Gating within limbic-cortical circuits and its alteration in a developmental disruption model of schizophrenia

Hippocampal, amygdala and nucleus accumbens volume in first-episode schizophrenia patients and individuals at high familial risk: A cross-sectional comparison

It is unknown whether brain changes occur prior to onset of schizophrenia or after it develops. Prospective familial high risk studies provide a good method to investigate this. In the Edinburgh High Risk Study, structural MRI scans of 150 young individuals at familial high risk of schizophrenia, 34 patients with first-episode schizophrenia and 36 matched controls were obtained. Of the high risk participants with scans suitable for analysis, 17 developed schizophrenia after the scans were taken, whilst 57 experienced isolated or sub-clinical psychotic symptoms, and 70 remained well. We used Freesurfer to extract volumetric measurements of the hippocampus, amygdala and nucleus accumbens with the aim of assessing whether any alterations found were present in all those at high risk, or selectively in the high risk cohort based on future clinical outcome, or only in those experiencing their first-episode of psychosis. We found no significant differences in any examined regions between controls and those at high risk, or between those at high risk who later developed schizophrenia and those who remained well. However, patients with first-episode schizophrenia demonstrated significant volumetric reductions in the bilateral hippocampus, left amygdala, and right nucleus accumbens compared to high risk individuals and healthy controls, which were not significantly associated with the intake of anti-psychotic medication or duration of illness. We found that patients had significantly smaller left amygdalae and bilateral hippocampus compared to HR[ill]. Our findings suggest that volumetric reductions of the hippocampus, amygdala and nucleus accumbens occur early in the first-episode of psychosis. The apparent absence of high risk versus control differences we found using Freesurfer is at odds with our previous studies conducted on the same sample, and possible methodological reasons for these apparent discrepancies are discussed.

Neurophysiological correlates of emotional directed-forgetting in persons with Schizophrenia: An event-related brain potential study

BACKGROUND

Recent research has shown that patients with schizophrenia (SCZ) exhibit reduced directed forgetting (DF) for negative words, suggesting impaired ability to instantiate goal-directed inhibition in order to suppress a competing, emotion-driven responses (i.e., emotional memory enhancement). However, disrupted inhibition is not the only possible mechanism by which patients could manifest reduced emotional DF. Therefore, the primary objective of the current study was to use event-related brain potential (ERP) recordings to investigate alternative hypotheses.

METHODS

ERPs were recorded while patients and controls completed an item-method DF paradigm using negative and neutral words. The N2 indexed goal-directed inhibition of to-be-forgotten items. The late positive potential (LPP) indexed emotional memory enhancement for negative study items. The P300 indexed selective rehearsal of to-be-remembered items.

RESULTS

The SCZ group exhibited a reduced DF effect overall, but this was not modulated by emotion. N2 amplitude at anterior sites was larger for forget versus remember cues in the control group only, but this effect was not modulated by emotion. LPP amplitude was greater for negative versus neutral words in both groups, independent of region. P300 amplitude at posterior sites was greater for remember versus forget cues in the control group only.

DISCUSSION

These data suggest that reduced DF in SCZ may be due, in part, to both diminished goal-directed inhibition of to-be-forgotten items and reduced selective rehearsal of to-be-remembered items. However, these data do not support the hypothesis that goal-directed, inhibitory processes are disrupted by competing, emotion-driven processes in SCZ. Patients' ERP data also suggested that they did not exhibit disproportionately heightened encoding of emotional stimuli, nor did they have deficient selective rehearsal of to-be-remembered emotional items.

Inhibiting reactions to emotional versus non-emotional response cues in schizophrenia: Insights from a motor-process paradigm

Recent models of schizophrenia suggest deficient use of contextual response cues when confronted with countermanding emotional cues. It is important to clinically validate these models by testing patients diagnosed with schizophrenia on tasks with competing emotional and contextual response determinants. Control and schizophrenia groups completed a novel task that elicited motor responses consistent with, or in opposition to, pre-potent emotional actions (i.e., approach vs. avoidance). An analogous non-emotional task was also used to examine cue-conflict impairment more generally. The groups demonstrated statistically equivalent performance decrements on incongruent versus congruent trials on both tasks. However, within the schizophrenia group, the incongruency effect was significantly greater in the emotional versus non-emotional task. These data suggest that, while patients with schizophrenia were able to employ contextual response cues to override competing emotional responses, they were slower to resolve emotional versus non-emotional response conflict. When patients were subdivided according to the presence or absence of disorganized symptoms, this effect was confined to patients with disorganized symptoms.

Reduced directed forgetting for negative words suggests schizophrenia-related disinhibition of emotional cues

BACKGROUND

Several psychological and neurobiological models imply that patients with schizophrenia (SCZ) are more inclined to utilize emotional cues as response determinants to the detriment of more task-appropriate cognitive or contextual cues. However, there is a lack of behavioural data from human clinical studies to support this assertion. Therefore, it is important to evaluate the performance of persons with SCZ using tasks designed to index the resolution between competing emotional and cognitive determinants of goal-directed behaviour.

METHOD

The current study employed a list-method, emotional directed-forgetting (DF) paradigm designed to invoke inhibitory mechanisms necessary to override emotional memory enhancement for successful task completion. Four psycholinguistically matched lists were constructed that were comprised of five negative, five positive, and five neutral words.

RESULTS

Compared with healthy controls, individuals with SCZ showed a reduced DF effect overall. When broken down according to valence, this effect was only observed for negative words, which, in turn, resulted from reduced forgetting of list 1 words following the forget cue.

CONCLUSIONS

These results indicate that individuals with SCZ were less able to engage strategic inhibitory mechanisms for the purpose of overriding recall of negative stimuli when tasks demand call for such action. Thus, our data support the theoretical assertion that SCZ patients have difficulty utilizing cognitive or contextual cues as determinants of goal-directed behaviour in the face of countermanding emotional cues.

Sexually dimorphic changes in the amygdala in relation to delusional beliefs in first episode psychosis

BACKGROUND

Few attempts have been made to examine the relationship between amygdala abnormalities and specific symptoms in psychosis. The present study explored the relationship between amygdala morphology and mood congruent and mood incongruent delusional beliefs.

METHODS

Amygdala volumes were measured in 43 patients presenting with delusional beliefs in the context of their first episode of psychosis and 43 healthy volunteers matched for age and gender.

RESULTS

Left-greater-than-right-asymmetry of the amygdala varied as a function of gender and mood congruence of delusional beliefs, due to asymmetrical enlargement of the left amygdala in women presenting with predominantly mood incongruent delusions. However, there was no difference in amygdala volumes across groups.

CONCLUSIONS

Amygdala abnormalities in women may be associated with aberrant emotional processing that could contribute to the development of mood incongruent delusional beliefs. Sexually dimorphic changes in the amygdala may contribute to differential phenotypic illness expression in men and women.

Object-location memory in schizophrenia: interference of symbolic threatening content

INTRODUCTION

Monitoring environmental stimuli for their emotional relevance is inherently associated with spatial processing. In schizophrenia, deficits in spatial working memory on one hand, and abnormal emotion processing on the other, have been documented, but these have not been related to each other. In the present study, we investigated whether a specific aspect of spatial memory (i.e., object-location memory), is impaired in patients with schizophrenia. Moreover, we hypothesised that symbolic threatening content of objects would interfere with spatial processing in patients with schizophrenia but not in healthy controls.

METHODS

Spatial memory for symbolic pictorial stimuli was assessed in 40 patients with schizophrenia compared to 41 healthy matched control participants using an object-relocation task.

RESULTS

Patients with schizophrenia performed worse in relocating objects, independent of overall intellectual ability. More specifically, patients were particularly worse in the relocation of objects with a symbolic threatening content.

CONCLUSIONS

These results suggest that a threatening semantic emotional content of schematic stimuli can interfere with spatial processing in schizophrenia. We hypothesise that a disproportional influence of the amygdala on other brain areas, such as the hippocampus, might underlie this specific emotional interference.

Decrease in parvalbumin-expressing neurons in the hippocampus and increased phencyclidine-induced locomotor activity in the rat methylazoxymethanol (MAM) model of schizophrenia

Treatment of rats with methylazoxymethanol (MAM) on gestational day (GD)17 disrupts corticolimbic development in the offspring (MAM-GD17 rats) and leads to abnormalities in adult MAM-GD17 rats resembling those described in schizophrenic patients. The underlying changes in specific cortical and limbic cell populations remain to be characterised. In schizophrenia, decreases in inhibitory gamma-aminobutyric acid (GABA)-containing interneurons that express the calcium-binding protein parvalbumin have been reported in the prefrontal cortex and hippocampus. In this study we analysed the expression of parvalbumin (PV), calretinin (CR) and calbindin (CB) in the prefrontal cortex and hippocampus of MAM-GD17 rats. Exposure in utero to MAM led to a significant decrease in the number of neurons expressing PV in the hippocampus, but not the prefrontal cortex. Neurons expressing CR or CB were not affected in either structure. The neurochemical changes in MAM-GD17 rats were accompagnied by increased hyperlocomotion after administration of phencyclidine (PCP), analogous to the hypersensitivity of schizophrenic patients to PCP. Therefore, the developmental MAM-GD17 model reproduces key neurochemical and behavioural features that reflect cortical and subcortical dysfunction in schizophrenia, and could be a useful tool in the development of new antipsychotic drugs.

Cognitive deficits caused by late gestational disruption of neurogenesis in rats: a preclinical model of schizophrenia

Late gestational disruption of neurogenesis in rats has been shown to induce behavioral abnormalities thought to mimic aspects of positive and negative symptoms of schizophrenia. Furthermore, it has been shown that the morphological changes produced by the perturbation are relevant to schizophrenia with reduced thickness of the hippocampus, thalamus, and cortical regions. In addition to the positive and negative symptoms, schizophrenia is associated with deficits in a wide variety of cognitive domains. In the present studies, we assessed whether the cognitive deficits are modeled by disruption of neurogenesis late during gestation (gestational day 17) in the rat. In the battery of tests utilized, we describe that rats in which neurogenesis was disrupted have deficits in a reversal-learning paradigm of the Morris water maze and in object recognition, and that they exhibit perseveration in the Porsolt forced swimming test. Additionally, we found deficient associative learning in an acquisition of an active avoidance paradigm and deficits in latent inhibition. No deficits were observed in the reference memory version of the Morris water maze and in a non-match-to position experiment, showing that the deficits are limited to certain aspects of cognition.