-pallido-pontine circuits exhibit poor gating of motor, sensory, or cognitive information and corresponding PPI deficits. These groups include patients with obsessive compulsive disorder, Tourette's syndrome, blepharospasm, temporal lobe epilepsy with psychosis, enuresis, and perhaps posttraumatic stress disorder (PTSD). Several pharmacological manipulations have been examined for their effects on PPI in healthy human subjects. In some cases, the alterations in PPI produced by these drugs in animals correspond to similar effects in humans. Specifically, dopamine agonists disrupt and nicotine increases PPI in at least some human studies. With some other compounds, however, the effects seen in humans appear to differ from those reported in animals. For example, the PPI-increasing effects of the glutamate antagonist ketamine and the serotonin releaser MDMA in humans are opposite to the PPI-disruptive effects of these compounds in rodents.

CONCLUSIONS

Considerable evidence supports a high degree of homology between measures of PPI in rodents and humans, consistent with the use of PPI as a cross-species measure of sensorimotor gating. Multiple investigations of PPI using a variety of methods and parameters confirm that deficits in PPI are evident in schizophrenia-spectrum patients and in certain other disorders in which gating mechanisms are disturbed. In contrast to the extensive literature on clinical populations, much more work is required to clarify the degree of correspondence between pharmacological effects on PPI in healthy humans and those reported in animals.

Impact of prepulse characteristics on the detection of sensorimotor gating deficits in schizophrenia

Schizophrenia patients have prominent deficits in information processing that can be detected by measures of prepulse inhibition (PPI) of the startle response. Deficient PPI in schizophrenia is thought to reflect a failure of brain-based information 'protective' mechanisms that normally inhibit responsivity for 30-500ms after a weak prepulse stimulus. The relationship between specific prepulse stimulus characteristics and PPI deficits in this study was examined in 31 schizophrenia patients and 34 normal comparison subjects. Schizophrenia patients had overall deficits in PPI across four conditions where the prepulse was either discrete (abrupt) or continuous (sustained) and consisted of either white noise or a pure tone. On inspection and analysis of the data, it appears that the white noise conditions, rather than tone conditions, account for the group differences. Thus, the discrete white noise prepulse was most effective in eliciting PPI deficits, resulting in a large effect size between groups (d=0.85; P<0.01). Deficits in information-protective mechanisms in schizophrenia may be differentially sensitive to specific stimulus characteristics; this observation may be relevant both to the neurobiology of information processing deficits in schizophrenia and to the methodologies for studying these deficits experimentally.

Working memory in schizophrenia: transient "online" storage versus executive functioning

Working memory has been described as the temporary "online" storage and the subsequent manipulation and retrieval of information. It has been suggested that the prefrontal cortex is a primary site of working memory. Schizophrenia patients, who are thought to have prefrontal cortical dysfunction, have demonstrated inconsistent deficits on a variety of verbal and spatial working memory tests. This has led to questions about how to define and measure working memory, whether these deficits are distinct to one cognitive domain, and what role factors such as intelligence and symptoms play in working memory performance. We compared schizophrenia patients to normal comparison subjects in four separate studies. Based upon the results we recommend that working memory tests be characterized as either transient "online" storage and retrieval tasks (where short-term storage and retrieval of information is required) or executive-functioning working memory tasks (where storage, manipulation, and retrieval of information is required). The importance of clearly identifying which distinct aspects of working memory are assessed is discussed.

Self-monitoring enhances Wisconsin Card Sorting Test performance in patients with schizophrenia: performance is improved by simply asking patients to verbalize their sorting strategy

Patients with schizophrenia have Wisconsin Card Sorting Test (WCST) deficits, which are commonly interpreted as reflecting frontal cortex-based executive dysfunction. One means of assessing the refractoriness of frontal-executive impairment is to utilize a training or modification strategy to improve WCST performance. In this study, 73 patients with schizophrenia were assigned to 1 of 2 groups. Group 1 received the standard WCST instructions for 64 cards (Condition 1). For the second 64-card deck, the patients were asked to verbalize the reason that they placed the card where they did after each sort (Condition 2). Group 2 received this modified instruction 1st (Condition 1) and then the standard instructions for the second deck (Condition 2). A group of normal comparison participants was also tested using standard instructions alone. Group 2 committed significantly fewer perseverative responses than did Group 1. Furthermore, there was no significant difference between Group 2 (Condition 1) and the normal participants. Group 1's performance improved when patients were exposed to the modified instructions (Condition 2). Additionally, poor premorbid factors and disorganized symptoms were associated with decreased benefit from the modified instructions across both groups. Cumulatively, these data suggest that a simple instruction may enhance executive function and impact WCST performance in patients with schizophrenia.

Translating the basic and clinical cognitive neuroscience of schizophrenia to drug development and clinical trials of antipsychotic medications

Neurocognitive deficits have become increasingly important defining features of schizophrenia and its treatment. Multiple domains of neurocognitive functions are impaired in schizophrenia patients, and these impairments are considered to be core features of the disorder. Many recent reports support the importance of the relationship of these neurocognitive deficits to measures of "functional outcome" such as social skills acquisition, social problem solving, and community outcome. Neurocognitive deficits appear to be improved with newer (atypical) antipsychotic medications across a broad range of domains in schizophrenia patients. Together with clinical neuroscience advances, basic research in cognitive neuroscience ranging from animal models of gating functions to early gene expression induced by antipsychotic medications has illuminated the specific neural basis of neurocognitive deficits in schizophrenia and the neurobiology of antipsychotic actions. These translational basic and clinical studies provide powerful screening tools and strategies for drug development and the subsequent assessment of the clinical efficacy of new antipsychotic medications. These interlocking clinical and basic research findings have substantial implications for improving both drug development and improving clinical trials methodology for antipsychotic medications. Thus, there is an informed translation and cross-fertilization between basic and clinical research focused on the development and assessment of putative new antipsychotic compounds.

Neurocognitive deficits and functional outcome in schizophrenia: are we measuring the "right stuff"?

There has been a surge of interest in the functional consequences of neurocognitive deficits in schizophrenia. The published literature in this area has doubled in the last few years. In this paper, we will attempt to confirm the conclusions from a previous review that certain neurocognitive domains (secondary verbal memory, immediate memory, executive functioning as measured by card sorting, and vigilance) are associated with functional outcome. In addition to surveying the number of replicated findings and tallying box scores of results, we will approach the review of the studies in a more thorough and empirical manner by applying a meta-analysis. Lastly, we will discuss what we see as a key limitation of this literature, specifically, the relatively narrow selection of predictor measures. This limitation has constrained identification of mediating variables that may explain the mechanisms for these relationships.

Trait contributions of complex dysregulated behavioral organization in schizophrenic patients

BACKGROUND

The "temporal architecture" of behavior is a construct that can be used to quantify the structure of behavioral sequences in the temporal domain-for example, by using a two-choice prediction task to investigate how past responses, stimuli, and outcomes influence the decision-making process. Using this task, previous investigations of the temporal architecture of the behavior in schizophrenic patients have identified an increased frequency of alternating highly predictable and highly unpredictable response sequences in the same test session in the same patient. Here, the hypothesis is tested that this dysregulation is stable over time and independent of psychosocial factors and symptomatic fluctuations.

METHODS

Ninety-one schizophrenic patients were tested on a 128 trial version of the two-choice prediction task; of those, 58 subjects completed a retest session 40 days later. Three sets of measures were obtained: simple response biases, dynamical entropy, and mutual information functions. These measures were subjected to a factor analysis, and the reliability of the resulting factors was examined.

RESULTS

First, three factors were obtained, which quantify 1) the level of dysregulation on this task; 2) the extent to which a win-stay/lose-shift strategy was used; and 3) the amount of simple response perseveration. Second, Crohnbach alpha for these factors was .699, .721, and .458, respectively. Third, there were no significant differences in the level of these factors within individual patients at the two time points. Fourth, neither symptom measures (Scale for the Assessment of Positive Symptoms and Scale for the Assessment of Negative Symptoms subscale scores) nor psychosocial or clinical variables (age, gender, illness duration, medication status) were able to predict the level of these factors at test or at retest.

CONCLUSIONS

These results support the hypothesis that the fundamental dysregulation of the temporal architecture of behavior in schizophrenic patients is stable across time and independent of symptomatic status. Future studies will examine the heritability of this dysfunction.

Prefrontal, parietal, and temporal cortex networks underlie decision-making in the presence of uncertainty

Decision-making in the presence of uncertainty, i.e., selecting a sequence of responses in an uncertain environment according to a self-generated plan of action, is a complex activity that involves both cognitive and noncognitive processes. Using functional magnetic resonance imaging, the neural substrates of decision-making in the presence of uncertainty are examined. Normal control subjects show a significant activation of a frontoparietal and limbic neural system during a two-choice prediction task relative to a two-choice response task. The most prevalent response strategy during the two-choice prediction task was "win-stay/lose-shift," where subjects will repeat the previous response if it successfully predicted the stimulus and switch to the alternative response otherwise. Increased frequency of responses that are consistent with this strategy is associated with activation in the superior temporal gyrus. In comparison, increased frequency of response inconsistent with win-stay/lose-shift is associated with parietal cortex activation. These results support the hypothesis that subjects use a frontoparietal neural system to establish a contingency based decision-making strategy even in the presence of random reinforcement.

Schizophrenia patients demonstrate a dissociation on declarative and non-declarative memory tests

Declarative memory refers to the recall and recognition of factual information. In contrast, non-declarative memory entails a facilitation of memory based on prior exposure and is typically assessed with priming and perceptual-motor sequencing tasks. In this study, schizophrenia patients were compared to normal comparison subjects on two computerized memory tasks: the Word-stem Priming Test (n=30) and the Pattern Sequence Learning Test (n=20). Word-stem Priming includes recall, recognition (declarative) and priming (non-declarative) components of memory. The schizophrenia patients demonstrated an impaired performance on recall of words with relative improvement during the recognition portion of the test. Furthermore, they performed normally on the priming portion of the test. Thus, on tests of declarative memory, the patients had retrieval deficits with intact performance on the non-declarative memory component. The Pattern Sequence Learning Test utilizes a serial reaction time paradigm to assess non-declarative memory. The schizophrenia patients' serial reaction time was significantly slower than that of comparison subjects. However, the patients' rate of acquisition was not different from the normal comparison group. The data suggest that patients with schizophrenia process more slowly than normal, but have an intact non-declarative memory. The schizophrenia patients' dissociation on declarative vs. non-declarative memory tests is discussed in terms of possible underlying structural impairment.

Modulation of the startle response and startle laterality in relatives of schizophrenic patients and in subjects with schizotypal personality disorder: evidence of inhibitory deficits

OBJECTIVE

Patients with schizophrenia spectrum disorders have been shown to have deficits in sensorimotor gating as assessed by prepulse inhibition of the startle response. The authors hypothesized that nonschizophrenic relatives of patients with schizophrenia would also have prepulse inhibition deficits, thereby reflecting a genetically transmitted susceptibility to sensorimotor gating deficits.

METHOD

Twenty-five comparison subjects, 23 patients with schizophrenia, 34 relatives of the schizophrenic patients, and 11 subjects with schizotypal personality disorder were assessed in an acoustic startle paradigm. The eye-blink component of the startle response was assessed bilaterally by using electromyographic recordings of orbicularis oculi.

RESULTS

The patients with schizophrenia, their relatives, and subjects with schizotypal personality disorder all had reduced prepulse inhibition relative to comparison subjects, and these deficits were more evident in measures of right eye-blink prepulse inhibition. Comparison subjects demonstrated greater right versus left eye-blink prepulse inhibition, whereas the probands, their relatives, and subjects with schizotypal personality disorder showed less asymmetry of prepulse inhibition.

CONCLUSIONS

These data suggest a genetically transmitted deficit in prepulse inhibition (sensorimotor gating) in patients with schizophrenia spectrum disorders, including subjects with schizotypal personality disorder and relatives of patients with schizophrenia.

Toward understanding the biology of a complex phenotype: rat strain and substrain differences in the sensorimotor gating-disruptive effects of dopamine agonists

Sensorimotor gating, measured by prepulse inhibition (PPI) of the startle reflex, is reduced in schizophrenia patients and in rats treated with dopamine agonists. Strain differences in the sensitivity to the PPI-disruptive effects of dopamine agonists may provide insight into the genetic basis for human population differences in sensorimotor gating. We reported strain differences in the sensitivity to the PPI-disruptive effects of the D1/D2 agonist apomorphine in adult rats, with greater sensitivity in Harlan Sprague Dawley (SDH) versus Wistar (WH) rats. However, Kinney et al. (1999) recently reported opposite findings, using Bantin-Kingman Sprague Dawley (SDBK) and Wistar (WBK) rats; in fact, SDBK rats did not exhibit clear apomorphine-induced reductions in sensorimotor gating. These new findings of Kinney et al. (1999) directly conflict with over 15 years of results from our laboratories and challenge interpretations from a large body of literature. The present studies carefully assessed drug effects on sensorimotor gating in SD versus W strains, across rat suppliers (H vs BK). Significantly greater SDH than WH apomorphine sensitivity in PPI measures was observed in both adult and 18 d pups, confirming that these strain differences are both robust and innate. These strain differences in apomorphine sensitivity were not found in adult BK rats. Supplier differences in sensitivity (SDH > SDBK) were also evident in the PPI-disruptive effects of D1 but not D2-family agonists; PPI was clearly disrupted by quinpirole in both SDH and SDBK rats. These findings demonstrate robust, innate, neurochemically specific, and apparently heritable phenotypic differences in an animal model of sensorimotor gating deficits in human neuropsychiatric disorders.

Animal models of deficient sensorimotor gating: what we know, what we think we know, and what we hope to know soon

Sensorimotor gating of the startle reflex can be studied in humans and laboratory animals using measures of prepulse inhibition (PPI) of the startle reflex. PPI is reduced in patients with specific neuropsychiatric disorders and in rats after manipulation of the limbic cortex, striatum, pallidum or pontine tegmentum. Studies are rapidly identifying the neurochemical and neuroanatomical substrates regulating PPI in laboratory animals; this detailed circuit information has been used as a 'blueprint' to identify possible candidate substrates responsible for PPI deficits in psychiatrically disordered humans. In parallel, studies have also begun to assess the homology of pharmacological effects on PPI across species, as an initial step towards translating detailed neural circuit information from rats to humans. Despite this rapid progress, there is an increasing danger of overlooking important methodological and interpretative issues that could impact either positively or negatively on the ultimate utility of models based on measures of PPI. Some of these issues--ranging from the cross-species methods for quantifying specific variables to the relevance of genetic drift to animal and human studies of PPI--and their implications for future studies are the focus of this review.

Environmental enrichment and isolation rearing in the rat: effects on locomotor behavior and startle response plasticity

BACKGROUND

Laboratory rats exhibit behavioral changes that reflect a continuum of early life experience, from isolation-reared to socially reared to enrichment-reared conditions. In this study, we further characterize the behavioral effects of isolation, social, and enriched rearing on locomotor activity, patterns of movement and exploration, startle reactivity, prepulse inhibition (PPI), and habituation in adult rats.

METHODS

Male Sprague-Dawley rat pups (21 days old) were housed under enrichment (three per cage with toys and exposure to enriched environments), normal social (three per cage), or isolation (one per cage) conditions. Eight weeks later, locomotor and exploratory behaviors, acoustic startle reactivity, PPI, and habituation were measured in the three groups.

RESULTS

Enrichment-reared rats exhibited reduced exploration and rapid habituation of locomotor activity, increased startle reactivity, and normal PPI and startle habituation compared with socially reared controls. Isolation-reared rats exhibited increased exploration and normal habituation of locomotor activity, increased startle reactivity, reduced PPI, and normal startle habituation.

CONCLUSIONS

Isolation- and enrichment-reared rats exhibited opposite changes in some behaviors and similar changes in other behaviors. Specifically, rats raised in enriched conditions appear more efficient at assimilating stimuli from their environment than do rats reared in isolation. Nevertheless, both enrichment- and isolation-rearing conditions increased startle reactivity, whereas only isolation rearing led to disruptions of PPI in adulthood. These results suggest that isolation- and enrichment-rearing conditions produce some common and some differential effects on how rats process environmental stimuli. For studies of isolation-rearing effects on PPI, however, the complex and resource-intensive enrichment condition seems to offer few advantages over the normal social condition.

Normal P50 suppression in schizophrenia patients treated with atypical antipsychotic medications

OBJECTIVE

Patients with schizophrenia have deficits in attention, cognition, and information processing. Measures such as P50 suppression are used to study cognitive and attentional dysfunction among these patients. P50 suppression is an operational measure of sensory gating that can be assessed by averaging electroencephalographic responses to multiple pairs of auditory clicks separated by 500 msec. Normally, the P50 response to the second click is smaller than the response to the first click. Many studies have demonstrated that schizophrenia patients have deficient P50 suppression, meaning that the difference between the first and second clicks is not as large as normal. Atypical antipsychotic medications may have superior clinical efficacy for negative symptoms and cognitive deficits. It is important, therefore, to evaluate the effects of atypical antipsychotic medications on measures such as P50 suppression.

METHOD

P50 suppression of 13 patients with schizophrenia receiving clinically effective doses of clozapine, olanzapine, or risperidone (classified as atypical antipsychotic medications) was compared to that of 13 patients receiving conventional antipsychotic medications.

RESULTS

The patient groups did not differ on clinical or demographic measures. The patients receiving atypical antipsychotic medications had normal-range P50 suppression (mean=72%). In contrast, the patients receiving typical antipsychotic medications had dramatically lower P50 suppression (mean=27%).

CONCLUSIONS

The results support the hypothesis that patients treated with atypical antipsychotic medications have normal P50 measures of sensory gating. Longitudinal within-subjects studies are warranted to clarify the mechanisms mediating this effect.

Do self-reports of perceptual anomalies reflect gating deficits in schizophrenia patients?

Jin and colleagues presented an innovative study examining P50 suppression and patients' self-reported perceptual anomalies as two related operational measures of sensory gating deficits in schizophrenia patients. They found that those schizophrenia patients who endorsed experiences of sensory inundation had normal levels of P50 suppression, whereas patients who tended to endorse fewer complaints of perceptual anomalies had P50 suppression deficits. Jin et al's finding challenges the common belief that P50 suppression deficits are associated with cognitive and sensory anomalies reflecting poor gating in schizophrenia patients. This article comments on how the dissociation between phenomenological experiences of gating disturbances and P50 suppression might be explained by the limits of self-report in schizophrenia patients who have deficient insight and self-awareness. We hypothesize that the self-reported inability to screen out irrelevant stimuli reflects a voluntary, controlled process that is different from the involuntary, automatic process measured by P50 suppression.

Sensory gating deficits assessed by the P50 event-related potential in subjects with schizotypal personality disorder

OBJECTIVE

The schizophrenia spectrum includes individuals with schizophrenia, their relatives, and individuals with schizotypal personality disorder. Subjects in the schizophrenia spectrum have disorders of attention, cognition, and information processing. Attention and information processing can be assessed by testing suppression of the P50 event-related potential; the amplitude of the P50 wave is measured in response to each of two auditory clicks. In normal subjects, the P50 wave following the second click is suppressed, or "gated." Schizophrenic patients and their relatives show less suppression of the second P50 wave. Deficits in P50 suppression have high heritability and show linkage to the alpha-7 subunit of the nicotinic cholinergic receptor gene in families with schizophrenia, suggesting that deficits in P50 suppression are trait markers for gating abnormalities in schizophrenia spectrum subjects. Although schizotypal subjects have been shown to have deficits in sensorimotor gating as measured by prepulse inhibition, to the authors' knowledge P50 sensory gating in schizotypal personality disorder has yet to be reported.

METHOD

P50 suppression in 26 subjects with schizotypal personality disorder and 23 normal subjects was assessed through auditory conditioning and testing.

RESULTS

The subjects with schizotypal personality had significantly less P50 suppression than did the normal subjects.

CONCLUSIONS

Subjects with schizotypal personality disorder may have trait-linked sensory gating deficits similar to those in patients with schizophrenia and their relatives. Because these subjects may manifest sensory gating deficits without overt psychotic symptoms, it is likely that these deficits represent a core cognitive dysfunction of the schizophrenia spectrum.

Amphetamine disrupts P50 suppression in normal subjects

BACKGROUND

P50 suppression is viewed as an operational measure of sensory "gating" that is reduced in patients with schizophrenia and their family members. Previous reports have demonstrated that neural gating is regulated by monoaminergic tone in rodent models of P50 suppression.

METHODS

In this study, 11 healthy subjects participated in P50 event-related potential recordings at baseline and after either oral administration of dextroamphetamine (.3 mg/kg) or placebo, to determine if the administration of a monoaminergic agonist produces P50 suppression deficits similar to those observed in patients with schizophrenia.

RESULTS

As hypothesized, amphetamine disrupted the suppression of the P50 event-related potential. There was a statistically significant decrement in P50 suppression during the amphetamine challenge condition (t10 = 3.15, p < .01, mean difference = -44.1%, d = -2.5) relative to the baseline P50 condition. A comparison of P50 suppression in the placebo and amphetamine conditions (both after a baseline recording session) revealed a significant amphetamine-induced disruption of P50 suppression (t6 = 3.71, p < .01, mean difference = -54.4%, d = -3.14).

CONCLUSIONS

The biochemical alterations associated with an amphetamine-induced disruption of P50 suppression in this study may be related to the pathophysiology of P50 suppression deficits in schizophrenia. The findings are consistent with several careful examinations of suppression deficits in rodent models that have identified the monoaminergic regulation of P50 suppression. These data indicate that amphetamine induces a disruption of P50 suppression in normal subjects.

Human and animal studies of schizophrenia-related gating deficits

Prepulse Inhibition (PPI) of the startle response and the P50 auditory-evoked potential suppression are used to assess impairments in the regulation of the neural substrates and to determine the clinical significance of inhibitory deficits in schizophrenia. The study of gating deficits in schizophrenia and in related animal model studies have already advanced our understanding of the neural substrates of information processing abnormalities in patients with schizophrenia. Individuals with schizotypal personality disorder as well as clinically unaffected family members of patients with schizophrenia show PPI and P50 suppression deficits. These "schizophrenic spectrum" populations are not grossly psychotic, nor are they receiving antipsychotic medications. Therefore, the gating deficits are presumed to reflect core (eg, intermediate phenotypic) schizophrenia-linked information processing abnormalities. Several studies have reported that gating deficits are associated with clinical ratings of psychiatric symptoms, thought disorder, and neuropsychologic deficits in patients with schizophrenia. In addition, recent human pharmacologic studies have indicated that gating deficits can be reversed by rationally-selected compounds. Animal model studies have generally shown convergence with the human studies and may lead to improved identification of efficacious new antipsychotic medications for patients with schizophrenia.

Sex differences in sensorimotor gating of the human startle reflex: all smoke?

RATIONALE

A recent report described sex differences in the effects of nicotine use and withdrawal on prepulse inhibition of acoustic startle (PPI), but no sex differences in PPI in non-smokers.

OBJECTIVE

To determine whether previously reported male>female acoustic PPI reflect sex differences in smoking effects on PPI, rather than simple sex differences in the regulation of PPI. A retrospective analyses of >600 carefully screened normals tested over the past 12 years was completed.

RESULTS

Male>female acoustic PPI was detected in analyses that included: 1) all subjects; or 2) self-declared non-smokers.

CONCLUSIONS

Sex differences in PPI cannot be accounted for by smoking history, because they are present across a large sample of non-smoking normal controls.

The nonlinear, complex sequential organization of behavior in schizophrenic patients: neurocognitive strategies and clinical correlations

BACKGROUND

Thought disorder is a hallmark of schizophrenia and can be inferred from disorganized behavior. Measures of the sequential organization of behavior are important because they reflect the cognitive processes of the selection and sequencing of behavioral elements, which generate observable and analyzable behavioral patterns. In this context, sequences of choices generated by schizophrenic patients in a two-choice guessing task fluctuate significantly, which reflects an "oscillating dysregulation" between highly predictable and highly unpredictable subsequences within a single test session. In this study, we aimed to clarify the significance of dysregulation by seeing whether demographic, clinical, neuropsychological, and psychological measures predict the degree of dysregulation observed on this two-choice task.

METHODS

Thirty schizophrenic patients repeatedly performed a LEFT or RIGHT key press that was followed by a stimulus, which occurred randomly on the left or right side of the computer screen. Thus, the stimulus location had nothing to do with the key press behavior. The range of key press sequence predictabilities as measured by the dynamical entropy was used to quantify the dysregulation of response sequences and reflects the range of fixity and randomness of the responses. A factor analysis was performed and step-wise multiple regression analyses were used to relate the factor scores to demographic, clinical, symptomatic, Wisconsin Card Sorting Test (WCST), and Rorschach variables.

RESULTS

The LEFT/RIGHT key press sequences were determined by three factors: 1) the degree of win-stay/lose-shift strategy; 2) the degree of contextual influence on the current choice; and 3) the degree of dysregulation on the choice task. Demographic and clinical variables did not predict any of the three response patterns on the choice task. In contrast, the WCST and Rorschach test predicted performance on various factors of choice task response patterns.

CONCLUSIONS

Schizophrenic patients employ several rules, i.e., "win-stay/lose-shift" and "decide according to the previous choice," that fluctuate significantly when generating sequences on this task, confirming that a basic behavioral dysregulation occurs in a single schizophrenic subject across a single test session. The organization or the "temporal architecture" of the behavioral sequences is not related to symptoms per se, but is related to deficits in executive functioning, problem solving, and perceptual organizational abilities.

Cross-species studies of sensorimotor gating of the startle reflex

Sensorimotor gating of the startle reflex can be assessed across species, using similar stimuli to elicit comparable response characteristics. As measured by prepulse inhibition (PPI), gating is reduced in patients with some neuropsychiatric disorders, and in rats after manipulations of limbic cortex, striatum, pallidum, or pontine tegmentum. This limbic "CSPP" circuitry can be studied in rats to reveal the neurochemical and neuroanatomical substrates regulating PPI at a high level of resolution. This detailed circuit information is used as a "blueprint" to identify substrates that may lead to PPI deficits in psychiatric-disordered humans. Some human disorders with identifiable, localized lesions in CSPP circuitry, for example, Huntington's disease, provide direct validation for this cross-species model. Studies have begun to assess the pharmacological homology of PPI across species, as an initial step towards translating detailed neural circuit information from rats to humans. These initial studies suggest the possibility that the effects of dopaminergic (DAergic) drugs on PPI (reducing PPI) may be homologous across species; nicotinic drugs may also produce similar effects on PPI across species (increasing PPI). By contrast, the effects of glutamatergic and serotonergic drugs may exhibit disparate effects on PPI across species. The use of DAergic agonists in human studies is complicated by their significant side effects, but new studies demonstrate that several "human friendly" direct DA agonists disrupt PPI in rats and are thus good candidates for further studies of the cross-species homology of the DAergic regulation of PPI. In this manner, PPI can be used to probe the sensitivity of DAergic systems, and perhaps other CSPP elements, across normal and neuropsychiatric-disordered populations.

Cognitive functions in schizotypal personality disorder

OBJECTIVE

Schizophrenia spectrum subjects have cognitive deficits in a variety of domains. Schizotypal personality disordered (SPD) subjects do not have many of the confounds seen in schizophrenic patients, but may have the same pattern of cognitive deficits in attention and executive functioning.

HYPOTHESIS

We hypothesized that SPD subjects would have impairments on measures of attention, abstract reasoning, cognitive inhibition, working memory and verbal recognition memory when compared to normal subjects, and that these deficits would be intermediate to those observed in schizophrenic patients.

METHOD

SPD subjects (N=20) were compared to age-, gender- and education-matched schizophrenic patients (N=20) and normal comparison subjects (N=20) on a battery of cognitive measures.

RESULTS

The data were analyzed using standard statistical methods, including effect sizes. Using a conservative alpha level of 0.01, schizophrenic patients had deficits on many of these measures compared to normal subjects. Although the SPD subjects did not significantly differ from normal comparison subjects at the p < 0.01 level, there were trends (p < 0.019-0.028) toward impairment on measures of working memory and general intellectual functioning. On further effect size analyses, SPD subjects performed intermediate to normals and schizophrenic patients on measures of attention, abstract reasoning, cognitive inhibition, verbal working memory, recognition memory, and general intellectual functioning, with moderate to large effect sizes separating groups.

CONCLUSIONS

These results suggest that SPD subjects have possible widespread cognitive deficits that are of lesser magnitude than those observed in schizophrenic patients.

Symptom correlates of prepulse inhibition deficits in male schizophrenic patients

OBJECTIVE

Information processing, inhibitory, and gating deficits in human and animal model studies of schizophrenia are demonstrated by using prepulse inhibition of the startle reflex. Prepulse inhibition deficits in schizophrenic patients correlate with core cognitive symptoms, such as thought disorder and distractibility, but their relationship to positive and negative symptoms of schizophrenia is less clear.

METHOD

Fifty-one male schizophrenic patients and 26 male normal comparison subjects were tested for prepulse inhibition of the eyeblink component of the startle reflex measured by electromyogram recording. Startling stimuli (118 dB) were presented alone (pulse only) or were preceded 60 msec by discrete prepulse stimuli of 2, 4, 8, or 16 dB above the background 70-dB noise level. In addition, patients were assessed for demographic variables, generalized symptoms (Brief Psychiatric Rating Scale), and positive and negative symptoms.

RESULTS

Schizophrenic and comparison groups differed significantly in the amount of prepulse inhibition produced by the 16-dB prepulse, with schizophrenic patients showing the expected deficient prepulse inhibition. Latency of the eyeblink response was generally slower for the schizophrenic patients, but the prepulse-induced latency facilitation for schizophrenic patients and comparison subjects did not differ significantly. The pattern of prepulse inhibition deficits in schizophrenic patients remained, with age and education controlled, in an analysis of covariance and subgroup matching. Deficient prepulse inhibition correlated with both positive and negative symptoms of schizophrenia.

CONCLUSIONS

Under these experimental conditions, schizophrenia-linked deficits in prepulse inhibition detected with a relatively strong prepulse are correlated with both positive and negative symptoms of schizophrenia. The level of correlation, while significant in this cohort, is not as robust as that in previous reports linking prepulse inhibition deficits with other measures, such as thought disorder. Future work should probably focus on the relationship of prepulse inhibition deficits to measures such as thought disorder rather than positive and negative symptoms.

Is there a critical developmental 'window' for isolation rearing-induced changes in prepulse inhibition of the acoustic startle response?

In a previous study, rats reared in isolation from weaning exhibited normal prepulse inhibition (PPI) before puberty, whilst after puberty (6-8 weeks post weaning) isolation reared rats exhibited deficits in PPI. The developmental timing of the onset of this isolation effect appears to be critical because similar isolation of adult rats has no effect on PPI. The present study examined the time and duration of the period or 'window' of isolation necessary to induce these behavioral changes. Male Sprague-Dawley rats were isolated for either only the first 2 weeks from weaning, only the first 4 weeks from weaning, only weeks 3 and 4, or continuously from weaning (ISO group), and compared with rats reared in normal social conditions (SOC group). Eight weeks after weaning, we compared acoustic and airpuff startle reactivity, acoustic and light PPI, and acoustic and airpuff startle habituation across the groups. There were no significant changes in any of the measures in the groups exposed to 2- or 4-week periods of isolation. In the ISO and SOC groups, acoustic or airpuff startle reactivity was similar, while acoustic PPI was reduced significantly in the ISO group. Airpuff startle habituation was increased significantly in the ISO group compared to SOC controls and there was a similar trend with acoustic startle habituation. These results indicate that only animals isolated for more than 4 weeks after weaning display deficits in PPI, and provide evidence that there is no critical pre-pubertal developmental window for inducing PPI deficits, rather, continuous post-weaning isolation is needed to induce the PPI deficit effect.

Sensorimotor gating and thought disturbance measured in close temporal proximity in schizophrenic patients

BACKGROUND

Sensorimotor gating abnormalities have been previously correlated with thought disturbance in schizophrenic patients. These correlative studies have led to the hypothesis that sensorimotor gating abnormalities may underlie thought disturbance. Several authors have cautioned, however, that this and similar hypotheses are supported by data recorded at different times or during resting states" and therefore incorrectly assume that the observed association represents a concurrent relationship. To address this issue, sensorimotor gating and thought disturbance were measured in close temporal proximity, thus strengthening the evidence for the association of these 2 abnormalities in schizophrenic patients.

METHODS

Twenty-one schizophrenic men were assessed on measures of sensorimotor gating and thought disturbance. Sensorimotor gating was examined operationally via the use of prepulse inhibition. Thought disturbance was assessed via the Rorschach test measures of perceptual inaccuracy, disordered cognition, and the expression of normally repressed contents. Symptom rating scales (the Scale for the Assessment of Positive Symptoms and the alogia subscale of the Scale for the Assessment of Negative Symptoms) were also used.

RESULTS

Deficient prepulse inhibition correlated significantly with 2 of the 3 Rorschach-derived thought disturbance measures. Prepulse inhibition was not correlated significantly with symptom rating scales. The Rorschach measure of impaired perceptual accuracy independently accounted for 60% of the variance in prepulse inhibition measures and contributed 35% of the unique variance beyond the effect attributable to the Scale for the Assessment of Positive Symptoms.

CONCLUSIONS

Assessment of information processing and thought disturbance measures in close temporal proximity resulted in strong evidence that gating deficits correlate highly with measures of perceptual and reasoning disturbances. This relationship may form an important basis for the cognitive dysfunction observed among schizophrenic patients.

Prepulse inhibition and habituation of the startle response are stable neurobiological measures in a normal male population

Prepulse inhibition (PPI) and habituation of the startle response are operational measures of sensorimotor gating and information processing. Changes in the normal inhibition and habituation of the startle response may provide trait markers for illnesses such as schizophrenia that have altered neurotransmitter control of the neural circuitry that modulates these measures. The stability of PPI and habituation was assessed in 10 normal male subjects. Prepulse inhibition was found to be most stable in the more intense prepulse conditions, and habituation was most stable in the early portion of the test session. These data support the hypothesis that PPI and habituation are relatively stable neurobiological markers.

Long-range correlations in choice sequences of schizophrenic patients

Schizophrenic patients significantly greater than normals exhibit long-range correlations in sequences of choices in a simple binary choice task. Moreover, schizophrenic patients also are significantly less influenced by external stimuli than are normal comparison subjects. These effects are not significantly correlated with each other, suggesting that they do not result from a uniform attentional deficit nor are they due to simple perseverative responding or any other uniform process. The interdependence of responses over many trials suggests that the response history of many previous behavioral responses contributes significantly to the temporal architecture of schizophrenic patients. In agreement with others (Lyon et al., 1994), we find that similar organizational principles apply to physical, economical, or biological systems and seem to play an important role in human psychopathology.

Poor P50 suppression among schizophrenia patients and their first-degree biological relatives

OBJECTIVE

This study's goal was to replicate the finding that family members of schizophrenia patients show poor P50 suppression during a paired-click auditory evoked response paradigm.

METHOD

The paired-click paradigm was used to test 44 schizophrenia patients, 60 of their clinically unaffected first-degree relatives, and 45 normal subjects. Two clicks (83 dB[A] over a 60-dB[A] white noise background) separated by 500 msec were presented 60 times to all subjects. P50 responses to the first and second clicks were selected from the digitally filtered data by using standard methods and the Cz recording site.

RESULTS

The schizophrenia patients had smaller P50 responses to click 1 than either their relatives or the normal subjects; the patients and their relatives, who did not significantly differ, had larger P50 responses to click 2 than the normal subjects. Schizophrenia patients had worse P50 suppression than either their family members or the normal subjects; the patients' family members had worse P50 suppression than the normal subjects.

CONCLUSIONS

Family members of schizophrenia patients have worse P50 suppression than normal subjects. To the authors' knowledge, this is the first demonstration independent of the group associated with the University of Colorado that schizophrenia patients' family members have poor P50 suppression. This result is intrinsically important, perhaps especially because a recent report suggests genetic linkage of poor P50 suppression to the cholinergic receptor's alpha7 nicotinic subunit.

A multimethod approach to assessing perseverations in schizophrenia patients

Perseverations have been associated with frontal lobe impairment and are often observed among schizophrenia patients. We assessed perseverations in schizophrenia patients (N = 71) using the Wisconsin Card Sorting Test (WCST) and a new Rorschach perseveration scale which yields three perseveration scores. We also compared the results of the schizophrenia patients with those of a normal comparison group (N = 71). We found that schizophrenia patients demonstrated a high number of perseverations on both the WCST and the Rorschach perseveration scale when compared to the normal comparison subjects. Among schizophrenia patients, WCST perseverative responses were significantly correlated with Rorschach-derived stuck-in-set perseverations, WAIS-R Vocabulary scores and negative symptom ratings. No significant differences in any of the measures of perseveration were found to be associated with diagnostic subtype. Finally, WCST and Rorschach measures for the schizophrenia and normal comparison participants were entered into a logistic regression. The WCST total errors and the three Rorschach perseveration measures resulted in the correct classification of 89.4% of the total cases, with a sensitivity of 91%, specificity of 91% and positive predictive power of 87.8%. These data provide evidence that perseverative behavior is widely observed in schizophrenia patients using a variety of instruments. The authors discuss the benefit of using multiple measures of perseveration in schizophrenia research.

The "incredible shrinking" P50 event-related potential

The P50 component of the auditory evoked response has been utilized in studies of sensory gating in schizophrenia for over 15 years. As P50 gating studies have had a greater impact in neuroscience research, investigators have refined several key variables (e.g., filtering) to enhance signal-to-noise ratios. A comprehensive review of P50 reports suggests P50 amplitude has been steadily decreasing over the years. Certain methodological "advances" are suggested as key reasons for this apparent reduction in P50 amplitude. Gating studies continue to yield interesting findings in neuropsychiatric research, especially when ratio vs. absolute difference scores are used.

Reversal of isolation rearing-induced deficits in prepulse inhibition by Seroquel and olanzapine

BACKGROUND

Prepulse inhibition (PPI) of startle provides an operational measure of sensorimotor gating in which a weak stimulus presented prior to a startling stimulus reduces the startle response. PPI deficits observed in schizophrenia patients can be modeled in rats by individual housing from weaning until adulthood. Deficits in PPI produced by isolation rearing can be reversed by antipsychotics.

METHODS

We evaluated the ability of Seroquel and olanzapine to reverse the isolation-induced disruption of PPI. Rats housed for 8 weeks singly or in groups of 3 were tested every 2 weeks after either Seroquel (0, 5.0 mg/kg) or olanzapine (0, 2.5, 5.0 mg/kg). Startle was elicited by 120-dB pulses presented either with or without prepulses (3, 6, or 12 dB above a 65-dB background).

RESULTS

Isolation rearing repeatedly disrupted PPI and sometimes increased startle reactivity. Seroquel reversed these deficits without affecting PPI in socially reared controls. Olanzapine (2.5 mg/kg) reversed the isolation rearing-induced PPI deficit and tended to increase basal PPI levels. Both antipsychotics antagonized the isolation rearing-induced increase in startle reactivity.

CONCLUSIONS

Isolation rearing produces deficits in sensorimotor gating in rats that are reversible by atypical antipsychotics, and may therefore aid in identifying new treatments for schizophrenia.

Multiple site evaluation of P50 suppression among schizophrenia and normal comparison subjects

Normally, when two brief, non-startling auditory stimuli are presented 500 ms apart, with long (e.g., 10 s) interpair intervals, the positive potential occurring approx. 50 ms after the first stimulus (P50) is relatively large, and the P50 to the second stimulus is smaller. In schizophrenia patients, however, the P50 to the second stimulus is larger than normal. In this study, 36 schizophrenia and 36 normal comparison subjects were tested in a two-click paradigm. Data were recorded from six electrode locations (F3, Fz, F4, C3, Cz, C4). The results support the hypothesis that schizophrenia patients have poor P50 suppression that is not an artifact of differential P50 wave morphology or differences in the number of usable trials between groups. In addition, the vertex location alone (Cz) was equal to, if not better than, any combination of sites for differentiating between groups. These results support the use of the Cz site alone in most investigations of P50 suppression deficits among schizophrenia spectrum patients. Further work investigating the neuropathological correlates of poor P50 suppression among schizophrenia patients by recording from multiple electrode locations, however, could be helpful.

Transient versus sustained visual channels in the visual backward masking deficits of schizophrenia patients

BACKGROUND

Schizophrenia patients have information-processing deficits that can be quantified using visual backward masking. The visual information processing system is divided functionally and structurally into transient and sustained visual channels. When visual stimuli are presented to a subject, the transient pathway detects the presence and location of the stimulus while the sustained pathway is involved in fine discrimination and identification of the stimulus. While independent subcortically, the transient and sustained visual channels converge cortically into the dorsal and ventral processing streams that assess spatial relationships and object recognition respectively.

METHODS

To better understand the underlying mechanisms of the visual backward masking deficits, 16 schizophrenia patients and 17 comparison subjects were tested on two different visual backward masking paradigms that required either locating or identifying a target letter.

RESULTS

Schizophrenia patients had visual backward masking deficits in a task that involved locating a target letter while there were no deficits in the task that involved identification of a target letter.

CONCLUSIONS

The visual backward masking deficits of schizophrenia patients suggest impairment in the processing of spatial information. These deficits are discussed in the context of our current knowledge of visual information processing and the neuropathophysiology of schizophrenia.

Information processing deficits of schizophrenia patients: relationship to clinical ratings, gender and medication status

Information processing deficits were explored in a large cohort of schizophrenia patients (N = 125) and non-psychiatric subjects (N = 52). Gender, medication status and symptom factors were assessed relative to measures of performance in critical stimulus duration (CSD), visual backward masking (VBM) and auditory reaction time (RT) paradigms. Schizophrenia patients exhibited significant impairments in measures of CSD, VBM and both RT speed and RT set. Females in both groups had inflated CSDs relative to males. Female schizophrenia patients showed slower RTs and elevated RT set scores, but comparable VBM performance, when compared to males. This gender difference was not observed in the non-psychiatric subjects. To test the hypothesis that impaired performance in the VBM and RT paradigms would be related to negative symptoms and thought disorder, regression analyses were performed using factor scores derived from a factor analysis of SANS and SAPS items that generated three symptom factors: negative, disorganized, and reality distortion. Significant variance in performance on VBM and RT measures was accounted for only by the negative symptom factor. We conclude that VBM and RT assess information processing deficits in schizophrenia patients that are more related to the negative versus positive or disorganized symptoms of schizophrenia. It is possible that VBM and RT share overlapping or interacting neural substrates.

Neuroanatomy of schizophrenia

The articles that appear in this issue offer a framework of insights about the neuroanatomy of schizophrenia from three learned and creative perspectives. All three articles advance our understanding of schizophrenia from a single locus/specific "lesion" model to more advanced perspectives of neural circuit dysfunction models. Goldman-Rakic and Selemon review their own and others' work on structure-activity relationships of the frontal cortex and related working memory dysfunction. This important but sometimes cloudy and complex area is illuminated by their highly specific, informative research. Jones focuses on thalamic abnormalities hypothetically linked to abnormal oscillations in large arrays of cortical and thalamic neurons, a critically important concept in understanding the functional consequences of abnormal (thalamic) brain structure and function. Graybiel describes her interest in abnormal basal ganglia activity-dependent loops that may access the thalamus and set the tone of thalamo-cortical transmission. This view allows for us to understand the "upward" influences on basal ganglia function (and dysfunction) relevant to schizophrenia. These intriguing articles raise a number of issues that await increased data and continued integrating insights. These issues include the need for more information about (1) the developmental timing of lesions or dysfunctions; (2) the extent and regional distribution of abnormalities; (3) the relationship of brain dysfunction to clinical/cognitive abnormalities; and (4) the variable expression of brain abnormalities across the schizophrenia spectrum. These three articles and their authors are at the forefront of our expanding knowledge about the neuroanatomy of schizophrenia and how complex structural and functional deficits are expressed in individuals in the group of schizophrenias.

P50 suppression among schizophrenia and normal comparison subjects: a methodological analysis

The present report investigated the relationship between P50 suppression and habituation among 20 schizophrenia and 20 normal comparison subjects. Subjects were presented with clicks delivered over headphones in a S1-S2 paradigm (clicks were separated by 500 msec; average intertrial interval was 8 sec). There were 60 total trials; the data were analyzed separately for the first and second 30 trials. The groups did not differ either on the number of usable trials or on the morphology of their P50 responses. Consistent with previous reports, schizophrenia patients demonstrated deficient P50 suppression. The overall suppression effect was not due to a group difference on S1 P50 amplitudes, but was associated with schizophrenia patients having smaller S1-S2 P50 amplitude difference scores than normal comparison subjects. Furthermore, the suppression effect appears to be more pronounced during the first than during the second block of trials. Thus, it may be important to evaluate changes in P50 responses over time among schizophrenia and normal comparison subjects.

Backward versus forward visual masking deficits in schizophrenic patients: centrally, not peripherally, mediated?

OBJECTIVE

Schizophrenic patients have repeatedly demonstrated the inability to rapidly process information when tasks are timed or the processing load is relatively high. Schizophrenic patients show consistent deficits in the visual backward masking paradigm. In visual backward masking, an informational target stimulus is presented, followed after an interstimulus interval by a masking stimulus that interferes with or interrupts target identification.

METHOD

In order to clarify whether the visual backward masking deficits of schizophrenic patients are indeed central rather than peripheral in origin, the authors compared visual backward masking to psychometrically matched visual forward masking performance in 35 normal comparison subjects and then 35 schizophrenic patients. In visual forward masking, the mask precedes the target, and visual forward masking mechanisms are felt to be more peripheral (retinal) than are visual backward masking mechanisms.

RESULTS

For psychometrically matched forward and backward masking tasks, the schizophrenic patients had a selective and differential deficit in the backward masking condition.

CONCLUSIONS

These results support the interpretation that the observed visual backward masking deficits of schizophrenic patients are centrally mediated.

The relationship of information-processing deficits and clinical symptoms in schizotypal personality disorder

Individuals with schizotypal personality disorder (SPD) are thought to be phenotypically related to individuals with schizophrenia. This assumption is partially supported by the fact that SPD patients have deficits on biological markers similar to those found in schizophrenia. Visual backward masking (VBM) performance and critical stimulus duration (CSD), measures of information processing found to be abnormal in schizophrenia patients, were assessed in 14 SPD and 21 comparison subjects. There was no significant difference between groups in VBM performance; however; there were significant correlations between VBM deficits and the number of SPD symptoms, as well as elevated scores on the Ego. Impairment Index (EII). Additionally, there was a trend (p = 056) toward elevations in CSD in the SPD versus the comparison group and CSD inflation appears to be most prominent in individuals with a greater number of social deficit symptoms and elevated physical anhedonia scores. These findings suggest an important relationship between symptoms of SPD and neurophysiologic deficits.

Positive symptoms of psychosis in posttraumatic stress disorder

The possible presence of hallucinations and delusional thoughts in posttraumatic stress disorder (PTSD) was investigated. Other symptom clusters were also assessed in order to further clarify the nature of PTSD. Twenty combat veterans with PTSD were compared to 18 combat veterans without PTSD on symptom rating scales. The subjects with PTSD exhibited a greater degree of depression, anxiety, agitation, anhedonia, and positive symptoms of psychosis than the comparison group. Specifically, the PTSD group manifested increased hallucinations, delusions, and bizarre behavior. Some of these positive symptoms did not appear to be due to reexperiencing of the trauma. The groups were not significantly different on indices of mania, thought disorder, or inertia. The clinical and diagnostic implications of the results are discussed. A diagnosis of PTSD should be considered with patients who have positive symptoms in the absence of thought disorder.

Latent inhibition in schizophrenia

Latent inhibition (LI) refers to the retarded acquisition of a conditioned response that occurs if the subject being tested is first preexposed to the to-be-conditioned stimulus (CS) without the paired unconditioned stimulus (UCS). Because the 'irrelevance' of the to-be-conditioned stimulus is established during non-contingent preexposure, the slowed acquisition of the CS-UCS association is thought to reflect the process of overcoming this learned irrelevance. Latent inhibition has been reported to be diminished in acutely hospitalized schizophrenia patients. If acutely hospitalized schizophrenia patients are preexposed to the CS, they learn the association as fast as, and perhaps faster than, patients who are not preexposed to the CS. This finding has been interpreted as reflecting the inability of acute schizophrenia patients to ignore irrelevant stimuli. In this study, the LI paradigm was identical to the one used in previous reports of LI deficits in schizophrenia patients (Baruch et al., 1988). Latent inhibition was observed in normal control subjects (n = 73), including individuals identified as 'psychosis-prone' based on established screening criteria, and in anxiety (n = 19) and mood disorder (n = 13) patients. Learning scores (trials to criterion) in "acutely' hospitalized as well as "chronic' hospitalized schizophrenia patients (n = 45) were significantly elevated in both preexposed and non-preexposed subjects, compared to controls. Acute schizophrenia patients exhibited intact LI. Separate cohorts of acute and chronic schizophrenia patients (n = 23) and normal controls (n = 34) exhibited intact LI when tested in a new, easier-to-acquire computerized LI paradigm. These results fail to identify specific LI deficits in schizophrenia patients, and raise the possibility that previously observed LI deficits in schizophrenia patients may reflect, at least in part, performance deficits related to learning acquisition.