Semantic memory impairment in schizophrenia--deficit in storage or access of knowledge?

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.

Semantic Memory Impairment Across the Schizophrenia Continuum: A Meta-Analysis of Category Fluency Performance

Semantic memory (SM) impairments are a core feature of schizophrenia and are present along the psychosis continuum. It is, however, unclear whether the degree of SM impairments vary along this continuum and if demographic and clinical factors affect impairment severity. This study performed meta-analyses of category fluency task performance (a task commonly used to assess SM) in 4 groups along the schizophrenia continuum: high schizotypes (HSZT), first-degree relatives (FDR), recent-onset patients (≤2 y; ROP) and chronic patients (CSZ). Electronic databases were searched for relevant studies published up to October 2019 resulting in the inclusion of 48 articles. The main analyses assessed fluency productivity scores in 2978 schizophrenia spectrum disorder patients, 340 first-degree relatives of schizophrenia spectrum disorder patients, and 3204 healthy controls. Further analyses assessed errors, mean cluster size, and switching data that were available in the CSZ group only. Results revealed significant impairments in fluency productivity were present in the FDR, ROP, and CSZ groups relative to healthy controls, but not in HSZT. In the CSZ group, significant differences relative to healthy controls were also observed in non-perseverative errors, mean cluster size, and number of switches. The findings collectively suggest that SM deficits are present at each stage of the continuum and are exacerbated post-illness onset. They also support the centrality of SM impairments in schizophrenia and most elevated risk groups. Future studies with more diverse measures of SM function are needed to replicate and extend this research.

Well-informed but not aware: The P.A.C.T.® psychoeducation program for schizophrenia improves knowledge about, but not insight into, the illness

BACKGROUND

Most individuals with schizophrenia (SZ) have little to no insight regarding the presence of their illness. Psychoeducational programs are state-of-the-art interventions that consist in delivering stabilized patients with accurate knowledge about their illness and its treatment. Evidence suggests a significant relationship between levels of illness-related knowledge and insight in SZ patients. However, the effect of psychoeducation on these related outcomes needs to be explored further.

METHODS

In this open label study involving 30 French-speaking patients with SZ, we propose to compare levels of knowledge and insight before and after the French P.A.C.T.® psychoeducation program to investigate how this approach affects both outcomes. Knowledge levels were measured with the self-questionnaire "What do I know?". Insight levels were measured using the Scale to Assess Unawareness of Mental Disorder (SUMD). Symptoms were assessed with the Positive And Negative Syndrome Scale (PANSS).

RESULTS

A large significant improvement of knowledge was observed (p < 0.001; d = 0.77). By contrast, the analysis reported no significant effect of psychoeducation on insight (p = 0.86; d = 0.07). PANSS total scores were significantly decreased after treatment (p = 0.001; d = 0.66).

CONCLUSIONS

Although the P.A.C.T.® program is a promising tool for improving illness-related knowledge in SZ patients, its use is not sufficient to significantly improve insight levels.

Differential patterns of contextual organization of memory in first-episode psychosis

Contextual information is used to support and organize episodic memory. Prior research has reliably shown memory deficits in psychosis; however, little research has characterized how this population uses contextual information during memory recall. We employed an approach founded in a computational framework of free recall to quantify how individuals with first episode of psychosis (FEP, N = 97) and controls (CON, N = 55) use temporal and semantic context to organize memory recall. Free recall was characterized using the Hopkins Verbal Learning Test-Revised (HVLT-R). We compared FEP and CON on three measures of free recall: proportion recalled, temporal clustering, and semantic clustering. Measures of temporal/semantic clustering quantified how individuals use contextual information to organize memory recall. We also assessed to what extent these measures relate to antipsychotic use and differentiated between different types of psychosis. We also explored the relationship between these measures and intelligence. In comparison to CON, FEP had reduced recall and less temporal clustering during free recall (p < 0.05, Bonferroni-corrected), and showed a trend towards greater semantic clustering (p = 0.10, Bonferroni-corrected). Within FEP, antipsychotic use and diagnoses did not differentiate between free recall accuracy or contextual organization of memory. IQ was related to free recall accuracy, but not the use of contextual information during recall in either group (p < 0.05, Bonferroni-corrected). These results show that in addition to deficits in memory recall, FEP differed in how they organize memories compared to CON.

First-episode psychosis patients exhibit impaired memory recall and deviation in how context is used to support recall ability. A US team of researchers led by the University of Pittsburgh’s Vishnu Murty examined how FEP affects an individual’s ability to organize memory based on context, by noting how well patients could recall words from a spoken list. Alongside recollection accuracy, Murty’s team assesed participant ability to recall words said proximally in sequence, and the ability to recall words from the same category—measuring ‘temporal clustering’ and ‘semantic clustering.’ The researchers found that patients with FEP had reduced recall ability and less temporal clustering. Recall accuracy and IQ were also found to be related. This study increases knowledge of FEP-related cognitive changes and could help to target specific therapies.

Are conceptual abilities impaired in schizophrenia?

Whereas semantic processing deficits are well-documented in schizophrenia, conceptual abilities have been poorly explored. This study aims at specifically exploring conceptualization abilities in 34 adults fulfilling schizophrenia according to DSM-IV and 34 healthy controls with similar socio-demographic characteristics. The 2 groups were assessed on the WAIS-R similarities test and the concept generation test (Raoux et al., 2014) consisting of free-sorting 6 cards of pictures of animals and geometric shapes to be separated in two groups or categories based on common attributes. After each sorting, the participant is asked to explain his/her sorting. Whereas the schizophrenic patients performed significantly poorer than the control participants in the semantic knowledge and lexico-semantic tests, there was no difference neither in the WAIS-R similarities test nor in the concept generation test, which supports the hypothesis of preserved high level conceptualization abilities in schizophrenia. However, qualitative differences in performing the concept generation test were evidenced. The patients used more often mixed criteria leading them to compare two different hierarchical levels (e.g., low-level physical attributes vs. high-level semantic criteria). Furthermore, the qualitative analysis based on the explanations provided by the participants shows that the categorizations achieved by schizophrenic patients are more often based on unexpected criteria.

Preserved strategic grain-size regulation in memory reporting in patients with schizophrenia

BACKGROUND

Cognitive and introspection disturbances are considered core features of schizophrenia. In real life, people are usually free to choose which aspects of an event they recall, how much detail to volunteer, and what degree of confidence to impart. Their decision will depend on various situational and personal goals. The authors explored whether schizophrenia patients are able to achieve a compromise between accuracy and informativeness when reporting semantic information.

METHODS

Twenty-five patients and 23 healthy matched control subjects answered general knowledge questions requiring numerical answers (how high is the Eiffel tower?), freely at first and then through a metamemory-based control. In the second phase, they answered with respect to two predefined intervals, one narrow and one broad; attributed a confidence judgment to both answers; and afterward selected one of the two answers. Data were analyzed using analyses of variance with group as the between-subjects factor.

RESULTS

Patients reported information at a self-paced level of precision less accurately than healthy participants. However, they benefited remarkably from the framing of the response and from the metamemory processes of monitoring and control to the point of improving their memory reporting and matching healthy subjects' accuracy.

CONCLUSIONS

In spite of their memory deficit during free reporting, after accuracy monitoring, patients strategically regulated the grain size of their memory reporting and proved able to manage the competing goals of accuracy and informativeness. These results give some cause for optimism as to the possibility for patients to adapt to everyday life situations.

The influence of semantic processing on odor identification ability in schizophrenia

Despite the well-documented observation of odor identification deficits in schizophrenia, less is known about where the disruption in the process of correctly identifying an odor occurs. This study aimed to determine the potential moderating effects of semantic processing on the observed olfactory dysfunction in schizophrenia. Schizophrenia patients and healthy comparison subjects completed two versions of the University of Pennsylvania Smell Identification Test (UPSIT): an uncued free-response version and the standard multiple-choice paradigm, as well as three semantic measures: The Boston Naming Test, Animal Naming, and Pyramids and Palm Tree Test. Schizophrenia patients yielded significantly lower scores than the comparison group on the standard UPSIT and on semantic measures. No relationship was observed between olfactory and semantic task performance in patients. These data suggest that odor identification deficits may not be primarily due to semantic processing deficits in schizophrenia.

Semantics, pragmatics, and formal thought disorders in people with schizophrenia

BACKGROUND

The aim of this study was to analyze how formal thought disorders (FTD) affect semantics and pragmatics in patients with schizophrenia.

METHODS

The sample comprised subjects with schizophrenia (n = 102) who met the criteria for the disorder according to the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition Text Revision. In the research process, the following scales were used: Positive and Negative Syndrome Scale (PANSS) for psychopathology measurements; the Scale for the Assessment of Thought, Language, and Communication (TLC) for FTD, Word Accentuation Test (WAT), System for the Behavioral Evaluation of Social Skills (SECHS), the pragmatics section of the Objective Criteria Language Battery (BLOC-SR) and the verbal sections of the Wechsler Adults Intelligence Scale (WAIS) III, for assessment of semantics and pragmatics.

RESULTS

The results in the semantics and pragmatics sections were inferior to the average values obtained in the general population. Our data demonstrated that the more serious the FTD, the worse the performances in the Verbal-WAIS tests (particularly in its vocabulary, similarities, and comprehension sections), SECHS, and BLOC-SR, indicating that FTD affects semantics and pragmatics, although the results of the WAT indicated good premorbid language skills.

CONCLUSION

The principal conclusion we can draw from this study is the evidence that in schizophrenia the superior level of language structure seems to be compromised, and that this level is related to semantics and pragmatics; when there is an alteration in this level, symptoms of FTD appear, with a wide-ranging relationship between both language and FTD. The second conclusion is that the subject's language is affected by the disorder and rules out the possibility of a previous verbal impairment.

Longitudinal changes in semantic categorization performance after symptomatic remission from first-episode psychosis: a 3-year follow-up study

Semantic categorization abnormalities have been observed in schizophrenia, but studies have rarely focused on the longitudinal trajectory. In this study, we consider semantic performance and the relationship with symptomatic changes during recovery from a first-episode of schizophrenia over a period of 3 years. Thirty-seven first-episode patients with schizophrenia were compared to thirty-seven matched controls in a categorization task. Patients were assessed at first episode, after clinical stabilization, and annually for the subsequent 3 years. In the task, participants indicated whether a word belonged to a given category. Each category contained words of varying degrees of semantic relatedness: typical, atypical, borderline, related-but-outside, and unrelated. Reaction times and proportion of 'yes' responses were analyzed. At first assessment, semantic categorization abnormalities were observed in first-episode patients. Patients assigned more semantically-dissimilar words to the categories than controls. As patients stabilized from acute states, their semantic categorization performance improved and then remained stable throughout the entire follow up period of 3 years. Interestingly, semantic performance deficits, particularly a diminished typicality effect, correlated with negative symptoms in the initial episode, but not at stabilization when symptoms subsided. No significant associations between positive and negative symptoms, or pre-defined categorization measures were identified. The data demonstrated semantic memory abnormalities in first-episode schizophrenia. However, an improvement of semantic categorization performance was observed in stabilized schizophrenia patients. Overall, the data are suggestive of a state effect in semantic abnormalities rather than a trait effect. The correlation between degree of impairment and symptoms may explain previous inconsistent findings.

Using ketamine to model semantic deficits in schizophrenia

Semantic deficits constitute a core cognitive abnormality in schizophrenia. In the current study, the N-methyl-d-aspartate receptor antagonist ketamine was administered to healthy individuals acutely while they performed semantic processing tasks that included word pairs of differing degrees of semantic relatedness. Two dimensions of semantic processing were investigated: (1) explicit versus implicit processing, that is, unconscious versus conscious processing of semantic relationships and (2) direct versus indirect processing, that is, word pairs that are closely (LION-TIGER) or distantly (LION-STRIPES) related. The immediate effects of ketamine (0.8 mg/kg per hour during 80 minutes with approximate target plasma levels of 200 ng/mL) were examined in a placebo-controlled double-blind repeated-measures group design with 19 participants. It was predicted that ketamine would disrupt access to semantic memory as evidenced in schizophrenia, especially the indirectly related word pairs. In addition, implicit processing and explicit processing were predicted to be differentially affected. Ketamine administration did result in an abnormal performance in the reaction time responses to implicitly presented indirectly related word pairs (ie, greater priming) and reduced accuracy for explicit pairs. Performance on the directly related word pair tasks (both implicit and explicit) was similar across ketamine and placebo conditions, except for the suggestion of abnormal semantic matching in the accuracy data in the implicit task. This study confirms that implicit indirect semantic processing is changed under the influences of ketamine akin to schizophrenia. Future research comparing a schizophrenia group and a ketamine group directly about these tasks is needed to determine the similarity of impairments.

Action (verb) fluency in schizophrenia: getting a grip on odd speech

BACKGROUND

Formal thought disorder (TD) is a key symptom of schizophrenia with a significant impact on interpersonal relationships. Current cognitive models emphasize disordered language functioning and abnormalities accessing semantic representations. The cortical mechanisms for language and motor function are closely linked, hence action-related language may be impaired in TD, yet existing studies have focussed exclusively on object (noun) rather than action (verb) semantics.

METHOD

In order to examine this issue both action (verb) and traditional semantic (tools, fruits, musical instruments) and phonological (FAS) fluency tasks were completed by individuals with schizophrenia (N=53) and healthy controls (N=69). Fluency performance was measured as the total number of correct words generated in 60s. The Schizotypal Personality Questionnaire (SPQ) was used to index odd and disorganized speech, as well as positive and negative symptoms.

RESULTS

Fluency on all tasks was impaired in schizophrenia, compared to controls, with a similar effect size. Within the schizophrenia group Odd Speech was correlated with poor fluency for actions, tools and musical instruments but not fruit or phonological fluency. These action-related fluency deficits were also correlated with Constricted Affect and Social Anxiety but not with Unusual Perceptions/Odd Beliefs.

CONCLUSION

These results point to a unique connection and possible common aetiology between action fluency and odd speech in schizophrenia rather than a general impairment in language/executive functions common to fluency tasks. The findings provide the first evidence of a specific role of action-based language production deficits in TD together with a joint effect on social interaction skills.

Production of atypical category exemplars in patients with schizophrenia

Previous studies have revealed semantic memory impairments in patients with schizophrenia, and suggested that certain of these impairments were related to thought disorganization. One explanation offered for this is a broadening of the boundaries of semantic categories in schizophrenia. We selected 16 semantic categories, and required a sample of 41 schizophrenia patients and 43 healthy control subjects to produce one exemplar from each category. The typicality of the subjects' responses was rated. The exemplars produced by the patients were on average less typical than those produced by the healthy controls. No significant association between typicality of the response and thought disorganization was revealed in the patient sample. Affective flattening, alogia, and anhedonia were significantly and inversely associated with the typicality score, that is, higher ratings of these symptoms were associated with more typical responses. Our results suggest that a broadening of semantic category boundaries is observed in patients with schizophrenia, but is unrelated to thought disorganization. This semantic abnormality is not a feature of the patients with high ratings of certain negative symptoms.

Neurocognition in schizophrenia

Neuropsychological deficits among schizophrenia patients have been consistently documented in research over the past 20 years and are reviewed in this chapter. Discussion of general abilities is presented as a background and is followed by analysis of functioning in specific cognitive domains. Overall intellectual deficits are indicated by results from both general intelligence tests and composite test battery scores. Within specific cognitive domains, effect size differences are noted in numerous areas, including attention, with indications that working memory is affected more severely than simple attention, likely due to inclusion of an executive component in such tasks. There is also evidence of slowed processing speed among schizophrenia patients, likely contributing to deficits in other domains which rely on rapid and efficient assimilation of information. Executive impairments have been found on tests assessing set-shifting abilities, selective attention, and inhibition of inappropriate responses. Learning and memory deficits have been demonstrated extensively, with some evidence that recall of verbal material is more affected than recall of visual information, and that recognition abilities are comparatively less impaired than recall for both modalities. Receptive and expressive language abilities are compromised in schizophrenia patients, as well as visual perceptual, constructional, and fine motor skills. Social cognition is an area of particular importance due to its relevance to functional outcome. Deficits in expression and recognition of facial and prosodic affect have been demonstrated, although subjective experience of emotion appears to be relatively well preserved. Neuropsychological deficits described in this review appear to generally remain stable throughout adulthood, supporting neurodevelopmental, rather than neurodegenerative, models of the illness. Finally, cognitive deficits are increasingly used as endophenotypes, which is likely an important direction of future research.

Neurological disorders in schizophrenia

Schizophrenia (SZ) is a complex, heterogeneous, and disabling psychiatric disorder that impairs multiple aspects of human cognitive, perceptual, emotional, and behavioral functioning. SZ is relatively frequent (prevalence around 1%), with onset usually during adolescence or early adulthood, and has a deteriorating course. The rapidly growing area of neuroimaging research has has found clear evidence of many cortical and subcortical abnormalities in individuals with SZ. In this article the most recent findings from multiple studies on neurological disorders in SZ are reviewed, and the authors make a strong argument for a neurological basis of the schizophrenic process.