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Altered Effective Connectivity within an Oculomotor Control Network in Unaffected Relatives of Individuals with Schizophrenia. Brain Sci 2021; 11:brainsci11091228. [PMID: 34573248 PMCID: PMC8467791 DOI: 10.3390/brainsci11091228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 09/10/2021] [Accepted: 09/12/2021] [Indexed: 11/17/2022] Open
Abstract
The ability to rapidly stop or change a planned action is a critical cognitive process that is impaired in schizophrenia. The current study aimed to examine whether this impairment reflects familial vulnerability to schizophrenia across two experiments comparing unaffected first-degree relatives to healthy controls. First, we examined performance on a saccadic stop-signal task that required rapid inhibition of an eye movement. Then, in a different sample, we investigated behavioral and neural responses (using fMRI) during a stop-signal task variant that required rapid modification of a prepared eye movement. Here, we examined differences between relatives and healthy controls in terms of activation and effective connectivity within an oculomotor control network during task performance. Like individuals with schizophrenia, the unaffected relatives showed behavioral evidence for more inefficient inhibitory processes. Unlike previous findings in individuals with schizophrenia, however, the relatives showed evidence for a compensatory waiting strategy. Behavioral differences were accompanied by more activation among the relatives in task-relevant regions across conditions and group differences in effective connectivity across the task that were modulated differently by the instruction to exert control over a planned saccade. Effective connectivity parameters were related to behavioral measures of inhibition efficiency. The results suggest that individuals at familial risk for schizophrenia were engaging an oculomotor control network differently than controls and in a way that compromises inhibition efficiency.
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Cutsuridis V. Behavioural and computational varieties of response inhibition in eye movements. Philos Trans R Soc Lond B Biol Sci 2017; 372:rstb.2016.0196. [PMID: 28242730 DOI: 10.1098/rstb.2016.0196] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/05/2016] [Indexed: 11/12/2022] Open
Abstract
Response inhibition is the ability to override a planned or an already initiated response. It is the hallmark of executive control as its deficits favour impulsive behaviours, which may be detrimental to an individual's life. This article reviews behavioural and computational guises of response inhibition. It focuses only on inhibition of oculomotor responses. It first reviews behavioural paradigms of response inhibition in eye movement research, namely the countermanding and antisaccade paradigms, both proven to be useful tools for the study of response inhibition in cognitive neuroscience and psychopathology. Then, it briefly reviews the neural mechanisms of response inhibition in these two behavioural paradigms. Computational models that embody a hypothesis and/or a theory of mechanisms underlying performance in both behavioural paradigms as well as provide a critical analysis of strengths and weaknesses of these models are discussed. All models assume the race of decision processes. The decision process in each paradigm that wins the race depends on different mechanisms. It has been shown that response latency is a stochastic process and has been proven to be an important measure of the cognitive control processes involved in response stopping in healthy and patient groups. Then, the inhibitory deficits in different brain diseases are reviewed, including schizophrenia and obsessive-compulsive disorder. Finally, new directions are suggested to improve the performance of models of response inhibition by drawing inspiration from successes of models in other domains.This article is part of the themed issue 'Movement suppression: brain mechanisms for stopping and stillness'.
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Caldani S, Amado I, Bendjemaa N, Vialatte F, Mam-Lam-Fook C, Gaillard R, Krebs MO, Pia Bucci M. Oculomotricity and Neurological Soft Signs: Can we refine the endophenotype? A study in subjects belonging to the spectrum of schizophrenia. Psychiatry Res 2017; 256:490-497. [PMID: 28759882 DOI: 10.1016/j.psychres.2017.06.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Revised: 06/02/2017] [Accepted: 06/04/2017] [Indexed: 12/24/2022]
Abstract
Alterations in eye tracking and motor impairments as well as Neurological Soft Signs (NSS) are frequently reported in patients with schizophrenia as well as in their relatives, and are proposed as endophenotype of the disease. This study investigated smooth pursuit eye movement and fixation task with distractors with a gap condition, two markers of inhibitory control mechanism, in 49 patients with schizophrenia, 24 ultra-high risk subjects, 41 full biological clinical siblings of patients and 48 controls. NSS were assessed as a marker of abnormal neurodevelopment. The results revealed more intrusive saccades respectively in smooth pursuit eye movement and in fixation task with distractors with a gap condition in patients, respect to controls and full siblings. Ultra high-risk participants with high NSS committed intrusive saccades compared to controls. Patients with schizophrenia with high NSS also displayed more of these abnormalities, compared to patients with schizophrenia with low NSS and controls. These findings highlight a global inhibitory control defect, and suggested that ultra-high risk subjects and patients with schizophrenia could share oculomotor abnormalities, especially when they express a high neurodevelopmental deviance. These oculomotor alterations might suggest that cerebral structures such as prefrontal and cerebellum could be involved in the expression of this vulnerability.
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Affiliation(s)
- Simona Caldani
- Université Paris Descartes, Sorbonne Paris Cité, INSERM, Centre de Psychiatrie et Neurosciences, UMR S 894, Physiopathologie des Maladies Psychiatriques, CNRS, GDR3557-Institut de Psychiatrie, Paris, France; UMR 1141 Inserm - Université Paris Diderot, Hôpital Robert Debré, 75019 Paris, France
| | - Isabelle Amado
- Université Paris Descartes, Sorbonne Paris Cité, INSERM, Centre de Psychiatrie et Neurosciences, UMR S 894, Physiopathologie des Maladies Psychiatriques, CNRS, GDR3557-Institut de Psychiatrie, Paris, France; Faculté de Médecine Paris Descartes, Centre Hospitalier Sainte-Anne, Service Hospitalo-Universitaire, Paris, France
| | - Narjes Bendjemaa
- Université Paris Descartes, Sorbonne Paris Cité, INSERM, Centre de Psychiatrie et Neurosciences, UMR S 894, Physiopathologie des Maladies Psychiatriques, CNRS, GDR3557-Institut de Psychiatrie, Paris, France
| | - François Vialatte
- UMR 8249 CNRS Laboratoire Plasticité du Cerveau, Paris 75005, France
| | - Célia Mam-Lam-Fook
- Université Paris Descartes, Sorbonne Paris Cité, INSERM, Centre de Psychiatrie et Neurosciences, UMR S 894, Physiopathologie des Maladies Psychiatriques, CNRS, GDR3557-Institut de Psychiatrie, Paris, France; Faculté de Médecine Paris Descartes, Centre Hospitalier Sainte-Anne, Service Hospitalo-Universitaire, Paris, France
| | - Raphael Gaillard
- Université Paris Descartes, Sorbonne Paris Cité, INSERM, Centre de Psychiatrie et Neurosciences, UMR S 894, Physiopathologie des Maladies Psychiatriques, CNRS, GDR3557-Institut de Psychiatrie, Paris, France; Faculté de Médecine Paris Descartes, Centre Hospitalier Sainte-Anne, Service Hospitalo-Universitaire, Paris, France
| | - Marie-Odile Krebs
- Université Paris Descartes, Sorbonne Paris Cité, INSERM, Centre de Psychiatrie et Neurosciences, UMR S 894, Physiopathologie des Maladies Psychiatriques, CNRS, GDR3557-Institut de Psychiatrie, Paris, France; Faculté de Médecine Paris Descartes, Centre Hospitalier Sainte-Anne, Service Hospitalo-Universitaire, Paris, France.
| | - Maria Pia Bucci
- UMR 1141 Inserm - Université Paris Diderot, Hôpital Robert Debré, 75019 Paris, France
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Caldani S, Bucci MP, Lamy JC, Seassau M, Bendjemaa N, Gadel R, Gaillard R, Krebs MO, Amado I. Saccadic eye movements as markers of schizophrenia spectrum: Exploration in at-risk mental states. Schizophr Res 2017; 181:30-37. [PMID: 27639418 DOI: 10.1016/j.schres.2016.09.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Revised: 09/01/2016] [Accepted: 09/01/2016] [Indexed: 01/27/2023]
Abstract
Schizophrenia is a neurodevelopmental disease with cognitive and motor impairments. Motor dysfunctions, such as eye movements or Neurological Soft Signs (NSS), are proposed as endophenotypic markers. Antisaccade (AS) and memory-guided saccades (MGS), two markers of inhibitory control mechanism, are altered in both patients with schizophrenia and their relatives, although these tools may have different sensitivities. Recently, emphasis has been put on identifying markers predictive of psychosis transition in subjects with ultra-high-risk psychosis in order to develop targeted prevention. This study investigates AS and MGS in 46 patients with schizophrenia, 23 ultra-high-risk subjects, and 39 full siblings compared to 47 healthy volunteers. NSS were assessed as a marker of abnormal neurodevelopment. The results revealed more errors in MGS in patients, ultra-high-risk subjects and siblings, than in controls, and more specifically ultra-high-risk subjects with high NSS scores. By contrast, the error rate in AS was significantly higher only in patients with schizophrenia compared to controls. These findings suggest that MGS could be more accurate to detect deficient inhibitory processes as a marker of vulnerability before the onset of schizophrenia. The use of the different paradigms (AS, MGS) revealed distinct profiles depending on the stage of the disease, indicating that some alterations could be pure endophenotypic markers of vulnerability for schizophrenia, while others could be markers of the disease progression.
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Affiliation(s)
- Simona Caldani
- UMR 1141 Inserm-Université Paris Diderot, Hôpital Robert Debré, 75019 Paris, France; INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France
| | - Maria Pia Bucci
- UMR 1141 Inserm-Université Paris Diderot, Hôpital Robert Debré, 75019 Paris, France
| | - Jean-Charles Lamy
- INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France; University Paris Descartes, Faculty of Medicine Paris Descartes, Service Hospitalo-Universitaire, Sainte-Anne Hospital, Paris, France
| | | | - Narjes Bendjemaa
- INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France; University Paris Descartes, Faculty of Medicine Paris Descartes, Service Hospitalo-Universitaire, Sainte-Anne Hospital, Paris, France
| | - Rémi Gadel
- INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France; University Paris Descartes, Faculty of Medicine Paris Descartes, Service Hospitalo-Universitaire, Sainte-Anne Hospital, Paris, France
| | - Raphael Gaillard
- INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France; University Paris Descartes, Faculty of Medicine Paris Descartes, Service Hospitalo-Universitaire, Sainte-Anne Hospital, Paris, France
| | - Marie-Odile Krebs
- INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France; University Paris Descartes, Faculty of Medicine Paris Descartes, Service Hospitalo-Universitaire, Sainte-Anne Hospital, Paris, France.
| | - Isabelle Amado
- INSERM U894, Laboratory of Pathophysiology of Psychiatric Diseases, Center of Psychiatry and Neurosciences, Institut de Psychiatrie, GDR3557, France; University Paris Descartes, Faculty of Medicine Paris Descartes, Service Hospitalo-Universitaire, Sainte-Anne Hospital, Paris, France
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5
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Abstract
The visual tract is prominently involved in schizophrenia, as evidenced by perceptual distortions and a type of nystagmus found in many individuals affected. Genetic explanations for these abnormalities have been suggested. This study proposes an alternate explanation based on infection. Several infectious agents thought to be associated with some cases of schizophrenia are known to cause both infection of the fetus and abnormalities of the eye. Toxoplasma gondii is examined in detail, and rubella, cytomegalovirus, varicella-zoster virus, and herpes simplex virus more briefly. Careful ophthalmic assessments, including funduscopy and direct examination of tissues for infectious agents, will clarify the role of such agents in ocular aspects of schizophrenia.
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Affiliation(s)
- E. Fuller Torrey
- Stanley Medical Research Institute, 10605 Concord Street, Suite 205, Kensington, MD 20895
| | - Robert H. Yolken
- Stanley Laboratory of Neurovirology, Johns Hopkins University, Baltimore, MD
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Myles JB, Rossell SL, Phillipou A, Thomas E, Gurvich C. Insights to the schizophrenia continuum: A systematic review of saccadic eye movements in schizotypy and biological relatives of schizophrenia patients. Neurosci Biobehav Rev 2016; 72:278-300. [PMID: 27916709 DOI: 10.1016/j.neubiorev.2016.10.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Revised: 10/05/2016] [Accepted: 10/27/2016] [Indexed: 10/20/2022]
Abstract
Myles, J.B., S. Rossell, A. Phillipou, Thomas, E and C. Gurvich. A systematic review of saccadic eye movements across the schizophrenia continuum: Characterisation, pathophysiology and genetic associations. NEUROSCI BIOBEHAV REV 21(1) XXX-XXX, 2015. One of the cognitive hallmarks of schizophrenia is impaired eye movements, particularly for the antisaccade task. Less saccade research has been conducted in relation to the broader schizophrenia continuum, that is, people with high schizotypy or first-degree relatives of people with schizophrenia. This systematic review sought to identify, collate and appraise prosaccade, antisaccade and memory-guided saccade studies involving behavioural, neuroimaging and genetic data published between 1980 and September 2016 in individuals with high schizotypy and first-degree relatives. A systematic literature search was conducted, using Ovid MEDLINE, PsycINFO, PubMed and SCOPUS databases. Of 913 references screened, 18 schizotypy, 29 family studies and two schizotypy and relatives articles studies were eligible for inclusion. Antisaccade error rate was the most consistent deficit found for high schizotypy. Relatives had intermediate antisaccade error rates between patients and healthy controls. Results from the limited genetic and neuroimaging studies echoed schizophrenia findings. Confounds were also identified. It was concluded that future research is required to refine the saccade endophenotype and to expand genetic and neuroimaging research.
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Affiliation(s)
- Jessica B Myles
- Monash Alfred Psychiatry research centre, The Alfred Hospital and Monash University Central Clinical School, Melbourne, Australia
| | - Susan L Rossell
- Monash Alfred Psychiatry research centre, The Alfred Hospital and Monash University Central Clinical School, Melbourne, Australia; Brain and Psychological Sciences Research Centre, Swinburne University of Technology, Melbourne, Australia; Department of Psychiatry, St Vincent's Hospital, Melbourne, Australia
| | - Andrea Phillipou
- Department of Psychiatry, St Vincent's Hospital, Melbourne, Australia; Department of Psychiatry, The University of Melbourne, Melbourne, Australia; Department of Mental Health, The Austin Hospital, Melbourne, Australia
| | - Elizabeth Thomas
- Monash Alfred Psychiatry research centre, The Alfred Hospital and Monash University Central Clinical School, Melbourne, Australia
| | - Caroline Gurvich
- Monash Alfred Psychiatry research centre, The Alfred Hospital and Monash University Central Clinical School, Melbourne, Australia.
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Karantinos T, Tsoukas E, Mantas A, Kattoulas E, Stefanis NC, Evdokimidis I, Smyrnis N. Increased intra-subject reaction time variability in the volitional control of movement in schizophrenia. Psychiatry Res 2014; 215:26-32. [PMID: 24238920 DOI: 10.1016/j.psychres.2013.10.031] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 08/09/2013] [Accepted: 10/24/2013] [Indexed: 11/26/2022]
Abstract
Increased Reaction Time (RT) studies intra-subject variability is an emerging and consistent finding in RT studies of schizophrenia. A group of 23 patients suffering from DSM-IV schizophrenia and a group of 23 age-matched control subjects performed two RT tasks requiring basic sensorimotor processing and engaging two different motor systems: the Finger Lift Reaction Time task and the Voluntary Saccade Reaction Time task. The Ex-Gaussian model was applied to the RT distributions measuring the mean (mu), and standard deviation (sigma) of a Gaussian component thought to reflect sensorimotor processing and an exponential component (tau), thought to reflect an intermediate decision process. In both tasks, a significantly larger RT intra-subject variability effectively dissociated patients from controls. RT intra-subject variability in the two tasks was highly correlated only for patients. Both sigma and tau were significantly higher in the patient group with tau being the best predictor of schizophrenia. Furthermore, only in the patient group were sigma and tau highly correlated between the two tasks. The results reflect a deficit in information processing that may not be confined to decision processes related to the frontal cortex; rather, they may indicate dysfunction in distributed neural networks modulating adaptive regulation of performance.
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Affiliation(s)
- Thomas Karantinos
- Psychiatry Department, National and Kapodistrian University of Athens, Eginition Hospital, 72 V. Sofias Ave, Athens 11528, Greece
| | - Evangelos Tsoukas
- Neurology Department, National and Kapodistrian University of Athens, Eginition Hospital, Athens, Greece
| | - Asimakis Mantas
- Neurology Department, National and Kapodistrian University of Athens, Eginition Hospital, Athens, Greece
| | - Emmanouil Kattoulas
- Psychiatry Department, National and Kapodistrian University of Athens, Eginition Hospital, 72 V. Sofias Ave, Athens 11528, Greece
| | - Nicholas C Stefanis
- Psychiatry Department, National and Kapodistrian University of Athens, Eginition Hospital, 72 V. Sofias Ave, Athens 11528, Greece; School of Psychiatry and Clinical Neurosciences, University of Western Australia, Centre for Clinical Research in Neuropsychiatry(CCRN), Perth, Australia
| | - Ioannis Evdokimidis
- Neurology Department, National and Kapodistrian University of Athens, Eginition Hospital, Athens, Greece
| | - Nikolaos Smyrnis
- Psychiatry Department, National and Kapodistrian University of Athens, Eginition Hospital, 72 V. Sofias Ave, Athens 11528, Greece.
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Abstract
Early phenomenological descriptions of schizophrenia have acknowledged the existence of milder schizophrenia spectrum disorders characterized by the presence of attenuated symptoms typically present in chronic schizophrenia. The investigation of the schizophrenia spectrum disorders offers an opportunity to elucidate the pathophysiological mechanisms giving rise to schizophrenia. Differences and similarities between subjects with schizotypal personality disorder (SPD), the prototypical schizophrenia personality disorder, and chronic schizophrenia have been investigated with genetic, neurochemical, imaging, and pharmacological techniques. Patients with SPD and the more severely ill patients with chronic schizophrenia share cognitive, social, and attentional deficits hypothesized to result from common neurodevelopmentally based cortical temporal and prefrontal pathology. However, these deficits are milder in SPD patients due to their capacity to recruit other related brain regions to compensate for dysfunctional areas. Individuals with SPD are also less vulnerable to psychosis due to the presence of protective factors mitigating subcortical DA hyperactivity. Given the documented close relationship to other schizophrenic disorders, SPD will be included in the psychosis section of DSM-5 as a schizophrenia spectrum disorder as well as in the personality disorder section.
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Landgraf S, Osterheider M. "To see or not to see: that is the question." The "Protection-Against-Schizophrenia" (PaSZ) model: evidence from congenital blindness and visuo-cognitive aberrations. Front Psychol 2013; 4:352. [PMID: 23847557 PMCID: PMC3696841 DOI: 10.3389/fpsyg.2013.00352] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 05/30/2013] [Indexed: 12/12/2022] Open
Abstract
The causes of schizophrenia are still unknown. For the last 100 years, though, both “absent” and “perfect” vision have been associated with a lower risk for schizophrenia. Hence, vision itself and aberrations in visual functioning may be fundamental to the development and etiological explanations of the disorder. In this paper, we present the “Protection-Against-Schizophrenia” (PaSZ) model, which grades the risk for developing schizophrenia as a function of an individual's visual capacity. We review two vision perspectives: (1) “Absent” vision or how congenital blindness contributes to PaSZ and (2) “perfect” vision or how aberrations in visual functioning are associated with psychosis. First, we illustrate that, although congenitally blind and sighted individuals acquire similar world representations, blind individuals compensate for behavioral shortcomings through neurofunctional and multisensory reorganization. These reorganizations may indicate etiological explanations for their PaSZ. Second, we demonstrate that visuo-cognitive impairments are fundamental for the development of schizophrenia. Deteriorated visual information acquisition and processing contribute to higher-order cognitive dysfunctions and subsequently to schizophrenic symptoms. Finally, we provide different specific therapeutic recommendations for individuals who suffer from visual impairments (who never developed “normal” vision) and individuals who suffer from visual deterioration (who previously had “normal” visual skills). Rather than categorizing individuals as “normal” and “mentally disordered,” the PaSZ model uses a continuous scale to represent psychiatrically relevant human behavior. This not only provides a scientific basis for more fine-grained diagnostic assessments, earlier detection, and more appropriate therapeutic assignments, but it also outlines a trajectory for unraveling the causes of abnormal psychotic human self- and world-perception.
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Affiliation(s)
- Steffen Landgraf
- Department for Forensic Psychiatry and Psychotherapy, District Hospital, University Regensburg Regensburg, Germany ; Berlin School of Mind and Brain, Humboldt Universität zu Berlin Berlin, Germany
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Beedie SA, Benson PJ, Giegling I, Rujescu D, St Clair DM. Smooth pursuit and visual scanpaths: Independence of two candidate oculomotor risk markers for schizophrenia. World J Biol Psychiatry 2012; 13:200-10. [PMID: 21545243 DOI: 10.3109/15622975.2011.566628] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVES Smooth pursuit and visual scanpath deficits are candidate trait markers for schizophrenia. It is not clear whether eye tracking dysfunction (ETD) and atypical scanpath behaviour are the product of the same underlying neurobiological processes. We have examined co-occurrence of ETD and scanpath disturbance in individuals with schizophrenia and healthy volunteers. METHODS Eye movements of individuals with schizophrenia (N = 96) and non-clinical age-matched comparison participants (N = 100) were recorded using non-invasive infrared oculography during smooth pursuit in both predictable (horizontal sinusoid) and less predictable (Lissajous sinusoid) conditions and a free viewing scanpath task. RESULTS Individuals with schizophrenia demonstrated scanning deficits in both tasks. There was no association between performance measures of smooth pursuit and scene scanpaths in patient or control groups. Odds ratios comparing the likelihood of scanpath dysfunction when ETD was present, and the likelihood of finding scanpath dysfunction when ETD was absent were not significant in patients or controls in either pursuit variant, suggesting that ETD and scanpath dysfunction are independent anomalies in schizophrenia. CONCLUSION ETD and scanpath disturbance appear to reflect independent oculomotor or neurocognitive deficits in schizophrenia. Each task may confer unique information about the pathophysiology of psychosis.
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Affiliation(s)
- Sara A Beedie
- School of Psychology, College of Life Sciences & Medicine, William Guild Building, University of Aberdeen, King's College, Aberdeen, UK.
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11
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Revisiting the suitability of antisaccade performance as an endophenotype in schizophrenia. Brain Cogn 2011; 77:223-30. [DOI: 10.1016/j.bandc.2011.08.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 07/26/2011] [Accepted: 08/04/2011] [Indexed: 02/06/2023]
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12
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Bär KJ, Berger S, Metzner M, Boettger MK, Schulz S, Ramachandraiah CT, Terhaar J, Voss A, Yeragani VK, Sauer H. Autonomic dysfunction in unaffected first-degree relatives of patients suffering from schizophrenia. Schizophr Bull 2010; 36:1050-8. [PMID: 19366982 PMCID: PMC2930351 DOI: 10.1093/schbul/sbp024] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Recent studies revealed cardiac autonomic dysfunction in patients with acute schizophrenia, which appears to be mainly related to reduced vagal and increased sympathetic modulation. To understand the significance of cardiac autonomic function in patients with schizophrenia, we extended these studies to relatives of patients. In this study, we assessed cardiac autonomic modulation in healthy first-degree relatives of patients with schizophrenia (n = 36) to investigate a putative genetic influence. Data were compared with control subjects matched for age, gender, and physical activity as well as to patients suffering from schizophrenia. First-degree relatives showed an attenuated, yet identical pattern in autonomic dysfunction as patients with decreased vagal modulation of heart rate, decreased baroreflex sensitivity, but no difference in blood pressure variability could be detected. The patients' relatives also showed a similar pattern in regards to QT variability. In addition, the subgroup comparison of offspring vs. siblings showed a significant difference in heart rate variability suggesting a higher degree of heritability in offspring. In conclusion, the pattern of autonomic dysfunction seen in patients and relatives might indicate underlying disease-inherent genetic vulnerability, especially because autonomic parameters are heritable. In addition, these findings may be of value to identify the high-risk group of patients' relatives in regards to serious cardiovascular events so that early preventive measures can be taken.
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Affiliation(s)
- Karl-Jürgen Bär
- Department of Psychiatry and Psychotherapy, University Hospital Jena, Philosophenweg 3, 07743 Jena, Germany.
| | - Sandy Berger
- Department of Psychiatry and Psychotherapy, Philosophenweg 3, University Hospital, Jena, Germany
| | - Maria Metzner
- Department of Psychiatry and Psychotherapy, Philosophenweg 3, University Hospital, Jena, Germany
| | - Michael K. Boettger
- Institute of Physiology I, Teichgraben 8, University Hospital, Jena, Germany
| | - Steffen Schulz
- Department of Medical Engineering and Biotechnology, University of Applied Sciences, Jena, Germany
| | | | - Janneke Terhaar
- Department of Psychiatry and Psychotherapy, Philosophenweg 3, University Hospital, Jena, Germany
| | - Andreas Voss
- Department of Medical Engineering and Biotechnology, University of Applied Sciences, Jena, Germany
| | - Vikram K. Yeragani
- Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI,Department of Psychiatry, University of Alberta, Edmonton, Canada
| | - Heinrich Sauer
- Department of Psychiatry and Psychotherapy, Philosophenweg 3, University Hospital, Jena, Germany
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Nkam I, Bocca ML, Denise P, Paoletti X, Dollfus S, Levillain D, Thibaut F. Impaired smooth pursuit in schizophrenia results from prediction impairment only. Biol Psychiatry 2010; 67:992-7. [PMID: 20110087 DOI: 10.1016/j.biopsych.2009.11.029] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2008] [Revised: 10/12/2009] [Accepted: 11/18/2009] [Indexed: 11/27/2022]
Abstract
BACKGROUND Oculomotor abnormality is one of the endophenotypes in schizophrenia. The predictive component of smooth pursuit can be studied by comparing the gain, i.e., the ratio of smooth eye position to target position, during predictable (pure sinusoidal) and unpredictable (pseudorandom) target motions. The aim of this experiment was to study predictive and nonpredictive components of smooth pursuit in two groups of schizophrenia patients compared with control subjects. METHODS Fifty-one schizophrenia patients (40 nondeficit and 11 deficit) and 21 control subjects were studied. During a predictable task, subjects were asked to track a sinusoidal target (.4 Hz). For the unpredictable task, the pseudorandom target motion consisted of five superimposed sinusoidal waveforms (.1, .2, .4, .6, and .8 Hz). The smooth eye position (eye position without saccades), gain, and phase were calculated for each frequency in each participant and for both tasks. RESULTS The mean sinusoidal smooth eye position gain was significantly lower in patients than in control subjects with no significant difference between deficit and nondeficit patients. During the pseudorandom task, all groups had a similar gain at .4 Hz. CONCLUSIONS Our study reveals that patients have a normal nonpredictive component of smooth pursuit, regardless of their level of negative symptoms. In contrast, the predictive mechanisms involved in eye pursuit were impaired in schizophrenia patients. These results indicate that poor pursuit performance during smooth pursuit is primarily a consequence of a predictive problem and is not related to the ability to generate an accurate pursuit maintenance response.
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Affiliation(s)
- Irene Nkam
- Rouen University Hospital-Charles Nicolle and Le Rouvray Hospital, Rouen School of Medicine, Rouen, France.
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14
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Radant AD, Dobie DJ, Calkins ME, Olincy A, Braff DL, Cadenhead KS, Freedman R, Green MF, Greenwood TA, Gur RE, Gur RC, Light GA, Meichle SP, Millard SP, Mintz J, Nuechterlein KH, Schork NJ, Seidman LJ, Siever LJ, Silverman JM, Stone WS, Swerdlow NR, Tsuang MT, Turetsky BI, Tsuang DW. Antisaccade performance in schizophrenia patients, their first-degree biological relatives, and community comparison subjects: data from the COGS study. Psychophysiology 2010; 47:846-56. [PMID: 20374545 DOI: 10.1111/j.1469-8986.2010.01004.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The antisaccade task is a widely used technique to measure failure of inhibition, an important cause of cognitive and clinical abnormalities found in schizophrenia. Although antisaccade performance, which reflects the ability to inhibit prepotent responses, is a putative schizophrenia endophenotype, researchers have not consistently reported the expected differences between first-degree relatives and comparison groups. Schizophrenia participants (n=219) from the large Consortium on the Genetics of Schizophrenia (COGS) sample (n=1078) demonstrated significant deficits on an overlap version of the antisaccade task compared to their first-degree relatives (n=443) and community comparison subjects (CCS; n=416). Although mean antisaccade performance of first-degree relatives was intermediate between schizophrenia participants and CCS, a linear mixed-effects model adjusting for group, site, age, and gender found no significant performance differences between the first-degree relatives and CCS. However, admixture analyses showed that two components best explained the distributions in all three groups, suggesting two distinct doses of an etiological factor. Given the significant heritability of antisaccade performance, the effects of a genetic polymorphism is one possible explanation of our results.
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Affiliation(s)
- Allen D Radant
- Department of Psychiatry and Behavioral Sciences, University of Washington and Department of Veteran Affairs, VISN-20, Mental Illness Research, Education, and Clinical Center, Seattle, Washington 98108, USA.
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15
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Allen AJ, Griss ME, Folley BS, Hawkins KA, Pearlson GD. Endophenotypes in schizophrenia: a selective review. Schizophr Res 2009; 109:24-37. [PMID: 19223268 PMCID: PMC2665704 DOI: 10.1016/j.schres.2009.01.016] [Citation(s) in RCA: 156] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Revised: 01/11/2009] [Accepted: 01/14/2009] [Indexed: 10/21/2022]
Abstract
BACKGROUND Given the wealth of data in the literature on schizophrenia endophenotypes, it is useful to have one source to reference their frequency data. We reviewed the literature on disease-liability associated variants in structural and functional magnetic resonance images (MRI), sensory processing measures, neuromotor abilities, neuropsychological measures, and physical characteristics in schizophrenia patients (SCZ), their first-degree relatives (REL), and healthy controls (HC). The purpose of this review was to provide a summary of the existing data on the most extensively published endophenotypes for schizophrenia. METHODS We searched PubMed and MedLine for all studies on schizophrenia endophenotypes comparing SCZ to HC and/or REL to HC groups. Percent abnormal values, generally defined as >2 SD from the mean (in the direction of abnormality) and/or associated effect sizes (Cohen's d) were calculated for each study. RESULTS Combined, the articles reported an average 39.4% (SD=20.7%; range=2.2-100%) of abnormal values in SCZ, 28.1% (SD=16.6%; range=1.6-67.0%) abnormal values in REL, and 10.2% (SD=6.7%; range=0.0-34.6%) in HC groups. CONCLUSIONS These findings are reviewed in the context of emerging hypotheses on schizophrenia endophenotypes, as well as a discussion of clustering trends among the various intermediate phenotypes. In addition, programs for future research are discussed, as instantiated in a few recent large-scale studies on multiple endophenotypes across patients, relatives, and healthy controls.
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Affiliation(s)
- Allyssa J. Allen
- Olin Neuropsychiatry Research Center, Institute of Living at Hartford Hospital, 200 Retreat Avenue, Hartford, CT 06106,Corresponding Author: Allyssa J. Allen, Olin Neuropsychiatry Research Center, Whitehall Building, 200 Retreat Avenue, Hartford, CT 06106, Tel: 860-459-7806, Fax: 860-545-7797,
| | - Mélina E. Griss
- Olin Neuropsychiatry Research Center, Institute of Living at Hartford Hospital, 200 Retreat Avenue, Hartford, CT 06106
| | - Bradley S. Folley
- Olin Neuropsychiatry Research Center, Institute of Living at Hartford Hospital, 200 Retreat Avenue, Hartford, CT 06106
| | - Keith A. Hawkins
- Dept. of Psychiatry, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06511
| | - Godfrey D. Pearlson
- Olin Neuropsychiatry Research Center, Institute of Living at Hartford Hospital, 200 Retreat Avenue, Hartford, CT 06106,Dept. of Psychiatry, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06511
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16
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Abstract
The objective of this paper is to highlight the potential role of eye tracking technology (ETT) in the assessment of delirious patients. Delirium occurs in one in five general hospital admissions (Siddiqi, 2006) and its frequency will increase as society gets older. Despite its frequency and significant independent impact upon morbidity and mortality, delirium remains under studied and is frequently missed, detected late, or misdiagnosed (Farrell & Ganzani, 1995; Inouye, 2001; Kakuma, 2003). Detection is a key target for both clinical and research efforts. Assessment of attention is key to diagnosing delirium, yet nurses and non-research medical staff often fail to correctly identify inattention (Inouye et al., 2001; Lemiengre et al., 2006; Ryan et al., 2008). Eye tracking measures have been used in a plethora of key areas of psychiatric research (Crawford et al., 2005; Corden, Chilvers, & Skuse, 2008; Hardin, Schroth, Pine, & Ernst, 2007; Holzman, Leonard, Proctor, & Hughes, 1973), and provide an accurate and non-invasive method in the assessment of cognitive function. The potential of ETT for direct clinical applications in the assessment of attention and comprehension, key cognitive symptoms of delirium, are promising. This paper considers potential new approaches which recent advancements in non-invasive ETT may bring to the examination and understanding of delirium.
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Affiliation(s)
- C Exton
- Department of Computer Science, University of Limerick, Limerick, Ireland.
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17
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Smyrnis N. Metric issues in the study of eye movements in psychiatry. Brain Cogn 2008; 68:341-58. [DOI: 10.1016/j.bandc.2008.08.022] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2008] [Indexed: 11/25/2022]
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18
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Gooding DC, Basso MA. The tell-tale tasks: a review of saccadic research in psychiatric patient populations. Brain Cogn 2008; 68:371-90. [PMID: 18950927 DOI: 10.1016/j.bandc.2008.08.024] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2008] [Indexed: 10/21/2022]
Abstract
This review focuses on saccade research with adult psychiatric patients. It begins with an introduction of the various types of saccades and the tasks used to evoke them. The functional significance of the different types of eye movements is briefly discussed. Research findings regarding the saccadic performance of different adult psychiatric patient populations are discussed in detail, with particular emphasis on findings regarding error rates, response latencies, and any specific task parameters that might affect those variables. Findings regarding the symptom, neurocognitive, and neural correlates of saccadic performance and the functional significance of patients' saccadic deficits are also discussed. We also discuss the saccadic deficits displayed by various patient groups in terms of circuitry (e.g. cortical/basal ganglia circuits) that may be implicated in the underlying pathophysiology of several of these disorders. Future directions for research in this growing area are offered.
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Affiliation(s)
- Diane C Gooding
- Department of Psychology, University of Wisconsin-Madison, College of Letters and Sciences, 1202 West Johnson Street, Madison, WI 53706, USA.
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19
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Calkins ME, Iacono WG, Ones DS. Eye movement dysfunction in first-degree relatives of patients with schizophrenia: a meta-analytic evaluation of candidate endophenotypes. Brain Cogn 2008; 68:436-61. [PMID: 18930572 DOI: 10.1016/j.bandc.2008.09.001] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/08/2008] [Indexed: 10/21/2022]
Abstract
Several forms of eye movement dysfunction (EMD) are regarded as promising candidate endophenotypes of schizophrenia. Discrepancies in individual study results have led to inconsistent conclusions regarding particular aspects of EMD in relatives of schizophrenia patients. To quantitatively evaluate and compare the candidacy of smooth pursuit, saccade and fixation deficits in first-degree biological relatives, we conducted a set of meta-analytic investigations. Among 18 measures of EMD, memory-guided saccade accuracy and error rate, global smooth pursuit dysfunction, intrusive saccades during fixation, antisaccade error rate and smooth pursuit closed-loop gain emerged as best differentiating relatives from controls (standardized mean differences ranged from .46 to .66), with no significant differences among these measures. Anticipatory saccades, but no other smooth pursuit component measures were also increased in relatives. Visually-guided reflexive saccades were largely normal. Moderator analyses examining design characteristics revealed few variables affecting the magnitude of the meta-analytically observed effects. Moderate effect sizes of relatives v. controls in selective aspects of EMD supports their endophenotype potential. Future work should focus on facilitating endophenotype utility through attention to heterogeneity of EMD performance, relationships among forms of EMD, and application in molecular genetics studies.
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Affiliation(s)
- Monica E Calkins
- Department of Psychiatry, University of Pennsylvania School of Medicine, Neuropsychiatry Section, Schizophrenia Research Center and Brain Behavior Laboratory, Philadelphia, PA 19104, USA.
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20
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Does performance on the standard antisaccade task meet the co-familiality criterion for an endophenotype? Brain Cogn 2008; 68:462-75. [PMID: 18842329 DOI: 10.1016/j.bandc.2008.08.027] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2008] [Indexed: 12/22/2022]
Abstract
The "co-familiality" criterion for an endophenotype has two requirements: (1) clinically unaffected relatives as a group should show both a shift in mean performance and an increase in variance compared with controls; (2) performance scores should be heritable. Performance on the antisaccade task is one of several candidate endophenotypes for schizophrenia. In this paper we examine whether the various measures of performance on the standard version of the antisaccade task meet the co-familiality criterion for an endophenotype. The three measures of performance-reflexive saccade errors, latency of correct antisaccades, and gain-show a wide range of effect sizes and variance ratios as well as evidence of significant or near significant heterogeneity. The estimated mean effect sizes [Cohen's d: error rate: 0.34 (SD: 0.29); latency: 0.33 (SD: 0.30); gain: 0.54 (SD: 0.38)] are significantly greater than 0, but the magnitude of the departures from 0 is relatively small, corresponding to modest effect sizes. The width of the 95% confidence intervals for the estimated effect sizes (error rate: 0.2-0.49; latency: 0.17-0.50; gain: 0.23-0.85) and the coefficients of variation in effect sizes (error rate: 85.3%; latency: 90.9%; gain: 68.4%) reflect heterogeneity in effect sizes. The effect sizes for error rate showed statistically significant heterogeneity and those for latency (P=.07) and gain (P=.09) showed a trend toward heterogeneity. These results indicate that the effect sizes are not consistent with a single mean and that the average effect size may be a biased estimate of the magnitude of differences in performance between relatives of schizophrenics and controls. Relatives of schizophrenics show a small but significant increase in variance in error rate, but the confidence interval is broad, perhaps reflecting the heterogeneity in effect size. The variance ratios for latency and gain did not differ in relatives of schizophrenics and controls. Performance, as measured by error rate, is moderately heritable. The data do not provide compelling support for a consistent shift in mean or variance in relatives of schizophrenia patients compared with nonpsychiatric controls, both of which are required for a major gene involved in co-familial transmission. This set of findings suggests that although intra-familial resemblance in antisaccade performance is due in part to genetic factors, it may not be related to a schizophrenia genotype. Based on the current literature, it would be premature to conclude that any of the measures of antisaccade performance unambiguously meets the co-familiality criterion for an endophenotype.
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Rommelse NNJ, Van der Stigchel S, Sergeant JA. A review on eye movement studies in childhood and adolescent psychiatry. Brain Cogn 2008; 68:391-414. [PMID: 18835079 DOI: 10.1016/j.bandc.2008.08.025] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2008] [Indexed: 10/21/2022]
Abstract
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.
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Affiliation(s)
- Nanda N J Rommelse
- Department of Psychiatry, Radboud University Medical Center, Reinier Postlaan 12, 6525 GC Nijmegen, The Netherlands.
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Landgraf S, Amado I, Bourdel MC, Leonardi S, Krebs MO. Memory-guided saccade abnormalities in schizophrenic patients and their healthy, full biological siblings. Psychol Med 2008; 38:861-870. [PMID: 17976251 DOI: 10.1017/s0033291707001912] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND Ocular-motor inhibition errors and saccadic hypometria occur at elevated rates in biological relatives of schizophrenic patients. The memory-guided saccade (MS) paradigm requires a subject to inhibit reflexive saccades (RSs) and to programme a delayed saccade towards a remembered target. METHOD MS, RS, and central fixation (CF) tasks were administered to 16 patients who met the criteria for DSM-IV schizophrenia, 19 of their psychiatrically healthy siblings, and 18 controls. RESULTS Patients and siblings showed elevated MS error rates reflecting a failure to inhibit RSs to a visible target, as required by the task. In contrast to controls, prior errors did not improve MS accuracy in patients and siblings. CONCLUSIONS The specific characteristics of the elevated MS error rate help to clarify the nature of the disinhibition impairment found in schizophrenics and their healthy siblings. Failure to inhibit premature saccades and to improve the accuracy of subsequent volitional saccades implicates a deficit in spatial working-memory integration, mental representation and/or motor learning processes in schizophrenia.
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Affiliation(s)
- S Landgraf
- INSERM U796, Physiopathology of Psychiatric Diseases, University Paris René Descartes, Faculty of Medicine, Sainte Anne Hospital, Paris, France.
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23
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Picard H, Amado I, Mouchet-Mages S, Olié JP, Krebs MO. The role of the cerebellum in schizophrenia: an update of clinical, cognitive, and functional evidences. Schizophr Bull 2008; 34:155-72. [PMID: 17562694 PMCID: PMC2632376 DOI: 10.1093/schbul/sbm049] [Citation(s) in RCA: 202] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The role of the cerebellum in schizophrenia has been highlighted by Andreasen's hypothesis of "cognitive dysmetria," which suggests a general dyscoordination of sensorimotor and mental processes. Studies in schizophrenic patients have brought observations supporting a cerebellar impairment: high prevalence of neurological soft signs, dyscoordination, abnormal posture and propioception, impaired eyeblink conditioning, impaired adaptation of the vestibular-ocular reflex or procedural learning tests, and lastly functional neuroimaging studies correlating poor cognitive performances with abnormal cerebellar activations. Despite those compelling evidences, there has been, to our knowledge, no recent review on the clinical, cognitive, and functional literature supporting the role of the cerebellum in schizophrenia. We conducted a Medline research focusing on cerebellar dysfunctions in schizophrenia. Emphasis was given to recent literature (after 1998). The picture arising from this review is heterogeneous. While in some domains, the role of the cerebellum seems clearly defined (ie, neurological soft signs, posture, or equilibrium), in other domains, the cerebellar contribution to schizophrenia seems limited or indirect (ie, cognition) if present at all (ie, affectivity). Functional models of the cerebellum are proposed as a background for interpreting these results.
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Affiliation(s)
- Hernàn Picard
- INSERM U796, Pathophysiology of psychiatric diseases, University Paris Descartes, Sainte-Anne Hospital, Paris, France.
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24
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The relation between antisaccade errors, fixation stability and prosaccade errors in schizophrenia. Exp Brain Res 2007; 186:273-82. [DOI: 10.1007/s00221-007-1235-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2006] [Accepted: 11/21/2007] [Indexed: 10/22/2022]
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