Lateralized attentional deficits in drug-free and medicated schizophrenic patients

Implications for the thalamic reticular nucleus in impaired attention and sleep in schizophrenia

The thalamic reticular nucleus (TRN) is an inhibitory shell positioned between the thalamus and the cortex. It is uniquely situated to modulate the flow of sensory information from the surroundings to the cortex as well as influencing ongoing cortical activity by modulating cortico-thalamo-cortical transmission. Although the thinness, architecture and location of the TRN deep in the brain has previously made this a difficult structure to study, novel optical and genetic tools have allowed for more precise targeting of this area. Recent research has implicated a role for the TRN in attention and sleep. Interestingly, impairments in attention and sleep resulting from TRN perturbation are strikingly similar to the clinical deficits observed in schizophrenia. This review aims to discuss recent evidence for the role of TRN in attention and sleep born from optogenetic work and connect these findings with those clinically observed in schizophrenia.

Imagined motor action and eye movements in schizophrenia

Visual exploration and planning of actions are reported to be abnormal in schizophrenia. Most of the studies monitoring eye movements in patients with schizophrenia have been performed under free-viewing condition. The present study was designed to assess whether mentally performing an action modulates the visuomotor behavior in patients with schizophrenia and in healthy controls. Visual scan paths were monitored in eighteen patients with schizophrenia and in eighteen healthy controls. Participants performed two tasks in which they were asked either to (1) look at a scene on a computer screen (free viewing), or (2) picture themselves making a sandwich in front of a computer screen (active viewing). The scenes contained both task-relevant and task-irrelevant objects. Temporal and spatial characteristics of scan paths were compared for each group and each task. The results indicate that patients with schizophrenia exhibited longer fixation durations, and fewer fixations, than healthy controls in the free viewing condition. The patients' visual exploration improved in the active viewing condition. However, patients looked less at task-relevant objects and looked more at distractors than controls in the active viewing condition in which they were asked to picture themselves making a sandwich in moving their eyes to task-relevant objects on an image. These results are consistent with the literature on deficits in motor imagery in patients with schizophrenia and it extends the impairment to visual exploration in an action imagery task.

Fragmented perception: slower space-based but faster object-based attention in recent-onset psychosis with and without Schizophrenia

Background

Schizophrenia is associated with impairments of the perception of objects, but how this affects higher cognitive functions, whether this impairment is already present after recent onset of psychosis, and whether it is specific for schizophrenia related psychosis, is not clear. We therefore tested the hypothesis that because schizophrenia is associated with impaired object perception, schizophrenia patients should differ in shifting attention between objects compared to healthy controls. To test this hypothesis, a task was used that allowed us to separately observe space-based and object-based covert orienting of attention. To examine whether impairment of object-based visual attention is related to higher order cognitive functions, standard neuropsychological tests were also administered.

Method

Patients with recent onset psychosis and normal controls performed the attention task, in which space- and object-based attention shifts were induced by cue-target sequences that required reorienting of attention within an object, or reorienting attention between objects.

Results

Patients with and without schizophrenia showed slower than normal spatial attention shifts, but the object-based component of attention shifts in patients was smaller than normal. Schizophrenia was specifically associated with slowed right-to-left attention shifts. Reorienting speed was significantly correlated with verbal memory scores in controls, and with visual attention scores in patients, but not with speed-of-processing scores in either group.

Conclusions

deficits of object-perception and spatial attention shifting are not only associated with schizophrenia, but are common to all psychosis patients. Schizophrenia patients only differed by having abnormally slow right-to-left visual field reorienting. Deficits of object-perception and spatial attention shifting are already present after recent onset of psychosis. Studies investigating visual spatial attention should take into account the separable effects of space-based and object-based shifting of attention. Impaired reorienting in patients was related to impaired visual attention, but not to deficits of processing speed and verbal memory.

Visuospatial processing in schizophrenia: does it share common mechanisms with pseudoneglect?

Schizophrenia patients demonstrate behavioural and cerebral lateralised anomalies, prompting some authors to suggest they exhibit a mild form of right unilateral neglect. To better describe and understand lateralised visuospatial anomalies in schizophrenia, three experiments were run using tasks often utilised to study visuospatial processing in healthy individuals and in neglect patients: the Behavioural Inattention Test (BIT), the manual line bisection task with and without a local cueing paradigm, the landmark task (or line bisection judgement), and the number bisection task. Although the schizophrenia patients did not exhibit the full-blown neglect syndrome, they did demonstrate marked spatial biases that differentiated them from controls on all but two tasks. More specifically, schizophrenia patients showed neither a simple perceptual deficit nor an asymmetry, but demonstrated (1) lateralised anomalies on a simple manual line bisection task; (2) unilateral attentional deficits for line bisection within a local cueing paradigm; and (3) a lateralised deficit in the visuospatial representations of numbers. Altogether, these results suggest a right hemineglect-like deficit in schizophrenia in attentional, representational, and motor-intentional processes. Yet it does not appear to be as strong a phenomenon. Indeed, it could be considered as an accentuation of the normal asymmetry in visuospatial processing.

Auditory orienting and inhibition of return in schizophrenia: a functional magnetic resonance imaging study

Patients with schizophrenia (SP) exhibit deficits in both attentional reorienting and inhibition of return (IOR) during visual tasks. However, it is currently unknown whether these deficits are supramodal in nature and how these deficits relate to other domains of cognitive dysfunction. In addition, the neuronal correlates of this pathological orienting response have not been investigated in either the visual or auditory modality. Therefore, 30 SP and 30 healthy controls (HC) were evaluated with an extensive clinical protocol and functional magnetic resonance imaging (fMRI) during an auditory cuing paradigm. SP exhibited both increased costs and delayed IOR during auditory orienting, suggesting a prolonged interval for attentional disengagement from cued locations. Moreover, a delay in the development of IOR was associated with cognitive deficits on formal neuropsychological testing in the domains of attention/inhibition and working memory. Event-related fMRI showed the characteristic activation of a frontoparietal network (invalid trials>valid trials), but there were no differences in functional activation between patients and HC during either attentional reorienting or IOR. Current results suggest that orienting deficits are supramodal in nature in SP, and are related to higher-order cognitive deficits that directly interfere with day-to-day functioning.

Useful visual field in patients with schizophrenia: a choice reaction time study

This study examined the size of the useful visual field in patients (9 men, 6 women) with schizophrenia. A choice reaction task was conducted, and performances at 2.5, 5, 7, 10, and 25 degrees in both visual fields were measured. Three key findings were shown. First, patients had slower choice reaction times (choice RTs) than normal controls. Second, patients had slower choice RTs in the right visual field than in the left visual field. Third, patients and normal controls showed the same U-shaped choice RT pattern. The first and second findings were consistent with those of other studies. The third finding was a clear indication of the patients' performance in peripheral vision, and a comparison with normal controls suggested that there was no difference in the size of the useful visual field, at least within

Visuospatial attention in schizophrenia: deficits in broad monitoring

Although selective attention is thought to be impaired in people with schizophrenia (PSZ), prior research has found no deficit in the ability to select one location and withdraw attention from another. PSZ and healthy control subjects (HCS) performed a stimulus detection task in which one, two, or all four peripheral target locations were cued. When one or two locations were cued, both PSZ and HCS responded faster when the target appeared at a cued than uncued location. However, increases in the number of validly cued locations had much more deleterious effects on performance for PSZ than HCS, especially for targets of low contrast whose detection was more dependent on attention. PSZ also responded more slowly in trials with four cued locations relative to trials with one or two invalidly cued locations. Thus, visuospatial attention deficits in schizophrenia arise when broad monitoring is required rather than when attention must be focused narrowly.

Enhanced facilitation of spatial attention in schizophrenia

OBJECTIVE

While attentional functions are usually found to be impaired in schizophrenia, a review of the literature on the orienting of spatial attention in schizophrenia suggested that voluntary attentional orienting in response to a valid cue might be paradoxically enhanced. We tested this hypothesis with orienting tasks involving the cued detection of a laterally presented target stimulus.

METHOD

Subjects were chronic schizophrenia patients (SZ) and matched healthy control subjects (HC). In Experiment 1 (15 SZ, 16 HC), cues were endogenous (arrows) and could be valid (100% predictive) or neutral with respect to the subsequent target position. In Experiment 2 (16 SZ, 16 HC), subjects performed a standard orienting task with unpredictive exogenous cues (brightening of the target boxes).

RESULTS

In Experiment 1, SZ showed a larger attentional facilitation effect on reaction time than HC. In Experiment 2, no clear sign of enhanced attentional facilitation was found in SZ.

CONCLUSIONS

The voluntary, facilitatory shifting of spatial attention may be relatively enhanced in individuals with schizophrenia in comparison to healthy individuals. This effect bears resemblance to other relative enhancements of information processing in schizophrenia such as saccade speed and semantic priming.

Preattentional processes and disorganization in schizophrenia: Influence of a 6-week risperidone treatment

INTRODUCTION

Visual orientation and attention are impaired in schizophrenia. Engagement and disengagement of attention and the ability to prompt responses to a stimulus in patients before and after six weeks of risperidone were compared to controls.

METHODS

Ten unmedicated (nine naïve) schizophrenic patients, and eleven controls performed 1) A visual orienting task, the Cued Target Detection task (CTD), with the detection of a visual stimulus in valid, invalid, no cue and double cue trials, two conditions for fixation offset for a modulation of visual fixation: Gap: 200 ms before target; No Gap: simultaneous with target, 2) Choice Reaction Time (CRT 0.5 and 2 s delays).

RESULTS

At baseline, patients showed longer RT than controls in CRT, but not in CTD, with in CTD, no facilitation of RT with the gap procedure. The alertness index was almost null in CTD-Gap and comparable to controls in CTD-No Gap. Efficiency to detect attended stimuli (CTD-No Gap) and warning effect (CRT 0.5 s) were negatively correlated to disorganization. After treatment, readiness to act in CRT had decreased. In CTD-No Gap, change in PANSS disorganization was correlated to an increased validity index, change in negative sub-score was correlated to decreased attention cost.

CONCLUSION

Untreated patients displayed a deficit of Gap effect and a slowing in sustained attention. Disorganization interfered with warning and visual detection. After treatment, its improvement and negative symptoms improvement were associated with better visual detection. These alterations in visual orienting provide new evidence for an oculomotor dysregulation of attentional engagement in schizophrenia.

Attention and visual orienting in siblings, schizophrenic patients, and controls: impairment in attentional disengagement

Visual orienting tasks reveal an impaired disengagement of attention in schizophrenia. We explored visual orientation in 20 schizophrenia patients (SZ), 20 full siblings (FS), and 20 controls (C) using a cued target detection (gap vs. no gap) and a choice reaction time task. SZ but not FS had longer reaction time with comparable reactions to warning. In contrast to C, SZ and FS did not display a significant gap effect. The disengagement deficit in schizophrenia patients and their siblings provides arguments for altered early attention mechanisms (in schizophrenic patients and their nonpsychotic relatives).

Attention network test (ANT) reveals gender-specific alterations of executive function in schizophrenia

The Attention Network Test (ANT) provides measures for three different components of visual attention: executive control (=conflict inhibition), orienting, and alerting. There is reasonable evidence that alterations of attention-mainly in the executive/conflict domain-are associated with susceptibility to psychiatric illness. Specific impairments may be a characteristic for a medical condition such as schizophrenia and thus shift our understanding from a neuropsychological endophenotype to a more precise genetic understanding of this disorder. Study subjects comprised 35 schizophrenic patients and 35 healthy controls (13 female and 22 male in both groups). The ANT was administered to all participants and rated individual responses for the three factors (alerting, orienting, and conflict) and their respective ratios relative to mean reaction times. With regard to gender differences, group comparisons were performed for schizophrenic patients vs. healthy controls. Significant differences between patients and controls could be detected for mean reaction time (639 vs. 538 ms) and for conflict ratio (0.158 vs. 0.191). The latter difference mainly resulted from gender-specific variances of the conflict network in opposite directions. The executive function as represented by the conflict network of visual attention of the ANT is affected in schizophrenia. We have detected hitherto unreported gender-specific differences between healthy controls and schizophrenic patients. Especially as regards the conflict network, the ANT offers a promising methodology to detect a neuropsychological endophenotype of schizophrenia.

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.

The construct of attention in schizophrenia

Schizophrenia is widely thought to involve deficits of attention. However, the term "attention" can be defined so broadly that impaired performance on virtually any task could be construed as evidence for a deficit in attention, and this has slowed cumulative progress in understanding attention deficits in schizophrenia. To address this problem, we divide the general concept of attention into two distinct constructs: input selection, the selection of task-relevant inputs for further processing; and rule selection, the selective activation of task-appropriate rules. These constructs are closely tied to working memory, because input selection mechanisms are used to control the transfer of information into working memory and because working memory stores the rules used by rule selection mechanisms. These constructs are also closely tied to executive function, because executive systems are used to guide input selection and because rule selection is itself a key aspect of executive function. Within the domain of input selection, it is important to distinguish between the control of selection--the processes that guide attention to task-relevant inputs--and the implementation of selection--the processes that enhance the processing of the relevant inputs and suppress the irrelevant inputs. Current evidence suggests that schizophrenia involves a significant impairment in the control of selection but little or no impairment in the implementation of selection. Consequently, the CNTRICS (Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia) participants agreed by consensus that attentional control should be a priority target for measurement and treatment research in schizophrenia.

Gaze-triggered orienting is reduced in chronic schizophrenia

Patients with schizophrenia have been reported to demonstrate subtle impairment in gaze processing, which in some cases indicates hypersensitivity to gaze, while in others, hyposensitivity. The neural correlate of gaze processing is situated in the superior temporal sulcus (STS), a major portion of which is constituted by the superior temporal gyrus (STG), and may be the underlying dysfunctional neural basis to the abnormal gaze sensitivity in schizophrenia. To identify the characteristics of gaze behavior in patients with chronic schizophrenia, in whom the STG has been reported to be smaller in volume, we tested 22 patients (mean duration of illness 29 years) in a spatial cueing paradigm using two central pictorial gaze cues, both of which effectively triggered attentional orienting in 22 age-matched normal controls. Arrow cues were also employed to determine whether any compromise in schizophrenia, if present, was gaze-specific. Results demonstrated that schizophrenic subjects benefit significantly less from congruent cues than normal subjects, which was evident for gaze cues but not for arrow cues. This finding is suggestive of a relatively gaze-specific hyposensitivity in patients with chronic schizophrenia, a finding that is in line with their clinical symptomatology and that may be associated with a hypoactive STS.

Orienting of attention in unmedicated patients with schizophrenia, prodromal subjects and healthy relatives

In typical orienting of attention tasks subjects have to respond as fast as possible to targets which appear in the periphery of the visual field and are preceded by spatial cues (e.g. brightening of a peripheral box where the target may subsequently appear). Reaction times (RT) are facilitated when cue and target appear at the same location (valid cueing) and the cue target interval is short (<250 ms). However, RTs slow down again when the target follows a valid cue after an interval of 250 ms and longer. This latter phenomenon is called Inhibition of Return (IOR) and is thought to reflect an automatic, inhibitory mechanism to protect the organism from redundant and distracting stimuli. Deficits of IOR were repeatedly reported in patients with schizophrenia. However, the role of medications and the nature of the deficit (trait or vulnerability indicator?) were unclear. In the present study we examined 15 unmedicated patients with schizophrenia (age: 31.2+/-11.1, m/f: 11/4, global scores SAPS: 48.33+/-33.09, SANS: 19.22+/-26.16), 29 subjects who were putatively in a prodromal state of psychosis, 30 first-degree relatives, another 8 first-degree relatives who had one child and at least one more relative with schizophrenia, and 50 healthy controls. We found an impairment of IOR only in the unmedicated patient group. In conclusion, blunted IOR in schizophrenia is not secondary to medications. According to this and previous studies blunted IOR may be most probably viewed as a trait cognitive feature of the schizophrenic disorder.

Neuroleptics reverse attentional effects in schizophrenia patients

Patients with schizophrenia show attention deficit characterized by a larger validity effect (fast responses to cued than uncued stimuli) in the right visual field than in the left visual field. In addition, schizophrenia patients do not show inhibition of return (IOR--a mechanism that enables efficient visual search), unless attention is summoned back to the center after the peripheral cue. The present study examined the short-term effect of neuroleptic medications on these two components of visual spatial attention in schizophrenia patients. In order to do this we tested schizophrenia patients that were treated with long-acting neuroleptic medication. These patients were treated once a month, which allowed us to test them with either low or high levels of medication. Here we show that neuroleptic medications reverse the attentional hemispheric asymmetry. In the group with a high level of medication fast RTs to cued trials were found in the right visual field, while in the group with a low level of medication the opposite pattern was found - fast RTs to cued trials were found in the left visual field. In addition, level of medication did not influence IOR - regardless of the level of medication, IOR was observed only when attention was summoned back to the center, unlike control group. These finding suggest an imbalance in dopaminergic activity, possibly in subcortical structures such as the basal ganglia. This study also shows a dissociation between the two components of visual orienting of attention and suggests that facilitation and inhibition are independent processes.

Pseudoneglect in schizophrenia: a line bisection study with cueing

INTRODUCTION

Numerous authors have reported the existence of lateralised abnormalities towards the right side in patients with schizophrenia.

METHODS

In the present study, a manual line bisection task was used to assess the existence of a visuospatial bias in patients with schizophrenia as compared to healthy subjects and left unilateral neglect patients. In addition, we used a local cueing paradigm (consisting of a number placed on the right, on the left, or at both ends of the line).

RESULTS

Healthy subjects showed a leftwards trend in the "no cue" condition (known as pseudoneglect) and neglect patients showed a right bias in all cue conditions. In contrast, patients with schizophrenia placed their manual estimation of the centre further to the left than healthy subjects in all cue conditions, reflecting neglect of the right side of the line. Moreover, like healthy subjects and neglect patients, patients with schizophrenia were affected by the local cueing.

CONCLUSION

Hence, patients with schizophrenia show a bias in their spatial representation, which does not interfere with local context processing.

Exaggerated leftward bias in the mental number line of patients with schizophrenia

Several visuo-motor tasks can be used to demonstrate biases towards left hemispace in schizophrenic patients, suggesting a minor right hemineglect. Recent studies in neglect patients used a new number bisection task to highlight a lateralized defect in their visuo-spatial representation of numbers. To test a possible lateralized representational deficit in schizophrenia, we used the number bisection task in 11 schizophrenic patients compared to 11 healthy controls. Participants were required to orally indicate the central number of an interval orally presented. Whereas healthy subjects showed no significant bias, schizophrenic patients presented a significant leftward bias. Therefore, these results suggest an impairment in higher order representations of the number space in patients with schizophrenia, an impairment that is qualitatively similar to the deficit described in neglect patients.

Inhibition of return in the human 5HT2A agonist and NMDA antagonist model of psychosis

Patients with schizophrenia exhibit disturbances of orienting of attention. However, findings have been inconsistent. Pharmacologic challenges with hallucinogens have been used as models for psychosis. The NMDA antagonist state (PCP, ketamine) resembles undifferentiated psychoses with positive and negative symptoms, while the 5-HT(2A) agonist state (LSD, dimethyltryptamine (DMT)) is thought to be an appropriate model for psychoses with prominent positive symptoms. The aim of this study was to investigate orienting of attention in the human NMDA antagonist and 5-HT(2A) agonist models of psychosis. A total of 15 healthy volunteers participated in a randomized, double-blind, crossover study with a low and a high dose of DMT and S-ketamine, which elicited subtle 'prepsychotic' or full-blown psychotic symptoms (low and high dose, respectively). Nine subjects completed both experimental days with the two doses of both drugs. Overall, both hallucinogens slowed down reaction times dose dependently (DMT >S-ketamine) and DMT diminished the general response facilitating (alerting) effect of spatially neutral cues. Inhibition of Return (IOR), that is, the normal reaction time disadvantage for validly cued trials with exogenous cues and long cue target intervals, was blunted after both doses of DMT and the low dose of S-ketamine. IOR reflects an automatic, inhibitory mechanism of attention, which is thought to protect the organism from redundant, distracting sensory information. In conclusion, our data suggest a deficit of IOR in both hallucinogen models of psychosis, with the effect being clearer in the serotonin model. Blunted IOR may underlie or predispose to different psychotic manifestations, but particularly to those with prominent positive symptoms.

Deficient inhibition of return in schizophrenia-further evidence from an independent sample

Previous studies on spatial orienting of attention in schizophrenia demonstrated a deficit of Inhibition of Return (IOR). However, other studies reported a delay in the manifestation, but an overall normal amount of IOR in patients with schizophrenia. However, the latter studies used a cue-back manipulation which is known to reinstate or speed up IOR. Hence, it is not clear whether even very long cue target intervals would allow IOR to develop in patients with schizophrenia in the absence of a cue-back manipulation. The aim of the present study was to study IOR in patients with schizophrenia using a single cue paradigm and a very long cue target interval of >1 s in order to differentiate between blunted and delayed IOR. We examined 32 inpatients with schizophrenia and 16 healthy controls with a covert orienting of attention task (COVAT) with non-predictive peripheral cues and three stimulus onset asynchronies (SOA: 100 ms, 800 ms and 1050 ms). We found a lack of Inhibition of Return (IOR) in patients with schizophrenia with both long SOAs of 800 and 1050 ms. As in a previous study of our group, the IOR deficit was unrelated to psychopathology, length of illness, number of previous psychotic episodes and type of neuroleptic medication. In summary, our study confirms and extends previous reports of deficient IOR in patients with schizophrenia. IOR seems to be not just delayed, but rather profoundly disturbed in schizophrenia. Deficient IOR in patients with schizophrenia might be viewed as a trait or alternatively as a vulnerability marker of the disorder.

Perceptional and executive deficits of chronic schizophrenic patients in attentional and intentional tasks

The present study investigated whether schizophrenic patients could develop appropriate visual orientation and motor set under precuing conditions which contrasted attentional (input selective) and intentional (output selective) information. The aim was to evaluate perceptual performance in processing visuospatial information, and executive performance in response preparation. Stimuli and/or elicited responses were controlled for selective hemispheric engagement. Age, sex and handedness matched groups of 33 chronic schizophrenic patients and 33 normal subjects were tested on choice reaction time (RT) tasks in which warning signals were manipulated regarding either where a target stimulus would occur (selective attention) or which hand to use for responding (response preparation). All subjects benefited from precued information regarding subsequent responses. However, schizophrenic patients were not able to use intentional cues as effectively as control subjects did. Interhemispheric asymmetry of spatial attention was found in patients with schizophrenia, with slowing of responses to uncued targets presented in the right visual field. There was also a decreased advantage of within-hemisphere stimulus-response conditions in the schizophrenic group. Our results support the notion that a dysfunction involving parietal and premotor areas has potential importance in the schizophrenic illness. We replicated findings which indicate that deficits of information processing in schizophrenia may affect left hemispheric mechanisms to a larger extent. The results also point toward a possible abnormal connectivity between frontal and parietal circuits in schizophrenia.

Blunted inhibition of return in schizophrenia-evidence from a longitudinal study

Previous cross-sectional studies on covert orienting of visual attention in schizophrenia have been inconsistent. In the present longitudinal study, we examined 40 medicated acutely ill inpatients with a covert orienting of attention task (COVAT) shortly after admission, and again 12-16 weeks after the initial examination, while most patients were in (partial) remission. We administered a COVAT with nonpredictive peripheral cues and two stimulus-onset asynchronies (SOA; 100 and 800 ms). In addition, we examined 34 healthy control subjects twice (2 weeks apart). The most important finding was a lack of inhibition of return (IOR) in patients with schizophrenia, both at the first examination in an acute psychotic state and at the follow-up examination after considerable clinical improvement. The IOR deficit was unrelated to psychopathology, length of illness, number of previous psychotic episodes, and type of neuroleptic (NL) medication. Deficient IOR in patients with schizophrenia appears to be state-independent and might be viewed as a trait or vulnerability marker of the disorder. Subsequent studies with never-medicated populations and with schizotypal or high-risk subjects are needed in order to further analyze the possible role of NL medications and to clarify whether blunted IOR might represent a vulnerability marker of schizophrenia.

Symmetry reversal in schizophrenia

Schizophrenia is associated with cortical asymmetries concentrated in the left fronto-temporal hemisphere. In order to look for functional asymmetries between the two hemispheres, the stimulus-response times of patients were split into smaller periods and the interhemispheric and intrahemispheric correlations between these periods were investigated. Three groups were compared to each other: 22 patients with schizophrenia (Diagnostic and Statistical Manual of Mental Disorders, 4th edn; DSM-IV) treated with neuroleptics; 24 psychiatric neuroleptic-treated patients without schizophrenia; and 30 healthy subjects. All subjects were investigated by simple (one stimulus-one response) and complex (two stimuli-two responses), auditory and visual, right-hemispheric and left-hemispheric stimulus-response tasks. There were no intrahemispheric but significant interhemispheric correlations between the two auditory and between the two visual time fragments in both the healthy and the neuroleptic control group. In contrast there was a significant intrahemispheric correlation between the auditory and visual time fragment in the left hemisphere of patients with schizophrenia and no interhemispheric correlation between the auditory times. The reduction of the interhemispheric auditory correlation is interpreted as an auditory disintegration, the appearance of the left-hemispheric audiovisual correlation as an audiovisual 'hyperintegration' in patients with schizophrenia. It is questionable as to whether these findings are due to schizophrenia or to the neuroleptic treatment.

Interhemispheric transfer and laterality effects in simple visual reaction time in schizophrenics

INTRODUCTION

There is evidence that schizophrenics have an abnormal corpus callosum and an abnormal pattern of cerebral asymmetries. We investigated whether there are corresponding functional abnormalities in interhemispheric transfer (IT) and laterality effects.

METHODS

Medicated schizophrenic patients and matched controls were tested in the Poffenberger paradigm, that is, a simple manual reaction time (RT) paradigm with laterally presented visual stimuli designed to provide a behavioural estimate of IT. By subtracting RT averaged across the uncrossed hand-hemifield conditions, from RT averaged across the crossed hand-hemifield conditions, one can obtain an estimate of IT time.

RESULTS

In schizophrenic patients the difference between crossed and uncrossed conditions was 0 because of an unusually prolonged RT in the uncrossed condition right hand/ right field. A broadly similar result has been obtained previously in the tactile modality (Ditchfield & Hemsley, 1990) and is consistent with a left hemisphere impairment. This effect was still present when the patients were retested about 2 years later.

CONCLUSIONS

These results demonstrate the existence in schizophrenic patients of a consistent slowing down of simple visuomotor responses subserved by the left hemisphere.

Why is magical ideation related to leftward deviation on an implicit line bisection task?

Right hemispatial inattention is a neurocognitive deficit observed in thought-disordered schizophrenia patients, persons with schizotypal personality disorder and healthy participants with high scores on schizotypy scales. We administered a schizotypy inventory, the Magical Ideation (MI) scale, to forty healthy, right-handed men who had copied and later recalled the Rey-Osterrieth complex figure. Implicit line bisection performances were defined as the bisecting lines of the complex figure's large rectangle and were recorded for the copy and delay conditions. MI scores were significantly correlated with a leftward shift in bisections in the delay but not copy condition, indicating a significant relationship between the degree of right hemispatial inattention and number of magical beliefs in healthy participants. We describe a model in which these beliefs are conceptualized as a consequence of a hemispheric imbalance, specifically, of a "right hemisphere processing bias". This model accounts for (1) the leftward shifts in spatial attention and (2) the language deficits associated with psychosis and related symptom clusters which have hitherto been addressed in separate literatures. Clinically, the Rey-Osterrieth test may provide a means to assess implicit hemispatial inattention in psychotic patients.

Attentional asymmetry in schizophrenia: disengagement and inhibition of return deficits

This research examined 2 components of visual orienting in medicated schizophrenia patients: the validity effect and the inhibition of return (IOR). In the 1st experiment, patients showed the expected asymmetry in orienting attention, that is, larger validity effect in the right visual field than in the left. However, this asymmetry was due to a deficit in facilitatory processes rather than a disengagement deficit. In addition, patients showed a deficit in IOR. In the 2nd experiment, a 2nd central cue for summoning attention, explicitly, back to the center was used. In this experiment, normal IOR in schizophrenia patients was found. Because it was shown that schizophrenia patients do not have a disengagement deficit, IOR possibly could not be observed because of the increased facilitation in that location. It was proposed that the abnormality in visual attention in schizophrenia is due to a deficit in inhibitory processes.

Neuropsychological dysfunctions in siblings discordant for schizophrenia

Although cognitive impairments are well recognized in patients with schizophrenia, it is unclear which impairments are due to a genetic predisposition and which are caused by secondary disease effects or phenotype. The aim of this study is to investigate the possible relationship between genetic vulnerability to schizophrenia and cognitive functioning. Three groups of subjects were compared: 14 patients with schizophrenia, 15 healthy siblings and 32 healthy control subjects. All subjects were tested neuropsychologically. The raw test data were rescaled to standard equivalents (z-scores). Subjects' z scores on tests assessing the same cognitive domain were clustered and analyzed. Differences in cognitive functioning were found in the domains of abstraction, attention, executive functioning, spatial memory, and sensory-motor functioning. The schizophrenic probands were impaired on all these five domains whereas the healthy probands showed impairments on executive functioning and partially on sensory-motor functioning. Furthermore, for spatial memory the significant finding could mainly be attributed to impaired functioning in the patients, but not healthy siblings or control subjects, whereas for executive functioning patients and healthy siblings seemed equally impaired as compared to control subjects. The planning time of the Tower of London (TOL) and the initiation time of the Motor Planning Task (MPT) were used for measures of executive functioning, while the 'time to move of the Motor Planning Task' was used as measures of sensory motor functioning. These results suggest that the cognitive abnormalities in schizophrenia that may be related to genotype are represented in the domain of executive functioning and to some extent in the domain of sensory-motor functioning.

Attention deficit/hyperactivity disorder children with a 7-repeat allele of the dopamine receptor D4 gene have extreme behavior but normal performance on critical neuropsychological tests of attention

An association of the dopamine receptor D4 (DRD4) gene located on chromosome 11p15.5 and attention deficit/hyperactivity disorder (ADHD) has been demonstrated and replicated by multiple investigators. A specific allele [the 7-repeat of a 48-bp variable number of tandem repeats (VNTR) in exon 3] has been proposed as an etiological factor in attentional deficits manifested in some children diagnosed with this disorder. In the current study, we evaluated ADHD subgroups defined by the presence or absence of the 7-repeat allele of the DRD4 gene, using neuropsychological tests with reaction time measures designed to probe attentional networks with neuroanatomical foci in D4-rich brain regions. Despite the same severity of symptoms on parent and teacher ratings for the ADHD subgroups, the average reaction times of the 7-present subgroup showed normal speed and variability of response whereas the average reaction times of the 7-absent subgroup showed the expected abnormalities (slow and variable responses). This was opposite the primary prediction of the study. The 7-present subgroup seemed to be free of some of the neuropsychological abnormalities thought to characterize ADHD.

Eye tracking in normals: spem asymmetries and association with schizotypy

SPEM was recorded electro-oculographically during visual tracking of sinusoidal targets oscillating at .4 and .8 cycles per second in one hundred nineteen undergraduates. The logarithms of median root mean square values were used to assess tracking accuracy for leftward and rightward halfcycles of tracking. Over the entire sample, there was a significant superiority of rightward over leftward tracking, which, given evidence for the ipsilateral mediation of SPEM at the cortical level, suggests a right hemisphere predominance in the control of SPEM in normal subjects. Individual tracking asymmetry was associated with overall tracking accuracy such that subjects with relatively deficient leftward tracking and those with a larger absolute magnitude of asymmetry had poorer overall tracking. High scores on an MMPI schizotypy measure (Sum 2-7-8-0) were significantly related to poorer overall SPEM accuracy, individual tracking asymmetry, the absolute magnitude of tracking asymmetry, and phase lag, though the subjects' sex, handedness, and crossed hand-foot dominance were found to affect the relationships between schizotypy and tracking accuracy. These findings suggest that although control of SPEM may be predominantly right hemispheric, in some persons with a vulnerability to schizophrenia spectrum disorders, expressed as poorer overall SPEM accuracy and high schizotypy scores, left hemisphere-mediated (leftward) SPEM may be particularly impaired.