Selective pair recognition memory impairment with no response bias in schizophrenia

Cross-modal associative memory impairment in schizophrenia

Impaired associative memory function in patients with schizophrenia has received considerable attention. However, previous studies have primarily concentrated on unisensory materials, which limits our understanding of the broader implications of this impairment. In this study, we sought to expand on this knowledge by examining two types of associative memory domains in individuals with schizophrenia, leveraging both visual (Vis) and auditory (Aud) materials. A total of 32 patients with schizophrenia and 29 healthy controls were recruited to participate in the study. Each participant participated in an experiment composed of three paradigms in which different abstract materials (Aud-Aud, Aud-Vis, and Vis-Vis) were presented. Subsequently, the discriminability scores of the two groups were calculated and compared in different modal tasks. Results from the study indicated that individuals with schizophrenia demonstrated varying degrees of associative memory dysfunction in both the same and cross-modalities, with the latter having a significantly lower score than healthy controls (t = 4.120, p < 0.001). Additionally, the cross-modal associative memory function was significantly and negatively correlated with the severity of negative symptoms among individuals diagnosed with schizophrenia (r = -0.362, p = 0.042). This study provides evidence of abnormalities in the processing and memorization of information that integrates multiple sensory modalities in individuals with schizophrenia. This is of great significance for further understanding the cognitive symptoms and pathological mechanisms of schizophrenia, potentially guiding the development of relevant interventions and treatment methods.

Spatial and non-spatial feature binding impairments in visual working memory in schizophrenia

Working memory (WM) impairments are well recognized in schizophrenia patients (PSZ) and contribute to poor psycho-social outcomes in this population. Distinct neural networks underlay the ability to encode and recall visual and spatial information raising the possibility that profile of visual working memory performance may help pinpoint dysfunctional neural correlates in schizophrenia. This study assessed the resolution and associative aspects of visual working memory deficits in schizophrenia and whether these deficits arise during encoding or maintenance processes. A total of 60 participants (30 PSZ and 30 healthy controls) matched in age, gender and education assessed on a modified object in place (OiPT), a delayed non-match-to-sample (DNMST) and a delayed spatial estimation (DSET) task. Patients demonstrated lower accuracy than controls in binding visual features of the same object and recognizing novel objects as well as lower precision recalling the location of a memorized target. Moreover, response choice set size affected recognition accuracy more in PSZ than controls. However, delay duration affected spatial recall precisions, binding, and recognition accuracy equally in the two groups. Our results suggest that visual working memory (vWM) impairments in schizophrenia predominantly reflect spatial and non-spatial binding deficits, with largely preserved discrete feature information. Moreover, these impairments likely arise more during encoding than during maintenance. These binding deficits may reflect impaired effective neural functional connectivity observed in schizophrenia.

Reduced Functional Connectivity in Brain Networks Underlying Paired Associates Memory Encoding in Schizophrenia

BACKGROUND

Deficits in relational episodic memory encoding are characteristic of schizophrenia (SZ), but whole-brain multivariate analyses of these deficits have been lacking. Open science has provided task-based functional magnetic resonance imaging (fMRI) data investigating paired associate encoding in SZ, but it has not yet been mobilized to address this gap in the literature. Therefore, in this study, we use previously unpublished task fMRI data to conduct the first network-level investigation of impaired relational episodic encoding in SZ.

METHODS

Using fMRI data acquired from 40 healthy control participants and 40 age- and sex-matched persons with SZ, we examined the networks involved in successful versus unsuccessful encoding of verbal paired associates using an associative semantic strategy.

RESULTS

Constrained principal component analysis for fMRI revealed 3 distinct functional networks recruited during encoding: a responding network, a linguistic processing/attention network, and the default mode network. Relative to the healthy control group, the SZ group exhibited aberrant activity in all 3 networks during successful encoding; namely, hypoactivation in the linguistic processing/attention network, lower peak activation in the responding network, and weaker suppression in the default mode network. Independent of group effects, a pattern of stronger anticorrelating linguistic processing/attention-default mode network activity during successful encoding significantly predicted subsequent retrieval of paired associates.

CONCLUSIONS

Together with previous observations of language network hypoactivation during controlled semantic processes, these results suggest that abnormalities in networks representing language and meaning may contribute to difficulties employing deep semantic strategies during relational episodic encoding in SZ.

Episodic Memory and Schizophrenia: From Characterization of Relational Memory Impairments to Neuroimaging Biomarkers

Episodic memory research in schizophrenia has a long history already which has clearly established significant impairments and strong associations with brain measures and functional outcome. The purpose of this chapter is not to make an exhaustive review of the recent literature but to highlight some relatively recent developments in the cognitive neuroscience field of episodic memory and schizophrenia. Hence, we present a contemporary view focusing specifically of relational memory which represents a form of episodic memory that refers to associations or binding among items or elements presented together. We describe the major tasks used and illustrate how their combination with brain imaging has: (1) favored the use of experimental memory tasks to isolate specific processes with specific neural correlates, (2) led to a distributed view of the neural correlates of memory impairments in schizophrenia where multiple regions are contributing, and (3) made possible the identification of fMRI biomarkers specific to episodic memory. We then briefly propose what we see as the next steps for memory research in schizophrenia so that the impact of this work can be maximized.

Relational Memory in the Early Stage of Psychosis: A 2-Year Follow-up Study

BACKGROUND

Relational memory, the ability to bind information into complex memories, is moderately impaired in early psychosis and severely impaired in chronic schizophrenia, suggesting relational memory may worsen throughout the course of illness.

METHODS

We examined relational memory in 66 early psychosis patients and 64 healthy control subjects, with 59 patients and 52 control subjects assessed longitudinally at baseline and 2-year follow-up. Relational memory was assessed with 2 complementary tasks, to test how individuals learn relationships between items (face-scene binding task) and make inferences about trained relationships (associative inference task).

RESULTS

The early psychosis group showed impaired relational memory in both tasks relative to the healthy control group. The ability to learn relationships between items remained impaired in early psychosis patients, while the ability to make inferences about trained relationships improved, although never reaching the level of healthy control performance. Early psychosis patients who did not progress to schizophrenia at follow-up had better relational memory than patients who did.

CONCLUSIONS

Relational memory impairments, some of which improve and are less severe in patients who do not progress to schizophrenia, are a target for intervention in early psychosis.

Impaired relational memory in the early stage of psychosis

BACKGROUND

Humans constantly take in vast amounts of information, which must be filtered, flexibly manipulated, and integrated into cohesive relational memories in order to choose relevant behaviors. Relational memory is impaired in chronic schizophrenia, which has been linked to hippocampal dysfunction. It is unclear whether relational memory is impaired in the early stage of psychosis.

METHODS

We studied eye movements during a face-scene pairs task as an indirect measure of relational memory in 89 patients in the early stage of psychosis and 84 healthy control participants. During testing, scenes were overlaid with three equally-familiar faces and participants were asked to recall the matching (i.e. previously-paired) face. During Match trials, one face had been previously paired with the scene. During Non-Match trials, no faces matched the scene. Forced-choice explicit recognition was recorded as a direct measure of relational memory.

RESULTS

Healthy control subjects rapidly (within 250-500 ms) showed preferential viewing of the matching face during Match trials. In contrast, preferential viewing was delayed in patients in the early stage of psychosis. Explicit recognition of the matching face was also impaired in the patient group.

CONCLUSIONS

This study provides novel evidence for a relational memory deficit in the early stage of psychosis. Patients showed deficits in both explicit recognition as well as abnormal eye-movement patterns during memory recall. Eye movements provide a promising avenue for the study of relational memory in psychosis, as they allow for the assessment of rapid, nonverbal memory processes.

Examining the neural correlates of active and passive forms of verbal-spatial binding in working memory

We designed an fMRI study to pinpoint the neural correlates of active and passive binding in working memory. Participants were instructed to memorize three words and three spatial locations. In the passive binding condition, words and spatial locations were directly presented as bound. Conversely, in the active binding condition, words and spatial locations were presented as separated, and participants were directed to intentionally create associations between them. Our results showed that participants performed better on passive binding relative to active binding. FMRI analysis revealed that both binding conditions induced greater activity within the hippocampus. Additionally, our analyses divulged regions specifically engaged in passive and active binding. Altogether, these data allow us to propose the hippocampus as a central candidate for working memory binding. When needed, a frontal-parietal network can contribute to the rearrangement of information. These findings may inform theories of working memory binding.

Altered emotional modulation of associative memory in first episode schizophrenia: An fMRI study

Alterations of associative memory, resulting from perturbations within the medial temporal lobe, are well established in schizophrenia. So far, all the studies having examined associative memory in schizophrenia have limited ecological validity, as people experience various emotional stimuli in their life. As such, emotion must be taken into account in order to fully understand memory. Thus, we designed an fMRI study aimed at investigating neural correlates of the effects of emotions on associative memory in schizophrenia. Twenty-four first episode schizophrenia (FES) patients and 20 matched controls were instructed to memorize 90 pairs of standardized pictures during a scanned encoding phase. Each of the 90 pairs was composed of a scene and an unrelated object. Furthermore, trials were either neutral or emotional as a function of the emotional valence of the scene comprising each pair. FES patients exhibited lower performance for both conditions than controls, with greater deficits in regard to emotional versus neutral associations. fMRI analyses revealed that these deficits were related to lower activations in mnemonic and limbic regions. This study provides evidence of altered associative memory and emotional modulation in schizophrenia, resulting from dysfunctions in the cerebral networks underlying memory, emotion, and encoding strategies. Together, our results suggest that all these dysfunctions may be targets for new therapeutic interventions known to improve cognitive deficits in schizophrenia.

Source retrieval is not properly differentiated from object retrieval in early schizophrenia: an fMRI study using virtual reality

Source memory, the ability to identify the context in which a memory occurred, is impaired in schizophrenia and has been related to clinical symptoms such as hallucinations. The neurobiological underpinnings of this deficit are not well understood. Twenty-five patients with recent onset schizophrenia (within the first 4.5 years of treatment) and twenty-four healthy controls completed a source memory task. Participants navigated through a 3D virtual city, and had 20 encounters of an object with a person at a place. Functional magnetic resonance imaging was performed during a subsequent forced-choice recognition test. Two objects were presented and participants were asked to either identify which object was seen (new vs. old object recognition), or identify which of the two old objects was associated with either the person or the place being presented (source memory recognition). Source memory was examined by contrasting person or place with object. Both patients and controls demonstrated significant neural activity to source memory relative to object memory, though activity in controls was much more widespread. Group differences were observed in several regions, including the medial parietal and cingulate cortex, lateral frontal lobes and right superior temporal gyrus. Patients with schizophrenia did not differentiate between source and object memory in these regions. Positive correlations with hallucination proneness were observed in the left frontal and right middle temporal cortices and cerebellum. Patients with schizophrenia have a deficit in the neural circuits which facilitate source memory, which may underlie both the deficits in this domain and be related to auditory hallucinations.

Contributions of Feature Binding During Encoding and Functional Connectivity of the Medial Temporal Lobe Structures to Episodic Memory Deficits Across the Prodromal and First-Episode Phases of Schizophrenia

Patients with and at risk for psychosis may have difficulty using associative strategies to facilitate episodic memory encoding and recall. In parallel studies, patients with first-episode schizophrenia (n = 27) and high psychosis risk (n = 28) compared with control participants (n = 22 and n = 20, respectively) underwent functional MRI during a remember-know memory task. Psychophysiological interaction analyses, using medial temporal lobe (MTL) structures as regions of interest, were conducted to measure functional connectivity patterns supporting successful episodic memory. During encoding, patients with first-episode schizophrenia demonstrated reduced functional coupling between MTL regions and regions involved in stimulus representations, stimulus selection, and cognitive control. Relative to control participants and patients with high psychosis risk who did not convert to psychosis, patients with high psychosis risk who later converted to psychosis also demonstrated reduced connectivity between MTL regions and auditory-verbal and visual-association regions. These results suggest that episodic memory deficits in schizophrenia are related to inefficient recruitment of cortical connections involved in associative memory formation; such deficits precede the onset of psychosis among those individuals at high clinical risk.

Revised associative inference paradigm confirms relational memory impairment in schizophrenia

OBJECTIVE

Patients with schizophrenia have widespread cognitive impairments, with selective deficits in relational memory. We previously reported a differential relational memory deficit in schizophrenia using the Associative Inference Paradigm (AIP), a task suggested by the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) initiative to examine relational memory. However, the AIP had limited feasibility for testing in schizophrenia because of high attrition of schizophrenia patients during training. Here we developed and tested a revised version of the AIP to improve feasibility.

METHOD

30 healthy control and 37 schizophrenia subjects received 3 study-test sessions on 3 sets of paired associates: H-F1 (house paired with face), H-F2 (same house paired with new face), and F3-F4 (two novel faces). After training, subjects were tested on the trained, noninferential Face-Face pairs (F3-F4) and novel, inferential Face-Face pairs (F1-F2), constructed from the faces of the trained House-Face pairs.

RESULTS

Schizophrenia patients were significantly more impaired on the inferential F1-F2 pairs than the noninferential F3-F4 pairs, providing evidence for a differential relational memory deficit. Only 8% of schizophrenia patients were excluded from testing because of poor training performance.

CONCLUSIONS

The revised AIP confirmed the previous finding of a relational memory deficit in a larger and more representative sample of schizophrenia patients.

Intact relational memory and normal hippocampal structure in the early stage of psychosis

BACKGROUND

Previous studies indicate that the transition to psychosis is associated with dynamic changes of hippocampal integrity. Here we explored hippocampal volume and neural activation during a relational memory task in patients who were in the early stage of a psychotic illness.

METHODS

Forty-one early psychosis patients and 34 healthy control subjects completed a transitive inference (TI) task used previously in chronic schizophrenia patients. Participants learned to select the "winner" of two sets of stimulus pairs drawn from an overlapping sequence (A > B > C > D > E) and a nonoverlapping set (a > b, c > d, e > f, g > h). During a functional magnetic resonance imaging scan, participants were tested on the trained pairs and made inferential judgments on novel pairings that could be solved based on training (e.g., B vs. D). Hippocampal volumes were manually segmented and compared between groups. Functional magnetic resonance imaging analyses included 27 early psychosis patients and 30 control subjects who met memory training criteria.

RESULTS

Groups did not differ on inference performance or hippocampal volume and exhibited similar activation of medial temporal regions when judging nonoverlapping pairs. However, patients who failed to meet memory training criteria had smaller hippocampal volumes. Neural activity during TI was less widespread in early psychosis patients, but between-group differences were not significant. Hippocampal activity during TI was positively correlated with inference performance only in control subjects.

CONCLUSIONS

Our results provide evidence that relational memory impairment and hippocampal abnormalities, well established in chronic schizophrenia, are not fully present in early psychosis patients. This provides a rationale for early intervention, targeting the possible delay, reduction, or prevention of these deficits.

Visuo-perceptual organization and working memory in patients with schizophrenia

We explore the mechanisms sub-tending the re-organization and memorization of visual information by studying how these mechanisms fail in patients with schizophrenia. Several studies have suggested that patients have difficulties in organizing information in perception and memory. We explore to what extent prompting patients to group items influences memory performance. We distinguish automatic grouping from top-down grouping processes, which are especially involved in re-organizing information. The main task was to memorize pairs of figures. Following manipulation of proximity, pairs of figures were part of the same perceptual group (within-group pair, formed on the basis of automatic grouping) or belonged to different groups (between-group pairs, re-grouped through top-down processes). Prior to the memory task, subjects ran a perception task prompting them to prioritize either within-group or between-group pairs. Unlike patients, controls globally benefited from grouping by proximity in the memory task. In addition, the results showed that prioritizing between-group pairs had a deleterious effect in patients, but with a large decrement in memory performance in the case of within-group rather than between-group figures. This occurred despite preserved focalization on within-group figures, as shown by eye-movement recordings. The suggestion is that when patients are prompted to re-group separate items, they can do so, but the benefit derived from automatic grouping is then not only lost but also reversed. This suggests re-organizing visual information not only involves re-grouping separate items but also integrating these new groups in a unified representation, which is impaired in patients with schizophrenia.

Persisting cognitive deficits induced by low-dose, subchronic treatment with MK-801 in adolescent rats

Cognitive impairments have been proposed as a core feature of schizophrenia. Studies have shown that chronic or subchronic treatment with N-methyl-d-aspartate (NMDA) antagonists could induce cognitive deficits that resemble the symptoms of schizophrenia, yet few studies have investigated the effects of repeated NMDA blockade during adolescence on cognition. In the current study, adolescent, male rats were treated with an intraperitoneal injection of MK-801 (0.05, 0.1, and 0.2mg/kg) once daily for 14days. They were then tested 24h and 14days after drug cessation, respectively, in a series of behavioural tasks, including the object recognition task, the object-in-context recognition task and the working memory task of the Morris water maze (MWM). Results showed that object-in-context recognition and spatial working memory in the MWM were significantly impaired by repeated MK-801 treatment when animals were tested 24h after drug cessation, but object recognition was left intact. In particular, such deficits were observed 14days after drug cessation in the 0.2mg/kg group. The cognition-impairing effect of MK-801 could not be attributed to malnutrition or alterations in motor functions. Taken together, this study may provide support for establishing an animal model of cognitive deficits of schizophrenia based on low-dose, repeated treatment of MK-801 during adolescence.

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.

Use of eye movement monitoring to examine item and relational memory in schizophrenia

BACKGROUND

Patients with schizophrenia may be impaired at remembering interitem and item-context relationships (relational memory), even when memory for items is intact. Here, we applied the novel approach of using eye movements to assess integrity of item and relational memory in schizophrenia. This method does not rely on introspection and may be more readily translated to animal models than traditional behavioral methods.

METHODS

Sixteen healthy control subjects and 16 patients were administered a scene memory task while eye movements were monitored. During testing, participants indicated whether the scenes were unchanged, contained a new item (item manipulation), had a change in item location (relational manipulation), or were new. It was predicted that memory would be disproportionately impaired when relational changes were made.

RESULTS

Results confirmed that tasks were equally difficult and showed that patients were impaired identifying all scene types. These behavioral impairments were associated with more severe disorganization and negative symptoms. Eye movement results were more specific. Both groups looked disproportionately at critical regions of repeated versus novel scenes-an effect of scene repetition. However, in contrast with predictions, patients showed equivalent eye-movement-based memory impairment whether changes were relational or item-based.

CONCLUSIONS

This is the first experiment to demonstrate that eye movements can be used to investigate item and relational memory in schizophrenia. The eye movement procedure was well tolerated and was more specific than behavioral measures with respect to memory impairment. Results suggest that eye movements may be of use in clinical trials and translational studies employing animal models.

Eye-movement behavior reveals relational memory impairment in schizophrenia

BACKGROUND

Previous studies have demonstrated impaired relational memory in schizophrenia. We studied eye-movement behavior as an indirect measure of relational memory, together with forced-choice recognition as an explicit measure.

METHODS

Thirty-five patients with schizophrenia and 35 healthy participants were trained to associate a face with a background scene. During testing, scenes were presented as a cue and then overlaid with three previously studied faces. Participants were asked to recall the matching face, and both eye movements and forced-choice recognition were recorded. During Non-Match trials, no faces matched the scene. During Match trials, one of the faces had previously been paired with the scene.

RESULTS

On Non-Match trials, when no relational memory trace was present, both groups viewed the three faces equally. In contrast, on Match trials, control participants quickly (within 500 msec) and consistently (70%-75% of test trial viewing) showed preferential viewing of the matching face. Viewing of the matching face was significantly delayed and reduced in schizophrenia participants. Forced-choice recognition of the matching face was also impaired in the patient group. An analysis of all correct Match trials revealed that preferential viewing was significantly reduced and delayed in participants with schizophrenia.

CONCLUSIONS

This study provides novel evidence for a specific relational memory impairment in schizophrenia. Patients showed deficits in their forced-choice recognition responses, as well as abnormal eye-movement patterns during memory recall, even on trials when behavioral responses were accurate. We propose that eye movements provide a promising new avenue for studying relational memory in schizophrenia.

Parietal cortex and episodic memory retrieval in schizophrenia

People with schizophrenia consistently show memory impairment on varying tasks including item recognition memory. Relative to the correct rejection of distracter items, the correct recognition of studied items consistently produces an effect termed the old/new effect that is characterized by increased activity in parietal and frontal cortical regions. This effect has received only scant attention in schizophrenia. We examined the old/new effect in 15 people with schizophrenia and 18 controls during an item recognition test, and neural activity was examined with event-related functional magnetic resonance imaging. Both groups performed equally well during the recognition test and showed increased activity in a left dorsolateral prefrontal region and in the precuneus bilaterally during the successful recognition of old items relative to the correct rejection of new items. The control group also exhibited increased activity in the dorsal left parietal cortex. This region has been implicated in the top-down modulation of memory which involves control processes that support memory-retrieval search, monitoring and verification. Although these processes may not be of paramount importance in item recognition memory performance, the present findings suggest that people with schizophrenia may have difficulty with such top-down modulation, a finding consistent with many other studies in information processing.