Reduced context effects on retrieval in first-episode schizophrenia

Schizophrenia-associated SAP97 mutations increase glutamatergic synapse strength in the dentate gyrus and impair contextual episodic memory in rats

Mutations in the putative glutamatergic synapse scaffolding protein SAP97 are associated with the development of schizophrenia in humans. However, the role of SAP97 in synaptic regulation is unclear. Here we show that SAP97 is expressed in the dendrites of granule neurons in the dentate gyrus but not in the dendrites of other hippocampal neurons. Schizophrenia-related perturbations of SAP97 did not affect CA1 pyramidal neuron synapse function. Conversely, these perturbations produce dramatic augmentation of glutamatergic neurotransmission in granule neurons that can be attributed to a release of perisynaptic GluA1-containing AMPA receptors into the postsynaptic densities of perforant pathway synapses. Furthermore, inhibiting SAP97 function in the dentate gyrus was sufficient to impair contextual episodic memory. Together, our results identify a cell-type-specific synaptic regulatory mechanism in the dentate gyrus that, when disrupted, impairs contextual information processing in rats.

The effects of SAP97 mutations associated with schizophrenia on synaptic function are unclear. Here, the authors show that schizophrenia-related SAP97 mutations enhance glutamatergic synapse strength in the dentate gyrus, impairing contextual episodic memory in rats.

Impaired memory for temporal context in schizophrenia patients with hallucinations and thought disorganisation

INTRODUCTION

Context processing deficiencies have been established in patients with schizophrenia and it has been proposed that these deficiencies are involved in the formation of positive symptoms.

METHOD

We administered a temporal context discrimination task to 60 schizophrenia patients and 60 healthy individuals. Pictures were presented in two sessions separated by half an hour and the participants were required to remember afterwards whether the pictures had been presented in the first or the second session.

RESULTS

The number of temporal context errors was significantly increased in the patient group. More specifically, it was highly significantly increased in a subgroup of patients presenting hallucinations, while the patients without hallucinations were equivalent to the healthy individuals. Regression analyses revealed that, independently of memory of the pictures themselves, verbal and visual hallucinations, as well as thought disorganisation, were associated with more temporal context errors. In contrast, affective flattening and anhedonia were associated with fewer of these errors.

CONCLUSION

Inability to process or remember the temporal context of production of events might be a mechanism underlying both hallucinations and thought disorganisation.

Δ9-Tetrahydrocannabinol During Encoding Impairs Perceptual Details yet Spares Context Effects on Episodic Memory

BACKGROUND

With the growing acceptance of cannabis use, it is crucial to understand the drug's effects on episodic memory accuracy and distortion. We investigated the impact of the administration of Δ9-tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, on a context-based memory illusion.

METHODS

In a double-blind, placebo-controlled, within-subjects design, healthy infrequent cannabis users (N = 24) memorized object pictures that were superimposed over scenes (e.g., gray cat on beach) after pretreatment with placebo or THC (15 mg oral). Two days later under sober conditions, memory for the object pictures was tested by asking participants to discriminate between previously seen objects or perceptually similar lures (e.g., different gray cat). Context reinstatement was manipulated by presenting objects on their original or different scenes (e.g., beach or forest).

RESULTS

THC impaired memory for perceptual details of objects compared with placebo, and the context illusion was obtained in each condition: context reinstatement increased high-confidence false recognition along with correct recognition of previously seen objects. Although THC did not interact with these context effects overall, post hoc analyses showed that THC magnified the context illusion when objects were semantically congruent with their encoding contexts but abolished the context illusion when objects were incongruent with their encoding contexts.

CONCLUSIONS

These results are consistent with the hypothesis that THC impairs the encoding of specific object information more than item-context associations. As a result, THC may spare the distorting effects of context reinstatement on memory. In fact, THC may increase these distorting effects under conditions when objects are semantically congruent with context.

Time-dependent effects of psychosocial stress on the contextualization of neutral memories

Memories about stressful experiences need to be both specific and generalizable to adequately guide future behavior. Memory strength is influenced by emotional significance, and contextualization (i.e., encoding experiences with their contextual details) enables selective context-dependent retrieval and protects against overgeneralization. The current randomized-controlled study investigated how the early and late phase of the endogenous stress response affects the contextualization of neutral and negative information. One hundred healthy male participants were randomly divided into three experimental groups that performed encoding either 1) without stress (control), 2) immediately after acute stress (early) or 3) two hours after acute stress (late). Stress was induced via the Trier Social Stress Test and salivary alpha-amylase and cortisol levels were measured throughout the experiment. In the Memory Contextualization Task, neutral and angry faces (items) were depicted against unique context pictures during encoding. During testing 24 h later, context-dependent recognition memory of the items was assessed by presenting these in either congruent or incongruent contexts (relative to encoding). Multilevel analyses revealed that neutral information was more contextualized when encoding took place two hours after psychosocial stress, than immediately after the stressor. Results suggest that the late effects in the unique, time-dependent sequence of a healthy endogenous stress response, could complement reduced contextualization immediately after stress. The contextualization of negative information was not influenced by psychosocial stress, as opposed to earlier reported effects of exogenous hydrocortisone administration. An imbalance between the early and late effects of the endogenous stress response could increase vulnerability for stress-related psychopathology.

Memory Contextualization: The Role of Prefrontal Cortex in Functional Integration across Item and Context Representational Regions

Memory recall is facilitated when retrieval occurs in the original encoding context. This context dependency effect likely results from the automatic binding of central elements of an experience with contextual features (i.e., memory "contextualization") during encoding. However, despite a vast body of research investigating the neural correlates of explicit associative memory, the neural interactions during encoding that predict implicit context-dependent memory remain unknown. Twenty-six participants underwent fMRI during encoding of salient stimuli (faces), which were overlaid onto unique background images (contexts). To index subsequent context-dependent memory, face recognition was tested either in intact or rearranged contexts, after scanning. Enhanced face recognition in intact relative to rearranged contexts evidenced successful memory contextualization. Overall subsequent memory effects (brain activity predicting whether items were later remembered vs. forgotten) were found in the left inferior frontal gyrus (IFG) and right amygdala. Effective connectivity analyses showed that stronger context-dependent memory was associated with stronger coupling of the left IFG with face- and place-responsive areas, both within and between participants. Our findings indicate an important role for the IFG in integrating information across widespread regions involved in the representation of salient items and contextual features.

Destination memory in schizophrenia: "Did I told Elvis Presley about the thief?"

Destination memory refers to the ability to remember to whom a piece of information was previously transmitted. Our paper assessed this ability in schizophrenia. Twenty-five patients with schizophrenia and 25 control participants told proverbs (e.g., "send a thief to catch a thief") to pictures of celebrities (e.g., Elvis Presley). Afterward, participants had to indicate to which celebrity they had previously said the proverbs. Participants also completed a binding task in which they were required to associate letters with their corresponding context (i.e., location). Analysis revealed worse destination memory and binding in patients with schizophrenia than in controls. In both populations, destination memory was significantly correlated with performances on the binding task. Our findings suggest difficulty in the ability to attribute information to its appropriate destination in schizophrenia. This difficulty may be related to compromise in binding separate cues together to form a coherent representation of an event in memory.

Effectiveness of fast mapping to promote learning in schizophrenia

Fast mapping (FM), a process that promotes the expeditious incidental learning of information, is thought to support rapid vocabulary acquisition in young children through extra-medial temporal lobe (MTL) regions. A recent study suggested that patients with MTL damage resulting in profound amnesia were able to learn novel word–image associations using an FM paradigm. The present study investigated whether FM would be an effective strategy to promote learning for individuals with schizophrenia, a severe mental illness associated with compromised MTL functionality. Twenty-five patients with schizophrenia and 27 healthy control subjects completed trials of incidental FM encoding (experimental condition) and explicit encoding (EE, control condition) over the course of three visits spaced one week (± 2 days) apart. All participants were evaluated for recognition 10 min after each encoding condition was presented, and again one week (± 2 days) later. Results indicate that both groups performed better on the EE recognition trials when compared to FM (p's < 0.05). For the FM recognition trials, both groups performed similarly. However, participants with schizophrenia performed significantly worse on the EE recognition trials than healthy control participants (p's < 0.05). While participants with schizophrenia did not perform significantly worse when assessed for FM recognition, these results do not provide enough evidence to suggest that FM facilitates learning to a greater extent in schizophrenia when compared to EE. Whether FM may benefit a subgroup of patients with schizophrenia remains a focus of further investigation.

Phenomenology and neurobiology of self disorder in schizophrenia: Primary factors

Schizophrenia is a heterogeneous syndrome, varying between persons and over course of illness. In this and a companion article, we argue that comprehension of this condition or set of conditions may require combining a phenomenological perspective emphasizing disorders of basic-self experience ("ipseity disturbance") with a multidimensional appreciation of possible neurobiological correlates--both primary and secondary. Previous attempts to link phenomenology and neurobiology generally focus on a single neurocognitive factor. We consider diverse aspects of schizophrenia in light of a diverse, albeit interacting, set of neurocognitive abnormalities, examining both synchronic (structural) interdependence and diachronic (temporal) succession. In this article we focus on the primary or foundational role of early perceptual and motoric disturbances that affect perceptual organization and especially intermodal or multisensory perceptual integration (“perceptual dys-integration”). These disturbances are discussed in terms of their implications for three interconnected aspects of selfhood in schizophrenia, primary forms of: disrupted "hold" or "grip" on the world, hyperreflexivity, diminished self-presence (self-affection). Disturbances of organization or integration imply forms of perceptual incoherence or diminished cognitive coordination. The effect is to disrupt one's ability to apprehend the world in holistic, vital, or contextually grounded fashion, or to fully identify with or experience the unity of one's own body or thinking--thereby generating an early and profound (albeit often subtle) disruption or diminishment of basic or core self and of the sense of existing in a coherent world. We discuss interrelationships or possible complementarities between these three aspects, and consider their relevance for a neurodevelopmental account of schizophrenia.

Novelty's effect on memory encoding

It is often thought that novelty benefits memory formation. However, support for this idea mostly comes from paradigms that are open to alternative explanations. In the present study we manipulated novelty in a word-learning task through task-irrelevant background images. These background images were either standard (presented repeatedly), or novel (presented only once). Two types of background images were used: Landscape pictures and fractals. EEG was also recorded during encoding. Contrary to the idea that novelty aids memory formation, memory performance was not affected by the novelty of the background. In the evoked response potentials, we found evidence of distracting effects of novelty: both the N1 and P3b components were smaller to words studied with novel backgrounds, and the amplitude of the N2b component correlated negatively with subsequent retrieval. We conclude that although evidence from other studies does suggest benefits on a longer time scale, novelty has no instantaneous benefits for learning.

Altered neural basis of the reality processing and its relation to cognitive insight in schizophrenia

It has been reported that reality evaluation and recognition are impaired in patients with schizophrenia and these impairments are related to the severity of psychotic symptoms. The current study aimed to investigate the neural basis of impairments in reality evaluation and recognition and their relationships with cognitive insight in schizophrenia. During functional magnetic resonance imaging, 20 patients with schizophrenia and 20 healthy controls performed a set of reality evaluation and recognition tasks, in which subjects judged whether scenes in a series of drawings were real or unreal and whether they were familiar or novel. During reality evaluation, patients showed decreased activity in various regions including the inferior parietal lobule, retrosplenial cortex and parahippocampal gyrus, compared with controls. Particularly, parahippocampal gyrus activity was correlated with the severity of positive symptoms in patients. During recognition, patients also exhibited decreased activity in various regions, including the dorsolateral prefrontal cortex, inferior parietal lobule and posterior cingulate cortex. Particularly, inferior parietal lobule activity and posterior cingulate cortex activity were correlated with cognitive insight in patients. These findings provide evidence that neural impairments in reality evaluation and recognition are related to psychotic symptoms. Anomalous appraisal of context by dysfunctions in the context network may contribute to impairments in the reality processing in schizophrenia, and abnormal declarative memory processes may be involved in cognitive insight in patients with schizophrenia.

Perceptually or conceptually driven recognition: on the specificities of the memory deficit in schizophrenia

This study explored the effects of exemplar changes on visual object recognition in patients with schizophrenia and paired control subjects. The experimental design was derived from the process-dissociation procedure (PDP: Jacoby, 1991). The objects presented at test could be the same exemplar as at study (physically identical picture), a different exemplar of the same object category, or a new, non-studied object. In the inclusion task, participants had to generalize their recognition to the conceptual level by accepting both different and identical exemplars as old. In the exclusion task, on the other hand, they had to accept only the same exemplars of the studied objects as old. Overall, performance was better on the inclusion task than on the exclusion task; schizophrenia patients performed worse than controls on the inclusion task but not the exclusion task, misrecognizing different exemplars more often than healthy controls. The present findings reveal that both recollection and familiarity are impaired in patients with schizophrenia, who present a relational, conceptually driven memory deficit. This deficit does not allow them to recognize an object as a member of a specific category independently of perceptual variations. This retrieval mode influences their subjective awareness of items׳ familiarity, and should be considered as a target for remediation.

Verbal episodic memory along the course of schizophrenia and bipolar disorder: a new perspective

Impairment on episodic memory (EM) has been strongly correlated with psychiatric disorders, including schizophrenia (SZ) and bipolar disorder (BD). Morevover, the effects of course and progression of the illness on cognitive functioning have not been well established. The aim of the present study is to assess performance of episodic memory in BD and SZ according to their clinical stages. Subjects who met DSM-IV criteria for bipolar disorder (n=43) and schizophrenia (31), on euthymia or clinical remission, were recruited from the outpatients facilities at Hospital de Clínicas de Porto Alegre (Brazil). They were classified into two clinical stages (early or late for BD, and recent onset or chronic for SZ) and compared to 54 healthy controls. Episodic memory performance was assessed by means the Hopkins Verbal Learning Test-Revised (HVLT-R) that measures verbal learning and episodic memory in both disorders. Our results showed that patients in early stage of BD (EBD) performed better performance on the total immediate free recall (p<0.0001, F=12.060) as well as in delayed free recall (p<0.0001, F=13.914) compared to late stage (LBD) and SZ groups. In the ability to retain words learned, LBD and chronic (CSZ) were more impaired than other groups. Furthermore, the variation of learning (i.e, learning effects) along the 3 trials of immediate free recall was similar between groups. In conclusion, we found a cognitive decline alongside with the progression of BD whereas such impairment was evident in the early of SZ. Despite this, both groups (BD and SZ) seem to maintain the ability to learn. It emphasizes the relevance of studying new therapeutic strategies, in particular, cognitive rehabilitation/remediation techniques as promissory treatment for psychiatric patients, even in those with moderate disabilities.

Processing of facial and nonsocial information is differentially associated with severity of symptoms in patients with multiepisode schizophrenia

Patients with schizophrenia show impairments in social cognitive abilities, such as recognizing facial emotions. However, the relation to symptoms remains unclear. The goal of this study was to explore whether facial emotion recognition and face identity recognition are associated with severity of symptoms and to which extent associations with symptoms differ for processing of social versus nonsocial information. Facial emotion recognition, face recognition, and abstract pattern recognition were evaluated in 98 patients with multiepisode schizophrenia. Severity of symptoms was measured using a five-factor model of the Positive and Negative Syndrome Scale. Results show that facial emotion recognition and, to a lesser extent, face recognition were predominantly associated with severity of disorganization symptoms. In contrast, recognition of nonsocial patterns was associated with negative symptoms, excitement, and emotional distress. Reaction time rather than accuracy of social cognition explained variance in symptomatology. These results lead to the conclusion that facial emotion processing in schizophrenia appears to be associated with severity of symptoms, especially disorganization.

Cortisol mediates the effects of stress on the contextual dependency of memories

Stress is known to exert considerable impact on learning and memory processes. Typically, human studies have investigated memory for single items (e.g., pictures, words), but it remains unresolved how exactly stress may alter the storage of memories into their original encoding context (i.e., memory contextualization). Since neurocircuitry underlying memory contextualization processes is sensitive to the well-known stress hormone cortisol, we here investigated whether cortisol mediates stress effects on memory contextualization. Forty healthy young men were randomly assigned to a psychosocial stress or control group. Ten minutes after stress manipulation offset, participants were instructed to learn and remember neutral and negative words, each of which was depicted against a unique background picture. Approximately 24h later, memory was tested by means of cued retrieval and recognition tasks. To assess memory contextualization half of the words were tested in intact item-contexts pairs, and half in rearranged item-context combinations. Recognition data showed that cortisol, but no other indices of stress such as heart rate or subjective stress, mediated the effects of stress on contextualization of neutral and negative memories. The mediation analysis further showed that stress resulted in increases in cortisol and that cortisol was positively related to memory contextualization, but unrelated to other measures of memory. Thus, there seems to be a specific role for cortisol in the integration of a central memory into its surrounding context.

Time, not sleep, unbinds contexts from item memory

Contextual cues are known to benefit memory retrieval, but whether and how sleep affects this context effect remains unresolved. We manipulated contextual congruence during memory retrieval in human volunteers across 12 h and 24 h intervals beginning with either sleep or wakefulness. Our data suggest that whereas contextual cues lose their potency with time, sleep does not modulate this process. Furthermore, our results are consistent with the idea that sleep's beneficial effect on memory retention depends on the amount of waking time that has passed between encoding and sleep onset. The findings are discussed in the framework of competitive consolidation theory.

Association of impaired reality processing with psychotic symptoms in schizophrenia

Reality evaluation (i.e., the discrimination of things existing outside of oneself and figments of others' imagination) may be impaired in patients with schizophrenia, and impairment in reality evaluation may be related to psychotic symptoms such as hallucinations and delusions. In this study, we investigated the nature of impairment of reality processing and its relationship with hallucinations and delusions in schizophrenia. Twenty-six patients with schizophrenia and 25 healthy controls completed the reality evaluation task, in which subjects judged whether scenes in a series of drawings were real or unreal and whether they were familiar or novel. The patient group exhibited significantly lower accuracy in reality evaluation than the control group, and lower accuracy in the patient group was related to more severe hallucinations and delusions. These findings provide preliminary evidence that impaired reality evaluation is related to the formation or maintenance of hallucinations and delusions in schizophrenia.

Time-dependent effects of cortisol on the contextualization of emotional memories

BACKGROUND

The inability to store fearful memories into their original encoding context is considered to be an important vulnerability factor for the development of anxiety disorders like posttraumatic stress disorder. Altered memory contextualization most likely involves effects of the stress hormone cortisol, acting via receptors located in the memory neurocircuitry. Cortisol via these receptors induces rapid nongenomic effects followed by slower genomic effects, which are thought to modulate cognitive function in opposite, complementary ways. Here, we targeted these time-dependent effects of cortisol during memory encoding and tested subsequent contextualization of emotional and neutral memories.

METHODS

In a double-blind, placebo-controlled design, 64 men were randomly assigned to one of three groups: 1) received 10 mg hydrocortisone 30 minutes (rapid cortisol effects) before a memory encoding task; 2) received 10 mg hydrocortisone 210 minutes (slow cortisol) before a memory encoding task; or 3) received placebo at both times. During encoding, participants were presented with neutral and emotional words in unique background pictures. Approximately 24 hours later, context dependency of their memories was assessed.

RESULTS

Recognition data revealed that cortisol's rapid effects impair emotional memory contextualization, while cortisol's slow effects enhance it. Neutral memory contextualization remained unaltered by cortisol, irrespective of the timing of the drug.

CONCLUSIONS

This study shows distinct time-dependent effects of cortisol on the contextualization of specifically emotional memories. The results suggest that rapid effects of cortisol may lead to impaired emotional memory contextualization, while slow effects of cortisol may confer protection against emotional memory generalization.

The adaptive significance of adult neurogenesis: an integrative approach

Adult neurogenesis in mammals is predominantly restricted to two brain regions, the dentate gyrus (DG) of the hippocampus and the olfactory bulb (OB), suggesting that these two brain regions uniquely share functions that mediate its adaptive significance. Benefits of adult neurogenesis across these two regions appear to converge on increased neuronal and structural plasticity that subserves coding of novel, complex, and fine-grained information, usually with contextual components that include spatial positioning. By contrast, costs of adult neurogenesis appear to center on potential for dysregulation resulting in higher risk of brain cancer or psychological dysfunctions, but such costs have yet to be quantified directly. The three main hypotheses for the proximate functions and adaptive significance of adult neurogenesis, pattern separation, memory consolidation, and olfactory spatial, are not mutually exclusive and can be reconciled into a simple general model amenable to targeted experimental and comparative tests. Comparative analysis of brain region sizes across two major social-ecological groups of primates, gregarious (mainly diurnal haplorhines, visually-oriented, and in large social groups) and solitary (mainly noctural, territorial, and highly reliant on olfaction, as in most rodents) suggest that solitary species, but not gregarious species, show positive associations of population densities and home range sizes with sizes of both the hippocampus and OB, implicating their functions in social-territorial systems mediated by olfactory cues. Integrated analyses of the adaptive significance of adult neurogenesis will benefit from experimental studies motivated and structured by ecologically and socially relevant selective contexts.

Memory binding in clinical and non-clinical psychotic experiences: how does the continuum model fare?

INTRODUCTION

Both clinical and non-clinical auditory hallucinations (AH) have been associated with source memory deficits, supporting a continuum of underlying cognitive mechanisms, though few studies have employed the same task in patient and nonpatient samples. Recent commentators have called for more debate on the continuum model of psychosis. Consequently, the current study investigated the continuity model of AH with reference to memory binding.

METHODS

We used an identical voice and word recognition memory task to assess binding in two separate studies of: (1) healthy hallucination-prone individuals and controls (30 high and 30 low scorers on the Launay-Slade Hallucination Scale-Revised) and (2) schizophrenia patient samples (32 with AH, 32 without AH) and 32 healthy controls.

RESULTS

There was no evidence of impaired binding in high hallucination-prone, compared to low hallucination-prone individuals. In contrast, individuals with schizophrenia (both with and without AH) had difficulties binding (remembering "who said what"), alongside difficulties remembering individual words and voices. Binding ability and memory for voices were also negatively linked to the loudness of hallucinated voices reported by patients with AH.

CONCLUSIONS

These findings suggest that different mechanisms may exist in clinical and non-clinical hallucinators, adding to the growing debate on the continuum model of psychotic symptoms.

Source memory errors in schizophrenia, hallucinations and negative symptoms: a synthesis of research findings

BACKGROUND

Previous research has shown associations between source memory errors and hallucinations in patients with schizophrenia. We bring together here findings from a broad memory investigation to specify better the type of source memory failure that is associated with auditory and visual hallucinations.

METHOD

Forty-one patients with schizophrenia and 43 healthy participants underwent a memory task involving recall and recognition of lists of words, recognition of pictures, memory for temporal and spatial context of presentation of the stimuli, and remembering whether target items were presented as words or pictures.

RESULTS

False recognition of words and pictures was associated with hallucination scores. The extra-list intrusions in free recall were associated with verbal hallucinations whereas the intra-list intrusions were associated with a global hallucination score. Errors in discriminating the temporal context of word presentation and the spatial context of picture presentation were associated with auditory hallucinations. The tendency to remember verbal labels of items as pictures of these items was associated with visual hallucinations. Several memory errors were also inversely associated with affective flattening and anhedonia.

CONCLUSIONS

Verbal and visual hallucinations are associated with confusion between internal verbal thoughts or internal visual images and perception. In addition, auditory hallucinations are associated with failure to process or remember the context of presentation of the events. Certain negative symptoms have an opposite effect on memory errors.

Facilitation of memory by contextual cues in patients with diencephalic or medial temporal lobe dysfunction

Item-context binding is crucial for successful episodic memory formation, and binding deficits have been suggested to underlie episodic-memory deficits. Here, our research investigated the facilitation of cued recall and recognition memory by contextual cues in 20 patients with Korsakoff's amnesia, 20 unilateral medial-temporal lobectomy (MTL) patients and 36 healthy controls. In a computerized task participants had to learn 40 nouns that were randomly combined with a photograph of an everyday scene. Korsakoff patients showed a general memory deficit in both the cued recall and the recognition condition. A less severe memory impairment was found in the patients with medial-temporal lobectomy. Contextual cues facilitated cued recall to an equal extent in unilateral temporal lobectomy patients and healthy controls. However, no facilitation was observed in Korsakoff patients, suggesting an impairment in item-context binding during cued recall tasks. In contrast to the presumed exclusive dependency of recognition memory on item information, all groups equally profited from the contextual cues in recognition tasks. Our findings show that unilateral lesions as with MTL result in normal binding of context and item information, while bilateral dysfunction of the hippocampal-diencephalic system results in impaired context and item binding.

Perceptual organization impairment in schizophrenia and associated brain mechanisms: review of research from 2005 to 2010

Perceptual organization (PO) refers to the processes by which visual information is structured into coherent patterns such as groups, contours, perceptual wholes, and object representations. Impairments in PO have been demonstrated in schizophrenia since the 1960s and have been linked to several illness-related factors including poor premorbid functioning, poor prognosis, and disorganized symptoms. This literature was last reviewed in 2005. Since then, electrophysiological (electroencephalographic, event-related potential, and magnetoencephalographic) and fMRI studies in both patient and nonpatient samples have clarified brain mechanisms involved in the impairment, and additional behavioral studies in patients and nonpatients have clarified the computational mechanisms. In addition, data now exist on the functional consequences of PO impairments, in terms of secondary difficulties in face processing, selective attention, working memory, and social cognition. Preliminary data on drug effects on PO and on changes in response to treatment suggest that anomalies in PO may furnish a biomarker for the integrity of its associated biological mechanisms. All of this recent evidence allows for a clearer picture of the nature of the impairment and how it relates to broader aspects of brain and behavioral functioning in schizophrenia.

Computational cognitive models of prefrontal-striatal-hippocampal interactions in Parkinson's disease and schizophrenia

Disruption to different components of the prefrontal cortex, basal ganglia, and hippocampal circuits leads to various psychiatric and neurological disorders including Parkinson's disease (PD) and schizophrenia. Medications used to treat these disorders (such as levodopa, dopamine agonists, antipsychotics, among others) affect the prefrontal-striatal-hippocampal circuits in a complex fashion. We have built models of prefrontal-striatal and striatal-hippocampal interactions which simulate cognitive dysfunction in PD and schizophrenia. In these models, we argue that the basal ganglia is key for stimulus-response learning, the hippocampus for stimulus-stimulus representational learning, and the prefrontal cortex for stimulus selection during learning about multidimensional stimuli. In our models, PD is associated with reduced dopamine levels in the basal ganglia and prefrontal cortex. In contrast, the cognitive deficits in schizophrenia are associated primarily with hippocampal dysfunction, while the occurrence of negative symptoms is associated with frontostriatal deficits in a subset of patients. In this paper, we review our past models and provide new simulation results for both PD and schizophrenia. We also describe an extended model that includes simulation of the different functional role of D1 and D2 dopamine receptors in the basal ganglia and prefrontal cortex, a dissociation we argue is essential for understanding the non-uniform effects of levodopa, dopamine agonists, and antipsychotics on cognition. Motivated by clinical and physiological data, we discuss model limitations and challenges to be addressed in future models of these brain disorders.