Reinforcement ambiguity and novelty do not account for transitive inference deficits in schizophrenia

Towards a resolution of some outstanding issues in transitive research: An empirical test on middle childhood

Transitive Inference (deduce B > D from B > C and C > D) can help us to understand other areas of sociocognitive development. Across three experiments, learning, memory, and the validity of two transitive paradigms were investigated. In Experiment 1 (N = 121), 7-year-olds completed a three-term nontraining task or a five-term task requiring extensive-training. Performance was superior on the three-term task. Experiment 2 presented 5–10-year-olds with a new five-term task, increasing learning opportunities without lengthening training (N = 71). Inferences improved, suggesting children can learn five-term series rapidly. Regarding memory, the minor (CD) premise was the best predictor of BD-inferential performance in both task-types. However, tasks exhibited different profiles according to associations between the major (BC) premise and BD inference, correlations between the premises, and the role of age. Experiment 3 (N = 227) helped rule out the possible objection that the above findings simply stemmed from three-term tasks with real objects being easier to solve than computer-tasks. It also confirmed that, unlike for five-term task (Experiments 1 & 2), inferences on three-term tasks improve with age, whether the age range is wide (Experiment 3) or narrow (Experiment 2). I conclude that the tasks indexed different routes within a dual-process conception of transitive reasoning: The five-term tasks indexes Type 1 (associative) processing, and the three-term task indexes Type 2 (analytic) processing. As well as demonstrating that both tasks are perfectly valid, these findings open up opportunities to use transitive tasks for educability, to investigate the role of transitivity in other domains of reasoning, and potentially to benefit the lived experiences of persons with developmental issues.

Mutations in neuroligin-3 in male mice impact behavioral flexibility but not relational memory in a touchscreen test of visual transitive inference

Cognitive dysfunction including disrupted behavioral flexibility is central to neurodevelopmental disorders such as Autism Spectrum Disorder (ASD). A cognitive measure that assesses relational memory, and the ability to flexibly assimilate and transfer learned information is transitive inference. Transitive inference is highly conserved across vertebrates and disrupted in cognitive disorders. Here, we examined how mutations in the synaptic cell-adhesion molecule neuroligin-3 (Nlgn3) that have been documented in ASD impact relational memory and behavioral flexibility. We first refined a rodent touchscreen assay to measure visual transitive inference, then assessed two mouse models of Nlgn3 dysfunction (Nlgn3^−/y and Nlgn3^R451C). Deep analysis of touchscreen behavioral data at a trial level established we could measure trajectories in flexible responding and changes in processing speed as cognitive load increased. We show that gene mutations in Nlgn3 do not disrupt relational memory, but significantly impact flexible responding. Our study presents the first analysis of reaction times in a rodent transitive inference test, highlighting response latencies from the touchscreen system are useful indicators of processing demands or decision-making processes. These findings expand our understanding of how dysfunction of key components of synaptic signaling complexes impact distinct cognitive processes disrupted in neurodevelopmental disorders, and advance our approaches for dissecting rodent behavioral assays to provide greater insights into clinically relevant cognitive symptoms.

Transitive inference deficits in unaffected biological relatives of schizophrenia patients

Currently available treatments have limited efficacy in remediating cognitive impairment in schizophrenia. Efforts to facilitate cognition-enhancing drug discovery recommend the use of varied experimental cognitive paradigms (including relational memory) as assessment tools in clinical drug trials. Although relational memory deficits are increasingly being recognized as a reliable cognitive marker of schizophrenia, relational memory performance among unaffected biological relatives remains unknown. Therefore, we evaluated 73 adolescents or young adults (22 first- and 26 second-degree relatives of schizophrenia patients and 25 healthy controls (HC)) using a well-validated transitive inference (TI) experimental paradigm previously used to demonstrate relational memory impairment in schizophrenia. We found that TI deficits were associated with schizophrenia risk with first-degree relatives showing greater impairment than second-degree relatives. First-degree relatives had poorer TI performance with significantly lower accuracy and longer response times than HC when responding to TI probe pairs. Second-degree relatives had significantly quicker response times than first-degree relatives and were more similar to HC in TI performance. We further explored the relationships between TI performance and neurocognitive domains implicated in schizophrenia. Among HC, response times were inversely correlated with FSIQ, verbal learning, processing speed, linguistic abilities and working memory. In contrast, relatives (first-degree in particular) had a differing pattern of TI-neurocognition relationships, which suggest that different brain circuits may be used when relatives encode and retrieve relational memory. Our finding that unaffected biological relatives of schizophrenia patients have TI deficits lends further support for the use of relational memory construct in future pro-cognition drug studies.

Factors and processes in children's transitive deductions

Transitive tasks are important for understanding how children develop socio-cognitively. However, developmental research has been restricted largely to questions surrounding maturation. We asked 6-, 7- and 8-year-olds (N = 117) to solve a composite of five different transitive tasks. Tasks included conditions asking about item-C (associated with the marked relation) in addition to the usual case of asking only about item-A (associated with the unmarked relation). Here, children found resolving item-C much easier than resolving item-A, a finding running counter to long-standing assumptions about transitive reasoning. Considering gender perhaps for the first time, boys exhibited higher transitive scores than girls overall. Finally, analysing in the context of one recent and well-specified theory of spatial transitive reasoning, we generated the prediction that reporting the full series should be easier than deducing any one item from that series. This prediction was not upheld. We discuss amendments necessary to accommodate all our earlier findings.

Genetic basis of a cognitive complexity metric

Relational complexity (RC) is a metric reflecting capacity limitation in relational processing. It plays a crucial role in higher cognitive processes and is an endophenotype for several disorders. However, the genetic underpinnings of complex relational processing have not been investigated. Using the classical twin model, we estimated the heritability of RC and genetic overlap with intelligence (IQ), reasoning, and working memory in a twin and sibling sample aged 15-29 years (N = 787). Further, in an exploratory search for genetic loci contributing to RC, we examined associated genetic markers and genes in our Discovery sample and selected loci for replication in four independent samples (ALSPAC, LBC1936, NTR, NCNG), followed by meta-analysis (N>6500) at the single marker level. Twin modelling showed RC is highly heritable (67%), has considerable genetic overlap with IQ (59%), and is a major component of genetic covariation between reasoning and working memory (72%). At the molecular level, we found preliminary support for four single-marker loci (one in the gene DGKB), and at a gene-based level for the NPS gene, having influence on cognition. These results indicate that genetic sources influencing relational processing are a key component of the genetic architecture of broader cognitive abilities. Further, they suggest a genetic cascade, whereby genetic factors influencing capacity limitation in relational processing have a flow-on effect to more complex cognitive traits, including reasoning and working memory, and ultimately, IQ.

Developing treatments for cognitive deficits in schizophrenia: the challenge of translation

Schizophrenia is a life-long debilitating mental disorder affecting tens of millions of people worldwide. The serendipitous discovery of antipsychotics focused pharmaceutical research on developing a better antipsychotic. Our understanding of the disorder has advanced however, with the knowledge that cognitive enhancers are required for patients in order to improve their everyday lives. While antipsychotics treat psychosis, they do not enhance cognition and hence are not antischizophrenics. Developing pro-cognitive therapeutics has been extremely difficult, however, especially when no approved treatment exists. In lieu of stumbling on an efficacious treatment, developing targeted compounds can be facilitated by understanding the neural mechanisms underlying altered cognitive functioning in patients. Equally importantly, these cognitive domains will need to be measured similarly in animals and humans so that novel targets can be tested prior to conducting expensive clinical trials. To date, the limited similarity of testing across species has resulted in a translational bottleneck. In this review, we emphasize that schizophrenia is a disorder characterized by abnormal cognitive behavior. Quantifying these abnormalities using tasks having cross-species validity would enable the quantification of comparable processes in rodents. This approach would increase the likelihood that the neural substrates underlying relevant behaviors will be conserved across species. Hence, we detail cross-species tasks which can be used to test the effects of manipulations relevant to schizophrenia and putative therapeutics. Such tasks offer the hope of providing a bridge between non-clinical and clinical testing that will eventually lead to treatments developed specifically for patients with deficient cognition.

Facilitation of relational learning in schizophrenia

Abnormal hippocampal function likely contributes to relational learning deficits observed in schizophrenia. It is unknown whether these deficits can be attenuated with a training intervention. The purpose of this project was to determine if training could facilitate relational learning of the transverse patterning task in schizophrenia. Healthy and schizophrenia subjects completed a version of transverse patterning that incorporated training. The majority of subjects with schizophrenia successfully learned transverse patterning when provided with training. A subgroup (approximately 25%) of schizophrenia subjects showed no tendency to learn with training. These results were replicated in a second study with a separate cohort and different stimuli. This study illustrates that relational learning of the transverse patterning can be facilitated in schizophrenia with training.

A hierarchical finite mixture model that accommodates zero-inflated counts, non-independence, and heterogeneity

A number of mixture modeling approaches assume both normality and independent observations. However, these two assumptions are at odds with the reality of many data sets, which are often characterized by an abundance of zero-valued or highly skewed observations as well as observations from biologically related (i.e., non-independent) subjects. We present here a finite mixture model with a zero-inflated Poisson regression component that may be applied to both types of data. This flexible approach allows the use of covariates to model both the Poisson mean and rate of zero inflation and can incorporate random effects to accommodate non-independent observations. We demonstrate the utility of this approach by applying these models to a candidate endophenotype for schizophrenia, but the same methods are applicable to other types of data characterized by zero inflation and non-independence.

Relational memory generalization and integration in a transitive inference task with and without instructed awareness

Two experiments investigated the potential facilitative effects of prior instructed awareness and predetermined learning criteria on humans' ability to make transitive inference (TI) judgments. Participants were first exposed to a learning phase and required to learn five premise pairs (A+B-, B+C-, C+D-, D+E-, E+F-). Testing followed, where participants made judgments on novel non-endpoint (BD, BE and CE) and endpoint inferential pairs (AC, AD, AE, AF, BF, CF and DF), as well as learned premise pairs. Across both experiments, one group were made aware that the stimuli could be arranged in a hierarchy, while another group were not given this instruction. Results demonstrated that prior instructional task awareness led to a minor performance advantage, but that this difference was not significant. Furthermore, in Experiment 2, inferential test trial accuracy was not correlated with a post-experimental measure of awareness. Thus, the current findings suggest that successful TI task performance may occur in the absence of awareness, and that repeated exposure to learning and test phases may allow weak inferential performances to emerge gradually. Further research and alternative methods of measuring awareness and its role in TI are needed.

Reduced habituation in patients with schizophrenia

BACKGROUND

Neural habituation, the decrease in brain response to repeated stimulation, is a basic form of learning. There is strong evidence for behavioral and physiological habituation deficits in schizophrenia, and one previous study found reduced neural habituation within the hippocampus. However, it is unknown whether neural habituation deficits are specific to faces and limited to the hippocampus. Here we studied habituation of several brain regions in schizophrenia, using both face and object stimuli. Post-scan memory measures were administered to test for a link between hippocampal habituation and memory performance.

METHODS

During an fMRI scan, 23 patients with schizophrenia and 21 control subjects viewed blocks of a repeated neutral face or neutral object, and blocks of different neutral faces and neutral objects. Habituation in the hippocampus, primary visual cortex and fusiform face area (FFA) was compared between groups. Memory for faces, words, and word pairs was assessed after the scan.

RESULTS

Patients showed reduced habituation to faces in the hippocampus and primary visual cortex, but not the FFA. Healthy control subjects exhibited a pattern of hippocampal discrimination that distinguished between repeated and different images for both faces and objects, and schizophrenia patients did not. Hippocampal discrimination was positively correlated with memory for word pairs.

CONCLUSION

Patients with schizophrenia showed reduced habituation of the hippocampus and visual cortex, and a lack of neural discrimination between old and new images in the hippocampus. Hippocampal discrimination correlated with memory performance, suggesting reduced habituation may contribute to the memory deficits commonly observed in schizophrenia.

Cognitive abilities on transitive inference using a novel touchscreen technology for mice

Cognitive abilities are impaired in neurodevelopmental disorders, including autism spectrum disorder (ASD) and schizophrenia. Preclinical models with strong endophenotypes relevant to cognitive dysfunctions offer a valuable resource for therapeutic development. However, improved assays to test higher order cognition are needed. We employed touchscreen technology to design a complex transitive inference (TI) assay that requires cognitive flexibility and relational learning. C57BL/6J (B6) mice with good cognitive skills and BTBR T+tf/J (BTBR), a model of ASD with cognitive deficits, were evaluated in simple and complex touchscreen assays. Both B6 and BTBR acquired visual discrimination and reversal. BTBR displayed deficits on components of TI, when 4 stimuli pairs were interspersed, which required flexible integrated knowledge. BTBR displayed impairment on the A > E inference, analogous to the A > E deficit in ASD. B6 and BTBR mice both reached criterion on the B > D comparison, unlike the B > D impairment in schizophrenia. These results demonstrate that mice are capable of complex discriminations and higher order tasks using methods and equipment paralleling those used in humans. Our discovery that a mouse model of ASD displays a TI deficit similar to humans with ASD supports the use of the touchscreen technology for complex cognitive tasks in mouse models of neurodevelopmental disorders.

Relational memory and hippocampal function in psychotic bipolar disorder

Recent cognitive, genetic, and histological studies have highlighted significant overlap between psychotic bipolar disorder and schizophrenia. Specifically, both bipolar disorder and schizophrenia are characterized by interneuron dysfunction within the hippocampus, an essential structure for relational memory. Relational memory impairments are a common feature of schizophrenia, but have yet to be investigated in psychotic bipolar disorder. Here, we tested the hypothesis that psychotic bipolar disorder is characterized by relational memory deficits. We used a transitive inference (TI) paradigm, previously employed to quantify relational memory deficits in schizophrenia, to assess relational memory performance in 17 patients with psychotic bipolar disorder and 22 demographically matched control participants. Functional magnetic resonance imaging was used to examine hippocampal activity during recognition memory in patients and controls. Hippocampal volumes were assessed by manual segmentation. In contrast to our hypothesis, we found similar TI performance, hippocampal volume, and hippocampal recruitment during recognition memory in both groups. Both psychotic bipolar disorder patients and controls exhibited a positive correlation between hippocampal volume and relational memory performance. These data indicate that relational memory impairments are not a shared feature of non-affective and affective psychosis.

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

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

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.

Impaired associative inference in patients with schizophrenia

The ability to learn, store, and retrieve information about relationships is impaired in schizophrenia. Here, we tested 38 control and 61 schizophrenia subjects for their ability to identify the novel pairing of stimuli, based on associations learned during training. Subjects were trained on 3 sets of paired associates: 30 face-house pairs (H-F1), 30 face-house pairs (H-F2, same house with new face), and 30 face-face pairs (F3-F4). After training, participants were tested on the 3 explicitly trained pair types, as well as 30 new face-face pairs (F1-F2), which could only be linked together via the same house during the H-F1/H-F2 training blocks. Of 99 subjects tested, 37 patients with schizophrenia and 36 age-matched healthy control subjects learned the premise pairs and performed the relational memory test. Healthy control subjects were significantly more accurate in identifying the inferential (F1-F2) pairs than the noninferential (F3-F4) pairs. In contrast, schizophrenia patients were equally accurate on inferential and noninferential pairs, providing evidence for a relational memory deficit in schizophrenia. However, the current version of the associative inference paradigm, suggested by the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia initiative, has limited feasibility, calling into question the generalizability of the findings for the larger schizophrenia population.

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.

Cognition in schizophrenia: core psychological and neural mechanisms

The challenge in understanding cognitive impairment in schizophrenia is that people with this illness have deficits in an array of domains. Here, we briefly review evidence regarding the pattern of deficits within three domains: context processing, working memory and episodic memory. We suggest that there may be a common mechanism driving deficits in these domains - an impairment in the ability to actively represent goal information in working memory to guide behavior, a function we refer to as proactive control. We suggest that such deficits in proactive control reflect impairments in dorsolateral prefrontal cortex, its interactions with other brain regions, such as parietal cortex, thalamus and striatum, and the influence of neurotransmitter systems, such as dopamine, GABA and glutamate.

Transitive inference in adults with autism spectrum disorders

Individuals with autism spectrum disorders (ASDs) exhibit intact rote learning with impaired generalization. A transitive inference paradigm, involving training on four sequentially presented stimulus pairs containing overlapping items, with subsequent testing on two novel pairs, was used to investigate this pattern of learning in 27 young adults with ASDs and 31 matched neurotypical individuals (TYPs). On the basis of findings about memory and neuropathology, we hypothesized that individuals with ASDs would use a relational flexibility/conjunctive strategy reliant on an intact hippocampus, versus an associative strength/value transfer strategy requiring intact interactions between the prefrontal cortex and the striatum. Hypotheses were largely confirmed. ASDs demonstrated reduced interference from intervening pairs in early training; only TYPs formed a serial position curve by test; and ASDs exhibited impairments on the novel test pair consisting of end items with intact performance on the inner test pair. However, comparable serial position curves formed for both groups by the end of the first block.

Bilateral hippocampal dysfunction in schizophrenia

The hippocampus has long been known to be important for memory, with the right hippocampus particularly implicated in nonverbal/visuo-spatial memory and the left in verbal/narrative or episodic memory. Despite this hypothesized lateralized functional difference, there has not been a single task that has been shown to activate both the right and left hippocampi differentially, dissociating the two, using neuroimaging. The transverse patterning (TP) task is a strong candidate for this purpose, as it has been shown in human and nonhuman animal studies to theoretically and empirically depend on the hippocampus. In TP, participants choose between stimuli presented in pairs, with the correct choice being a function of the specific pairing. In this project, TP was used to assess lateralized hippocampal function by varying its dependence on verbal material, with the goal of dissociating the two hippocampi. Magnetoencephalographic (MEG) data were collected while controls performed verbal and nonverbal versions of TP in order to verify and validate lateralized activation within the hippocampi. Schizophrenia patients were evaluated to determine whether they exhibited a lateralized hippocampal deficit. As hypothesized, patients' mean level of behavioral performance was poorer than controls' on both verbal and nonverbal TP. In contrast, patients had no decrement in performance on a verbal and nonverbal non-hippocampal-dependent matched control task. Also, controls but not patients showed more right hippocampal activation during nonverbal TP and more left hippocampal activation during verbal TP. These data demonstrate the capacity to assess lateralized hippocampal function and suggest a bilateral hippocampal behavioral and activation deficit in schizophrenia.

Internal representation of hierarchical sequences involves the default network

BACKGROUND

The default network is a set of brain regions that exhibit a reduction in BOLD response during attention-demanding cognitive tasks, and distinctive patterns of functional connectivity that typically include anti-correlations with a fronto-parietal network involved in attention, working memory, and executive control. The function of the default network regions has been attributed to introspection, self-awareness, and theory of mind judgments, and some of its regions are involved in episodic memory processes.

RESULTS

Using the method of psycho-physiological interactions, we studied the functional connectivity of several regions in a fronto-parietal network involved in a paired image discrimination task involving transitive inference. Some image pairs were derived from an implicit underlying sequence A>B>C>D>E, and some were independent (F>G, H>J, etc). Functional connectivity between the fronto-parietal regions and the default network regions depended on the presence of the underlying sequence relating the images. When subjects viewed learned and novel pairs from the sequence, connectivity between these two networks was higher than when subjects viewed learned and novel pairs from the independent sets.

CONCLUSIONS

These results suggest that default network regions were involved in maintaining the internal model that subserved discrimination of image pairs derived from the implicit sequence, and contributed to introspective access of an internal sequence model built during training. The default network may not be a unified entity with a specific function, but rather may interact with other functional networks in task-dependent ways.