Elsevier

Biological Psychiatry

Volume 48, Issue 3, 1 August 2000, Pages 197-203
Biological Psychiatry

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

https://doi.org/10.1016/S0006-3223(00)00825-8Get rights and content

Abstract

Background: Smooth pursuit eye movement (SPEM) abnormalities are found in schizophrenia. These deficits often are explained in the context of the attentional and inhibitory deficits central to schizophrenia psychopathology. It remains unclear, however, whether these attention-associated eye movement abnormalities are specific to schizophrenia or are a nonspecific expression of attentional deficits found in many psychiatric disorders. Adult attention-deficit/hyperactivity disorder (ADHD) is an alternative disorder with chronic attentional and inhibitory dysfunction. Thus, a comparison of SPEM in adult schizophrenia and adult ADHD will help assess the specificity question.

Methods: SPEM is recorded during a 16.7° per second constant velocity task in 17 adults with ADHD, 49 adults with schizophrenia, and 37 normal adults; all groups included individuals between ages 25–50 years.

Results: Smooth pursuit gain and the frequency of anticipatory and leading saccades are worse in schizophrenic subjects, with normal and ADHD subjects showing no differences on these variables.

Conclusions: Many attention-associated SPEM abnormalities are not present in most subjects with ADHD, supporting the specificity of these findings to the attentional deficits seen in schizophrenia.

Introduction

More than 90 years ago, Diefendorf and Dodge (Diefendorf and Dodge 1908) first reported that individuals with schizophrenia had difficulty tracking a predictably moving object. Abnormal eye tracking, one of the most frequently studied and consistently reproduced psychophysiologic abnormalities associated with schizophrenia (Levy et al 1993), may help refine the neurophysiologic description of schizophrenia (Ross et al 1998b) and facilitate genetic studies of schizophrenia (Clementz 1998). Ocular tracking of a moving target, commonly referred to as smooth pursuit eye movements (SPEM), requires the coordinated activation of both smooth pursuit and saccadic systems (Gaymard and Pierrot-Deseilligny 1999). The roles of each of these eye-movement abnormalities in producing the eye-tracking abnormalities in schizophrenia have yet to be fully determined.

SPEM abnormalities often can be at least partially normalized with attention enhancement techniques (Rosenberg et al 1997), and at least one of the pathologic components of SPEM performance, task-inappropriate intrusion of anticipatory saccades, has been conceptualized as a failure of inhibitory control Friedman et al 1992, Rosenberg et al 1997, Ross et al 1996, Strik et al 1992. Attentional and inhibitory control subjects thus appear to play a major role in the SPEM abnormalities seen in schizophrenia. Despite this focus on the interplay between attentional and inhibitory processes, there has been only minimal exploration of SPEM in another chronic psychiatric disorder of attentional and inhibitory dysfunction—attention-deficit/hyperactivity disorder (ADHD). A primary deficit in ADHD is a failure in response inhibition (Barkley 1997), a deficit that can be identified in saccadic eye-movement tasks (Ross et al 1994) in a manner similar to that found in schizophrenia (Ross et al 1998b). If SPEM abnormalities associated with schizophrenia are due to nonspecific attentional dysfunction, individuals with ADHD should demonstrate similar SPEM abnormalities. Reports have been contradictory as to whether performance during a SPEM task is abnormal in children with ADHD American Psychiatric Association 1994, Bylsma and Pivik 1989, Jacobsen et al 1996, Shapira et al 1980. There is no published literature on SPEM performance in adult ADHD and no published reports that include information on anticipatory saccades in ADHD individuals of any age. This study compares adults with schizophrenia, adults with ADHD, and a comparison group of normal subjects on a smooth pursuit eye movement task.

Section snippets

Subjects

Because normal aging can impact SPEM performance Hutton et al 1993, Kanayama et al 1994, Kuechenmeister et al 1977, Larsby et al 1988, Ross et al 1999a, Sharpe and Sylvester 1978, Spooner et al 1980, all subjects were restricted to individuals between ages 25 and 50 years. Seventeen adult ADHD subjects were recruited from an adult outpatient clinic for ADHD. All subjects were recruited early in the diagnostic process. None had received stimulant medications for at least 10 years before

Results

Table 2shows results for each eye-movement variable. A significant effect of group was found for each eye-movement measure, with post hoc analyses demonstrating differences between the schizophrenic and normal groups on all measures. Significant differences between schizophrenic and ADHD groups were found in gain and the frequencies of anticipatory and leading saccades. Significant differences between the ADHD and normal groups were only identified for the percentage of total eye movements due

Discussion

Schizophrenic adults performed more poorly than did normal adults on each of the SPEM measures examined. This sample contains some individuals who have been discussed in previous reports and thus cannot be considered a replication; however, this is the largest sample of schizophrenic subjects and normal subjects we have published in this age range, suggesting these differences remain even within larger groups. Additionally, the broad range of eye-movement deficits is consistent with what has

Acknowledgements

This research was funded by a NARSAD Junior Investigator Award (RGR), by The Veterans Administration Medical Research Service, and by USPHS Grants Nos. MH56539, MH44212, and MH38321.

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