Procedural learning in schizophrenia can reflect the pharmacologic properties of the antipsychotic treatments

Impaired Sensorimotor Adaption in Schizophrenia in Comparison to Age-Matched and Elderly Controls

BACKGROUND

The "cognitive dysmetria hypothesis" of schizophrenia proposes a disrupted communication between the cerebellum and cerebral cortex, resulting in sensorimotor and cognitive symptoms. Sensorimotor adaptation relies strongly on the function of the cerebellum.

OBJECTIVES

This study investigated whether sensorimotor adaptation is reduced in schizophrenia compared with age-matched and elderly healthy controls.

METHODS

Twenty-nine stably treated patients with schizophrenia, 30 age-matched, and 30 elderly controls were tested in three motor adaptation tasks in which visual movement feedback was unexpectedly altered. In the "rotation adaptation task" the perturbation consisted of a rotation (30° clockwise), in the "gain adaptation task" the extent of the movement feedback was reduced (by a factor of 0.7) and in the "vertical reversal task," up- and downward pen movements were reversed by 180°.

RESULTS

Patients with schizophrenia adapted to the perturbations, but their movement times and errors were substantially larger than controls. Unexpectedly, the magnitude of adaptation was significantly smaller in schizophrenia than elderly participants. The impairment already occurred during the first adaptation trials, pointing to a decline in explicit strategy use. Additionally, post-adaptation aftereffects provided strong evidence for impaired implicit adaptation learning. Both negative and positive schizophrenia symptom severities were correlated with indices of the amount of adaptation and its aftereffects.

CONCLUSIONS

Both explicit and implicit components of sensorimotor adaptation learning were reduced in patients with schizophrenia, adding to the evidence for a role of the cerebellum in the pathophysiology of schizophrenia. Elderly individuals outperformed schizophrenia patients in the adaptation learning tasks.

Reinforcement learning as an intermediate phenotype in psychosis? Deficits sensitive to illness stage but not associated with polygenic risk of schizophrenia in the general population

BACKGROUND

Schizophrenia is a complex disorder in which the causal relations between risk genes and observed clinical symptoms are not well understood and the explanatory gap is too wide to be clarified without considering an intermediary level. Thus, we aimed to test the hypothesis of a pathway from molecular polygenic influence to clinical presentation occurring via deficits in reinforcement learning.

METHODS

We administered a reinforcement learning task (Go/NoGo) that measures reinforcement learning and the effect of Pavlovian bias on decision making. We modelled the behavioural data with a hierarchical Bayesian approach (hBayesDM) to decompose task performance into its underlying learning mechanisms. Study 1 included controls (n = 29, F|M = 0.81), At Risk Mental State for psychosis (ARMS, n = 23, F|M = 0.35) and FEP (First-episode psychosis, n = 26, F|M = 0.18). Study 2 included healthy adolescents (n = 735, F|M = 1.06), 390 of whom had their polygenic risk scores for schizophrenia (PRSs) calculated.

RESULTS

Patients with FEP showed significant impairments in overriding Pavlovian conflict, a lower learning rate and a lower sensitivity to both reward and punishment. Less widespread deficits were observed in ARMS. PRSs did not significantly predict performance on the task in the general population, which only partially correlated with measures of psychopathology.

CONCLUSIONS

Reinforcement learning deficits are observed in first episode psychosis and, to some extent, in those at clinical risk for psychosis, and were not predicted by molecular genetic risk for schizophrenia in healthy individuals. The study does not support the role of reinforcement learning as an intermediate phenotype in psychosis.

Cognitive function in schizophrenia: conflicting findings and future directions

INTRODUCTION

Schizophrenia is a severe mental disorder with multiple psychopathological domains being affected. Several lines of evidence indicate that cognitive impairment serves as the key component of schizophrenia psychopathology. Although there have been a multitude of cognitive studies in schizophrenia, there are many conflicting results. We reasoned that this could be due to individual differences among the patients (i.e. variation in the severity of positive vs. negative symptoms), different task designs, and/or the administration of different antipsychotics.

METHODS

We thus review existing data concentrating on these dimensions, specifically in relation to dopamine function. We focus on most commonly used cognitive domains: learning, working memory, and attention.

RESULTS

We found that the type of cognitive domain under investigation, medication state and type, and severity of positive and negative symptoms can explain the conflicting results in the literature.

CONCLUSIONS

This review points to future studies investigating individual differences among schizophrenia patients in order to reveal the exact relationship between cognitive function, clinical features, and antipsychotic treatment.

A neuroimaging study of emotion-cognition interaction in schizophrenia: the effect of ziprasidone treatment

Functional and structural brain changes associated with the cognitive processing of emotional visual stimuli were assessed in schizophrenic patients after 16 weeks of antipsychotic treatment with ziprasidone. Forty-five adults aged 18 to 40 were recruited: 15 schizophrenia patients (DSM-IV criteria) treated with ziprasidone (mean daily dose = 120 mg), 15 patients treated with other antipsychotics, and 15 healthy controls who did not receive any medication. Functional and structural neuroimaging data were acquired at baseline and 16 weeks after treatment initiation. In each session, participants selected stimuli, taken from standardized sets, based on their emotional valence. After ziprasidone treatment, several prefrontal regions, typically involved in cognitive control (anterior cingulate and ventrolateral prefrontal cortices), were significantly activated in patients in response to positive versus negative stimuli. This effect was greater whenever they had to select negative compared to positive stimuli, indicating an asymmetric effect of cognitive treatment of emotionally laden information. No such changes were observed for patients under other antipsychotics. In addition, there was an increase in the brain volume commonly recruited by healthy controls and patients under ziprasidone, in response to cognitive processing of emotional information. The structural analysis showed no significant changes in the density of gray and white matter in ziprasidone-treated patients compared to patients receiving other antipsychotic treatments. Our results suggest that functional changes in brain activity after ziprasidone medication precede structural and clinical manifestations, as markers that the treatment is efficient in restoring the functionality of prefrontal circuits involved in processing emotionally laden information in schizophrenia.

Preserved priming effect in individuals with schizophrenia: cues towards rehabilitation

INTRODUCTION

Individuals with schizophrenia and affective disorders show relatively intact implicit memory as compared to declarative memory. Implicit memory is usually assessed with skill learning and priming tasks. Whereas priming is thought to involve storage changes in the posterior neocortex, skill learning is thought to rely more on the corticostriatal pathway. Since frontostriatal and frontotemporal dysfunctions are, respectively, found in schizophrenia and affective disorders, we hypothesised that individuals with schizophrenia and first-episode psychosis would exhibit disturbances in skill learning, but not priming.

METHODS

Thirty-five patients (11 first-episode psychosis; 11 schizophrenia; 13 affective disorders) and 10 controls completed a procedural learning and priming task. Participants had to identify fragmented images throughout five training sessions. The improvement of the threshold at which the images could be identified between the first and last session was used as an index of procedural learning. In a final session, the identification thresholds for old and new images were compared to assess the priming effect.

RESULTS

Whereas individuals with schizophrenia and first-episode psychosis showed impaired skill learning, the priming effect was similar in all groups.

CONCLUSION

Even though some aspects of learning and memory are affected in schizophrenia, our results suggest that the posterior cortical pathway remains efficient at modulating the priming effect. This intact ability could be used to guide the elaboration of new rehabilitation programmes.

Common and distinct neural effects of risperidone and olanzapine during procedural learning in schizophrenia: a randomised longitudinal fMRI study

RATIONALE

Most cognitive domains show only minimal improvement following typical or atypical antipsychotic treatments in schizophrenia, and some may even worsen. One domain that may worsen is procedural learning, an implicit memory function relying mainly on the integrity of the fronto-striatal system.

OBJECTIVES

We investigated whether switching to atypical antipsychotics would improve procedural learning and task-related neural activation in patients on typical antipsychotics. Furthermore, we explored the differential effects of the atypical antipsychotics risperidone and olanzapine.

METHODS

Thirty schizophrenia patients underwent functional magnetic resonance imaging during a 5-min procedural (sequence) learning task on two occasions: at baseline and 7-8 weeks later. Of 30 patients, 10 remained on typical antipsychotics, and 20 were switched randomly in equal numbers to receive either olanzapine (10-20 mg) or risperidone (4-8 mg) for 7-8 weeks.

RESULTS

At baseline, patients (all on typical antipsychotics) showed no procedural learning. At follow-up, patients who remained on typical antipsychotics continued to show a lack of procedural learning, whereas those switched to atypical antipsychotics displayed significant procedural learning (p = 0.001) and increased activation in the superior-middle frontal gyrus, anterior cingulate and striatum (cluster-corrected p < 0.05). These neural effects were present as a linear increase over five successive 30-s blocks of sequenced trials. A switch to either risperidone or olanzapine resulted in comparable performance but with both overlapping and distinct task-related activations.

CONCLUSIONS

Atypical antipsychotics restore procedural learning deficits and associated neural activity in schizophrenia. Furthermore, different atypical antipsychotics produce idiosyncratic task-related neural activations, and this specificity may contribute to their differential long-term clinical profiles.

Translational studies of goal-directed action as a framework for classifying deficits across psychiatric disorders

The ability to learn contingencies between actions and outcomes in a dynamic environment is critical for flexible, adaptive behavior. Goal-directed actions adapt to changes in action-outcome contingencies as well as to changes in the reward-value of the outcome. When networks involved in reward processing and contingency learning are maladaptive, this fundamental ability can be lost, with detrimental consequences for decision-making. Impaired decision-making is a core feature in a number of psychiatric disorders, ranging from depression to schizophrenia. The argument can be developed, therefore, that seemingly disparate symptoms across psychiatric disorders can be explained by dysfunction within common decision-making circuitry. From this perspective, gaining a better understanding of the neural processes involved in goal-directed action, will allow a comparison of deficits observed across traditional diagnostic boundaries within a unified theoretical framework. This review describes the key processes and neural circuits involved in goal-directed decision-making using evidence from animal studies and human neuroimaging. Select studies are discussed to outline what we currently know about causal judgments regarding actions and their consequences, action-related reward evaluation, and, most importantly, how these processes are integrated in goal-directed learning and performance. Finally, we look at how adaptive decision-making is impaired across a range of psychiatric disorders and how deepening our understanding of this circuitry may offer insights into phenotypes and more targeted interventions.

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.

Probabilistic classification and gambling in patients with schizophrenia receiving medication: comparison of risperidone, olanzapine, clozapine and typical antipsychotics

RATIONALE

We have previously shown that patients with schizophrenia treated with typical antipsychotics were impaired on the weather prediction probabilistic classification learning (PCL) task that relies on striatal function, and that similar patients treated with atypical antipsychotics were impaired on the Iowa gambling task (IGT) that depends on medial prefrontocortical function.

OBJECTIVES

We tested the hypothesis that test performance of patients treated with risperidone will be more similar to those treated with typical rather than atypical antipsychotics.

RESULTS

Groups of schizophrenia patients treated with risperidone, olanzapine, clozapine or typical antipsychotics did not differ on the Positive and Negative Syndrome Scale or the Mini Mental State Exam (MMSE) but scored lower than controls on the MMSE. For the PCL task, patients treated with clozapine improved over trials while those treated with typical antipsychotics, olanzapine, or risperidone did not. For the IGT, patients treated with typical antipsychotics or risperidone improved over trials while those treated with clozapine or olanzapine did not.

CONCLUSIONS

Results generally supported the hypothesis that patients treated with risperidone perform more like those treated with typical antipsychotics than those treated with other atypical antipsychotics.

More than just tapping: index finger-tapping measures procedural learning in schizophrenia

BACKGROUND

Finger-tapping has been widely studied using behavioral and neuroimaging paradigms. Evidence supports the use of finger-tapping as an endophenotype in schizophrenia, but its relationship with motor procedural learning remains unexplored. To our knowledge, this study presents the first use of index finger-tapping to study procedural learning in individuals with schizophrenia or schizoaffective disorder (SCZ/SZA) as compared to healthy controls.

METHODS

A computerized index finger-tapping test was administered to 1169 SCZ/SZA patients (62% male, 88% right-handed), and 689 healthy controls (40% male, 93% right-handed). Number of taps per trial and learning slopes across trials for the dominant and non-dominant hands were examined for motor speed and procedural learning, respectively.

RESULTS

Both healthy controls and SCZ/SZA patients demonstrated procedural learning for their dominant hand but not for their non-dominant hand. In addition, patients showed a greater capacity for procedural learning even though they demonstrated more variability in procedural learning compared to healthy controls. Left-handers of both groups performed better than right-handers and had less variability in mean number of taps between non-dominant and dominant hands. Males also had less variability in mean tap count between dominant and non-dominant hands than females. As expected, patients had a lower mean number of taps than healthy controls, males outperformed females and dominant-hand trials had more mean taps than non-dominant hand trials in both groups.

CONCLUSIONS

The index finger-tapping test can measure both motor speed and procedural learning, and motor procedural learning may be intact in SCZ/SZA patients.

[Schizophrenia, executive control and memory]

Schizophrenia affects 1% of the general population. In addition to disabling clinical symptoms, cognitive deficits have also been updated. It has further been proposed that the well-known diversity of schizophrenia in terms of functional outcome and recovery from acute episode is best characterized by cognitive deficits, but not by its classical symptoms. DSM-V acknowledges the importance of cognition in schizophrenia, and could recommend a formal neuropsychological assessment in individuals with psychosis. Schizophrenic patient's cognitive functioning has been studied extensively in the domain of memory and executive control. To date, the studies highlight important deficits in both of these domains. However, within the memory systems, some of them remain unaffected. Altogether, the data invalidate the hypothesis of a global damage and are in favor of specific cognitive deficits. The observed deficits would depend on the dominant symptoms and pre-morbid functioning. The interest of these results was to give impulse to the development of comprehensive assessment battery designed to evaluate the cognitive profiles of each patient and develop a personalized program of cognitive remediation.

Computational cognitive models of prefrontal-striatal-hippocampal interactions in Parkinson's disease and schizophrenia

Disruption to different components of the prefrontal cortex, basal ganglia, and hippocampal circuits leads to various psychiatric and neurological disorders including Parkinson's disease (PD) and schizophrenia. Medications used to treat these disorders (such as levodopa, dopamine agonists, antipsychotics, among others) affect the prefrontal-striatal-hippocampal circuits in a complex fashion. We have built models of prefrontal-striatal and striatal-hippocampal interactions which simulate cognitive dysfunction in PD and schizophrenia. In these models, we argue that the basal ganglia is key for stimulus-response learning, the hippocampus for stimulus-stimulus representational learning, and the prefrontal cortex for stimulus selection during learning about multidimensional stimuli. In our models, PD is associated with reduced dopamine levels in the basal ganglia and prefrontal cortex. In contrast, the cognitive deficits in schizophrenia are associated primarily with hippocampal dysfunction, while the occurrence of negative symptoms is associated with frontostriatal deficits in a subset of patients. In this paper, we review our past models and provide new simulation results for both PD and schizophrenia. We also describe an extended model that includes simulation of the different functional role of D1 and D2 dopamine receptors in the basal ganglia and prefrontal cortex, a dissociation we argue is essential for understanding the non-uniform effects of levodopa, dopamine agonists, and antipsychotics on cognition. Motivated by clinical and physiological data, we discuss model limitations and challenges to be addressed in future models of these brain disorders.

Procedural learning in schizophrenia: reconciling the discrepant findings

BACKGROUND

Studies of procedural learning in schizophrenia have been inconsistent, sometimes finding it to be preserved and sometimes impaired. This study examined three factors that could account for the variability among findings: type of task, presence of general intellectual impairment, and the extrapyramidal side effects of neuroleptic treatment.

METHODS

Forty-three patients with schizophrenia and 22 normal control subjects were examined with three different paradigms: the pursuit rotor, mirror reading, and probabilistic learning ("weather prediction"). A subgroup of intellectually preserved patients was also examined. Patients with and without tardive dyskinesia and with and without Parkinsonism were also compared.

RESULTS

The schizophrenic patients showed learning comparable to the control subjects on the pursuit rotor and mirror reading but were impaired on the probabilistic learning task. However, this last difference disappeared when the subgroup of intellectually preserved patients was compared with a subgroup of matched control subjects. Patients with and without tardive dyskinesia or Parkinsonism showed similar learning on all three tasks, but patients with tardive dyskinesia showed poorer overall performance than those without.

CONCLUSIONS

Procedural learning tends to be preserved in schizophrenia, and when impairment is found, differences in the overall level of intellectual function might be the determining factor.

Clozapine versus other atypical antipsychotics for schizophrenia

BACKGROUND

Clozapine is an atypical antipsychotic demonstrated to be superior in the treatment of refractory schizophrenia which causes fewer movement disorders. Clozapine, however, entails a significant risk of serious blood disorders such as agranulocytosis which could be potentially fatal. Currently there are a number of newer antipsychotics which have been developed with the purpose to find both a better tolerability profile and a superior effectiveness.

OBJECTIVES

To compare the clinical effects of clozapine with other atypical antipsychotics (such as amisulpride, aripiprazole, olanzapine, quetiapine, risperidone, sertindole, ziprasidone and zotepine) in the treatment of schizophrenia and schizophrenia-like psychoses.

SEARCH STRATEGY

We searched the Cochrane Schizophrenia Groups Register (June 2007) and reference lists of all included randomised controlled trials. We also manually searched appropriate journals and conference proceedings relating to clozapine combination strategies and contacted relevant pharmaceutical companies.

SELECTION CRITERIA

All relevant randomised, at least single-blind trials, comparing clozapine with other atypical antipsychotics, any dose and oral formulations, for people with schizophrenia or related disorders.

DATA COLLECTION AND ANALYSIS

We selected trials and extracted data independently. For dichotomous data we calculated relative risks (RR) and their 95% confidence intervals (CI) based on a random-effects model. We calculated numbers needed to treat/harm (NNT/NNH) where appropriate. For continuous data, we calculated mean differences (MD) again based on a random-effects model.

MAIN RESULTS

The review currently includes 27 blinded randomised controlled trials, which involved 3099 participants. Twelve randomised control trials compared clozapine with olanzapine, five with quetiapine, nine with risperidone, one with ziprasidone and two with zotepine. Attrition from these studies was high (overall 30.1%), leaving the interpretation of results problematic. Clozapine had a higher attrition rate due to adverse effects than olanzapine (9 RCTs, n=1674, RR 1.60 CI 1.07 to 2.40, NNT 25 CI 15 to 73) and risperidone (6 RCTs, n=627, RR 1.88 CI 1.11 to 3.21, NNT 16 CI 9 to 59). Fewer participants in the clozapine groups left the trials early due to inefficacy than risperidone (6 RCTs, n=627, RR 0.40 CI 0.23 to 0.70, NNT 11 CI 7 to 21), suggesting a certain higher efficacy of clozapine.Clozapine was more efficacious than zotepine in improving the participants general mental state (BPRS total score: 1 RCT, n=59, MD -6.00 CI -9.83 to -2.17), but not consistently more than olanzapine, quetiapine, risperidone and ziprasidone. There was no significant difference between clozapine and olanzapine or risperidone in terms of positive or negative symptoms of schizophrenia. According to two studies from China quetiapine was more efficacious for negative symptoms than clozapine (2 RCTs, n=142, MD 2.23 CI 0.99 to 3.48).Clozapine produced somewhat fewer extrapyramidal side-effects than risperidone (use of antiparkinson medication: 6 RCTs, n=304, RR 0.39 CI 0.22 to 0.68, NNT 7 CI 5 to 18) and zotepine (n=59, RR 0.05 CI 0.00 to 0.86, NNT 3 CI 2 to 5). More participants in the clozapine group showed decreased white blood cells than those taking olanzapine, more hypersalivation and sedation than those on olanzapine, risperidone and quetiapine and more seizures than people on olanzapine and risperidone. Also clozapine produced an important weight gain not seen with risperidone.Other differences in adverse effects were less documented and should be replicated, for example, clozapine did not alter prolactin levels whereas olanzapine, risperidone and zotepine did; compared with quetiapine, clozapine produced a higher incidence of electrocardiogram (ECG) alterations; and compared with quetiapine and risperidone clozapine produced a higher increase of triglyceride levels. Other findings that should be replicated were: clozapine improved social functioning less than risperidone and fewer participants in the clozapine group had to be hospitalised to avoid suicide attempts compared to olanzapine.Other important outcomes such as service use, cognitive functioning, satisfaction with care or quality of life were rarely reported.

AUTHORS' CONCLUSIONS

Clozapine may be a little more efficacious than zotepine and risperidone but further trials are required to confirm this finding. Clozapine differs more clearly in adverse effects from other second generation antipsychotics and the side-effect profile could be key in the selection of treatment depending on the clinical situation and a patient's preferences. Data on other important outcomes such as cognitive functioning, quality of life, death or service use are currently largely missing, making further large and well-designed trials necessary. It is also important to take into account that the large number of people leaving the studies early limits the validity and interpretation of our findings.

Long-term skill proceduralization in schizophrenia

Previous studies had revealed no specific effect under haloperidol (typical) and risperidone (atypical) neuroleptic (NLP) treatments for schizophrenia (SZ) on a variety of neurocognitive functions relying on the dopaminergic meso-cortico-limbic system (Rémillard et al., 2005, 2008). Considering the different affinities of D2 dopamine receptors for typical and atypical NLPs, these drugs may differentially affect the functions of the striatum, a determinant brain structure involved in procedural learning. The influence of risperidone (2-6 mg) and haloperidol (2-40 mg) on a nonmotor procedural task involving semantically related pairs of words with inverted letters was investigated in this double-blind study. The performance of 26 patients with SZ, randomly assigned to risperidone or haloperidol, was compared to that of 18 healthy controls at baseline, 3, 6, and 12 months. Results revealed that all patients with SZ exhibited slower reading speed of the word pairs than healthy controls at all assessment periods. In addition, procedural learning - characterized as a significant decrease in the time taken to read aloud the target word pairs - was more impaired in the haloperidol- than in the risperidone-treated group at all assessment periods. Healthy controls showed steady improvement in reading speed over the 12 months of the study, in contrast to SZ patients, who reached a plateau in their capacity to improve mirror-reading skill over time. However, all SZ participants in the study showed near normal learning profiles from exposure to semantic associations embedded in the procedural memory task, providing evidence for the preservation of associative connections in the semantic network of these patients. The observed impairment in procedural learning in SZ may thus reflect, at least in part, the influence of neuroleptic medication on striatal functions.

Imaging genetic liability to schizophrenia: systematic review of FMRI studies of patients' nonpsychotic relatives

There is a growing literature on brain activity in the nonpsychotic first-degree relatives of patients with schizophrenia as measured using functional imaging. This systematic review examined 20 studies in 4 domains of cognition, including cognitive control (7 samples), working memory (5 samples), long-term memory (4 samples), and language (4 samples). While the literature was widely divergent, these studies did consistently find activation differences between patients' relatives and controls. The most consistent increases in activation within hemisphere were found in right ventral prefrontal cortex (PFC) and right parietal cortex. Abnormal activity, defined as significant increases or decreases in activation relative to controls irrespective of hemisphere, was found in about two-thirds of contrasts in the cerebellum, dorsal prefrontal, lateral temporal, and parietal cortices, and thalamus, with basal ganglia and ventral PFC showing abnormalities in approximately half of those contrasts. Anterior cingulate was generally spared in patients' relatives. The diversity of findings in studies of patients' relatives may derive from differences between the cognitive demands across studies. We identify avenues for building a more accurate and cumulative literature, including symmetrical inclusion criteria for relatives and controls, recording in-scanner responses, using both a priori and whole-brain tests, explicitly reporting threshold values, reporting main effects of task, reporting effect sizes, and quantifying the risk of false negatives. While functional imaging in the relatives of schizophrenia patients remains a promising methodology for understanding the impact of the unexpressed genetic liability to schizophrenia, no single region or mechanism of abnormalities has yet emerged.

Turning it upside down: areas of preserved cognitive function in schizophrenia

Patients with schizophrenia demonstrate marked impairments on most clinical neuropsychological tests. These findings suggest that patients suffer from a generalized form of cognitive impairment, with little evidence of spared performance documented in several large meta-analytic reviews of the clinical literature. In contrast, we review evidence for relative sparing of aspects of attention, procedural memory, and emotional processing observed in studies that have employed experimental approaches adapted from the cognitive and affective neuroscience literature. These islands of preserved performance suggest that the cognitive deficits in schizophrenia are not as general as they appear to be when assayed with clinical neuropsychological methods. The apparent contradiction in findings across methods may offer important clues about the nature of cognitive impairment in schizophrenia. The documentation of preserved cognitive function in schizophrenia may serve to sharpen hypotheses about the biological mechanisms that are implicated in the illness.

Motor sequence learning in primate: role of the D2 receptor in movement chunking during consolidation

Motor learning disturbances have been shown in diseases involving dopamine insufficiency such as Parkinson's disease and schizophrenic patients under antipsychotic drug treatment. In non-human primates, motor learning deficits have also been observed following systemic administration of raclopride, a selective D2-receptor antagonist. These deficits were characterized by persistent fluctuations of performance from trial to trial, and were described as difficulties in consolidating movements following a learning period. Moreover, it has been suggested that these raclopride-induced fluctuations can result from impediments in grouping separate movements into one fluent sequence. In the present study, we explore the hypothesis that such fluctuations during movement consolidation can be prevented through the use of sumanirole - a highly selective D2 agonist - if administered before raclopride. Two monkeys were trained to execute a well known sequence of movements, which was later recalled under three pharmacological conditions: (1) no drug, (2) raclopride, and (3) sumanirole+raclopride. The same three pharmacological conditions were repeated with the two monkeys, trained this time to learn new sequences of movements. Results show that raclopride has no deleterious effect on the well known sequence, nor the sumanirole+raclopride co-administration. However, results on the new sequence to be learned revealed continuous fluctuations of performances in the raclopride condition, but not in the sumanirole+raclopride condition. These fluctuations occurred concurrently with a difficulty in merging separate movement components, known as a "chunking deficit". D2 receptors seem therefore to be involved in the consolidation of new motor skills, and this might involve the chunking of separate movements into integrated motor sequences.

Sensorimotor adaptation in Parkinson's disease: evidence for a dopamine dependent remapping disturbance

Sensorimotor adaptation is thought to involve a remapping of the kinematic and kinetic parameters associated with movements performed within a changing environment. Patients with Parkinson's disease (PD) are known to be affected on this type of learning process, although the specific role of dopamine depletion in these deficits has not yet been elucidated. The present study was an attempt to clarify whether dopamine depletion in PD may directly affect the capacity to internally reorganize the visuomotor remapping of a distorted environment. Fourteen PD patients were tested twice, while they were treated and while they were withdrawn from their regular levodopa treatment. Fourteen control subjects were also enrolled and tested twice. Two parallel forms of the Computed Mirror Pointing Task (CMPT), requiring making a reaching movement in a visually transformed environment (mirror inversion), were administered to each participant. Each of them had to perform 40 trials at each of the 2 testing sessions. At each trial, sensorimotor adaptation was evaluated by the initial direction angle (IDA), which reflects the direction of movement before any visually guided readjustment. Results revealed no IDA difference at baseline, between control subject and PD patients, whether they were treated or not. In all group, IDA values at that time were large, reflecting a tendency to make movements according to the real life visuomotor mapping (based on the natural direct vision). However, striking differences appeared during sensorimotor learning, in that IDA reduction along trials was poorer in patient not treated with levodopa than both control subjects and the same PD patient treated with levodopa. No difference was observed between the treated PD patients and control subjects. Given that IDA is thought to reflect the internal representation of the visuomotor mapping, it is concluded that dopamine depletion in PD would affects sensorimotor adaptation, in that it facilitates old and poorly adapted movements (real life mapping), instead of new and more adapted ones (mirror transformed mapping).

Interactive memory systems and category learning in schizophrenia

Schizophrenia is a devastating mental disorder with multiple facets, including the impairment of learning and memory. Recent evidence suggests that information is processed and represented by multiple interacting memory systems in the brain, including prefrontal cortex, basal ganglia, and medial temporal lobe. These structures are critical in the pathophysiology of schizophrenia. Whereas executive and declarative memory dysfunctions are well known in schizophrenia, habit learning deficits related to the basal ganglia are less clear, despite the fact that dopaminergic and other neurochemical processes in the basal ganglia may play a crucial role in the pathophysiology and pharmacology of schizophrenia. In this article, I propose that the investigation of different classification learning functions, including reward- and feedback-guided learning and acquired equivalence learning, may shed light on the neuropsychology, pathophysiology, pharmacology, and behavioral genetics of schizophrenia.

Raclopride-induced motor consolidation impairment in primates: role of the dopamine type-2 receptor in movement chunking into integrated sequences

Results obtained in patients with schizophrenia have shown that antipsychotic drugs may induce motor learning deficits correlated with the striatal type-2 dopamine receptors (D(2)R) occupancy. Other findings suggest that the role of the striatum in motor learning could be related to a process of "chunking" discrete movements into motor sequences. We therefore hypothesized that a D(2)R blocking substance, such as raclopride, would affect motor learning by specifically disrupting the grouping of movements into sequences. Two monkeys were first trained to perform a baseline-overlearned sequence (Seq. A) drug free. Then, a new sequence was learned (Seq. B) and the overlearned sequence was recalled OFF-drug (Seq. A recall OFF-drug). The effect of raclopride was then assessed on the learning of a third sequence (Seq. C), and on the recall of the overlearned sequence (Seq. A recall ON-drug). Results showed that performance related to the overlearned sequence remained the same in the three experimental conditions (Seq. A, Seq. A recall OFF-drug, Seq. A recall ON-drug), whether the primates received raclopride or not. On the other hand, new sequence learning was significantly affected during raclopride treatment (Seq. C), when compared with new sequence learning without the effect of any drug (Seq. B). Raclopride-induced disturbances consisted in performance fluctuations, which persisted even after many days of trials, and prevented the monkeys from reaching a stable level of performance. Further analyses also showed that these fluctuations appeared to be related to monkeys' inability to group movements into single flowing motor sequences. The results of our study suggest that dopamine is involved in the stabilization or consolidation of motor performances, and that this function would involve a chunking of movements into well-integrated sequences.

Dopamine and incentive learning: a framework for considering antipsychotic medication effects

Hyperfunction of brain dopamine (DA) systems is associated with psychosis in schizophrenia and the medications used to treat schizophrenia are DA receptor blockers. DA also plays a critical role in incentive learning produced by rewarding stimuli. Using DA as the link, these results suggest that psychosis in schizophrenia can be understood from the point of view of excessive incentive learning. Incentive learning is mediated through the non-declarative memory system and may rely on the striatum or medial prefrontal cortex depending on the task. Typical and atypical antipsychotics differentially affect expression of the immediate early gene c-fos, producing greater activity in the striatum and medial prefrontal cortex, respectively. This led to the hypothesis that performance of schizophrenic patients on tasks that depend on the striatum or medial prefrontal cortex will be differentially affected by their antipsychotic medication. Results from a number of published papers supported this dissociation. Furthermore, the effects of two atypical drugs, clozapine and olanzapine, on c-fos expression were different from another atypical, risperidone that resembles the typical antipsychotics. Similarly, in tests of incentive learning, risperidone acted like the typical antipsychotics. Thus, typical and atypical antipsychotic drugs differed in the types of cognitive performance they affected and, furthermore, members of the atypical class differed in their effects on cognition. It remains the task of researchers and clinicians to sort out the symptoms associated with the endogenous illness from possible iatrogenic symptoms resulting from the antipsychotic medications used to treat schizophrenia.

Procedural learning in schizophrenia investigated with functional magnetic resonance imaging

A cerebral basis for the acquisition and retention of procedural knowledge in schizophrenia was examined with 1.5 T functional MRI during an embedded sequence Serial Reaction Time Task (SRTT) in 10 chronic medicated patients and 15 healthy controls. Comparable procedural learning was observed in both groups, suggesting that the impairment reported in previous schizophrenia samples may not be robust. Consistent with previous fMRI reports, procedural learning in the control group was associated with activity in the dorsal striatum, anterior cingulate, parietal cortex and frontal cortex. Greater procedural learning related activity was observed in the control relative to the schizophrenia group in the bilateral frontal, left parietal and bilateral caudate regions. Patients did not activate frontal or parietal areas while responding to the embedded sequence within the SRTT, but greater activation during procedural learning was observed relative to the control sample in the right anterior cingulate, left globus pallidus and the right superior temporal gyrus. Thus, despite comparable instantiation of procedural learning in schizophrenia, the cerebral activation associated with this cognitive skill was abnormal. The paucity of activity in bilateral frontal cortex, left parietal cortex and bilateral caudate nucleus may represent cerebral dysfunction associated with schizophrenia, whereas the hyperactivation of the right superior temporal gyrus, the right anterior cingulate cortex and the left globus pallidus may represent a compensatory cerebral action capable of facilitating near-normal task performance. The results are thus consistent with a neurodevelopmental pathology impinging on fronto-subcortical circuitry.

Deficit in schizophrenia to recruit the striatum in implicit learning: a functional magnetic resonance imaging investigation

In schizophrenia, explicit learning deficits have been well established although it is less clear whether these patients have deficits in implicit learning (IL). IL is thought to depend on intact striatal functioning. This study examined the hypothesis that schizophrenia patients show deficient recruitment of striatal activation during an IL paradigm, relative to performance-matched healthy comparison subjects. Ten subjects with schizophrenia on atypical antipsychotic medication and 10 age, gender, education, and performance matched healthy comparison subjects underwent fMRI while performing an IL task. On the basis of whole-brain and striatal region-of-interest analyses, we found a relative lack of striatal activation in schizophrenia patients. This result is consistent with convergent evidence of striatal dysfunction in schizophrenia.