Encoding vs. retention: differential effects of cue manipulation on working memory performance in schizophrenia

Construct identification in the neuropsychological battery: What are we measuring?

OBJECTIVE

Major obstacles to data harmonization in neuropsychology include lack of consensus about what constructs and tests are most important and invariant across healthy and clinical populations. This study addressed these challenges using data from the National Neuropsychology Network (NNN).

METHOD

Data were obtained from 5,000 NNN participants and Pearson standardization samples. Analyses included variables from four instruments: Wechsler Adult Intelligence Scale, 4th Edition (WAIS-IV); Wechsler Memory Scale, 4th Edition (WMS-IV); California Verbal Learning Test, 3rd Edition (CVLT3); and Delis-Kaplan Executive Function System (D-KEFS). We used confirmatory factor analysis to evaluate models suggested by prior work and examined fit statistics and measurement invariance across samples. We examined relations of factor scores to demographic and clinical characteristics.

RESULTS

For each instrument, we identified four first-order and one second-order factor. Optimal models in patients generally paralleled the best-fitting models in the standardization samples, including task-specific factors. Analysis of the NNN data prompted specification of a Recognition-Familiarity factor on the WMS-IV and an Inhibition-Switching factor on the D-KEFS. Analyses showed strong to strict factorial invariance across samples with expected differences in factor means and variances. The Recognition-Familiarity factor correlated with age more strongly in NNN than in the standardization sample.

CONCLUSIONS

Factor models derived from healthy groups generally fit well in patients. NNN data helped identify novel Recognition-Familiarity and Inhibition-Switching factors that were also invariant across samples and may be clinically useful. The findings support efforts to identify evidence-based and optimally efficient measurements of neuropsychological constructs that are valid across groups. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Cognitive Impairment Associated with Schizophrenia: From Pathophysiology to Treatment

Cognitive impairment is a core feature of schizophrenia and a major contributor to poor functional outcomes. Methods for assessment of cognitive dysfunction in schizophrenia are now well established. In addition, there has been increasing appreciation in recent years of the additional role of social cognitive impairment in driving functional outcomes and of the contributions of sensory-level dysfunction to higher-order impairments. At the neurochemical level, acute administration of N-methyl-d-aspartate receptor (NMDAR) antagonists reproduces the pattern of neurocognitive dysfunction associated with schizophrenia, encouraging the development of treatments targeted at both NMDAR and its interactome. At the local-circuit level, an auditory neurophysiological measure, mismatch negativity, has emerged both as a veridical index of NMDAR dysfunction and excitatory/inhibitory imbalance in schizophrenia and as a critical biomarker for early-stage translational drug development. Although no compounds have yet been approved for treatment of cognitive impairment associated with schizophrenia, several candidates are showing promise in early-phase testing.

Working Memory Impairment as an Endophenotypic Marker in Patients with Schizophrenia: Failures in Encoding or Maintenance?

INTRODUCTION

Although working memory (WM) dysfunction has been proposed as a schizophrenia (SZ) endophenotype, the specific impaired component (encoding or maintenance) in patients and unaffected relatives remains inconclusive. We compared auditory-verbal and visuospatial WM in patients with SZ, unaffected siblings (USs), and healthy controls under 2 response conditions: immediate (encoding condition) and delayed (maintenance condition).

METHODS

We included 22 participants per group, similar in age and gender. Three WM tests (Spatial Span, Backward Digit Span, and Letter-Number Span) were administered under both conditions in a counterbalanced manner to all participants.

RESULTS

Poorer performance was found in the SZ group for all tests (p < 0.001). USs showed a better performance than patients, but worse than controls (p < 0.05), except for the Backward Digit Span test, in which their performance was similar to that of the SZ group. The effect of the delayed response in all tasks was not significant in any group.

CONCLUSION

Our results indicate that WM impairment, including auditory-verbal and visuospatial modalities, corresponds to a stable feature of the disease as it is present in USs, thus confirming its potential endophenotypic property in SZ patients. No effect of the delayed response was observed, suggesting failures in encoding in both patients and USs.

Transdiagnostic comparison of visual working memory capacity in bipolar disorder and schizophrenia

BACKGROUND

Impaired working memory is a core cognitive deficit in both bipolar disorder and schizophrenia. Its study might yield crucial insights into the underpinnings of both disorders on the cognitive and neurophysiological level. Visual working memory capacity is a particularly promising construct for such translational studies. However, it has not yet been investigated across the full spectrum of both disorders. The aim of our study was to compare the degree of reductions of visual working memory capacity in patients with bipolar disorder (PBD) and patients with schizophrenia (PSZ) using a paradigm well established in cognitive neuroscience.

METHODS

62 PBD, 64 PSZ, and 70 healthy controls (HC) completed a canonical visual change detection task. Participants had to encode the color of four circles and indicate after a short delay whether the color of one of the circles had changed or not. We estimated working memory capacity using Pashler's K.

RESULTS

Working memory capacity was significantly reduced in both PBD and PSZ compared to HC. We observed a small effect size (r = .202) for the difference between HC and PBD and a medium effect size (r = .370) for the difference between HC and PSZ. Working memory capacity in PSZ was also significantly reduced compared to PBD with a small effect size (r = .201). Thus, PBD showed an intermediate level of impairment.

CONCLUSIONS

These findings provide evidence for a gradient of reduced working memory capacity in bipolar disorder and schizophrenia, with PSZ showing the strongest degree of impairment. This underscores the importance of disturbed information processing for both bipolar disorder and schizophrenia. Our results are compatible with the cognitive manifestation of a neurodevelopmental gradient affecting bipolar disorder to a lesser degree than schizophrenia. They also highlight the relevance of visual working memory capacity for the development of both behavior- and brain-based transdiagnostic biomarkers.

Mechanisms Underlying Visuospatial Working Memory Impairments in Schizophrenia

Working memory deficits are observed in the vast majority of individuals diagnosed with schizophrenia and those at risk for the disorder. Working memory impairments are present during the prodromal stage and persist throughout the course of schizophrenia. Given the importance of cognition in functional outcome, working memory deficits are an important therapeutic target for schizophrenia. This chapter examines mechanisms underlying working memory deficits in schizophrenia, focusing on the roles of perception and attention in the encoding process. Lastly, we present a comprehensive discussion of neural oscillation and internal noise in the context of the etiology of working memory deficits in schizophrenia and introduce noninvasive treatment strategies that could improve encoding processes.

Evidence for a differential contribution of early perceptual and late cognitive processes during encoding to episodic memory impairment in schizophrenia

OBJECTIVES

Schizophrenia is characterised by significant episodic memory impairment that is thought to be related to problems with encoding, however the neuro-functional mechanisms underlying these deficits are not well understood. The present study used a subsequent recognition memory paradigm and event-related potentials (ERPs) to investigate temporal aspects of episodic memory encoding deficits in schizophrenia.

METHODS

Electroencephalographic data was recorded in 24 patients and 19 healthy controls whilst participants categorised single words as pleasant/unpleasant. ERPs were generated to subsequently recognised versus unrecognised words on the basis of a forced-choice recognition memory task. Subsequent memory effects were examined with the late positive component (LPP). Group differences in N1, P2, N400 and LPP were examined for words correctly recognised.

RESULTS

Patients performed more poorly than controls on the recognition task. During encoding patients had significantly reduced N400 and LPP amplitudes than controls. LPP amplitude correlated with task performance however amplitudes did not differ between patients and controls as a function of subsequent memory. No significant differences in N1 or P2 amplitude or latency were observed.

CONCLUSIONS

The present results indicate that early sensory processes are intact and dysfunctional higher order cognitive processes during encoding are contributing to episodic memory impairments in schizophrenia.

Memory-guided saccades in youth-onset psychosis and attention deficit hyperactivity disorder (ADHD)

AIM

Working memory deficits have been shown to be present in children and adolescents with schizophrenia and attention deficit hyperactivity disorder. Considering the differences in clinical characteristics between these disorders, it was the goal of this study to assess differences in the specific components of working memory in children and adolescents with psychosis and attention deficit hyperactivity disorder.

METHODS

Children and adolescents (age range 8-20 years) with either a non-affective psychotic disorder (n = 25), attention deficit hyperactivity disorder (n = 33) and controls (n = 58) were administered an oculomotor delayed-response task using both a recall and a control condition. Memory-guided saccades were measured during delay periods of 2, 8 and 20 s.

RESULTS

Although both clinical groups were less accurate than controls, there was no evidence of a disproportionate impairment in recall. In addition, there was no evidence of a delay-dependent impairment in psychosis; however, there was a delay-dependent impairment in attention deficit hyperactivity disorder when corrective saccades were included. Speed of information processing was correlated with distance errors in psychosis, suggesting that speed of encoding the stimulus location may have constrained the accuracy of the saccades.

CONCLUSIONS

Our findings support impairments during encoding in the psychosis group and a delay-dependent deficit in the attention deficit hyperactivity disorder group.

The When and Where of Working Memory Dysfunction in Early-Onset Schizophrenia-A Functional Magnetic Resonance Imaging Study

Behavioral evidence indicates that working memory (WM) in schizophrenia is already impaired at the encoding stage. However, the neurophysiological basis of this primary deficit remains poorly understood. Using event-related fMRI, we assessed differences in brain activation and functional connectivity during the encoding, maintenance and retrieval stages of a visual WM task with 3 levels of memory load in 17 adolescents with early-onset schizophrenia (EOS) and 17 matched controls. The amount of information patients could store in WM was reduced at all memory load levels. During encoding, activation in left ventrolateral prefrontal cortex (VLPFC) and extrastriate visual cortex, which in controls positively correlated with the amount of stored information, was reduced in patients. Additionally, patients showed disturbed functional connectivity between prefrontal and visual areas. During retrieval, right inferior VLPFC hyperactivation was correlated with hypoactivation of left VLPFC in patients during encoding. Visual WM encoding is disturbed by a failure to adequately engage a visual-prefrontal network critical for the transfer of perceptual information into WM. Prefrontal hyperactivation appears to be a secondary consequence of this primary deficit. Isolating the component processes of WM can lead to more specific neurophysiological markers for translational efforts seeking to improve the treatment of cognitive dysfunction in schizophrenia.

Ammons Quick Test Validity among Randomly Selected Referrals

After selection using a random number table, from volunteer referrals, 89 Youth (61 boys, 28 girls; 48 African Americans, 2 Asian Americans, 27 Euro-Americans, 12 Hispanic Americans), and 147 Adults (107 men, 40 women; 11 African Americans, 6 Asian Americans, 124 Euro-Americans, 6 Hispanic Americans) were administered the Amnions Quick Test (QT). Means, confidence intervals, standard deviations, and Pearson product-moment correlations among tests were computed. The Amnions QT was moderately to strongly and significantly correlated statistically with: the Peabody Picture Vocabulary Test-3b (PPVT-3b); the Vineland Adaptive Behavior Scales-2 Parent/Teacher Form; the Wechsler Intelligence Scale for Children (WISC-4) or the Wechsler Adult Intelligence Scale (WAIS-4); and the Wide Range Achievement Test-Fourth Edition (WRAT-4) Blue and Green Forms. After 51 years, the original norms for the Amnions QT remain valid measures of receptive vocabulary, verbal intelligence, and auditory information processing useful to clinicians.

Abnormal task modulation of oscillatory neural activity in schizophrenia

Schizophrenia patients have deficits in cognitive function that are a core feature of the disorder. AX-CPT is commonly used to study cognition in schizophrenia, and patients have characteristic pattern of behavioral and ERP response. In AX-CPT subjects respond when a flashed cue “A” is followed by a target “X,” ignoring other letter combinations. Patients show reduced hit rate to “go” trials, and increased false alarms to sequences that require inhibition of a prepotent response. EEG recordings show reduced sensory (P1/N1), as well as later cognitive components (N2, P3, CNV). Behavioral deficits correlate most strongly with sensory dysfunction. Oscillatory analyses provide critical information regarding sensory/cognitive processing over and above standard ERP analyses. Recent analyses of induced oscillatory activity in single trials during AX-CPT in healthy volunteers showed characteristic response patterns in theta, alpha, and beta frequencies tied to specific sensory and cognitive processes. Alpha and beta modulated during the trials and beta modulation over the frontal cortex correlated with reaction time. In this study, EEG data was obtained from 18 schizophrenia patients and 13 controls during AX-CPT performance, and single trial decomposition of the signal yielded power in the target wavelengths. Significant task-related event-related desynchronization (ERD) was observed in both alpha and beta frequency bands over parieto-occipital cortex related to sensory encoding of the cue. This modulation was reduced in patients for beta, but not for alpha. In addition, significant beta ERD was observed over motor cortex, related to motor preparation for the response, and was also reduced in patients. These findings demonstrate impaired dynamic modulation of beta frequency rhythms in schizophrenia, and suggest that failures of oscillatory activity may underlie impaired sensory information processing in schizophrenia that in turn contributes to cognitive deficits.

The effects of perceptual encoding on the magnitude of object working memory impairment in schizophrenia

Deficits in the visual working memory (WM) system have been consistently reported in schizophrenia patients, but the relative contribution of initial perceptual encoding to these deficits remains unsettled. We assessed the role of visual perceptual encoding on performance on an object WM task. Schizophrenia patients (N=37) and nonpsychiatric control subjects (N=33) were tested on an object WM task involving three delay periods: 200 ms, 3s, and 10s. Schizophrenia patients performed significantly less accurately than controls on all three conditions. However, after controlling for the effect of perceptual encoding (accuracy on the 200 ms delay condition) on performance in the two memory load conditions, schizophrenia patients demonstrated intact WM in the 3s delay condition, and showed a weak trend for decreased accuracy on the 10s delay compared with controls. Analysis of individual differences in pattern of performance revealed that a distinct subgroup of poor encoder patients had a significantly greater reduction in accuracy at 3s than the other patient subgroups and controls. In contrast, among schizophrenia patients who performed poorly on the 10s delay, accuracy was equivalently reduced independent of encoding ability. WM deficits in controls were independent of encoding ability at both delay intervals. These results indicate that encoding ability titrates the magnitude of WM impairment in schizophrenia patients but not in controls, and that heterogeneity has to be taken into account to correctly estimate the effects of perceptual encoding on visual object WM deficits in schizophrenia.

Cognitive training for impaired neural systems in neuropsychiatric illness

Neuropsychiatric illnesses are associated with dysfunction in distributed prefrontal neural systems that underlie perception, cognition, social interactions, emotion regulation, and motivation. The high degree of learning-dependent plasticity in these networks-combined with the availability of advanced computerized technology-suggests that we should be able to engineer very specific training programs that drive meaningful and enduring improvements in impaired neural systems relevant to neuropsychiatric illness. However, cognitive training approaches for mental and addictive disorders must take into account possible inherent limitations in the underlying brain 'learning machinery' due to pathophysiology, must grapple with the presence of complex overlearned maladaptive patterns of neural functioning, and must find a way to ally with developmental and psychosocial factors that influence response to illness and to treatment. In this review, we briefly examine the current state of knowledge from studies of cognitive remediation in psychiatry and we highlight open questions. We then present a systems neuroscience rationale for successful cognitive training for neuropsychiatric illnesses, one that emphasizes the distributed nature of neural assemblies that support cognitive and affective processing, as well as their plasticity. It is based on the notion that, during successful learning, the brain represents the relevant perceptual and cognitive/affective inputs and action outputs with disproportionately larger and more coordinated populations of neurons that are distributed (and that are interacting) across multiple levels of processing and throughout multiple brain regions. This approach allows us to address limitations found in earlier research and to introduce important principles for the design and evaluation of the next generation of cognitive training for impaired neural systems. We summarize work to date using such neuroscience-informed methods and indicate some of the exciting future directions of this field.

Early sensory contributions to contextual encoding deficits in schizophrenia

CONTEXT

The AX version of the visual continuous performance task (AX-CPT) is widely used for investigating visual working memory dysfunction in schizophrenia. Event-related potentials (ERP) provide an objective index of brain function and can be used to evaluate brain substrates underlying impaired cognition in schizophrenia.

OBJECTIVE

To assess the mechanisms that underlie visual working memory dysfunction in schizophrenia relative to impairment of early visual processing.

DESIGN

Case-control study.

SETTING

Inpatient and outpatient facilities associated with the Nathan Kline Institute for Psychiatric Research.

PARTICIPANTS

A total of 30 individuals with schizophrenia and 17 healthy comparison subjects.

INTERVENTIONS

Three versions of the AX-CPT, with parametric variations in the proportions of trial types, were used to test performance and underlying neural activity during differential challenge situations. Contrast sensitivity measures were obtained from most subjects.

MAIN OUTCOME MEASURES

Behavioral performance was assessed using d' context scores. Integrity of stimulus- and task-related cortical activation to both cue and probe stimuli was assessed using sensory (C1, P1, N1) and cognitive (N2, contingent negative variation [CNV]) ERP components. Early magnocellular/parvocellular function was assessed using contrast sensitivity. Linear regression and path analyses were used to assess relations between physiological and behavioral parameters.

RESULTS

Patients showed reduced amplitude of both early sensory (P1, N1) and later cognitive (N2, CNV) ERP components. Deficits in sensory (N1) and cognitive (N2) component activation to cue stimuli contributed independently to impaired behavioral performance. In addition, sensory deficits predicted impaired cognitive ERP generation. Finally, deficits in performance correlated with impairments in contrast sensitivity to low, but not high, spatial frequency stimuli.

CONCLUSIONS

Working memory deficits in schizophrenia have increasingly been attributed to impairments in stimulus encoding rather than to failures in memory retention. This study provides objective physiological support for encoding hypotheses. Further, deficits in sensory processing contribute significantly to impaired working memory performance, consistent with generalized neurochemical models of schizophrenia.

Attentional modulation of external speech attribution in patients with hallucinations and delusions

A range of psychological theories have been proposed to account for the experience of auditory hallucinations and delusions in schizophrenic patients. Most influential theories are those implicating the defective self-monitoring of inner speech. Some recent studies measured response bias independently of self-monitoring and found the results inconsistent with the defective self-monitoring model, but explained by an externalizing response bias. We aimed to investigate the role of attentional bias in external misattribution of source by modulating participant's endogenous expectancies. Comparisons were made between patients with paranoid schizophrenia (N=23) and matched healthy controls (N=23) who participated in two different versions of an audio-visual task, which differed based upon level of the cue predictiveness. The acoustic characteristic of voice was altered in half of the trials by shifting the pitch (distortion). Participants passively listened to recordings of single adjectives spoken in their own and another person's voice (alien) preceded by their own or another person's (alien) face and made self/non self judgments about the source. The patients showed increased error rates comparing to controls, when listening to the distorted self spoken words, misidentifying their own speech as produced by others. Importantly, patients made significantly more errors across all the invalid cue conditions. This suggests not only the presence of pathological misattribution bias, but also an inadequate balance between top-down and bottom-up attentional processes in the patients, which could be responsible for misattribution of the ambiguous sensory material.

Abnormal medial temporal activity for bound information during working memory maintenance in patients with schizophrenia

Alterations of binding in long-term memory in schizophrenia are well established and occur as a result of aberrant activity in the medial temporal lobe (MTL). In working memory (WM), such a deficit is less clear and the pathophysiological bases remain unstudied. Seventeen patients with schizophrenia and 17 matched healthy controls performed a WM binding task while undergoing functional magnetic resonance imaging. Binding was assessed by contrasting two conditions comprising an equal amount of verbal and spatial information (i.e., three letters and three spatial locations), but differing in the absence or presence of a link between them. In healthy controls, MTL activation was observed for encoding and maintenance of bound information but not for its retrieval. Between-group comparisons revealed that patients with schizophrenia showed MTL hypoactivation during the maintenance phase only. In addition, BOLD signals correlated with behavioral performance in controls but not in patients with schizophrenia. Our results confirm the major role that the MTL plays in the pathophysiology of schizophrenia. Short-term and long-term relational memory deficits in schizophrenia may share common cognitive and functional pathological bases. Our results provide additional information about the episodic buffer that represents an integrative interface between WM and long-term memory.

Schizophrenia patients show task switching deficits consistent with N-methyl-d-aspartate system dysfunction but not global executive deficits: implications for pathophysiology of executive dysfunction in schizophrenia

Schizophrenia is associated with cognitive processing deficits, including deficits in executive processing, that represent a core component of the disorder. In the Task Switching Test, subjects view ambiguous stimuli and must alternate between competing rules to generate correct responses. Subjects show worse performance (prolonged response time and/or increased error rates) on the first response after a switch than on subsequent responses ("switch costs"), as well as performing worse when stimuli are incongruent as opposed to congruent ("congruence costs"). Finally, subjects show worse performance in the dual vs single task condition ("mixing costs"). In monkeys, the N-methyl-D-aspartate (NMDA) antagonist ketamine has been shown to increase congruence but not switch costs. Here, subjects viewed colored letters and had to respond alternately based upon letter (X vs O) or color (red vs blue). Switch, congruence and mixing costs were calculated. Patients with schizophrenia (n = 16) and controls (n = 17) showed similar switch costs, consistent with prior literature. Patients nevertheless showed increased congruence and mixing costs. In addition, relative to controls, patients showed worse performance across conditions in the letter vs color tasks, suggesting deficits in form vs color processing. Overall, while confirming executive dysfunction in schizophrenia, this study indicates that not all aspects of executive control are impaired and that the task switching paradigm may be useful for evaluating neurochemical vs neuroanatomic hypotheses of schizophrenia.

Has an important test been overlooked? Closure flexibility in schizophrenia

Deficits in visual processing are now recognized as a core feature of schizophrenia. In the 1940s, Louis Thurstone developed a series of tests designed to evaluate specific aspects of visual perceptual processing including the Closure Flexibility Test (CFT), which was designed to measure "the ability to hold a configuration in mind despite distraction." The present study evaluated patients' performance on this task and its relationship to other tests of neuropsychological function, particularly to a measure of sustained visual attention. Thirty-nine patients with schizophrenia or schizoaffective disorder and 40 controls participated. The CFT was administered both in its original form (10 min) and also in a briefer form (3 min) in which only a portion of stimuli were given. Patients showed highly significant large effect-size deficits on both the original (d=1.6) and brief (d=1.2) CFT. Between-group deficits in performance survived co-variation for IQ. In addition, the CFT score was significantly related to performance on the MATRICS measure of attention/vigilance, the Continuous Performance Test-Identical Pairs version (CPT-IP). This correlation remained significant even after controlling for non-specific intercorrelations among neurocognitive measures. Results confirm the severity of early visual processing deficits in schizophrenia. In addition, the CFT is a brief, easy to administer alphabet-independent, paper-and-pencil test with established psychometric properties that may be useful as an index of the sustained visual attention construct in schizophrenia.

Timing is everything: neural response dynamics during syllable processing and its relation to higher-order cognition in schizophrenia and healthy comparison subjects

Successful linguistic processing requires efficient encoding of successively-occurring auditory input in a time-constrained manner, especially under noisy conditions. In this study we examined the early neural response dynamics to rapidly-presented successive syllables in schizophrenia participants and healthy comparison subjects, and investigated the effects of noise on these responses. We used magnetoencephalography (MEG) to reveal the time-course of stimulus-locked activity over bilateral auditory cortices during discrimination of syllable pairs that differed either in voice onset time (VOT) or place of articulation (POA), in the presence or absence of noise. We also examined the association of these early neural response patterns to higher-order cognitive functions. The M100 response, arising from auditory cortex and its immediate environs, showed less attenuation to the second syllable in patients with schizophrenia than healthy comparison subjects during VOT-based discrimination in noise. M100 response amplitudes were similar between groups for the first syllable during all three discrimination conditions, and for the second syllable during VOT-based discrimination in quiet and POA-based discrimination in noise. Across subjects, the lack of M100 attenuation to the second syllable during VOT-based discrimination in noise was associated with poorer task accuracy, lower education and IQ, and lower scores on measures of Verbal Learning and Memory and Global Cognition. Because the neural response to the first syllable was not significantly different between groups, nor was a schizophrenia-related difference obtained in all discrimination tasks, early linguistic processing dysfunction in schizophrenia does not appear to be due to general sensory input problems. Rather, data suggest that faulty temporal integration occurs during successive syllable processing when the signal-to-noise ratio is low. Further, the neural mechanism by which the second syllable is suppressed during noise-challenged VOT discrimination appears to be important for higher-order cognition and provides a promising target for neuroscience-guided cognitive training approaches to schizophrenia.

Examining the effects of two factors on working memory maintenance of bound information in schizophrenia

Integrating information in space and time is a central feature of episodic memory. Although disturbance of the binding processes in episodic memory is well established in patients with schizophrenia, data on working memory (WM) remain discrepant. In a change detection procedure, two target displays of pairs of letters located in cells of grid were successively presented. Participants attempted to detect changes in binding information (i.e., recombination of studied features) or feature information (i.e., a novel letter and/or a novel spatial location). Recombinations consisted of features belonging to the same display (intradisplay) or different displays (interdisplays). Results showed that patients demonstrated overall lower performance, with no specific deficit for recognizing bound information or feature information. In addition, patients did not demonstrate deficits for interdisplay recombinations or intradisplay recombinations. Patients' ability to remember temporal occurrence of stimuli was not affected. Together, these results suggest that in patients with schizophrenia, binding processes in WM are not specifically disturbed.

Regulation of cognitive resources during an n-back task in youth-onset psychosis and attention-deficit/hyperactivity disorder (ADHD)

The goals of the current study were to use behavioral and pupillary measures to examine working memory on a spatial n-back task in 8-20-year-olds with youth-onset psychosis or ADHD (Combined subtype) and healthy controls to determine the contribution of different attentional factors to spatial working memory impairments, and to examine if age-related changes in performance differed across groups. Although both clinical groups had lower perceptual sensitivity on both 0- and 1-back, there was no evidence of an impairment in spatial working memory or differential order effects on the 0-back. Instead, results suggest that both clinical groups had difficulty encoding the stimuli. They also appeared to have difficulty maintaining attention and/or readiness to respond, and, to a lesser extent, recruiting resources on a trial-to-trial basis. It is likely that these attentional problems prevented the clinical groups from encoding the stimuli effectively and contributed to their general performance deficits.

Short article: Impaired context maintenance in mild to moderately depressed students

We test the hypothesis that people with depression experience difficulties in maintaining task-relevant context information over longer periods of time using the AX version of the continuous performance task (AX-CPT). The AX-CPT requires that participants maintain a context cue (A) in an active state in order to respond correctly to a target cue (X) presented after a short delay. A total of 40 nondepressed and mild to moderately depressed students completed versions of the task with short (1-s) or long (10-s) interstimulus intervals (ISIs). Mildly depressed participants made significantly more context-dependent (BX) errors, unlike controls who made more errors on trials where good context processing would impair performance (AY). This pattern of errors was only evident in the long ISI condition, suggesting poor maintenance of contextual information.

Assessment of single and bound features in a working memory task in schizophrenia

If disturbance of binding in long term memory is well established in schizophrenia, data concerning working memory maintenance are less clear. Feature binding in working memory was investigated in 19 patients with schizophrenia and 19 healthy controls. Binding was assessed by comparing two conditions in which participants had to retain four letters and four spatial locations. These features were presented either bound or separate. Results showed that both groups had better performances for bound than separate features, despite the fact that patients performed significantly worse than controls. When maintenance for isolated features was assessed, patients were severely disturbed for spatial locations but not for letters. Such a result suggests that reduced working memory performance in patients with schizophrenia for bound features is probably a consequence of a spatial deficit rather than a specific deficit of the binding process. Thus, not all form of binding are disturbed in schizophrenia.

Neurophysiological biomarkers for drug development in schizophrenia

Schizophrenia represents a pervasive deficit in brain function, leading to hallucinations and delusions, social withdrawal and a decline in cognitive performance. As the underlying genetic and neuronal abnormalities in schizophrenia are largely unknown, it is challenging to measure the severity of its symptoms objectively, or to design and evaluate psychotherapeutic interventions. Recent advances in neurophysiological techniques provide new opportunities to measure abnormal brain functions in patients with schizophrenia and to compare these with drug-induced alterations. Moreover, many of these neurophysiological processes are phylogenetically conserved and can be modelled in preclinical studies, offering unique opportunities for use as translational biomarkers in schizophrenia drug discovery.