Smooth pursuit eye movements in schizophrenia and attentional dysfunction: adults with schizophrenia, ADHD, and a normal comparison group

Evidence from comprehensive independent validation studies for smooth pursuit dysfunction as a sensorimotor biomarker for psychosis

Smooth pursuit eye movements are considered a well-established and quantifiable biomarker of sensorimotor function in psychosis research. Identifying psychotic syndromes on an individual level based on neurobiological markers is limited by heterogeneity and requires comprehensive external validation to avoid overestimation of prediction models. Here, we studied quantifiable sensorimotor measures derived from smooth pursuit eye movements in a large sample of psychosis probands (N = 674) and healthy controls (N = 305) using multivariate pattern analysis. Balanced accuracies of 64% for the prediction of psychosis status are in line with recent results from other large heterogenous psychiatric samples. They are confirmed by external validation in independent large samples including probands with (1) psychosis (N = 727) versus healthy controls (N = 292), (2) psychotic (N = 49) and non-psychotic bipolar disorder (N = 36), and (3) non-psychotic affective disorders (N = 119) and psychosis (N = 51) yielding accuracies of 65%, 66% and 58%, respectively, albeit slightly different psychosis syndromes. Our findings make a significant contribution to the identification of biologically defined profiles of heterogeneous psychosis syndromes on an individual level underlining the impact of sensorimotor dysfunction in psychosis.

Automatic diagnosis of schizophrenia and attention deficit hyperactivity disorder in rs-fMRI modality using convolutional autoencoder model and interval type-2 fuzzy regression

Nowadays, many people worldwide suffer from brain disorders, and their health is in danger. So far, numerous methods have been proposed for the diagnosis of Schizophrenia (SZ) and attention deficit hyperactivity disorder (ADHD), among which functional magnetic resonance imaging (fMRI) modalities are known as a popular method among physicians. This paper presents an SZ and ADHD intelligent detection method of resting-state fMRI (rs-fMRI) modality using a new deep learning method. The University of California Los Angeles dataset, which contains the rs-fMRI modalities of SZ and ADHD patients, has been used for experiments. The FMRIB software library toolbox first performed preprocessing on rs-fMRI data. Then, a convolutional Autoencoder model with the proposed number of layers is used to extract features from rs-fMRI data. In the classification step, a new fuzzy method called interval type-2 fuzzy regression (IT2FR) is introduced and then optimized by genetic algorithm, particle swarm optimization, and gray wolf optimization (GWO) techniques. Also, the results of IT2FR methods are compared with multilayer perceptron, k-nearest neighbors, support vector machine, random forest, and decision tree, and adaptive neuro-fuzzy inference system methods. The experiment results show that the IT2FR method with the GWO optimization algorithm has achieved satisfactory results compared to other classifier methods. Finally, the proposed classification technique was able to provide 72.71% accuracy.

Oculomotor deficits in attention deficit hyperactivity disorder (ADHD): A systematic review and comprehensive meta-analysis

Atypical motor coordination and cognitive processes, such as response inhibition and working memory, have been extensively researched in individuals with attention deficit hyperactivity disorder (ADHD). Oculomotor neural circuits overlap extensively with regions involved in motor planning and cognition, therefore studies of oculomotor function may offer unique insights into motor and cognitive control in ADHD. We performed a series of pairwise meta-analyses based on data from 26 oculomotor studies in ADHD to examine whether there were differences in performance on visually-guided saccade, gap, antisaccade, memory-guided, pursuit eye movements and fixation tasks. These analyses revealed oculomotor disturbances in ADHD, particularly for difficulties relating to saccade inhibition, memorizing visual target locations and initiating antisaccades. There was no evidence for pursuit eye movement disturbances or saccade dysmetria. Investigating oculomotor abnormalities in ADHD may provide insight into top-down cognitive control processes and motor control, and may serve as a promising biomarker in ADHD research and clinical practice.

[Circuit mechanisms of spatial perception and visuomotor integration]

Animals can make appropriate decisions based on sensory information about the environment. Vision is one of the most critical ability for survival in dynamic situations in nature, particularly for mammalian species, such as primates, carnivores, and rodents. Although there is a huge computational cost involved in processing visual information, the brain can perform this task very rapidly using well-organized parallel and hierarchical neural circuits, enabling animals to rapidly sense the environment and, in turn, perform adaptive actions. Physiological, psychophysical, and clinical studies over hundreds of years have delineated the neural circuit mechanisms of the visual system. Artificial intelligence and robotics have also started making progress in this area. However, due to technical limitations, there are still many open questions that elude explanation in understanding the neural mechanism of visuomotor integration. Herein, we initially describe the anatomical structures of occipital cortices related to vision and then provide an overview of the physiological and clinical studies of the dorsal visual pathway related to spatial perception and prediction in non-human primate species. Finally, we introduce recent approaches in which rodents have been used as model species to elucidate the neural circuit mechanism of visually-guided behavior. Uncovering neural implementation of the association between visual-spatial perception and visuomotor function could provide key insights into the engineering of highly active robots and could also contribute to the development of novel therapeutic strategies addressing visual impairment and psychiatric/neurological disorders.

Clinical Validation of Eye Vergence as an Objective Marker for Diagnosis of ADHD in Children

OBJECTIVE

ADHD youth show poor oculomotor control. Recent research shows that attention-related eye vergence is weak in ADHD children.

METHOD

To validate vergence as a marker to classify ADHD, we assessed the modulation in the angle of vergence of children ( n = 43) previously diagnosed with ADHD while performing an attention task and compared the results with age-matched clinical controls ( n = 19) and healthy peers ( n = 30).

RESULTS

We observed strong vergence responses in healthy participants and weak vergence in the clinical controls. ADHD children showed no significant vergence responses. Machine-learning models classified ADHD patients ( n = 21) from healthy controls ( n = 21) with an accuracy of 96.3% (false positive [FP]: 5.12%; false negative [FN]: 0%; area under the curve [AUC]: 0.99) and ADHD children ( n = 11) from clinical controls ( n = 14) with an accuracy of 85.7% (FP: 4.5%; FN: 19.2%, AUC: 0.90).

CONCLUSION

In combination with an attention task, vergence responses can be used as an objective marker to detect ADHD in children.

Metabolomic Biomarkers in Mental Disorders: Bipolar Disorder and Schizophrenia

Psychiatric disorders are some of the most impairing human diseases. Among them, bipolar disorder and schizophrenia are the most common. Both have complicated diagnostics due to their phenotypic, biological, and genetic heterogeneity, unknown etiology, and the underlying biological pathways, and molecular mechanisms are still not completely understood. Given the multifactorial complexity of these disorders, identification and implementation of metabolic biomarkers would assist in their early detection and diagnosis and facilitate disease monitoring and treatment responses. To date, numerous studies have utilized metabolomics to better understand psychiatric disorders, and findings from these studies have begun to converge. In this chapter, we briefly describe some of the metabolomic biomarkers found in these two disorders.

Possible Medication-Resistant Deficits in Adult ADHD

OBJECTIVE

The nature of ADHD, especially in adulthood, is not well-understood. Therefore, we explored subcomponents of attention in adult ADHD.

METHOD

Twenty-three adults with ADHD were tested on neurocognitive and visual tracking performance both while on their regular prescription stimulant medication and while abstaining from the medication for 1 day. Pairwise comparisons to 46 two-for-one matched normal controls were made to detect medication-resistant effects of ADHD, and within-participant comparisons were made to detect medication-sensitive effects in patients.

RESULTS

Even when on medication, patients performed more poorly than controls on a spatial working memory task, and on visual tracking and simple reaction time tasks immediately following other attention-demanding tasks. Patients' visual tracking performance degraded while off-medication in a manner consistent with reduced vigilance.

CONCLUSION

There may be persistent cognitive impairments in adult ADHD despite medication. In addition, the benefit of stimulants seems reduced under cognitive fatigue.

Effect of Stimulus Type and Motion on Smooth Pursuit in Adults and Children

PURPOSE

This study presents a two-degree customized animated stimulus developed to evaluate smooth pursuit in children and investigates the effect of its predetermined characteristics (stimulus type and size) in an adult population. Then, the animated stimulus is used to evaluate the impact of different pursuit motion paradigms in children.

METHODS

To study the effect of animating a stimulus, eye movement recordings were obtained from 20 young adults while the customized animated stimulus and a standard dot stimulus were presented moving horizontally at a constant velocity. To study the effect of using a larger stimulus size, eye movement recordings were obtained from 10 young adults while presenting a standard dot stimulus of different size (1° and 2°) moving horizontally at a constant velocity. Finally, eye movement recordings were obtained from 12 children while the 2° customized animated stimulus was presented after three different smooth pursuit motion paradigms. Performance parameters, including gains and number of saccades, were calculated for each stimulus condition.

RESULTS

The animated stimulus produced in young adults significantly higher velocity gain (mean: 0.93; 95% CI: 0.90-0.96; P = .014), position gain (0.93; 0.85-1; P = .025), proportion of smooth pursuit (0.94; 0.91-0.96, P = .002), and fewer saccades (5.30; 3.64-6.96, P = .008) than a standard dot (velocity gain: 0.87; 0.82-0.92; position gain: 0.82; 0.72-0.92; proportion smooth pursuit: 0.87; 0.83-0.90; number of saccades: 7.75; 5.30-10.46). In contrast, changing the size of a standard dot stimulus from 1° to 2° did not have an effect on smooth pursuit in young adults (P > .05). Finally, smooth pursuit performance did not significantly differ in children for the different motion paradigms when using the animated stimulus (P > .05).

CONCLUSIONS

Attention-grabbing and more dynamic stimuli, such as the developed animated stimulus, might potentially be useful for eye movement research. Finally, with such stimuli, children perform equally well irrespective of the motion paradigm used.

Bodily Experience in Schizophrenia: Factors Underlying a Disturbed Sense of Body Ownership

Emerging evidence is now challenging the view that patients diagnosed with schizophrenia experience a selective deficit in their sense of agency. Additional disturbances seem to exist in their sense of body ownership. However, the factors underlying this disturbance in body ownership remain elusive. Knowledge of these factors, and increased understanding of how body ownership is related to other abnormalities seen in schizophrenia, could ultimately advance development of new treatments. Research on body ownership in schizophrenia has mainly been investigated with the rubber hand illusion (RHI). Schizophrenia patients show higher susceptibility to the RHI, which may be explained by a stronger reliance on multisensory information over weaker stored body representations. This review shows that a coherent sense of body ownership arises from the integration of both bottom-up sensory processes and higher order, top-down bodily- and perceptual representations. Multisensory integration, temporal binding, anticipation, intention and efferent signals all partly modulate the complex experience of body ownership. Specifically, we propose that patients with schizophrenia have weaker stored body representations, and rely to a greater extent on external stimuli, such as visual information, due to imprecise or highly variable internal predictions. Moreover, the reduced sense of agency in schizophrenia may additionally contribute to the disturbed sense of body ownership, as evidence from healthy participants suggests that agency and body ownership are interrelated. Vice versa, a reduced sense of body ownership may also contribute to a reduced sense of agency. Future studies should explicitly target the precise relationship between the two in schizophrenia.

The Interpretation of Emotion from Facial Expression for Children with Visual Processing Problems

A significant proportion of people with learning difficulties have social problems, which are often considered to be the product of school failure. However, a number of studies have suggested that these social skill problems may relate to the inability to decode subtle visual cues of body language and facial expression. The majority of studies of facial expression, however, have viewed learning disability as a unitary condition, without taking account of specific sub‐types which may have more difficulty in processing visual cues, especially for facial emotion. This study investigated children aged 8 to 12 years who were divided into three learning disability sub‐groups: 1) a visual‐perceptual sub‐type called Irlen Syndrome (n=41); 2) a group with learning disabilities, but no indications of Irlen Syndrome (n=30); and 3) a normally achieving control group (n=31). The Irlen Syndrome sub‐group had significantly lower scores for interpreting emotion from facial expression than the two other groups. The learning disabled non‐lrlen sub‐group also had significantly lower scores than the control group, but with much smaller levels of significance than those between the Irlen and control groups.

Raising attention to attention deficit hyperactivity disorder in schizophrenia

Schizophrenia and attention deficit hyperactivity disorder (ADHD) are two psychiatric disorders with a negative impact on quality of life of individuals affected. Although they are classified into distinct disorders categories, attentional dysfunction is considered as a core feature in both conditions, either at the clinical then pathophysiological level. Beyond the obvious clinical overlap between these disorders, the Research Domain Criteria approach might offer an interesting perspective for disentangling common circuits underpinning both disorders. Hence, we review evidences regarding the overlap between schizophrenia and ADHD, at the clinical level, and at the level of underlying brain mechanisms. The evidence regarding the influence of environmental risk factors in the emergence of both disorders, and their developmental trajectories is also reviewed. Among these, we will try to elucidate the complex relationship between stimulants use and psychotic symptoms, discussing the potential role of ADHD medication in inducing psychosis or in exacerbating it. We aim that, taken together, these findings may promote further investigation with important implications both for clinicians and research. In fact, considering the amounting evidence on the overlap between schizophrenia and ADHD, the delineation of their boundaries might help in the decision for diagnosis and treatment. Moreover, it may help to promote interventions focused on the prevention of both schizophrenia and ADHD, by the reduction of recognized environmental risk factors.

Upcoming tactile events and body ownership in schizophrenia

Schizophrenic patients may report unusual perception of their own body. Studies using the rubber hand illusion (RHI) proposed that they exhibit a distorted sense of body ownership. However, since the RHI is mostly achieved with the contribution of visuo-tactile integration, the stronger RHI observed in schizophrenic patients could reflect either a general increase of the response to multisensory stimuli or a larger influence of visual cues on the tactile sensory experience. The purpose of the present study is to investigate patients' perception of their own body by means of a behavioral paradigm that measures their proneness to the RHI without relying on multisensory integration occurring during actual experience of touch. In a previous study we demonstrated in healthy participants that expectation of touch experience arising at the sight of a human hand approaching a rubber hand is enough to induce a sense of ownership over the same hand. Here we take advantage of the same paradigm to investigate body ownership in schizophrenia. Patients observed the experimenter's hand while approaching--without touching--either a rubber hand or a piece of wood placed in front of them. The seen object could be either aligned to participant's hand or rotated by 180°. Phenomenology of the illusion revealed that schizophrenic patients exhibited sense of ownership over the rubber hand, but more weakly than healthy controls. The present study sheds new light on the experience of body ownership in schizophrenic patients, corroborating the notion that alterations of bodily self-awareness play an important role in schizophrenia.

A similar but distinctive pattern of impaired cortical excitability in first-episode schizophrenia and ADHD

BACKGROUND

First-episode schizophrenia (FE-SZ) and attention deficit hyperactivity disorder (ADHD) are both neuropsychiatric disorders associated with an impaired dopaminergic transmission. Though displaying different clinical phenotypes, a common pathophysiological pathway is discussed controversially. Several studies using transcranial magnetic stimulation (TMS) revealed abnormalities in human motor cortex excitability in both schizophrenia and ADHD patients. Studies on cortical excitability comparing these two diseases directly are lacking.

METHOD

In this study, a total of 94 subjects were analyzed. Twenty-five FE-SZ patients were directly compared with 28 ADHD patients and 41 healthy controls (HC). We investigated cortical excitability (inhibitory and facilitatory networks) with single- and paired-pulse TMS to the left and right motor cortex.

RESULTS

Compared to HC, FE-SZ/ADHD patients displayed an impaired cortical inhibition over the left hemisphere. Apart from an enhanced intracortical facilitation, FE-SZ patients did not differ compared to ADHD patients in the main outcome measures. Both patient groups presented a dysfunctional hemispheric pattern of cortical inhibition and facilitation in comparison with HC.

CONCLUSION

The results of this study indicate a pattern of cortical disinhibition and abnormal hemispheric balance of intracortical excitability networks in two different psychiatric diseases. These effects might be associated with an imbalance in GABAergic and dopaminergic transmission and might provide evidence for a common pathophysiological pathway of both diseases.

Horizontal gaze nystagmus: a review of vision science and application issues

The Horizontal Gaze Nystagmus (HGN) test is one component of the Standardized Field Sobriety Test battery. This article reviews the literature on smooth pursuit eye movement and gaze nystagmus with a focus on normative responses, the influence of alcohol on these behaviors, and stimulus conditions similar to those used in the HGN sobriety test. Factors such as age, stimulus and background conditions, medical conditions, prescription medications, and psychiatric disorder were found to affect the smooth pursuit phase of HGN. Much less literature is available for gaze nystagmus, but onset of nystagmus may occur in some sober subjects at 45 degrees or less. We conclude that HGN is limited by large variability in the underlying normative behavior, from methods and testing environments that are often poorly controlled, and from a lack of rigorous validation in laboratory settings.

Eye tracking dysfunction in schizophrenia: characterization and pathophysiology

Eye tracking dysfunction (ETD) is one of the most widely replicated behavioral deficits in schizophrenia and is over-represented in clinically unaffected first-degree relatives of schizophrenia patients. Here, we provide an overview of research relevant to the characterization and pathophysiology of this impairment. Deficits are most robust in the maintenance phase of pursuit, particularly during the tracking of predictable target movement. Impairments are also found in pursuit initiation and correlate with performance on tests of motion processing, implicating early sensory processing of motion signals. Taken together, the evidence suggests that ETD involves higher-order structures, including the frontal eye fields, which adjust the gain of the pursuit response to visual and anticipated target movement, as well as early parts of the pursuit pathway, including motion areas (the middle temporal area and the adjacent medial superior temporal area). Broader application of localizing behavioral paradigms in patient and family studies would be advantageous for refining the eye tracking phenotype for genetic studies.

Comparison of smooth pursuit eye movement deficits in multiple system atrophy and Parkinson's disease

Because of the large overlap and quantitative similarity of eye movement alterations in Parkinson's disease (PD) and multiple system atrophy (MSA), a measurement of eye movement is generally not considered helpful for the differential diagnosis. However, in view of the pathophysiological differences between MSA and PD as well as between the cerebellar (MSA-C) and Parkinsonian (MSA-P) subtypes of MSA, we wondered whether a detailed investigation of oculomotor performance would unravel parameters that could help to differentiate between these entities. We recorded eye movements during sinusoidal pursuit tracking by means of video-oculography in 11 cases of MSA-P, 8 cases of MSA-C and 27 cases of PD and compared them to 23 healthy controls (CTL). The gain of the smooth pursuit eye movement (SPEM) component exhibited significant group differences between each of the three subject groups (MSA, PD, controls) but not between MSA-P and MSA-C. The similarity of pursuit impairment in MSA-P and in MSA-C suggests a commencement of cerebellar pathology in MSA-P despite the lack of clinical signs. Otherwise, SPEM gain was of little use for differential diagnosis between MSA and PD because of wide overlap. However, inspection of the saccadic component of pursuit tracking revealed that in MSA saccades typically correct for position errors accumulated during SPEM epochs ("catch-up saccades"), whereas in PD, saccades were often directed toward future target positions ("anticipatory saccades"). The differences in pursuit tracking between PD and MSA were large enough to warrant their use as ancillary diagnostic criteria for the distinction between these disorders.

Increased extent of object-selective cortex in schizophrenia

Schizophrenia patients exhibit deficits in various stages of visual information processing. Despite recent informative efforts to examine visual processing in schizophrenia with functional magnetic resonance imaging (fMRI), much remains unknown about the basic function, structure, and organization of key early visual processing areas in schizophrenia. This study examined magnitude and topography of regional brain activity in three early visual processing areas: early retinotopically organized areas (V1-V4), motion-sensitive areas (human area MT, hMT+), and object-recognition areas (lateral occipital complex, LO). Using visual stimuli that are known to preferentially activate each respective region, we compared responses in these areas in 22 schizophrenia patients and 19 normal controls. Activity in all three regions was of similar amplitude in schizophrenia patients and normal controls. Activity in retinotopically organized areas and hMT+ showed good spatial overlap between groups. However, activation of LO was more widely distributed in patients compared with normal controls. The findings of abnormal spatial organization of LO in schizophrenia patients may converge with behavioral evidence of deficits in schizophrenia patients for object-recognition tasks that are believed to be mediated by LO activity.

Smooth pursuit in schizophrenia: a meta-analytic review of research since 1993

Abnormal smooth pursuit eye-tracking is one of the most replicated deficits in the psychophysiological literature in schizophrenia [Levy, D. L., Holzman, P. S., Matthysse, S., & Mendell, N. R. (1993). Eye tracking dysfunction and schizophrenia: A critical perspective. Schizophrenia Bulletin, 19, 461-505]. We used meta-analytic procedures to quantify patient-control differences in eye-tracking and to evaluate potential moderators of effect size including patient and target characteristics and characteristics of the control population (matched or not). The magnitude of patient-control differences in pursuit depended on the measure. Global measures had large effect sizes. Among specific measures, maintenance gain and leading saccades yielded large effect sizes, with gain also yielding the narrowest confidence interval. Effect sizes associated with specific measures of smooth pursuit vs. specific measures of intrusive saccades did not clearly implicate one system over the other. Patient demographics and target characteristics generally had little influence on effect sizes. However, studies that failed to sex-match patients and controls tended to have smaller effect sizes for maintenance gain and catch-up saccade rate. Average effect sizes and confidence limits for global measures of pursuit and for maintenance gain place these measures alongside the very strongest neurocognitive measures in the literature [Heinrichs, R. W. (2004). Meta-analysis, and the science of schizophrenia: Variant evidence or evidence of variants? Neuroscience and Biobehavioral Reviews, 28, 379-394] for distinguishing between patients with schizophrenia and controls.

A review on eye movement studies in childhood and adolescent psychiatry

The neural substrates of eye movement measures are largely known. Therefore, measurement of eye movements in psychiatric disorders may provide insight into the underlying neuropathology of these disorders. Visually guided saccades, antisaccades, memory guided saccades, and smooth pursuit eye movements will be reviewed in various childhood psychiatric disorders. The four aims of this review are (1) to give a thorough overview of eye movement studies in a wide array of psychiatric disorders occurring during childhood and adolescence (attention-deficit/hyperactivity disorder, oppositional deviant disorder and conduct disorder, autism spectrum disorders, reading disorder, childhood-onset schizophrenia, Tourette's syndrome, obsessive compulsive disorder, and anxiety and depression), (2) to discuss the specificity and overlap of eye movement findings across disorders and paradigms, (3) to discuss the developmental aspects of eye movement abnormalities in childhood and adolescence psychiatric disorders, and (4) to present suggestions for future research. In order to make this review of interest to a broad audience, attention will be given to the clinical manifestation of the disorders and the theoretical background of the eye movement paradigms.

The Standardized Field Sobriety Tests: a review of scientific and legal issues

This article details the history and development of the National Highway and Safety Administration's Standardized Field Sobriety Tests. They are reviewed in terms of relevant scientific, psychometric, and legal issues. It is concluded that the research that supports their use is limited, important confounding variables have not been thoroughly studied, reliability is mediocre, and that their developers and prosecution-oriented publications have oversold the tests. Further, case law since their development has severed the tests from their validation data, so that they are not admissible on the criterion for which they were validated (blood alcohol concentration), and admissible for a criterion for which they were not (mental, physical, or driving impairment). Directions for further research are presented.

Neurocognitive allied phenotypes for schizophrenia and bipolar disorder

Psychiatric disorders are genetically complex and represent the end product of multiple biological and social factors. Links between genes and disorder-related abnormalities can be effectively captured via assessment of phenotypes that are both associated with genetic effects and potentially contributory to behavioral abnormalities. Identifying intermediate or allied phenotypes as a strategy for clarifying genetic contributions to disorders has been successful in other areas of medicine and is a promising strategy for identifying susceptibility genes in complex psychiatric disorders. There is growing evidence that schizophrenia and bipolar disorder, rather than being wholly distinct disorders, share genetic risk at several loci. Further, there is growing evidence of similarity in the pattern of cognitive and neurobiological deficits in these groups, which may be the result of the effects of these common genetic factors. This review was undertaken to identify patterns of performance on neurocognitive and affective tasks across probands with schizophrenia and bipolar disorder as well as unaffected family members, which warrant further investigation as potential intermediate trait markers. Available evidence indicates that measures of attention regulation, working memory, episodic memory, and emotion processing offer potential for identifying shared and illness-specific allied neurocognitive phenotypes for schizophrenia and bipolar disorder. However, very few studies have evaluated neurocognitive dimensions in bipolar probands or their unaffected relatives, and much work in this area is needed.

Neurophysiological endophenotypes across bipolar and schizophrenia psychosis

The search for liability genes of the world's 2 major psychotic disorders, schizophrenia and bipolar disorder I (BP-I), has been extremely difficult even though evidence suggests that both are highly heritable. This difficulty is due to the complex and multifactorial nature of these disorders. They encompass several intermediate phenotypes, some overlapping across the 2 psychotic disorders that jointly and/or interactively produce the clinical manifestations. Research of the past few decades has identified several neurophysiological deficits in schizophrenia that frequently occur before the onset of psychosis. These include abnormalities in smooth pursuit eye movements, P50 sensory gating, prepulse inhibition, P300, mismatch negativity, and neural synchrony. Evidence suggests that many of these physiological deficits are distinct from each other. They are stable, mostly independent of symptom state and medications (with some exceptions) and are also observed in non-ill relatives. This suggests a familial and perhaps genetic nature. Some deficits are also observed in the BP-I probands and to a lesser extent their relatives. These deficits in physiological measures may represent the intermediate phenotypes that index small effects of genes (and/or environmental factors). The use of these measures in genetic studies may help the hunt for psychosis liability genes and clarify the extent to which the 2 major psychotic disorders share etio-pathophysiology. In spite of the rich body of work describing these neurophysiological measures in psychotic disorders, challenges remain: Many of the neurophysiological phenotypes are still relatively complex and are associated with low heritability estimates. Further refinement of these physiological phenotypes is needed that could identify specific underlying physiological deficits and thereby improve their heritability estimates. The extent to which these neurophysiological deficits are unique or overlap across BP-I and schizophrenia is unclear. And finally, the clinical and functional consequences of the neurophysiological deficits both in the probands and their relatives are not well described.

Which perspectives can endophenotypes and biological markers offer in the early recognition of schizophrenia?

The early recognition of schizophrenia seems crucial; various studies relate a longer duration-of-untreated-psychosis to a worse prognosis. We give an overview over common psychopathological early recognition instruments (BSABS, CAARMS, SIPS, IRAOS, ERIraos). However, many clinical symptoms of prodromal schizophrenia stages are not sufficiently specific. Thus we review recent contributions of neuroimaging and electrophysiological as well as genetic studies: which new diagnostic perspectives offer endophenotypes (such as P300, P50 sensory gating, MMN, smooth pursuit eye movements; indicating a specific genetic vulnerability) together with a better understanding of schizophrenic pathophysiology (state-dependent biological markers, e.g. aggravated motor neurological soft signs during psychosis) in prodromal schizophrenia when still ambiguous clinical symptoms are present. Several examples (e.g. from COMT polymorphisms to working memory deficits) illustrate more specific underlying neuronal mechanisms behind behavioural symptoms. This way, a characteristic pattern of disturbed cerebral maturation might be distinguished in order to complement clinical instruments of early schizophrenia detection.

ADHD and schizophrenia phenomenology: visual scanpaths to emotional faces as a potential psychophysiological marker?

Commonalities in the clinical phenomenology and psychopharmacology of ADHD and schizophrenia are reviewed. The potential of psychostimulants to produce psychotic symptoms emphasizes the need for objective psychophysiological distinctions between these disorders. Impaired emotion perception in both disorders is discussed. It is proposed that visual scanpaths to facial expressions of emotion might prove a potentially useful psychophysiological distinction between ADHD and schizophrenia. There is consistent evidence that both facial affect recognition and scanpaths to facial expressions are impaired in schizophrenia, with emerging empirical evidence showing that facial affect recognition is impaired in ADHD also. Brain imaging studies show reduced activity in the medial prefrontal and limbic (amygdala) brain regions required to process emotional faces in schizophrenia, but suggest more localized loss of activity in these regions in ADHD. As amygdala activity in particular has been linked to effective visual scanning of face stimuli, it is postulated that condition-specific breakdowns in these brain regions that subserve emotional behavior might manifest as distinct scanpath aberrations to facial expressions of emotion in schizophrenia and ADHD.

Role of anticipation in schizophrenia-related pursuit initiation deficits

Schizophrenia patients exhibit several smooth pursuit abnormalities including poor pursuit initiation. Velocity discrimination is also impaired and is correlated with pursuit initiation performance-suggesting that pursuit deficits are related to impairments in processing velocity information. Studies suggest that pursuit initiation is influenced by prior target motion information and/or expectations and that this is likely caused by expectation-based changes in the perceptual inputs to the pursuit system. We examined whether poor pursuit initiation in schizophrenia results from inaccurate encoding of immediate velocity signals, or whether these deficits reflect a failure to use prior target motion information to "optimize" the response. Twenty-eight patients and 24 controls performed an adapted version of a "remembered pursuit task." Trials consisted of a series of target motions, the first of which occurred unexpectedly, followed by four to seven identical targets each preceded by an auditory cue and a "catch target" in which a cue was given followed by target extinction. Initiation eye velocity in response to unexpected, first targets was similar in the patient and control groups. In contrast, patients showed lower eye velocity in response to repeated, cued targets compared with controls. Patients also showed reduced eye velocity in response to catch targets. Reduction in pursuit latency across repeated targets was less robust in patients. Results suggest that processing of immediate velocity information is unaffected in schizophrenia and that pursuit initiation deficits reflect an inability to accurately generate, store, and/or access "remembered" velocity signals.

Disruption of smooth pursuit eye movements in cirrhosis: relationship to hepatic encephalopathy and its treatment

Smooth pursuit eye movements (SPEM) are the conjugate movements used to track the smooth trajectory of small dots. Jerky or 'saccadic' ocular pursuit has been reported in patients with cirrhosis, but no formal assessment of SPEM has ever been undertaken. The aim of this study was to evaluate SPEM in patients with cirrhosis and varying degrees of hepatic encephalopathy. The patient population comprised 56 individuals (31 men, 25 women) of mean age 51.1 (range, 25-70) years, with biopsy-proven cirrhosis, classified, using clinical, electroencephalographic, and psychometric variables, as either neuropsychiatrically unimpaired or as having minimal or overt hepatic encephalopathy; patients were further categorized in relation to their treatment status. The reference population comprised 28 healthy volunteers (12 men, 16 women) of mean age 47.3 (range, 26-65) years. SPEM was assessed using an electro-oculographic technique. Visual inspection of the SPEM recordings showed clear disruption of smooth pursuit in the patients with minimal hepatic encephalopathy, and more pronounced disruption, if not complete loss, of smooth pursuit in patients with overt hepatic encephalopathy. The differences observed in quantifiable SPEM indices between the healthy volunteers/unimpaired patients and those with overt hepatic encephalopathy were significant (P < .05). In conclusion, SPEM performance is impaired in patients with hepatic encephalopathy in parallel with the degree of neuropsychiatric disturbance: the pathophysiology of these changes is unknown, but retinal, extrapyramidal, and attentional abnormalities are likely to play a role. Treatment status confounds the classification of neuropsychiatric status and should be taken into account when categorizing these patients.

Towards an understanding of unique and shared pathways in the psychopathophysiology of ADHD

Most attention deficit hyperactivity disorder (ADHD) research has compared cases with unaffected controls. This has led to many associations, but uncertainties about their specificity to ADHD in contrast with other disorders. We present a selective review of research, comparing ADHD with other disorders in neuropsychological, neurobiological and genetic correlates. So far, a specific pathophysiological pathway has not been identified. ADHD is probably not specifically associated with executive function deficits. It is possible, but not yet established, that ADHD symptoms may be more specifically associated with motivational abnormalities, motor organization and time perception. Recent findings indicating common genetic liabilities of ADHD and other conditions raise questions about diagnostic boundaries. In future research, the delineation of the pathophysiological mechanisms of ADHD needs to match cognitive, imaging and genetic techniques to the challenge of defining more homogenous clinical groups; multi-site collaborative projects are needed.

Reliability of a portable head-mounted eye tracking instrument for schizophrenia research

Smooth pursuit eye movement (SPEM) abnormalities are some of the most consistently observed neurophysiological deficits associated with genetic risk for schizophrenia. SPEM has been traditionally assessed by infrared or video oculography using laboratory-based fixed-display systems. With growing interest in using SPEM measures to define phenotypes in large-scale genetic studies, there is a need for measurement instruments that can be used in the field. Here we test the reliability of a portable, head-mounted display (HMD) eye movement recording system and compare it with a fixed-display system. We observed comparable, modest calibration changes across trials between the two systems. The between-methods reliability for the most often used measure of pursuit performance, maintenance pursuit gain, was high (ICC = 0.96). This result suggests that the portable device is comparable with a lab-based system, which makes possible the collection of eye movement data in community-based and multicenter familial studies of schizophrenia.

Effects of nicotine on leading saccades during smooth pursuit eye movements in smokers and nonsmokers with schizophrenia

Several studies have shown that schizophrenic patients and their biological relatives generate a greater number of leading saccades during smooth pursuit eye movement (SPEM) tasks. This abnormality may reflect a failure of cortical and/or cerebellar areas to coordinate saccadic and pursuit eye movements during visual tracking. The pharmacology of this phenomenon is not known. Here, we sought to replicate and extend the findings of Olincy et al (1998), who found that nicotine transiently reduced the number of leading saccades during SPEMs. A total of 27 subjects with schizophrenia (17 males; 14 smokers), and 25 healthy comparison subjects (nine males; 14 smokers) completed an eye-tracking task after receiving a 1.0 mg nasal spray of nicotine and during drug-free conditions. Results confirm that nicotine reduces the number of leading saccadic eye movements during visual tracking in schizophrenic patients. Baseline impairments and the beneficial effects of nicotine were not restricted to patient smokers, as nonsmoker patients exhibited the greatest number of leading saccades in the no drug condition and exhibited the most pronounced improvements after nicotine administration. Improvement in patient nonsmokers was not a function of previous smoking history. No effect of nicotine was observed in control nonsmokers. In contrast to the previous study, nicotine appeared to improve performance in control smokers. Overall, the study results support a functional role of nACh receptors in improving eye-tracking performance, and are consistent with the hypothesis, articulated by several investigators, that nACh receptor system abnormalities are responsible for a number of schizophrenia-related neurophysiological deficits.

Early expression of a pathophysiological feature of schizophrenia: saccadic intrusions into smooth-pursuit eye movements in school-age children vulnerable to schizophrenia

OBJECTIVE

Neurodevelopmental hypotheses of schizophrenia propose that the responsible pathology occurs much earlier than the usual onset of illness in late adolescence. Nonspecific neurocognitive and behavioral deficits found in children vulnerable to schizophrenia support this hypothesis. This report describes early deficits in a putative genetic endophenotype, saccadic intrusions into smooth-pursuit eye movements (SPEM).

METHOD

SPEM were recorded in 189 children aged 6-15 years: 49 children with schizophrenia, 60 nonpsychotic first-degree relatives, and 80 typically developing children.

RESULTS

Children with schizophrenia demonstrated poorer gain and a significantly increased frequency of leading saccades and large anticipatory saccades; however, only leading saccades differentiated first-degree relatives from typical children. Admixture analysis indicates that 94% of children with schizophrenia, 50% of first-degree relatives, and 19% of typically developing children have abnormally increased frequencies of leading saccades.

CONCLUSIONS

Typically developing young school-age children have a leading saccade phenotype similar to that of adults, suggesting this brain function is fully developed by early school-age years. The abnormal leading saccade phenotype, a schizophrenia-associated familial brain dysfunction, is present by 6 years of age, more than a decade before the highest risk for onset of psychosis. Treatment and prevention strategies will need to consider the early neurodevelopmental nature of schizophrenia.

Differential effects of cigarette smoking on performance of a smooth pursuit and a saccadic eye movement task in schizophrenia

Schizophrenic patients demonstrate a number of physiological defects including smooth pursuit eye movement dysfunction (SPEM), involuntary reflexive saccades to a prepotent stimulus during saccadic tasks, and increased response to the second of two identical auditory stimuli, the P50 evoked potential response. The P50 deficit appears to be mediated by the alpha7 nicotinic cholinergic receptor. This study compared the failure of saccadic inhibition demonstrated in two different eye movement tasks, to see if either deficit, like the P50 inhibitory deficit, was normalized by nicotine. Fifteen smoking schizophrenic patients and 15 smoking non-schizophrenic subjects were compared on the percentage of premature saccades in a memory-guided saccadic task, and the frequency of intrusive small and large anticipatory saccades during a SPEM task. No significant effects or interactions of smoking, group or time on premature or large anticipatory saccades were detected. However, leading saccades demonstrated a significant group x time x smoking interaction. Leading saccades may therefore be a measure of cholinergic inactivity and thus part of the alpha7 nicotinic receptor dysfunction observed in schizophrenia. However, premature saccades and large anticipatory saccades, although measures of inhibitory dysfunction in schizophrenia, appear to be unrelated to the nicotinic system.

Altered performance on an ocular fixation task in attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder without validated objective markers. Eye movement studies may be useful in providing objective criteria for characterizing the disorder.

METHODS

We compared 53 children (29 girls) with ADHD to 44 healthy control children (18 girls) on a 21-sec fixation task. Large saccades (> 4 degrees ) away from the fixation point were analyzed.

RESULTS

Children with ADHD made more large saccades that interrupted fixation than did control children (p =.001). Mean scores of the ADHD group did not change significantly with subsequent retesting on placebo (p =.11); however, there was poor intrasubject correlation (r =.16).

CONCLUSIONS

Both boys and girls with ADHD made significantly more intrusive saccades during fixation than did control subjects, possibly reflecting intrinsic neurologic dysfunction; however, a probable "floor effect" obviates conclusions about the reliability of this measure.