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

Finding normal-to-better neurocognitive indexes in individuals with schizotypal traits using a social role task

Schizophrenia patients make more errors and have longer reaction times (RTs) than healthy controls in most cognitive tasks. Deficits are also observed in subclinical participants having high scores on the schizotypal personality questionnaire (SPQ). They are accompanied by smaller amplitudes of the event-related brain potentials (ERPs) that index attention and semantic- and working-memory. These functions are thus thought to be impaired in individuals having various schizophrenia attributes (SzAs). Nevertheless, normal RTs were recently found in SzAs during a particular self-referential task where half of the stimuli were names of extraordinary social roles (e.g., genius). Each name (ordinary or extraordinary) was presented individually, and participants were asked to decide whether or not they would consider themselves performing the role at any moment of their lives. To further test an absence of cognitive deficits in this task, the ERPs elicited by names of social roles were also examined in 175 healthy participants. The absence of longer RTs in high- than in low-SPQs was replicated. Moreover, the ERPs of high SPQs had larger occipital N1s, larger P2s and larger occipital N400s than those of low SPQs while late positive potentials (LPPs) were of similar amplitudes. Such results are consistent with clinical observations of greater attention and faster processing of stimuli related to extraordinary/delusional beliefs. Further studies should test whether the cognitive deficits found in SzAs are due to the use of tasks and stimuli that are less within their focus of interest than within that of healthy controls.

Relational memory function in schizophrenia: Electrophysiological evidence for early perceptual and late associative abnormalities

We used event-related potentials (ERPs) to examine encoding and retrieval during episodic memory in people with schizophrenia (SZ) and biological relatives of SZ (SZr). To isolate contextual from item-specific aspects of memory, we employed the Relational and Item-Specific Encoding (RISE) task. Twenty two healthy controls (HCs), 22 SZ, and 19 SZr, encoded visual depictions of objects when displayed alone (item-specific) or in pairs (relational encoding), and were later tested on recognition of specific objects and whether pairs of objects had appeared together. An early posterior component (P2) during encoding predicted later recognition and was diminished in SZ. A late negative potential (LNP) over left frontal brain regions during recognition was larger for relationally encoded objects than new and item-specific encoded objects in HCs. This pattern was absent for SZ and SZr. Smaller P2 and LNP components were associated with greater self-reported cognitive-perceptual abnormalities. Early posterior brain responses likely relevant to perceptual functions supporting memory formation were diminished in schizophrenia. Late frontal electrophysiological responses associated with relational aspects of memory appear diminished in SZ and SZr, potentially reflecting the influence of genetic liability for schizophrenia on brain functions supporting episodic memory.

Unveiling the Associations between EEG Indices and Cognitive Deficits in Schizophrenia-Spectrum Disorders: A Systematic Review

Cognitive dysfunctions represent a core feature of schizophrenia-spectrum disorders due to their presence throughout different illness stages and their impact on functioning. Abnormalities in electrophysiology (EEG) measures are highly related to these impairments, but the use of EEG indices in clinical practice is still limited. A systematic review of articles using Pubmed, Scopus and PsychINFO was undertaken in November 2021 to provide an overview of the relationships between EEG indices and cognitive impairment in schizophrenia-spectrum disorders. Out of 2433 screened records, 135 studies were included in a qualitative review. Although the results were heterogeneous, some significant correlations were identified. In particular, abnormalities in alpha, theta and gamma activity, as well as in MMN and P300, were associated with impairments in cognitive domains such as attention, working memory, visual and verbal learning and executive functioning during at-risk mental states, early and chronic stages of schizophrenia-spectrum disorders. The review suggests that machine learning approaches together with a careful selection of validated EEG and cognitive indices and characterization of clinical phenotypes might contribute to increase the use of EEG-based measures in clinical settings.

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.

Immediate Early Genes, Memory and Psychiatric Disorders: Focus on c-Fos, Egr1 and Arc

Many psychiatric disorders, despite their specific characteristics, share deficits in the cognitive domain including executive functions, emotional control and memory. However, memory deficits have been in many cases undervalued compared with other characteristics. The expression of Immediate Early Genes (IEGs) such as, c-fos, Egr1 and arc are selectively and promptly upregulated in learning and memory among neuronal subpopulations in regions associated with these processes. Changes in expression in these genes have been observed in recognition, working and fear related memories across the brain. Despite the enormous amount of data supporting changes in their expression during learning and memory and the importance of those cognitive processes in psychiatric conditions, there are very few studies analyzing the direct implication of the IEGs in mental illnesses. In this review, we discuss the role of some of the most relevant IEGs in relation with memory processes affected in psychiatric conditions.

The Relationship between Cytokines and Verbal Memory in Individuals with Schizophrenia and Their Unaffected Siblings

BACKGROUND

Verbal memory impairment may be considered an endophenotype in schizophrenia (SZ), also affecting the siblings of SZ subjects. Furthermore, the immune-inflammatory system response has an important modulatory effect on brain processes, especially on memory circuits.

OBJECTIVE

Investigating the relationship between TNF-α and IL-6 and memory performance in patients with SZ, their unaffected siblings (SB) and healthy controls (HC).

METHODS

35 subjects with SZ, 36 SB, and 47 HC underwent a neurocognitive assessment for verbal memory by means of the revised Hopkins Verbal Learning Test (HVLT-R) in addition to serum cytokines analyses.

RESULTS

SZ patients performed worse in HVLT-R than SB and HC, but SB and HC were not different. Regarding the biomarker levels, we found significant results of TNF-α for both groups. However, we did not find differences between groups after multiple-comparisons analysis. There were no significant correlations between episodic verbal memory, TNF-α, and IL-6.

CONCLUSION

The results are compatible with the hypothesis that deficits in verbal memory of individuals with SZ could be secondary to inadequate functioning of cognitive processing areas, such as proactive cognitive control.

An Event Related Potentials Study of Semantic Coherence Effect during Episodic Encoding in Schizophrenia Patients

The objective of this electrophysiological study was to investigate the processing of semantic coherence during encoding in relation to episodic memory processes promoted at test, in schizophrenia patients, by using the N400 paradigm. Eighteen schizophrenia patients and 15 healthy participants undertook a recognition memory task. The stimuli consisted of pairs of words either semantically related or unrelated to a given category name (context). During encoding, both groups exhibited an N400 external semantic coherence effect. Healthy controls also showed an N400 internal semantic coherence effect, but this effect was not present in patients. At test, related stimuli were accompanied by an FN400 old/new effect in both groups and by a parietal old/new effect in the control group alone. In the patient group, external semantic coherence effect was associated with FN400, while, in the control group, it was correlated to the parietal old/new effect. Our results indicate that schizophrenia patients can process the contextual information at encoding to enhance familiarity process for related stimuli at test. Therefore, cognitive rehabilitation therapies targeting the implementation of semantic encoding strategies can mobilize familiarity which in turn can overcome the recollection deficit, promoting successful episodic memory performance in schizophrenia patients.