Regional cerebral blood flow during the Wisconsin Card Sorting Test in normal subjects studied by xenon-133 dynamic SPECT: comparison of absolute values, percent distribution values, and covariance analysis

Genetic Influences on Cognitive Dysfunction in Schizophrenia

Schizophrenia is a severe and debilitating psychotic disorder that is highly heritable and relatively common in the population. The clinical heterogeneity associated with schizophrenia is substantial, with patients exhibiting a broad range of deficits and symptom severity. Large-scale genomic studies employing a case-control design have begun to provide some biological insight. However, this strategy combines individuals with clinically diverse symptoms and ignores the genetic risk that is carried by many clinically unaffected individuals. Consequently, the majority of the genetic architecture underlying schizophrenia remains unexplained, and the pathways by which the implicated variants contribute to the clinically observable signs and symptoms are still largely unknown. Parsing the complex, clinical phenotype of schizophrenia into biologically relevant components may have utility in research aimed at understanding the genetic basis of liability. Cognitive dysfunction is a hallmark symptom of schizophrenia that is associated with impaired quality of life and poor functional outcome. Here, we examine the value of quantitative measures of cognitive dysfunction to objectively target the underlying neurobiological pathways and identify genetic variants and gene networks contributing to schizophrenia risk. For a complex disorder, quantitative measures are also more efficient than diagnosis, allowing for the identification of associated genetic variants with fewer subjects. Such a strategy supplements traditional analyses of schizophrenia diagnosis, providing the necessary biological insight to help translate genetic findings into actionable treatment targets. Understanding the genetic basis of cognitive dysfunction in schizophrenia may thus facilitate the development of novel pharmacological and procognitive interventions to improve real-world functioning.

The Legacy of the TTASAAN Report-Premature Conclusions and Forgotten Promises: A Review of Policy and Practice Part I

Brain perfusion single photon emission computed tomography (SPECT) scans were initially developed in 1970's. A key radiopharmaceutical, hexamethylpropyleneamine oxime (HMPAO), was originally approved in 1988, but was unstable. As a result, the quality of SPECT images varied greatly based on technique until 1993, when a method of stabilizing HMPAO was developed. In addition, most SPECT perfusion studies pre-1996 were performed on single-head gamma cameras. In 1996, the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology (TTASAAN) issued a report regarding the use of SPECT in the evaluation of neurological disorders. Although the TTASAAN report was published in January 1996, it was approved for publication in October 1994. Consequently, the reported brain SPECT studies relied upon to derive the conclusions of the TTASAAN report largely pre-date the introduction of stabilized HMPAO. While only 12% of the studies on traumatic brain injury (TBI) in the TTASAAN report utilized stable tracers and multi-head cameras, 69 subsequent studies with more than 23,000 subjects describe the utility of perfusion SPECT scans in the evaluation of TBI. Similarly, dementia SPECT imaging has improved. Modern SPECT utilizing multi-headed gamma cameras and quantitative analysis has a sensitivity of 86% and a specificity of 89% for the diagnosis of mild to moderate Alzheimer's disease-comparable to fluorodeoxyglucose positron emission tomography. Advances also have occurred in seizure neuroimaging. Lastly, developments in SPECT imaging of neurotoxicity and neuropsychiatric disorders have been striking. At the 25-year anniversary of the publication of the TTASAAN report, it is time to re-examine the utility of perfusion SPECT brain imaging. Herein, we review studies cited by the TTASAAN report vs. current brain SPECT imaging research literature for the major indications addressed in the report, as well as for emerging indications. In Part II, we elaborate technical aspects of SPECT neuroimaging and discuss scan interpretation for the clinician.

Neurocomputational Nosology: Malfunctions of Models and Mechanisms

Executive dysfunctions, psychopathologies arising from problems in the control and regulation of behavior, can occur as a result of the faulty execution of formal information processing models or as a result of malfunctioning neural mechanisms. The models correspond to the formal descriptions of how signals in the environment must be transformed in order to behave adaptively, and the mechanisms correspond to the signal transformations that nervous systems implement in order to execute those cognitive functions. Mechanisms in the form of repeated patterns of neural dynamics execute information processing models. Two distinct modes of malfunction can occur when neural dynamics execute models of information processing. The processing models describing behavior may fail to be executed correctly by neural mechanisms. Or, the neural mechanisms may malfunction, failing to implement the right computation. As an example of malfunctioning models in executive cognition, purported failures of rule following can be understood as failures to appropriately execute a suite of processing models. As an example of malfunctioning mechanisms of executive cognition, maladaptive behavior resulting from dysfunction in the medial prefrontal cortex (mPFC) can be understood as failures in the signal transformations carried out therein. The purpose of these examples is to illustrate the potential benefits of considering models and mechanisms in the diagnosis and etiology of neuropsychological illness and dysfunction, especially disorders of executive cognition.

Neuroimaging predictors of cognitive performance across a standardized neurocognitive battery

OBJECTIVE

The advent of functional MRI (fMRI) enables the identification of brain regions recruited for specific behavioral tasks. Most fMRI studies focus on group effects in single tasks, which limits applicability where assessment of individual differences and multiple brain systems is needed.

METHOD

We demonstrate the feasibility of concurrently measuring fMRI activation patterns and performance on a computerized neurocognitive battery (CNB) in 212 healthy individuals at 2 sites. Cross-validated sparse regression of regional brain amplitude and extent of activation were used to predict concurrent performance on 6 neurocognitive tasks: abstraction/mental flexibility, attention, emotion processing, and verbal, face, and spatial memory.

RESULTS

Brain activation was task responsive and domain specific, as reported in previous single-task studies. Prediction of performance was robust for most tasks, particularly for abstraction/mental flexibility and visuospatial memory.

CONCLUSIONS

The feasibility of administering a comprehensive neuropsychological battery in the scanner was established, and task-specific brain activation patterns improved prediction beyond demographic information. This benchmark index of performance-associated brain activation can be applied to link brain activation with neurocognitive performance during standardized testing. This first step in standardizing a neurocognitive battery for use in fMRI may enable quantitative assessment of patients with brain disorders across multiple cognitive domains. Such data may facilitate identification of neural dysfunction associated with poor performance, allow for identification of individuals at risk for brain disorders, and help guide early intervention and rehabilitation of neurocognitive deficits.

Frontal cerebral blood flow changes after hormone replacement therapy in depressed postmenopausal women

We investigated the effects of hormone replacement therapy (HRT) on frontal cerebral blood flow (CBF), depressive symptoms, and cognitive function in depressed postmenopausal women. Fourteen postmenopausal women with depressive symptoms underwent HRT, and seven controls not undergoing HRT were studied. We evaluated frontal CBF, expressed as frontal/cerebellum (F/C) ratio, using Tc-99m hexamethyl propylene amine oxime single photon emission computed tomography (Tc-99m HMPAO SPECT), cognitive function using the Mini-Mental Status Examination (MMSE), and depression using the HAD (Hospital Anxiety and Depression) scale. All studies were carried out at initial status and after 9 months. Single photon emission computed tomography was performed at rest and at activation during the Wisconsin Card Sorting Test (WCST). Initial frontal CBF was not different between groups. After 9 months, resting frontal CBF was similar between groups. However, activated frontal CBF was significantly higher in the HRT group than in controls (F/C ratio: 0.924+/-0.04 versus 0.853+/-0.05, P=0.007). Furthermore, the increase in the activated F/C ratio was inversely associated with years since menopause. Mini-Mental Status Examination scores improved after HRT, but depression scores did not. Hormone replacement therapy improved frontal CBF and cognitive function but not depression in postmenopausal women. The changes in frontal CBF were detected only during WCST activation and were most apparent during early postmenopausal years.

A cognitive neuroscience-based computerized battery for efficient measurement of individual differences: standardization and initial construct validation

There is increased need for efficient computerized methods to collect reliable data on a range of cognitive domains that can be linked to specific brain systems. Such need arises in functional neuroimaging studies, where individual differences in cognitive performance are variables of interest or serve as confounds. In genetic studies of complex behavior, which require particularly large samples, such trait measures can serve as endophenotypes. Traditional neuropsychological tests, based on clinical pathological correlations, are protracted, require extensive training in administration and scoring, and leave lengthy paper trails (double-entry for analysis). We present a computerized battery that takes an average of 1h and provides measures of accuracy and speed on 9 neurocognitive domains. They are cognitive neuroscience-based in that they have been linked experimentally to specific brain systems with functional neuroimaging studies. We describe the process of translating tasks used in functional neuroimaging to tests for assessing individual differences. Data are presented on each test with samples ranging from 139 (81 female) to 536 (311 female) of carefully screened healthy individuals ranging in age from 18 to 84. Item consistency was established with acceptable to high Cronbach alpha coefficients. Inter-item correlations were moderate to high within domain and low to nil across domains, indicating construct validity. Initial criterion validity was demonstrated by sensitivity to sex differences and the effects of age, education and parental education. These results encourage the use of this battery in studies needing an efficient assessment of major neurocognitive domains such as multi-site genetic studies and clinical trials.

Risk/reward decision-making in schizophrenia: a preliminary examination of the influence of tobacco smoking and relationship to Wisconsin Card Sorting Task performance

BACKGROUND

Individuals with schizophrenia show deficits in cognitive functioning, as evidenced by deficits on neurocognitive tasks such as the Wisconsin Card Sorting Task (WCST). Studies of risk/reward decision-making in individuals with schizophrenia have yielded mixed results, and few studies have examined systematically the relationship between these domains and their relationship with clinical factors.

METHOD

Thirty-two smokers with schizophrenia, ten non-smokers with schizophrenia, nine non-psychiatric non-smokers and ten non-psychiatric smokers were administered computerized versions of the Iowa Gambling Task (IGT) and the WCST. Smokers were allowed to smoke adlibitum during designated breaks in order to prevent deprivation.

RESULTS

Subjects with schizophrenia performed significantly worse than non-psychiatric controls on both the IGT and the WCST, and performance on these tasks was significantly correlated across subject groups. Among women with schizophrenia, smokers performed significantly better than non-smokers on the IGT.

CONCLUSIONS

Individuals with schizophrenia perform worse than controls on the IGT, suggesting impairments in risk/reward decision-making. Correlations between IGT and WCST performance suggest a shared element underlying task performance, such as a deficit in set-shifting or perseverance. Further research is needed to establish the relationship between cigarette smoking and IGT performance in schizophrenia.

The Wisconsin Card Sorting Test and the cognitive assessment of prefrontal executive functions: a critical update

For over four decades the Wisconsin Card Sorting Test (WCST) has been one of the most distinctive tests of prefrontal function. Clinical research and recent brain imaging have brought into question the validity and specificity of this test as a marker of frontal dysfunction. Clinical studies with neurological patients have confirmed that, in its traditional form, the WCST fails to discriminate between frontal and non-frontal lesions. In addition, functional brain imaging studies show rapid and widespread activation across frontal and non-frontal brain regions during WCST performance. These studies suggest that the concept of an anatomically pure test of prefrontal function is not only empirically unattainable, but also theoretically inaccurate. The aim of the present review is to examine the causes of these criticisms and to resolve them by incorporating new methodological and conceptual advances in order to improve the construct validity of WCST scores and their relationship to prefrontal executive functions. We conclude that these objectives can be achieved by drawing on theory-guided experimental design, and on precise spatial and temporal sampling of brain activity, and then exemplify this using an integrative model of prefrontal function [i.e., Miller, E. K. (2000). The prefrontal cortex and cognitive control. Nature Reviews Neuroscience, 1, 59-65.] combined with the formal information theoretical approach to cognitive control [Koechlin, E., & Summerfield, C. (2007). An information theoretical approach to prefrontal executive function. Trends in Cognitive Sciences, 11, 229-235.].

Functional magnetic resonance imaging assessment of cognitive function in childhood-onset systemic lupus erythematosus: a pilot study

OBJECTIVE

To investigate changes in brain activation patterns detected by functional magnetic resonance imaging (FMRI), and the relationship between FMRI activation patterns and results of formal neuropsychological testing, in patients with childhood-onset systemic lupus erythematosus (SLE).

METHODS

Ten patients with childhood-onset SLE underwent formal neuropsychological testing and FMRI using 3 paradigms: a continuous performance task (CPT) to evaluate attention, an N-Back task to assess working memory, and verb generation to evaluate language processing. Composite Z maps were generated to summarize the brain activation patterns for each FMRI paradigm in patients with childhood-onset SLE and to compare these patterns with those observed in healthy controls. Between-group comparison Z maps showing differences in activation between childhood-onset SLE patients and controls were generated, using a significance level of P < 0.05 in a general linear model.

RESULTS

Compared with the control group, the childhood-onset SLE group showed statistically significant increased activation of brain areas involved in the CPT, N-Back, and verb generation tasks. In contrast, in the absence of active stimulus, e.g., during times of the paradigm control tasks, childhood-onset SLE patients consistently undersuppressed activity in the expected brain areas. Activation in selected cortical areas was found to correlate negatively with results of a subset of individual neuropsychological test scores.

CONCLUSION

FMRI abnormalities are present in childhood-onset SLE, manifesting as an imbalance between active and inhibitory responses to an array of stimuli. Differences in brain activation patterns compared with those observed in controls suggest that childhood-onset SLE may be associated with abnormalities in white matter connectivity resulting in neuronal network dysfunction, rather than injury of specific gray matter areas.

Neurobiological underpinnings of insight deficits in schizophrenia

Impaired insight into illness is commonly observed across various psychiatric illnesses, but is most frequent in patients with schizophrenia. The clinical relevance and public health impact of poor insight is reflected by its close association with important clinical outcome measures, such as treatment non-adherence, lower psychosocial functioning, poor prognosis, involuntary hospitalization, and higher utilization of emergency services. Although the neurobiology of insight has not been determined, data from neurocognitive and a few structural imaging studies provide some understanding of the neurobiological underpinnings of insight function in schizophrenia. Using published and preliminary data, we propose a hypothetical model of insight that may help initiate neurobiological investigations in this complex area.

Right frontal event related EEG coherence (ERCoh) differentiates good from bad performers of the Wisconsin Card Sorting Test (WCST)

AIM

To investigate changes in Event-Related Coherence (ERCoh) associated to good and bad resolution of the Wisconsin Card Sorting Test (WCST).

METHODS

Event-Related Potentials (ERPs) were recorded from a sample of 30 university students while they performed a computerized version of the WCST. ERCoh was calculated for frontal and parietal electrodes for two specific moments: immediately before the response and after the feedback cues.

RESULTS

Bad performers presented significantly reduced ERCoh at the right frontal region (in alpha, beta-1 and beta-2 bands), while no consistent group differences emerged for parietal ERCoh. Furthermore, the strength of functional coupling (ERCoh) between midfrontal and right-frontal electrodes was a good predictor of WCST behavioural parameters, such as the percentage of perseverative errors or the number of categories achieved.

CONCLUSIONS

The results suggest that the right prefrontal cortex is specifically involved in executive functions, such as planning and foresight, tapped by the WCST. Although the specificity of the WCST to explore frontal lesions has been recently questioned, the present findings support that prefrontal areas are specifically involved in the successful resolution of the test by healthy subjects.

Comorbidity implications in brain disease: Neuronal substrates of symptom profiles

The neuronal substrates underlying aspects of comorbidity in brain disease states may be described over psychiatric and neurologic conditions that include affective disorders, cognitive disorders, schizophrenia, obsessive-compulsive disorder, substance abuse disorders as well as the neurodegenerative disorders. Regional and circuitry analyses of biogenic amine systems that are implicated in neural and behavioural pathologies are elucidated using neuroimaging, electrophysiological, neurochemical, neuropharmacological and neurobehavioural methods that present demonstrations of the neuropathological phenomena, such as behavioural sensitisation, cognitive impairments, maladaptive reactions to environmental stress and serious motor deficits. Considerations of neuronal alterations that may or may not be associated with behavioural abnormalities examine differentially the implications of discrete areas within brains that have been assigned functional significance; in the case of the frontal lobes, differential deficits of ventromedial and dorsolateral prefrontal cortex may be associated with different aspects of cognition, affect, remission or response to medication thereby imparting a varying aspect to any investigation of comorbidity.

Cortical blood flow during rest and Wisconsin Card Sorting Test performance in schizophrenia

BACKGROUND

The aim of this study is to examine if patients with schizophrenia differ in prefrontal, orbitofrontal, temporal, parietal and occipital blood flow from healthy controls during performance of the Wisconsin Card Sorting Test (WCST).

METHODS

We conducted a 99mTc-hexamethylpropylene amine oxime-SPECT study in patients with schizophrenia (n = 21) and in healthy controls (n = 18). The assessment of relative regional cerebral blood flow (relCBF) was achieved by comparing blood flow of well-defined cortical regions to whole brain blood flow. relCBF at rest and during WCST was compared between the groups and in the groups.

RESULTS

Significant bilateral prefrontal and right-sided parietal increases of relCBF were found in patients (p < 0.05) during resting conditions, while prefrontal and parietal interhemispheric asymetry were higher in patients (p < 0.005). However, patients failed to increase right prefrontal and frontobasal relCBF as well as orbitofrontal interhemispheric asymetry during WCST performance in contrast to the control group (p < 0.05). The right occipital relCBF increased significantly in patients only (p < 0.05).

CONCLUSIONS

In our study we could confirm the common hypothesis of schizophrenic hypofrontality at rest and during WCST performance. Moreover, due to our method, we identified significant frontal and parietal interhemispheric asymmetries in schizophrenia at rest as well as right occipital hyperperfusion during WCST.

Executive function and the frontal lobes: a meta-analytic review

Currently, there is debate among scholars regarding how to operationalize and measure executive functions. These functions generally are referred to as "supervisory" cognitive processes because they involve higher level organization and execution of complex thoughts and behavior. Although conceptualizations vary regarding what mental processes actually constitute the "executive function" construct, there has been a historical linkage of these "higher-level" processes with the frontal lobes. In fact, many investigators have used the term "frontal functions" synonymously with "executive functions" despite evidence that contradicts this synonymous usage. The current review provides a critical analysis of lesion and neuroimaging studies using three popular executive function measures (Wisconsin Card Sorting Test, Phonemic Verbal Fluency, and Stroop Color Word Interference Test) in order to examine the validity of the executive function construct in terms of its relation to activation and damage to the frontal lobes. Empirical lesion data are examined via meta-analysis procedures along with formula derivatives. Results reveal mixed evidence that does not support a one-to-one relationship between executive functions and frontal lobe activity. The paper concludes with a discussion of the implications of construing the validity of these neuropsychological tests in anatomical, rather than cognitive and behavioral, terms.

Insight and frontal cortical function in schizophrenia: a review

Insight into illness has been identified as a clinically important phenomenon, in no small part due to an association with treatment-adherence. An increasing number of studies, but not all, have observed poor insight to be a reflection of cognitive dysfunction in schizophrenia. A review of 34 published English-language studies found a significant number (i.e., 21) reporting a relationship between insight deficits and impaired performance on cognitive tasks primarily mediated by frontal cortex. A significant number of reviewed studies examined insight function in more than one psychiatric population, including bipolar and schizoaffective disorder. The most replicated findings from these studies were the correlations between insight deficits and impaired performance on the Wisconsin Card Sorting Test (WCST). More specifically, WCST perseverative errors correlated positively and the number of categories completed correlated negatively with poor insight, suggesting that impaired insight may be mediated by deficiencies in conceptual organization and flexibility in abstract thinking. Since the WCST requires the ability to demonstrate conceptual flexibility through the generation, maintenance and switching of mental sets along with the capacity to use verbal feedback to correct errors, it would appear that such 'executive' functions are most related to insight. In addition, recently identified structural correlates of poor insight in schizophrenia show some association with anosognosia in neurological patients. This review will discuss the implications of these findings and directions for future research.

Correlational study of the Chinese version of the executive interview (C-EXIT25) to other cognitive measures in a psychogeriatric population in Hong Kong Chinese

OBJECTIVES

This study is designed to pilot test the feasibility and correlational properties of the adapted Chinese version of Executive Interview (C-EXIT25) to other cognitive measures in a psychogeriatric population in Hong Kong Chinese.

METHOD

Eighty-five community dwelling elders from different levels of residential care facilities were assessed with C-EXIT25, Cantonese version of Mini-Mental State Examination (C-MMSE), Chinese version of Mattis Dementia Rating Scale (CDRS) and Nelson's Modified Card Sorting Test (MCST).

RESULTS

The C-EXIT25 has high internal consistency (Cronbach's alpha = 0.7995) and inter-rater reliability (r = 0.91). The C-EXIT25 has superior correlational property to performance indices of MCST than the C-MMSE and CDRS, after adjusting for age, gender and educational level. It also discriminates among subjects at different stages on Clinical Dementia Rating.

CONCLUSIONS

The C-EXIT25 is a potentially feasible and valid bedside tool for assessment of executive cognitive functions in the psychogeriatric population in Hong Kong Chinese.

The case for the development and use of "ecologically valid" measures of executive function in experimental and clinical neuropsychology

This article considers the scientific process whereby new and better clinical tests of executive function might be developed, and what form they might take. We argue that many of the traditional tests of executive function most commonly in use (e.g., the Wisconsin Card Sorting Test; Stroop) are adaptations of procedures that emerged almost coincidentally from conceptual and experimental frameworks far removed from those currently in favour, and that the prolongation of their use has been encouraged by a sustained period of concentration on "construct-driven" experimentation in neuropsychology. This resulted from the special theoretical demands made by the field of executive function, but was not a necessary consequence, and may not even have been a useful one. Whilst useful, these tests may not therefore be optimal for their purpose. We consider as an alternative approach a function-led development programme which in principle could yield tasks better suited to the concerns of the clinician because of the transparency afforded by increased "representativeness" and "generalisability." We further argue that the requirement of such a programme to represent the interaction between the individual and situational context might also provide useful constraints for purely experimental investigations. We provide an example of such a programme with reference to the Multiple Errands and Six Element tests.

The effect of neuroleptic treatments on executive function and symptomatology in schizophrenia: a 1-year follow up study

Cognitive dysfunctions (as in memory, attention and executive function) have been recognized as fundamental features of schizophrenia. Executive dysfunction is a major obstacle to functional outcome, community functioning and rehabilitation success and it is crucial to assess the effects of so-called neuroleptic (NLP) medications in this domain of cognitive functioning. Risperidone, an atypical NLP, has been reported to improve executive function in schizophrenia (SZ), but there is controversy regarding these findings. The aim of the current study was to assess the differential effects of risperidone (2-6 mg) and conventional (2-40 mg haloperidol) NLPs on executive skills in 31 individuals with SZ over a 12-month period. The performance of both NLP groups was compared to the performance of 17 age- and education-matched healthy controls. In this randomized, double blind study, the Wisconsin Card Sorting Test (WCST) was administered at baseline, 3, 6, and 12 months after initiating medication. The relationship between executive functioning and the course of clinical symptoms, as assessed by the Positive and Negative Syndrome Scale (PANSS) was also investigated. Results showed that, relative to healthy controls, individuals with SZ showed marked impairment in WCST from baseline through 12 months of treatment. Also, participants under haloperidol or risperidone NLP medication performed similarly on the WCST at all assessment periods showing that risperidone and haloperidol do not differ in their effect on executive functioning. Risperidone treatment, however, was more effective in the reduction of negative symptoms. The differential efficacy of risperidone over negative symptoms and WCST performance strongly suggests that the executive impairments are to some extent the result of brain abnormalities independent of those that produce the major psychopathology manifestations seen in SZ.

Multimodal assessment of cortical activation during apple peeling by NIRS and fMRI

An intriguing application of neuroimaging is directly measuring actual human brain activities during daily living. To this end, we investigated cortical activation patterns during apple peeling. We first conducted a pilot study to assess the activation pattern of the whole lateral cortical surface during apple peeling by multichannel near-infrared spectroscopy (NIRS) and detected substantial activation in the prefrontal region in addition to expected activations extending over the motor, premotor and supplementary motor areas. We next examined cortical activation during mock apple peeling by simultaneous measurement using multichannel NIRS and functional magnetic resonance imaging (fMRI) in four subjects. We detected activations extending over the motor, premotor and supplementary motor areas, but not in the prefrontal cortex. Thus, we finally focused on the prefrontal cortex and examined its activation during apple peeling in 12 subjects using a multichannel NIRS. We subsequently found that regional concentrations of oxygenated hemoglobin significantly increased in the measured region, which encompassed portions of the dorsolateral, ventrolateral and frontopolar areas of the prefrontal cortex. The current study demonstrated that apple peeling as practiced in daily life recruited the prefrontal cortex but that such activation might not be detected for less laborious mock apple peeling that can be performed in an fMRI environment. We suggest the importance of cortical study of an everyday task as it is but not as a simplified form; we also suggest the validity of NIRS for this purpose. Studies on everyday tasks may serve as stepping stone toward understanding human activities in terms of cortical activations.

Association between regional cerebral blood flow and eye-tracking performance and the Wisconsin Card Sorting Test in schizophrenics: a single photon emission computed tomography study

The objectives of this study were (1). to examine the changes in regional cerebral blood flow (rCBF) during Wisconsin Card Sorting Test (WCST) performance in two different eye-tracking groups; (2). to explore the relationship between eye-tracking movement and rCBF at rest; and (3). to estimate the association between WCST performance and rCBF in patients with schizophrenia. A total of 17 patients with schizophrenia were recruited. SPECT with Tc-99m HMPAO (Tc-99m hexamethylpropyleneamine oxime) was carried out while patients were performing the WCST and resting. Brodmann area 9 of the prefrontal cortex, a part of the dorsal lateral prefrontal cortex (DLPFC), was less activated during performance of the WCST in poor trackers (relative to good trackers). The eye pursuit tracking error measure in schizophrenic patients was negatively associated with decreases in rCBF in the middle temporal area, superior parietal lobule, thalami, and caudate nuclei. The rCBF increased significantly in the superior temporal gyri, inferior parietal lobe, and some frontal regions during WCST performance; however, this was not the case in the DLPFC. Additionally, significant correlations were found between WCST scores and rCBF during WCST performance in the prefrontal lobes, and in thalamic and cerebellar regions. Our findings suggest that the rCBF changes during WCST performance may be distinctive in different eye-tracking groups. Our results confirm the hypothesis that the middle temporal area, superior parietal lobule, thalami, and caudate nuclei-mainly parts of the oculomotor circuit-are involved in eye pursuit tracking. Surprisingly, no significant association was found in the frontal eye field. Although the frontal lobe plays a significant role in WCST performance, our findings demonstrate that WCST performance is widely involved with other regions in patients with schizophrenia.

The effect of melperone, an atypical antipsychotic drug, on cognitive function in schizophrenia

Melperone, a butyrophenone, has been shown to possess atypical antipsychotic properties, i.e. ability to produce an antipsychotic effect in man at doses that cause minimal extrapyramidal side effects. In addition, melperone shares the following with other atypical antipsychotic drugs: (1) effectiveness for ameliorating negative symptoms; (2) no prolactin elevation; and (3) effectiveness in the treatment of some patients with neuroleptic-resistant schizophrenia. Other atypical antipsychotic drugs have been reported to improve cognitive function. This study was performed to investigate the effect of melperone on cognitive function. Nineteen patients with schizophrenia or schizoaffective disorder, including 11 neuroleptic-resistant patients, were treated with melperone for 6 weeks. A comprehensive neurocognitive test battery and psychopathological ratings (Brief Psychiatric Rating Scale, BPRS) were administered at baseline and after 6 weeks of melperone treatment. Treatment with melperone was associated with improvement in executive function, as measured by the Wisconsin Card Sorting Test (WCST)-Categories and WCST-Percent Perseveration. On the other hand, visuospatial manipulation, as measured by the Wechsler Intelligent Scale for Children-Revised (WISC-R) Maze, worsened during melperone treatment. There were no significant changes in other domains of cognition, i.e. verbal learning and memory, verbal working memory, verbal fluency and sustained attention. Scores of WCST-Categories and Perseveration at 6 weeks were predicted from the relevant cognitive test scores at baseline and the change in BPRS Total and Positive scores. These results suggest the usefulness of melperone for facilitating work and social function in patients with schizophrenia. The differences in the cognition-enhancing abilities between melperone and clozapine are discussed.

The relationship between regional cerebral blood flow and the Wisconsin Card Sorting Test in negative schizophrenia

The purpose of this study was to explore the relationship between regional cerebral blood flow (rCBF) and problem-solving thinking in negative schizophrenia. Twenty-one negative schizophrenic patients and 12 normal controls were studied with single photon emission computed tomography (SPECT). Measures of regional cerebral blood flow (rCBF) were taken both at rest and during a prefrontal activation task using Wisconsin Card Sorting Test (WCST). Compared with controls, poor performances on the WCST of total trials category (TT), perseverative errors (PE) and non-perseverative errors (NE) were found in negative schizophrenic (P < 0.05). During WCST activation, patients showed interhemispheric differences in the prefrontal region, but under rest conditions, no such differences manifested. The negative schizophrenia group had a significantly lower rCBF change rate in profrontal lobe during stimulant WCST than those in normal controls (P < 0.05). The negative schizophrenic patient has executive function deficits and lower rCBF perfusion in left profrontal lobes, which suggest that the negative schizophrenic patient has dysfunction of the left profrontal region.

Age-related changes in regional activation during working memory in young adults: an fMRI study

Several lines of evidence suggest that working memory diminishes with advancing age, with concomitant functional changes in associated neuronal activation in frontal cortical regions and hippocampi. No studies to date, however, have investigated age-related changes in neuronal activation in these regions during performance of a working memory task in younger subjects without working memory deficits. In this study, we utilized fMRI to examine changes in brain activation with increasing age in specific regions-of-interest. Eleven healthy subjects performed a "two-back" working memory task and a matched "zero-back" attention task during fMRI. There was no association between age and performance on either task. Left hippocampal activation significantly correlated with age (P = 0.01) and right hippocampal activation showed an association with age (P = 0.09). This study demonstrates that increasing age is associated with increased activation of hippocampus even in young patients without evidence of working memory deficits and suggests that functional changes may precede overt evidence of working memory deficits.

Interhemispheric asymmetry of EEG alpha activity at rest and during the Wisconsin Card Sorting Test: relations with performance

There are conflicting results regarding the functional asymmetry of the prefrontal cortex. Spectral power analysis of electroencephalographic (EEG) activity can provide important clues about the cortical mechanisms. In this study, interhemispheric EEG alpha power asymmetry of healthy individuals was investigated during the execution of the Wisconsin Card Sorting Test (WCST) and during rest. We analyzed alpha-1 (8.6-10.2 Hz) and alpha-2 (10.9-12.5 Hz) bands separately and found some evidence to indicate that lower and upper alpha bands reflect different cortical processes. On the other hand, greater alpha power during resting correlated with higher performance on the WCST. The lower left frontal alpha power during WCST correlated significantly with the higher WCST performance. However, greater bilateral parietal alpha power during WCST correlated with higher performance. Significant correlations between EEG activity and WCST performance were, in general, restricted to lower alpha power, both at rest and during the task. These findings are discussed with regard to attention processes reflected by lower alpha activity.

Amygdala-hippocampal volume and verbal memory in first-degree relatives of schizophrenic patients

Verbal memory deficits have been related to reduced volume of medial temporal structures in several neurological and psychiatric populations, including schizophrenic patients. Impairments in verbal memory have been proposed to be a marker of risk for schizophrenia. Recently, relatives of schizophrenic patients have been reported to have reduced volume of the amygdala-hippocampal complex. In this study, we evaluate the possibility that amygdala-hippocampal volume reductions may constitute one neural substrate of verbal memory deficits in first-degree relatives. Subjects were 20 healthy first-degree relatives of schizophrenic patients and 14 demographically similar controls. Verbal memory was assessed with the Logical Memory Test. Subjects were scanned with high-resolution MRI and the images were transformed into Talairach space. Volumes of interest were amygdala-anterior hippocampus and posterior hippocampus. Relatives of schizophrenic patients had intact immediate verbal memory but significantly poorer delayed verbal memory than controls. Relatives also had significantly reduced amygdala-anterior hippocampus volumes. Across all subjects, delayed verbal memory was significantly correlated with amygdala-anterior hippocampus volume. The magnitude of the correlation did not differ between the groups. These data provide an empirical link between memory performance and volumetric abnormalities in the amygdala-hippocampal complex in the relatives of schizophrenic patients.

Does the Wisconsin Card Sorting Test measure prefontral function?

This review describes a research program aimed at evaluating the validity and specificity of the Wisconsin Card Sorting Test (WCST), one of the most widely used tests of prefrontal function in clinical and experimental neuropsychology. In spite of its extensive use, voices of caution have arisen against the use of WCST scores as direct markers of prefrontal damage or dysfunction. Adopting a cognitive neuroscience approach, the present research program integrates behavioral, physiological, and anatomical information to investigate the cognitive and neural mechanisms behind WCST performance. The results show that WCST performance evokes conspicuous physiological changes over frontal as well as posterior brain regions. Moreover, WCST scores confound very heterogeneous cognitive and neural processes. This confounding effect may have led many authors to overlook the relative importance of certain dysfunctional states such as those indexed by random errors. These findings strongly suggest that WCST scores cannot be regarded as valid nor specific markers of prefrontal lobe function. However, they do provide some relevant clues to update our current knowledge about prefrontal function. In the long run, the integrative approach of cognitive neuroscience may help us design and develop more valid and sensitive tools for neuropsychological assessment.

Ethanol reduces rCFB activation of left dorsolateral prefrontal cortex during a verbal fluency task

In a previous study in normal subjects (Wendt et al., 1994), using a reversing checkerboard as activation stimulus, we found that the coupling between local neuronal activity and regional cerebral blood flow was preserved following ethanol, and that a right-sided occipital activation response seen during sobriety became symmetrical during inebriation. In the present study we investigated if ethanol has a detrimental effect also on the activation of the left dorsolateral prefrontal cortex found in normals during verbal fluency. Measurements of regional cerebral blood flow in 20 healthy, young, male, right-handed volunteers during rest and verbal fluency were made during sobriety and inebriation (0.06% blood alcohol concentration) with a 1-week interval. We found a decrease in word production during inebriation. The normal activation within the frontotemporal part of the left dorsolateral prefrontal cortext was preserved during inebriation. The activation of this region seems thus to be robust to the effects of ethanol. During inebriation no activation response to the word fluency test was found in the anterior prefrontal part of the dorsolateral prefrontal cortex. This region is important for working, temporal, and short-term memory functions, processes that are affected by ethanol. Hemispheric functioning and specialization seem to be adversely affected by ethanol, regardless of which hemisphere is most involved while sober.

The classical stroop interference task as a prefrontal activation probe: a validation study using 99Tcm-ECD brain SPECT

This study investigated the feasibility of brain single photon emission computed tomography (SPECT) functional imaging in a neuropsychological test setting, following a single-day protocol with a split-dose paradigm. The Stroop Color Word Test (SCWT) is an example of a well-documented prefrontal activation task. In a split-dose protocol, ten right-handed healthy volunteers were injected twice with 370 MBq 99Tcm-ethyl cysteinate dimer while performing consecutively both series of card-reading of the SCWT. Images were reconstructed using filtered back-projection and normalized to a standard template in Talairach coordinates. Statistical Parametric Mapping (SPM96) was used to determine voxelwise significant changes. A first activation cluster was found in the left medial prefrontal cortex, consisting of the gyrus cinguli anterior and the gyrus frontalis medius and superior. A second activation cluster included the right gyrus frontalis dorsalis and medius. These findings confirm to a large extent the results of previous functional magnetic resonance imaging, positron emission tomography studies of Stroop-like tasks. The choice and validity of various methodological characteristics of the experimental design leading to these results is critically discussed. It is concluded that brain SPECT activation with the Stroop Color Word Test under standard neuropsychological conditions in healthy volunteers, is both technically and practically feasible.

Neuropharmacological studies with SPECT in neuropsychiatric disorders

The last decade saw a rapid development of single photon emission computed tomography (SPECT) from a tool to assess cerebral blood flow to the study of specific neurotransmitter systems. Because of the relatively long half-life of SPECT radioisotopes, it is practical to measure the availability of neuroreceptors and transporters in conditions approaching equilibrium. The cost-efficiency of SPECT allowed studies in relatively large samples of patients with various neuropsychiatric disorders. We have applied this approach in studies of dopaminergic, serotonergic, and muscarinergic neurotransmission in patients with dementia, extrapyramidal disorders, schizophrenia, and alcoholism. No simple associations were observed between a single defect in one neurotransmitter system and a certain neuropsychiatric disease. Instead, complex dysfunction of several neurotransmitter systems in multiple, partially connected brain circuits have been implicated. Treatment effects also have been characterized. Microdialysis and neurotransmitter depletion studies showed that most radioligands and endogenous neurotransmitters compete for binding at receptors and transporters. Future research directions include the assessment of endogenous neurotransmitter concentrations measured by depletion studies and of genetic effects on neuroreceptor and transporter expression.

Processing of context information in schizophrenia: relation to clinical symptoms and WCST performance

Failure in contextual information processing has been hypothesized as being the single function responsible for several impairments in cognitive tasks and symptoms, through an involvement of the prefrontal cortex, in patients with schizophrenia. A variant of the Continuous Performance Test (CPT) designed specifically to elicit deficits in the processing of contextual information has been administered to 20 schizophrenic patients and 20 healthy controls. The relation to Wisconsin Card Sorting Test (WCST), relatively specific to prefrontal damage and executive dysfunctioning, and clinical status by using scales for the assessment of positive, negative symptoms and outcome has been investigated. The data show that multi-episode schizophrenic patients manifest inability to use contextual information to inhibit habitual response to an ambiguous stimulus and to maintain information across delay, without a general attention deficit. We also found a relationship between contextual reasoning and WCST unique errors, hallucinations, formal thought disorders, and outcome evaluation. Our results further support the hypothesis that the deficit of contextual reasoning could account for cognitive impairments and symptoms of patients with schizophrenia.

Wisconsin Card Sorting Test performance in patients with focal frontal and posterior brain damage: effects of lesion location and test structure on separable cognitive processes

Forty-six patients with single focal lesions (35 frontal, 11 nonfrontal) were administered the Wisconsin Card Sorting Test (WCST) under three conditions of test administration. The three conditions varied in the amount of external support provided via specificity of instructions. The WCST, while a multifactorial test, is specifically sensitive to the effects of frontal lobe damage if deficits in language comprehension and visual-spatial search are controlled. There is also specificity of functioning within the frontal lobes: patients with inferior medial frontal lesions, unilateral or bilateral, were not impaired on the standard measures although they had increased loss of set when informed of the sorting categories. Verbal instructions may provide a probe to improve diagnosis and prognosis, assessment of the potential efficacy of treatment, and the time frame of plasticity of specific cognitive operations.

Decreased frontal activation in schizophrenics during stimulation with the continuous performance test--a functional magnetic resonance imaging study

The Continuous Performance Test (CPT) has become an essential constituent of the neuropsychological investigation of schizophrenia. Also, a vast number of brain imaging studies, mostly PET investigations, have employed the CPT as a cognitive challenge and established a relative hypofrontality in schizophrenics compared to controls. The aim of the present investigation was to clarify whether this predescribed hypofrontality could also be verified using functional magnetic resonance imaging (fMRI). 20 healthy volunteers and 14 schizophrenics on stable neuroleptic medication were included. Imaging was performed using the CPT-double-T-version and a clinical 1.5 T MRI-scanner with a single slice technique and a T(2)*-weighted gradient-echo-sequence. The schizophrenics exhibited a decreased activation in the right mesial prefrontal cortex, the right cingulate and the left thalamus compared to controls. These results obtained by fMRI are discussed in relation to published findings using PET.

Frontotemporal cerebral blood flow change during executive and declarative memory tasks in schizophrenia: a positron emission tomography study

Schizophrenia affects prefrontal and temporal-limbic networks. These regions were examined by contrasting regional cerebral blood flow (rCBF) during executive (Wisconsin Card Sorting Test [WCST]), and declarative memory tasks (Paired Associate Recognition Test [PART]). The tasks, and a resting baseline, were administered to 15 patients with schizophrenia and 15 healthy controls during 10 min positron emission tomography 15O-water measures of rCBF. Patients were worse on both tasks. Controls activated inferior frontal, occipitotemporal, and temporal pole regions for both tasks. Similar results were obtained for controls matched to level of patient performance. Patients showed no activation of hypothesized regions during the WCST and activated the dorsolateral prefrontal cortex during the PART. On the PART, occipitotemporal activation correlated with better performance for controls only. Better WCST performance correlated with CBF increase in prefrontal regions for controls and in the parahippocampal gyrus for patients. Results suggest that schizophrenia may involve a breakdown in the integration of a frontotemporal network that is responsive to executive and declarative memory demands in healthy individuals.

Role of the cingulate gyrus during the Wisconsin Card Sorting Test: a single photon emission computed tomography study in normal volunteers

The purpose of this study was to investigate the effect of the Wisconsin Card Sorting Test (WCST) on frontal regional cerebral blood flow (rCBF) in normal subjects, separating the cingulate gyrus from the prefrontal cortex. Two technetium-99m-hexamethyl-propylene-amine-oxime brain single photon emission computed tomography (SPECT) scans, at rest and during WCST performance, were performed in randomized order on 13 right-handed normal volunteers. A statistically significant rCBF increase was found in the left inferior cingulate and the left posterior frontal region, although rCBF ratios in the left and right prefrontal cortex, and in the right inferior cingulate, were slightly higher during WCST performance in nine of the 13 subjects studied. No differences in activation scores (activated-resting rCBF ratios) were found between subjects who had the resting SPECT first and subjects who had the resting condition second. These results suggest that the inferior cingulate cortex, a limbic region that has been implicated in attentional mechanisms, plays a significant role in WCST performance. Furthermore, the motor component of the WCST may account for the activation of the left posterior frontal region. In addition, no order effect was found in this study. These findings illustrate the advantage of independently evaluating the cingulate gyrus and the prefrontal cortex in SPECT studies of frontal cognitive function.

High-energy phosphates in the frontal lobe correlate with Wisconsin Card Sort Test performance in controls, not in schizophrenics: a 31phosphorus magnetic resonance spectroscopic and neuropsychological investigation

In recent years, a number of 31phosphorus magnetic resonance spectroscopy (P-MRS) studies on the frontal lobe of schizophrenics have been performed, reporting alterations of phospholipids and high-energy phosphates. Deicken et al. (1994b) recently found positive correlations between left frontal phosphomonoester% (PME%) levels and the performance of a specific frontal lobe task, the Wisconsin Card Sorting Test (WCST), in schizophrenics. In the present paper, the correlations between phospholipids and high-energy phosphates in the frontal lobe of 26 schizophrenics and 23 controls measured with a volume-selective P-MRS method were investigated. Overall, we could not find any correlations between WCST results and phospholipid levels, but in controls phosphocreatine% (PCr%) and PCr/adenenosine triphosphate (ATP) ratios were negatively correlated with test performance. Since PCr behaves as a buffer of ATP, in the sense that when ATP is consumed by neuronal activity PCr is catalysed rapidly to ATP, increased PCr% values and, moreover, increased PCr/ATP ratios point to a decreased ATP consumption. Thus, the correlations found between PCr% and PCr/ATP and test performance in controls point to an association between reduced performance in a specific frontal lobe task and decreased energy demanding processes at rest. This association was not found in schizophrenics, possibly due to the influence of neuroleptic medication or the disease process per se.

SPECT brain blood flow changes with continuous ligand infusion during previously learned WCST performance

Performance of the Wisconsin Card Sorting Test (WCST) and related brain-activation patterns reflect both task learning and execution. Normal subjects learned the WCST prior to performance during slow SPECT ligand infusion. Blood flow increased in bilateral inferior frontal, right middle and inferior parietal cortices. Activity decreased in hippocampi, temporal cortex, anterior cingulate and caudate.

Saccadic eye movements in schizophrenic patients

The nature of saccadic abnormalities in schizophrenia was investigated in three different paradigms: (1) the visually guided saccade; (2) the antisaccade; and (3) the remembered saccade paradigm. Subjects comprised 14 schizophrenic patients and 14 normal volunteers. Deficits in the schizophrenic group were observed in the antisaccade and remembered saccade tasks, both of which were characterized by increased latency and reduced gain. Moreover, in the antisaccade task, schizophrenic patients showed an increased number of errors compared with control subjects. Saccadic abnormalities in the patients were correlated with impaired performance on the Wisconsin Card Sorting Test. These data suggest that schizophrenic patients have difficulty in inhibiting reflexive saccades and in producing voluntary saccades. The implications of these findings for a prefrontal cortex dysfunction involved in oculomotor control in schizophrenia are discussed.

Relationships between neuropsychological and oculomotor measures in schizophrenia patients and normal controls

Establishing the relationship between oculomotor and neuropsychological impairments might facilitate a more coherent description of schizophrenia-associated neurocognitive deficits. Therefore, we assessed several aspects of neuropsychological and oculomotor function in 25 medicated schizophrenia patients and 24 age-matched controls. Neuropsychological tasks included the Wisconsin Cart Sort Test (WCST), the Trail Making Test (TMT), the Rey Auditory Verbal Learning Test, and finger tapping speed. Oculomotor functions assessed included smooth pursuit, initiation of smooth pursuit, predictive pursuit, fixation, visually guided saccades, remembered saccades, and antisaccades. Among the schizophrenia patients, predictive pursuit performance correlated significantly with finger tapping (dominant hand), TMT (both parts), and one WCST measure (categories completed). The only other significant correlation among the schizophrenia patients was between antisaccade performance and part A of the TMT. Perseverative errors during the WCST and antisaccade performance were the only measures significantly correlated among the normals. Closely related neurocognitive deficits may be responsible for impairments in TMT, WCST, predictive pursuit, and antisaccade performance in schizophrenia.

Brain activation during cognitive stimulation with the Wisconsin Card Sorting Test--a functional MRI study on healthy volunteers and schizophrenics

It has been demonstrated by single photon emission computed tomography (SPECT) and positron emission tomography (PET) that frontal brain regions are stimulated during performance of the Wisconsin Card Sorting Test (WCST). The WCST is also regarded as one of the standard tests for the assessment of frontal activity in brain imaging studies of schizophrenia. In this study cerebral activation was assessed by means of functional magnetic resonance imaging (fMRI). In healthy volunteers WCST stimulation resulted in a right lateralized frontal activation. In 13 chronic schizophrenics on stable neuroleptic medication, a lack of activation in the right prefrontal cortex and--as a trend--an increased left temporal activity during execution of the WCST was noted compared to controls. Since a one-slice technique was used, no information about the activation pattern in adjacent brain regions was obtained. However, as fMRI possesses a superior spatial resolution compared to SPECT and PET, the anatomical localization of the activation effect in the measured slice can be defined more precisely. Beside these methodological considerations, the results are discussed in relation to prior findings of a reduced ability of schizophrenics to coordinate cerebral function.

Regional cerebral blood flow during the Wisconsin Card Sort Test in schizotypal personality disorder

Regional cerebral blood flow (rCBF) was measured by single photon emission computed tomography in 10 patients with schizotypal personality disorder (SPD) and nine age- and sex-matched normal volunteers. Subjects performed both the Wisconsin Card Sort Test (WCST) and a control task, the Symbol Matching Test (SMT). Four-way analyses of variance were performed to assess relative rCBF of the prefrontal cortex and of the medial temporal region. Normal volunteers showed more marked activation in the precentral gyrus, while SPD patients showed greater activation in the middle frontal gyrus. Relative flow in the left prefrontal cortex was correlated with better WCST performance in normal volunteers. SPD patients, however, showed no such correlations in the left prefrontal cortex, but demonstrated correlations of good and bad performance with CBF in the right middle and inferior frontal gyrus, respectively. Thus, at least some SPD patients demonstrate abnormal patterns of prefrontal activation, perhaps as a compensation for dysfunction in other regions.

Modulation of cognition-specific cortical activity by gonadal steroids: a positron-emission tomography study in women

There is considerable evidence from animal studies that gonadal steroid hormones modulate neuronal activity and affect behavior. To study this in humans directly, we used H215O positron-emission tomography to measure regional cerebral blood flow (rCBF) in young women during three pharmacologically controlled hormonal conditions spanning 4-5 months: ovarian suppression induced by the gonadotropin-releasing hormone agonist leuprolide acetate (Lupron), Lupron plus estradiol replacement, and Lupron plus progesterone replacement. Estradiol and progesterone were administered in a double-blind cross-over design. On each occasion positron-emission tomography scans were performed during (i) the Wisconsin Card Sorting Test, a neuropsychological test that physiologically activates prefrontal cortex (PFC) and an associated cortical network including inferior parietal lobule and posterior inferolateral temporal gyrus, and (ii) a no-delay matching-to-sample sensorimotor control task. During treatment with Lupron alone (i.e., with virtual absence of gonadal steroid hormones), there was marked attenuation of the typical Wisconsin Card Sorting Test activation pattern even though task performance did not change. Most strikingly, there was no rCBF increase in PFC. When either progesterone or estrogen was added to the Lupron regimen, there was normalization of the rCBF activation pattern with augmentation of the parietal and temporal foci and return of the dorsolateral PFC activation. These data directly demonstrate that the hormonal milieu modulates cognition-related neural activity in humans.

PET regional cerebral blood flow change during working and declarative memory: relationship with task performance

Functional and anatomical relationships between working and declarative memory were investigated by contrasting regional cerebral blood flow (rCBF) change during standard working (Wisconsin Card Sorting Test, WCST) and declarative memory (Paired Associate Recognition Test, PART) tasks using identical stimulus-response modalities. The tasks and a resting baseline were administered to 30 participants (16 men, 14 women) during successive 10-min positron emission tomography 15O-water measures of rCBF. For both tasks, rCBF increased over baseline in inferior frontal and occipitotemporal regions, with more consistent dorsolateral prefrontal activation for WCST than PART. Additional orbitofrontal increases and dorsomedial decreases were seen for the PART. Activation patterns diverged when performance was considered. For the WCST, high performers activated dorsolateral and inferior frontal regions, whereas top PART performers activated only the occipitotemporal region. These results suggest operation of a frontotemporal network subserving both types of memory function that becomes more focal as performance increases.

The Wisconsin Card Sorting Test and the assessment of frontal function: a validation study with event-related potentials

The Wisconsin Card Sorting Test (WCST) is generally regarded as the prototype of abstract reasoning task and has been routinely used to assess frontal lobe function in a variety of clinical and research contexts. However, there are growing concerns that the WCST fails to discriminate frontal patients from those with lesions in other brain regions or from normals. Event-related potentials (ERP) from frontal, fronto-temporal, temporal, parietal and occipital areas were recorded during the performance of a computerized version of the WCST in order to explore frontal versus non-frontal ERP indexes during WCST activation. The task protocol was contrived to focus on the differences between early and late trials of each WCST series. Cognitive processes underlying these two task conditions have been described as extradimensional and intradimensional shifts in attention, respectively. Differences between early and late WCST trials appeared as soon as 120 msec poststimulus and were associated with a negative field potential centred at the fronto-temporal region of the left hemisphere. Significantly larger amplitudes of the posterior P3b wave for late as compared with early WCST trials also lent support to claims of a strong involvement of working memory mechanisms during WCST performance. Results are discussed in terms of the implications for the utility of ERP measures in clinical neuropsychology.

Effects of four normalizing methods on data analytic results in functional brain imaging

Functional brain imaging data may contain large individual differences in information about whole brain and regional levels of activity, and it is common to remove these differences using arithmetic transformation (normalization) prior to statistical analysis. As no single transformation is widely accepted, we examine the effects of four normalizing methods (ratioing, residuals from regressions on global cerebral blood flow, Z scores, and subject residual profiles) on 1) profile shape, 2) correlations between regions, 3) correlations between subjects, and 4) analysis of variance results. These effects are evaluated using an empirical data set consisting of regional cerebral blood flow values from 22 regions of interest in 46 depressed adults and 48 age-matched normal controls obtained by 133Xe single photon emission computed tomography. Results show that normalization method has substantial but different effects on characteristics of the data and statistical results. The rationing method appears to be an optimal choice for most analyses.

Dextroamphetamine enhances "neural network-specific" physiological signals: a positron-emission tomography rCBF study

Previous studies in animals and humans suggest that monoamines enhance behavior-evoked neural activity relative to nonspecific background activity (i.e., increase signal-to-noise ratio). We studied the effects of dextroamphetamine, an indirect monoaminergic agonist, on cognitively evoked neural activity in eight healthy subjects using positron-emission tomography and the O15 water intravenous bolus method to measure regional cerebral blood flow (rCBF). Dextroamphetamine (0.25 mg/kg) or placebo was administered in a double-blind, counterbalanced design 2 hr before the rCBF study in sessions separated by 1-2 weeks. rCBF was measured while subjects performed four different tasks: two abstract reasoning tasks--the Wisconsin Card Sorting Task (WCST), a neuropsychological test linked to a cortical network involving dorsolateral prefrontal cortex and other association cortices, and Ravens Progressive Matrices (RPM), a nonverbal intelligence test linked to posterior cortical systems--and two corresponding sensorimotor control tasks. There were no significant drug or task effects on pCO2 or on global blood flow. However, the effect of dextroamphetamine (i.e., dextroamphetamine vs placebo) on task-dependent rCBF activation (i.e., task - control task) showed double dissociations with respect to task and region in the very brain areas that most distinctly differentiate the tasks. In the superior portion of the left inferior frontal gyrus, dextroamphetamine increased rCBF during WCST but decreased it during RPM (ANOVA F (1,7) = 16.72, p < 0.0046). In right hippocampus, blood flow decreased during WCST but increased during RPM (ANOVA F(1,7) = 18.7, p < 0.0035). These findings illustrate that dextroamphetamine tends to "focus" neural activity, to highlight the neural network that is specific for a particular cognitive task. This capacity of dextroamphetamine to induce cognitively specific signal augmentation may provide a neurobiological explanation for improved cognitive efficiency with dextroamphetamine.

Memory impairment in schizophrenia: its' relationship to executive function

The presence of memory impairment in schizophrenia has frequently been documented but much less attention has been given to the qualitative aspects of this impairment and its association to executive function. Using a cognitive-process approach, we examined memory and executive function in 25 patients who met DSM-III-R criteria for schizophrenia. Patients were matched with 25 healthy volunteers. The schizophrenic group was found to have a significant impairment in immediate memory, with relatively spared long-delay memory. Performance on verbal learning and recognition memory was similar to that of controls. Memory deficits were present irrespective of the encoding strategies used and were unrelated to chronicity. In addition, the schizophrenics performed worse than controls on tests of executive function, but the degree of impairment was greater on tests of response initiation and suppression. This pattern of performance resembled that found in patients with subcortical or frontal lesions which was supported by some significant correlations between aspects of memory and executive function. Our results suggest that in schizophrenia, specific executive functions may make a selective contribution to the pattern of memory performance in schizophrenia which is subserved by frontal and to a lesser extent hippocampal/diencephalic systems.

Functional lateralization of the prefrontal cortex during traditional frontal lobe tasks

We attempted to identify brain regions functionally lateralized during cognitive tasks traditionally linked to the prefrontal cortex (PFC) by measuring regional cerebral blood flow with H2(15)O positron emission tomography (PET). Fourteen normal subjects were scanned six times while performing six different cognitive conditions comprising three task paradigms putatively sensitive to PFC integrity: the Wisconsin Card Sort (WCS), Delayed Response Alternation (DA), and the Spatial Delayed Response (SDR) Tasks, and three matched sensorimotor control tasks. Multivariate and repeated measures analyses indicated that for all three cognitive paradigms there were no significant hemisphere, hemisphere-by-condition, or hemisphere-by-region effects. However, with more liberal statistical comparison (paired t tests), the superior frontal gyrus showed lateralization during both the WCS and SDR tasks (both R > L). These results suggest that, although some asymmetries may be found using liberal analyses, there is less evidence of lateralized brain function during performance of these tasks of PFC function, than in language and motor systems. Implications for testing PFC function in neuropsychiatric groups are discussed.

Ethanol reduces asymmetry of visual rCBF responses

Visual regional CBF (rCBF) responses were measured in 10 healthy male subjects before and after an ethanol dose of 1 g/kg body weight. This dose induces well-established cerebral vasodilatation. However, significant bilateral occipital increases were found in both conditions. Apparently, the coupling between neuronal activity and rCBF is preserved following ethanol. The occipital and posterior parietal flow increases were, however, larger on the right than the left side in the sober state. During inebriation the asymmetry disappeared, possibly representing a more undifferentiated processing of visual information. We propose that ethanol causes a reduced inhibition of the left posterior cortex and a reduction of right-hemisphere information processing.