Use of methods from chaos theory to quantify a fundamental dysfunction in the behavioral organization of schizophrenic patients

OBJECTIVE

This study aimed to quantify the complexity of behavioral sequences of patients with schizophrenia and comparison subjects by using methods from nonlinear dynamical systems theory.

METHOD

A simple choice task consisting of predicting 500 random right or left appearances of a stimulus was used to obtain binary response sequences in 22 patients with schizophrenia and 16 comparison subjects. Dynamical entropy was measured and the fluctuation spectrum of local subsequence entropies calculated to quantify the degree of interdependency between consecutive responses of patients and comparison subjects.

RESULTS

The response sequences generated by the schizophrenic patients exhibited a higher degree of interdependency than those of comparison subjects. Moreover, schizophrenic patients exhibited significantly less consistency in their response selection and ordering, characterized by a greater contribution of both highly perseverative and highly unpredictable subsequences of responses within a test session.

CONCLUSIONS

The result of the biological abnormality underlying schizophrenia may not be a simple increase or decrease of neuropsychological or neurobiological functions. Instead, the observed abnormalities in behavioral patterns reflect a quantifiable dysregulation and disorganization of these functions.

Increased sensitivity to the sensorimotor gating-disruptive effects of apomorphine after lesions of medial prefrontal cortex or ventral hippocampus in adult rats

Sensorimotor gating of the startle reflex is impaired in humans with schizophrenia and in rats after mesolimbic D2 dopamine receptor activation. The loss of startle gating after D2 activation in rats has been used as an animal model of impaired sensorimotor gating in schizophrenia, because the ability of antipsychotics to restore startle gating in D2-activated rats correlates significantly with antipsychotic clinical potency. Substantial evidence indicates that the pathophysiology of schizophrenia includes structural and functional deficits in prefrontal and temporal regions, particularly the dorsolateral prefrontal cortex and the hippocampus and parahippocampal gyrus. The present study assessed startle gating in adult rats after ibotenic acid lesions of the medial prefrontal cortex or ventral hippocampus. Medial prefrontal cortex lesioned rats exhibited normal startle amplitude and normal sensorimotor gating, as reflected by prepulse inhibition (PPI) of the startle reflex. Hippocampus lesioned rats exhibited elevated startle amplitude, and similar to rats with medial prefrontal cortex lesions, did not show significant changes in basal PPI. Low doses of the mixed dopamine agonist apomorphine did not significantly reduce PPI in sham lesioned rats, but significantly disrupted PPI in both medial prefrontal cortex- and ventral hippo-campus lesioned rats. These data are consistent with the hypothesis that cell damage in frontal and temporal cortex increases the sensitivity to the sensorimotor gating-disruptive effects of dopamine receptor activation.

Neonatal excitotoxic hippocampal damage in rats causes post-pubertal changes in prepulse inhibition of startle and its disruption by apomorphine

Neonatal excitotoxic hippocampal damage in the rat results in postpubertal onset of a variety of abnormal behaviors related to excessive dopaminergic transmission in the mesolimbic/nigrostriatal system, and thus may be considered an animal model of some aspects of schizophrenia. Because sensorimotor gating is impaired in adult patients with schizophrenia and in rats with experimentally induced mesolimbic dopamine hyperactivity, the present experiments investigated the effects of neonatal (postnatal day 7, PD7) ibotenic acid (3 micrograms) lesions of the ventral hippocampus (VH) on the amplitude and prepulse inhibition (PPI) of acoustic startle in prepubertal (PD35) and postpubertal (PD56) rats. Startle was elicited using 105 and 118-dB pulses alone or preceded by 4, 8, or 16 dB above-background prepulses in rats treated with vehicle or apomorphine (APO; 0.025 or 0.1 mg/kg SC). At PD35, PPI in VH-lesioned rats did not differ significantly from these measures in sham operated rats. Apomorphine significantly increased startle amplitude and reduced PPI in both sham operated and VH-lesioned rats at PD35. At PD56, startle amplitude in VH-lesioned rats was not significantly different from controls, but PPI was reduced significantly compared to controls. Ventral hippocampus lesioned rats also exhibited an exaggerated reduction in PPI after treatment with APO. These findings provide further evidence of postpubertal impairments that may be related to increased mesolimbic dopamine transmission and receptor sensitivity in rats with neonatal hippocampal damage, and provide further support for the fidelity of this animal model of schizophrenia.

Gender differences in schizophrenia

In an assessment of gender differences in schizophrenia, 85 outpatients (53 men and 32 women) with schizophrenia were evaluated for illness history, symptom severity, IQ, neurocognitive status, cerebral volume loss, and cortical asymmetry. Social functioning was assessed using marital status, independent living skills, and employment status. Significant gender differences were found, as women were on lower doses of neuroleptic medications and more frequently met criteria for paranoid and disorganized subtypes of schizophrenia than men. Women also were better educated and more often married, living independently, and employed. No gender differences were found in present age, symptom severity, neurocognitive functioning, or clinical magnetic resonance imaging scan readings. Our findings suggest that women may experience less of the adverse interpersonal psychosocial consequences of schizophrenia than men, even when symptom and neurocognitive status is equivalent between groups. However, more extensive investigations are warranted to better understand the role of pathophysiological or social mechanisms in gender differences.

"Normal" personality correlates of sensorimotor, cognitive, and visuospatial gating

Specific psychiatric disorders are characterized by impaired selective inhibition or "gating" of responses to sensory or cognitive information. Less is known about gating differences among normal individuals. We tested carefully screened controls in measures of central inhibition: prepulse inhibition (PPI) of startle, the Stroop test, and negative priming (NP). Subjects were defined as "normal" or "psychosis prone," based on theoretically and empirically derived MMPI criteria. Performance on all measures by "psychosis-prone" individuals suggested reduced sensorimotor gating and/or increased cognitive or visual interference. Performance was most impaired in individuals scoring highest on the MMPI Goldberg Index, which was originally designed to distinguish "psychotic" from "neurotic" inpatients. Inhibition in Stroop and NP was correlated across all subjects, but PPI was not correlated with other measures. Gender differences were noted in PPI (male > female), but not Stroop or NP. Performance deteriorated with age in Stroop and NP, but not PPI. The results are discussed as they relate to psychophysical and neural correlates of normal personality dimensions.

Impaired prepulse inhibition of acoustic and tactile startle response in patients with Huntington's disease

The corpus striatum serves a critical function in inhibiting involuntary, intrusive movements. Striatal degeneration in Huntington's disease results in a loss of motor inhibition, manifested by abnormal involuntary choreiform movements. Sensorimotor inhibition, or "gating", can be measured in humans using the startle reflex: the startle reflex is normally inhibited when the startling stimulus is preceded 30-500 ms earlier by a weak prepulse. In the present study, prepulse inhibition (PPI) was measured in patients with Huntington's disease to quantify and characterise sensorimotor gating. Compared with age matched controls, patients with Huntington's disease exhibit less PPI. Startle gating deficits are evident in patients with Huntington's disease when startle is elicited by either acoustic or tactile stimuli. Even with stimuli that elicit maximal PPI in normal subjects, patients with Huntington's disease exhibit little or no PPI, and their pattern of startle gating does not show the normal modulatory effects usually elicited by changing the prepulse interval or intensity. Startle amplitude and habituation and latency facilitation are largely intact in these patients, although reflex latency is significantly slowed. In patients with Huntington's disease, startle reflex slowing correlates with cognitive impairment measured by the dementia rating scale, and with the performance disruptive effects of interference measured by the Stroop test. These findings document a profound disruption of sensorimotor gating in patients with Huntington's disease and are consistent with preclinical findings that identify the striatum and striatopallidal GABAergic efferent circuitry as critical substrates for sensorimotor gating of the startle reflex.

The assessment of sequential response organization in schizophrenic and control subjects

1. A novel analysis is introduced for the sequential organization of behavioral elements derived from the ergodic theory of nonlinear dynamical systems and statistical mechanics of physical systems. 2. This analysis yields the fluctuation spectrum of local dynamical entropies, S (h), which quantifies the contributions of subsequences with different degrees of association between elements to the overall observed behavior. In addition, q-dependent order parameter functions assess the relationship between the degree of association between consecutive behavioral elements and qualitative aspects of the subsequences. 3. A binary choice task paradigm is used to extract thought-contingent responses in order to determine the organization of sequences of behavioral actions. 4. A group a schizophrenic patients and controls was tested with a binary choice task paradigm to determine the sequential organization of their responses. 5. The results indicate that the overall response sequences of both schizophrenics and controls are non-random. In addition, clear differences in qualitative aspects between response subsequences with different degrees of association are revealed. Finally, significant fluctuations within individual subjects were found between highly predictable and highly unpredictable response subsequences. 6. These results are discussed with respect to dysregulations in behavioral organization that could not be assessed previously and may provide new insights into the behavioral effects of the underlying dysregulated neural circuitry.

Information-processing deficits and thought disorder in schizophrenia

OBJECTIVE

The goal of this investigation was to study the relationship between information-processing deficits and thought disorder in schizophrenic patients.

METHOD

Fifty-two subjects diagnosed with schizophrenia were administered tests of information processing and thought disorder. The information-processing tests included visual backward masking and prepulse inhibition of the startle reflex. Thought disorder was measured with the Magical Ideation Scale, the Scale for the Assessment of Positive Symptoms, the alogia subscale of the Scale for the Assessment of Negative Symptoms, and the Ego Impairment Index-human experience variable and its subcomponents derived from the Rorschach.

RESULTS

Elevated poor responses on the Ego Impairment Index-human experience variable were significantly correlated with information-processing deficits. In a simultaneous multiple regression, the auditory prepulse inhibition measure was the best predictor of poor responses on the Ego Impairment Index-human experience variable.

CONCLUSIONS

The results suggest a correlative relationship between information-processing deficits and thought disorder. The relationship is most apparent when highly sensitive measures of both information processing and thought disorder are used. Furthermore, the prediction of poor responses on the Ego Impairment Index-human experience variable by auditory prepulse inhibition is important, since the neural circuitry of prepulse inhibition is known and involves the modulatory influences of the cortical-striatal-pallidal-thalamic circuit. These findings lend support to the hypothesis that information-processing failures are associated with cognitive fragmentation and thought disorder. More speculatively, these results allow us to hypothesize that impairments in part of the cortical-striatal-pallidal-thalamic circuit may lead to thought disorder, as well as prepulse inhibition deficits.

Assessing the validity of an animal model of deficient sensorimotor gating in schizophrenic patients

Psychiatric researchers need specific animal models to better understand the neurobiology of schizophrenia. Prepulse inhibition (PPI), the reduction in startle produced by a prepulse stimulus, is diminished in schizophrenic patients. Theoretically, deficient PPI in schizophrenic patients reflects a loss of sensorimotor gating that may lead to sensory flooding and cognitive fragmentation. In rats, PPI is disrupted by systemic administration of dopamine agonists or by manipulations of neural circuitry linking the limbic cortex, striatum, pallidum, and pontine reticular formation. This loss of PPI in rats may be a useful model for studying the neurobiology of impaired sensorimotor gating in schizophrenic patients. We assessed the face, predictive, and construct validity of this animal model. Face validity was supported: stimulus manipulations produced parallel changes in PPI in humans and rats, and the dopamine agonist apomorphine disrupted PPI in rats, mimicking PPI deficits in schizophrenics. Predictive validity was supported: the ability of antipsychotics to restore PPI in apomorphine-treated rats correlated with clinical antipsychotic potency (rs = .991) and D2-receptor affinity (rs = .893). Antipsychotics that restore PPI in apomorphine-treated rats include "typical" antipsychotics and the "atypical" antipsychotic clozapine. Construct validity was supported: PPI was disrupted in rats when dopamine was infused into the nucleus accumbens; this effect was blocked by haloperidol. The loss of PPI in dopamine-activated rats may be a valid animal model of sensorimotor gating deficits in schizophrenic patients. This model may help us understand the neurobiology of cognitive deficits in schizophrenic patients.

Impaired startle prepulse inhibition and habituation in patients with schizotypal personality disorder

OBJECTIVE

Information processing measures that serve as biological markers for schizophrenia can help to define the boundaries of schizophrenia. Prepulse inhibition and habituation of the blink reflex component of startle, which are thought to reflect an individual's ability to screen out or "gate" irrelevant sensory stimuli, are impaired in patients with schizophrenia. These deficits in sensorimotor gating and habituation in schizophrenic patients may lead to sensory overload and, secondarily, cognitive fragmentation, disorganization, and thought disorder. The goal of this study was to test two hypotheses: 1) patients with schizotypal personality disorder would show a loss of sensorimotor gating reflected by impaired prepulse inhibition of the human startle response and 2) patients with schizotypal personality disorder would show deficits in startle habituation consistent with the deficits seen in patients with schizophrenia.

METHOD

Prepulse inhibition and habituation were assessed in 12 men and four women who met DSM-III-R criteria for schizotypal personality disorder and in 22 normal comparison subjects.

RESULTS

Patients with schizotypal personality disorder had deficits in acoustic prepulse inhibition and habituation similar to the deficits observed in patients with schizophrenia. Although there were no differences between patients with schizotypal personality disorder and normal subjects in latency from acoustic startle stimuli to response, latency facilitation was produced by the prepulse in both groups.

CONCLUSIONS

This pattern of changes in amplitude and latency of the startle response suggests that subjects with schizotypal personality disorder perceive the prepulse stimuli but still demonstrate deficient sensorimotor gating of amplitude. These findings support the importance of startle prepulse inhibition and startle habituation as biological markers for schizophrenia spectrum disorders.

The abnormality of normal comparison groups: the identification of psychosis proneness and substance abuse in putatively normal research subjects

OBJECTIVE

Careful assessment of research subjects is important because the inclusion of subjects who manifest psychopathology and significant substance abuse in normal comparison groups will decrease statistical and experimental power. The current study evaluated the usefulness of an MMPI-derived algorithm in identifying tendencies toward psychosis and substance abuse in putatively normal research volunteers.

METHOD

Ninety-eight adults who were recruited as normal comparison research subjects completed the MMPI, psychiatric interviews, questionnaires, and selected neuropsychological tests. The MMPI classified 81 presumed normal subjects into four subgroups: 1) not psychosis prone/substance abuse not likely, 2) not psychosis prone/substance abuse likely, 3) psychosis prone/substance abuse not likely, and 4) psychosis prone/substance abuse likely.

RESULTS

The MMPI psychosis-prone and substance abuse factors identified significantly distressed and dysfunctional individuals with a relatively high degree of accuracy.

CONCLUSIONS

It is becoming increasingly apparent that the cursory self-report screening of normal subjects may result in unacceptable levels of psychopathology in comparison groups. The current results also indicate that an adequate substance abuse evaluation is extremely important and that brief self-report information may be misleading. Empirically derived assessment tools, such as the MMPI, may prove useful in allowing researchers to more accurately define control parameters and group membership.

Men are more inhibited than women by weak prepulses

The acoustic startle reflex is normally inhibited when the startling stimulus is preceded by a weak prepulse. We studied "prepulse inhibition" (PPI) to assess potential gender differences in this operational measure of sensorimotor gating. A review of data from our previously published studies in psychiatric patients and normal controls indicated that startle in women was less inhibited by weak prepulses than was startle in men, and that this gender difference narrowed when stronger prepulses were used to elicit maximal levels of PPI. Based on these observations, new subjects were selected for study using our established criteria to exclude individuals with psychiatric disorders, substance abuse, or serious neurologic or medical illness. Replicating our preliminary observation, women exhibited significantly less PPI than men, with the gender difference being most notable under conditions with weak prepulses. Potentially confounding variables, including electrode impedance, startle amplitude, habituation and latency did not differ between men and women. PPI was then measured in male and female rats, where no gender differences were noted. These findings identify significant gender differences in PPI in humans, and suggest that inhibitory "gating" processes are more robust in men than in women, when assessed using a sensitive range of inhibitory stimuli.

Sensory gating and inhibitory function in late-life schizophrenia

Although similarities between the cognitive deficits observed in schizophrenia and those observed in aging have been recognized for over 50 years, little work has been done to directly examine these similarities or their implications for late-life schizophrenia. We review studies of prepulse inhibition, habituation, latent inhibition, and negative priming that indicate marked similarities in the patterns of deficits observed in schizophrenia and in aging. We also present new data from preliminary studies of prepulse inhibition and negative priming in which we compare young normal controls, older adult normal controls, and late-life schizophrenia patients. For both measures, both schizophrenia patients and older adults showed an inhibitory deficit relative to young controls. In the case of negative priming, older schizophrenia patients showed evidence of greater inhibitory dysfunction than did normal older adults, suggesting that older schizophrenia patients suffer a deficit resulting from the combined effects of schizophrenia and aging. The implications of these results and directions for future research are discussed.

Information processing and attention dysfunctions in schizophrenia

Abnormalities of information processing have played a central role in understanding schizophrenia since the time of Kraepelin and Bleuler. Clearly, schizophrenia spectrum patients have profound problems focusing attention on salient cues and overcoming the disrupting effects of distracting stimuli. Theoretically, such patients are rendered vulnerable to stimulus inundation, cognitive fragmentation, and thought disorder induced by this inability to adequately process self-generated cognitive cues and stimuli from the complex world that surrounds us. Adding to the strength of such theories, investigators have made considerable progress in clarifying the functional significance and neurobiological basis of information-processing/attentional dysfunctions. This article focuses on our understanding of information-processing/attentional dysfunctions in schizophrenia. The relevant material will be presented in four parts: (1) an overview; (2) a review of specific, conceptual issues in information-processing research of the group of schizophrenias, including the roles of antipsychotic medications and generalized versus specific deficits; (3) a review of 10 common techniques used to tap the information processing and attention dysfunctions of schizophrenia patients; recent advances and novel applications of these techniques in "boundary" populations such as high-risk children and schizotypal patients are discussed and psychopharmacological probes, animal models, and basic strategies are also reviewed; and (4) an integration and suggestions for future directions in information-processing/attention research in schizophrenia. Overall, information-processing research provides an important viewpoint from which we can understand the group of schizophrenias.

Negative symptomatology in schizophrenic outpatients

This study examines the prevalence of negative symptoms, and assesses the convergence of negative and depressive symptoms in 60 chronically ill schizophrenic outpatients. Negative symptoms were assessed with the Scale for the Assessment of Negative Symptoms and the negative symptom cluster of the Brief Psychiatric Rating Scale (BPRS). Depressive symptoms were assessed with the depression subscale of the Brief Symptom Inventory and the depressive symptom cluster of the BPRS. A majority of patients in this group of relatively stable, schizophrenic outpatients demonstrated mild to moderate degrees of both negative and depressive symptoms. Correlations were not significant between negative symptom and depressive symptom measures, which suggests that the symptom constructs are relatively independent. Comparisons between a subgroup with prominent negative symptoms (N = 18) and a subgroup with minimal negative symptoms (N = 32) also revealed no significant group differences in variables that characterize clinical course (i.e., age of onset and frequency and duration of hospitalization) or in the severity of depressive symptoms. This lack of any significant differences on the clinical course variables may be partially explained by the heterogeneity of negative symptoms. The constellation of negative symptoms may differ not only in etiology but also in their temporal relationships to other aspects of the patient's clinical course. Longitudinal studies will be needed to track the long-term outcome of negative and depressive symptoms.

Wisconsin Card Sorting Test deficits in chronic paranoid schizophrenia. Evidence for a relatively discrete subgroup?

Some, although not all, researchers have reported dramatically increased numbers of perseverative responses on the Wisconsin Card Sorting Test (WCST) in schizophrenic patients compared to normal comparison subjects. The current study was designed to further explore the nature of possible WCST deficits in a group of paranoid schizophrenic patients compared to normal and psychiatric comparison subjects. In the current study, schizophrenic patients had significantly greater numbers of perserverative responses on the WCST than the comparison groups. The sample of patients with schizophrenia appeared to be characterized by a non-Gaussian distribution of perseverative responses on the WCST. WCST-impaired and WCST-nonimpaired schizophrenic subgroups were compared on cognitive and symptom measures, and increased perseverative responding was associated with negative symptoms, slowed reaction time, and more hospitalizations. While additional research is necessary to further investigate hypotheses of frontal versus generalized brain dysfunction in schizophrenic patients, WCST impairment seems to be present in a clinically meaningful subgroup of paranoid schizophrenic patients.

Sensory gating deficits in schizophrenia: new results

OBJECTIVE

It has been widely hypothesized that sensory gating failures and sensory overload occur in schizophrenic patients compared to normal subjects. The authors of this study sought to confirm and extend results of earlier studies that showed specific sensory gating deficits in schizophrenic patients.

METHOD

Age- and sex-matched schizophrenic patients (N = 20) and normal subjects (N = 20) were tested using electrophysiologically recorded P50 event-related potentials to assess the overall competence of the subjects' central sensory inhibitory capacity by measuring sensory filtering or gating. P50 area responses to two 75-dB (conditioning and test) click stimuli of 0.04-msec duration, averaged over 60 trials, were recorded for each subject. Normally, the first (conditioning) click stimulus induces gating mechanisms that result in diminished or gated P50 event-related potentials in response to the second click stimulus.

RESULTS

The schizophrenic subjects manifested a significant sensory gating deficit at frontal, central, and parietal electrode placement sites, with a nonsignificant tendency for the deficit to be most prominent in the frontal areas of the brain.

CONCLUSIONS

These data reflect a regionally diffuse loss of normal sensory gating in schizophrenic patients.

Gating and habituation of the startle reflex in schizophrenic patients

Schizophrenic patients exhibit impairments in both sensorimotor gating and habituation in a number of paradigms. Through human and animal model research, these fundamental cognitive deficits have well-described neurobiologic bases and offer insights into the neuroanatomic and neurotransmitter abnormalities that characterize patients with schizophrenic spectrum disorders. In this context, the startle response is particularly interesting, because it is a cross-species response to strong stimuli that is plastic or alterable using experimental and neurobiologic manipulations. Thirty-nine medicated schizophrenic patients and 37 normal control subjects were studied in a new electromyography based startle response paradigm in which both prepulse inhibition (an operational measure of sensorimotor gating) and habituation (the normal decrease in response magnitude to repeated stimuli over time) can be separated and assessed in one test session. The results indicate that schizophrenic patients have extensive deficits in both intramodal and cross-modal sensorimotor gating and a trend to show acoustic startle habituation deficits. The deficit in prepulse inhibition of startle amplitude exhibited by schizophrenic patients was evident when an acoustic prepulse stimulus preceded either an acoustic or a tactile startle stimulus. No deficit was observed in the prepulse-induced facilitation of startle latencies, indicating that the failure of gating was not due to a failure of stimulus detection. These findings suggest centrally mediated deficits in sensorimotor gating in schizophrenic patients.

The neural substrates of sensorimotor gating of the startle reflex: a review of recent findings and their implications

The startle reflex is a contraction of the skeletal and facial musculature in response to an intense sensory stimulus. While the 'primary' neural control of startle involves brain structures at, or below, the level of the mesencephalon, the startle reflex (SR) exhibits several forms of plasticity that are modulated by the forebrain. Sensorimotor gating of the SR occurs when the reflex is inhibited by a weak 'pre-pulse' that occurs 30-500 ms prior to the startling stimulus. Since 'pre-pulse inhibition' (PPI) of startle may be impaired in certain psychiatric and neurologic disorders (e.g. schizophrenia, schizotypal personality disorder and Huntington's disease), there has been considerable interest in determining the neural substrates of this form of startle plasticity. In rats, PPI is modulated by neural elements linking the limbic cortex with the striatum and pallidum. These substrates may include hippocampal glutamate efferents to the ventral striatum and striatal GABAergic efferents to the ventral pallidum. The striatal dopaminergic modulation of PPI appears to involve primarily D2, but not D1, receptors. Pallidal efferents may impinge directly on the 'primary' startle circuitry via projections to the mesencephalon or, indirectly, via projections to the thalamus. Evidence is reviewed for other neurochemical substrates of PPI-including acetylcholine and opiates. Sensorimotor gating of the startle reflex appears to have a discrete and identifiable set of neural substrates that may be important for our understanding of neuropsychiatric disorders characterized by deficient suppression or 'gating' of sensory, cognitive or motor processes.

Reply to cognitive therapy and schizophrenia

These interesting articles on cognitive deficits and rehabilitation in schizophrenic patients stimulate many questions, two of which are discussed in this reply. First, it seems likely that skepticism regarding the utilization and efficacy of cognitive rehabilitation strategies is born of despair that these treatments will ever be funded and delivered. This unfortunate state of affairs can only be corrected by effective social and political lobbying for adequate funding for mental health care. Second, the traditional tension between allocation and stage models of attention/information-processing deficits in schizophrenic patients may now be resolved by emerging theories that creatively integrate elements of stage and allocation theories. As we test these integrated theories, old "distinctions" seem to disappear and a clearer picture of information-processing dysfunctions in schizophrenic patients is emerging.

Magnetic resonance imaging abnormalities in lenticular nuclei and cerebral cortex in schizophrenia

Neuropathologic and brain imaging studies have produced evidence of brain abnormalities in schizophrenic patients, often within the cerebrum's limbic lobe, and, less frequently, within basal ganglia. In the present study we used magnetic resonance imaging morphometric techniques to estimate volumes of specific cerebral structures in schizophrenic patients and age- and sex-matched normal controls. Estimates of the volume of mesial temporal lobe structures were reduced and estimates of the volume of the lenticular nucleus were increased in the schizophrenic patients. There was also evidence of reduced cranial volume in some schizophrenics. The magnitude of the lenticular abnormality, but not the temporal lobe abnormality, was associated with age at first psychiatric contact; earlier onset was associated with larger lenticular nuclei. The possible relevance of these results to neurodevelopmental hypotheses about the pathogenesis of schizophrenia is discussed.

The generalized pattern of neuropsychological deficits in outpatients with chronic schizophrenia with heterogeneous Wisconsin Card Sorting Test results

Forty schizophrenic outpatients and 40 normal subjects were assessed using extensive clinical (eg, Brief Psychiatric Rating Scale, Scale for the Assessment of Negative Symptoms and Scale for the Assessment of Positive Symptoms) and neuropsychological (extended Halstead-Reitan Battery) measures. The schizophrenic patients had multiple neuropsychological deficits on tests of complex conceptual reasoning, psychomotor speed, new learning and incidental memory, and both motor and sensory-perceptual abilities. Neuropsychological impairment correlated more strongly with negative than positive symptoms. Overall, the schizophrenic outpatients showed relatively modest increases in the number of perseverative responses on the Wisconsin Card Sorting Test of abstraction flexibility. A subgroup of these schizophrenic patients seemed to be particularly impaired on the Wisconsin Card Sorting Test. This pattern of results, in conjunction with previous studies, supports the idea that, while some schizophrenic patients may have fixed, frontally based dysfunctions, these dysfunctions may be most prominent, and even fixed, in deteriorated, kraepelinian patients. These data provide evidence for diffuse and far-reaching deficits in a majority of outpatients with chronic schizophrenia.

Middle latency auditory evoked potentials (MAEPs) in chronic schizophrenics

Middle latency auditory evoked potentials were recorded in medicated chronic schizophrenics and controls at stimulation rates of 10/s, 2/s, and 1/s. Increasing the stimulation rate did not change Pa amplitude but decreased Pb amplitude. There was no difference between the two groups.