Implicit memory in schizotypal subjects and normal controls: effects of a secondary task on sequence learning

Impaired conscious memory in non-clinical schizotypy

INTRODUCTION

Impaired controlled and preserved/enhanced automatic memory processes have been reported in schizotypy. This memory pattern has been considered as a marker of vulnerability to schizophrenia. Our aim was to further explore this memory pattern in non-clinical schizotypy in order to determine which specific dimensions of schizotypy (i.e., positive, negative or disorganised), and more specifically which components of the dimensions, are most closely related to memory dysfunctions.

METHODS

Fifty-seven undergraduate students performed a category-production task. This was adapted for use with the process dissociation procedure in order to dissociate between automatic and controlled memory processes. The level of schizotypy was assessed using the Schizotypal Personality Questionnaire.

RESULTS

Regression analyses confirmed that controlled memory processes decreased as schizotypy increased. The positive factors (more specifically, the ideas of reference subscale) and disorganised factors (more specifically, the odd or eccentric behaviour subscale) were negatively correlated with the controlled memory processes.

CONCLUSIONS

Our study supports the idea that impaired controlled processes are an early cognitive marker of vulnerability to schizophrenia and confirm that the disorganised factor contributes the most to vulnerability to memory dysfunction. It also emphasises the importance of dissociating between each of the features characterising schizotypy rather than considering it as a whole.

Cerebellar-motor dysfunction in schizophrenia and psychosis-risk: the importance of regional cerebellar analysis approaches

Motor abnormalities in individuals with schizophrenia and those at-risk for psychosis are well documented. An accumulating body of work has also highlighted motor abnormalities related to cerebellar dysfunction in schizophrenia including eye-blink conditioning, timing, postural control, and motor learning. We have also recently found evidence for motor dysfunction in individuals at ultra high-risk for psychosis (1-3). This is particularly relevant as the cerebellum is thought to be central to the cognitive dysmetria model of schizophrenia, and these overt motor signs may point to more general cerebellar dysfunction in the etiology of psychotic disorders. While studies have provided evidence indicative of motor cerebellar dysfunction in at-risk populations and in schizophrenia, findings with respect to the cerebellum have been mixed. One factor potentially contributing to these mixed results is the whole-structure approach taken when investigating the cerebellum. In non-human primates, there are distinct closed-loop circuits between the cerebellum, thalamus, and brain with motor and non-motor cortical regions. Recent human neuroimaging has supported this finding and indicates that there is a cerebellar functional topography (4), and this information is being missed with whole-structure approaches. Here, we review cerebellar-motor dysfunction in individuals with schizophrenia and those at-risk for psychosis. We also discuss cerebellar abnormalities in psychosis, and the cerebellar functional topography. Because of the segregated functional regions of the cerebellum, we propose that it is important to look at the structure regionally in order to better understand its role in motor dysfunction in these populations. This is analogous to approaches taken with the basal ganglia, where each region is considered separately. Such an approach is necessary to better understand cerebellar pathophysiology on a macro-structural level with respect to the pathogenesis of psychosis.

Memory blocking in schizophrenia reflects deficient retrieval control mechanisms

Retrieval interference and orthographic processing were evaluated in schizophrenia, schizotypal personality disorder, and non-psychiatric control participants using a word fragment completion paradigm. Participants studied solutions and later completed corresponding fragments preceded by solutions, orthographically similar blocking words, or ampersands. Although schizophrenia patients completed fewest fragments, they showed equivalent repetition priming and blocking magnitude, supporting intact orthographic processing. Schizophrenia patients were more likely to commit intrusions in the blocking condition, whereas control participants displayed better mental control because they were more likely to withhold the response. These results suggest schizophrenia patients show abnormal functioning of control mechanisms responsible for selection and inhibition of competitors.

Incidental and intentional sequence learning in youth-onset psychosis and Attention-Deficit/Hyperactivity Disorder (ADHD)

The goal was to compare incidental and intentional spatial sequence learning in youth-onset psychosis and ADHD. The authors tested 8- to 19-year-olds with psychosis or ADHD and healthy controls on a serial reaction time (RT) task and used manual and oculomotor measures to examine learning. Participants were also administered a block in which they were explicitly instructed to learn a sequence. As in our previous studies with healthy adults and children, oculomotor anticipations and RTs showed learning effects similar to those in the manual modality. Results showed intact sequence-specific learning but fewer oculomotor anticipations in both clinical groups during incidental learning. In intentional learning, only the psychosis group showed impairments compared to controls. There were no interactions between age and diagnosis. Thus, the psychosis group showed relatively preserved incidental learning despite impairments in intentional learning. Additionally, both clinical groups showed impairments in the ability to search for, extract, and anticipate regularities (whether the regularities were there or not), but not in the ability to respond to these regularities when they were there.

Implicit and explicit procedural learning in patients recently remitted from severe major depression

In acute depression a high prevalence of deficits in learning and memory performance has been reported. Still, it is unclear whether these cognitive deficits are present after remission of clinical symptoms of depression. The present study compared 20 inpatients recently remitted from severe major depressive disorder (MDD) with 20 healthy matched control participants on two sequence learning tasks: a modified serial reaction-time task (SRT) for implicit learning, which is sensitive to subcortical and frontal impairments, and a serial generation task (SGT) for explicit learning. As compared with performance in healthy controls, implicit and explicit learning were not impaired in recently remitted inpatients with depression. Intentional acquisition of new information was related to the severity of depressive symptoms as patients with higher scores on Beck's Depression Inventory (BDI) showed poorer explicit learning. In contrast to findings in acute depression, our results suggest a normal degree of learning in remitted depression; these findings are consistent with unimpaired fronto-striatal functioning. However, although not statistically significant, patients remitted from melancholic MDD revealed poorer implicit learning performance compared with patients remitted from non--melancholic MDD. Longitudinal studies in patients with melancholic vs. non-melancholic MDD are needed to investigate the course of cognitive functioning during the recovery from MDD.

Reduced implicit and explicit sequence learning in first-episode schizophrenia

A high prevalence of deficits in explicit learning has been reported for schizophrenic patients, but it is less clear whether these patients are impaired in implicit learning. Deficits in implicit learning indicative of a fronto-striatal dysfunction have been reported using a serial reaction-time task (SRT), but the impact of typical neuroleptic medication and chronicity remains controversial. The present study compared 37 patients with first-episode schizophrenia treated with atypical neuroleptics and 37 healthy matched control participants on two sequence learning tasks: a modified SRT for implicit sequence learning and a serial generation task (SGT) for explicit sequence learning. The two tasks were designed to be procedurally equivalent, in order to provide better comparability between implicit and explicit performance. Although unaffected in global cognitive functioning, schizophrenic patients were significantly impaired in implicit and explicit sequence learning. Deficient sequence learning in schizophrenic patients was neither related to psychopathology nor to chlorpromazine equivalent daily dosage. As performance was impaired even though patients were exclusively treated with atypical neuroleptics, the present findings concur with converging evidence of a sequence learning deficit inherent in schizophrenia. This deficit would be consistent with a fronto-striatal dysfunction and might constitute a crucial factor for the acquisition of new information.