Eye movement task related to frontal lobe functioning in children with attention deficit disorder

Larger deficits in brain networks for response inhibition than for visual selective attention in attention deficit hyperactivity disorder (ADHD)

BACKGROUND

Brain activation differences between 12 control and 12 attention deficit hyperactivity disorder (ADHD) children (9- to 12-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI).

METHOD

Visual selective attention was measured with the visual search of a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go/no-go task.

RESULTS

There were limited group differences in the selective attention task, with control children showing significantly greater intensity of activation in a small area of the superior parietal lobule region of interest. There were large group differences in the response inhibition task, with control children showing significantly greater intensity of activation in fronto-striatal regions of interest including the inferior, middle, superior and medial frontal gyri as well as the caudate nucleus and globus pallidus.

CONCLUSION

The widespread hypoactivity for the ADHD children on the go/no-go task is consistent with the hypothesis that response inhibition is a specific deficit in attention deficit hyperactivity disorder.

Inhibitory deficits in ocular motor behavior in adults with attention-deficit/hyperactivity disorder

BACKGROUND

Many of the symptoms of attention-deficit/hyperactivity disorder (ADHD) have been attributed to deficits in behavioral inhibition mediated by the frontostriatal system. The ability to suppress unwanted saccadic eye movements is mediated by prefrontal cortex-basal ganglia circuitry and thus constitutes a useful measure of inhibitory ability.

METHODS

To evaluate the functional integrity of this circuitry in ADHD, adult ADHD subjects unmedicated for at least 48 hours and normal comparison adults were studied by means of a comprehensive battery of ocular motor paradigms.

RESULTS

On a prosaccade task, in which subjects were required to generate saccades toward a peripheral visual target after a short stimulus-free interval, ADHD subjects generated significantly more of anticipatory (premature) saccades (reaction time <90 msec) and of saccades toward the target on catch trials, in which they were supposed to inhibit eye movements. On the antisaccade task, in which they were required to inhibit gazing toward the target while moving their eyes in the opposite direction, ADHD subjects made significantly more directional errors than normal adults. The performance of ADHD adults was consistent with deficits in saccadic inhibition.

CONCLUSIONS

Given the recent evidence for the interdependence between the brain systems mediating visual attention and ocular motor behavior, these findings support the notion that deficits in inhibitory mechanisms might underlie the inattention characteristic of ADHD. These results also implicate abnormalities in prefrontal cortex-basal ganglia circuitry in ADHD.

A test of the integrity of the components of Baddeley's model of working memory in attention-deficit/hyperactivity disorder (ADHD)

BACKGROUND

The integrity of working memory in attention-deficit/hyperactivity disorder (ADHD) was tested within the framework of Baddeley's model. METHODS-1: Buffers and rehearsal mechanisms were assessed by presenting children with or without ADHD (ages 8 to 15) with 1-7 target letters and a probe after 2-10 s. They decided if the probe was the same (verbal task) or in the same location (spatial task) as any of the targets. RESULTS-1: There was no interaction between group and delay or memory load in either task. METHODS-2: The central executive was assessed on a dual task. RESULTS-2: Although children with ADHD did not differ from controls in simple response time (RT) or in digits recalled, they showed greater decrements in RT when performing the 2 tasks concurrently.

CONCLUSIONS

Findings suggest that children with ADHD (1) do not have generalized impairments in working memory, (2) rehearse verbal and spatial information in the same manner as healthy children, (3) may have an impairment in the central executive component of working memory, which controls ability to divide attention between two tasks.

A Psychophysical Measure of Attention Deficit in Children With Attention-Deficit/Hyperactivity Disorder

The authors explored the temporal mechanism of attention deficit in children with attention-deficit/hyperactivity disorder (ADHD). In rapid serial visual presentation tasks in which two targets (T-sub-1 and T-sub-2) were presented in close temporal proximity among distractors, participants tried to identify T-sub-1 and detect T-sub-2 in one (dual-task) experiment and only to detect T-sub-2 in a second control (single-task) experiment. The sensitivity of T-sub-2 detection was analyzed using signal detection theory. The attentional blink--the impairment in T-sub-2 detection following the identification of T-sub-1--was increased in magnitude and protracted in the patients. Moreover, some ADHD children appeared to have a blink largely normal in magnitude but temporally displaced toward a later time. The authors hypothesize that a slower closing of the attention gate may mediate this specific attention impairment in ADHD children.

Time perception deficits in attention-deficit/ hyperactivity disorder and comorbid reading difficulties in child and adolescent samples

BACKGROUND

Our objective was to investigate time perception in Attention-Deficit/Hyperactivity Disorder (ADHD) with and without comorbid reading difficulties (RD) in child and adolescent participants.

METHOD

In study 1, 50 children with ADHD (31 ADHD, 19 ADHD+RD) and age-matched healthy controls (n = 50) completed three psychophysical tasks: duration discrimination (target duration of 400 ms versus a foil duration), frequency discrimination (a control condition to evaluate general perceptual ability), and a duration estimation task using the method of reproduction for intervals of 400 ms, 2000 ms, and 6000 ms. Study 2 used the same tasks with an adolescent sample (35 ADHD, 24 ADHD+RD, 39 controls).

RESULTS

In both studies, children and adolescents with ADHD and ADHD+RD displayed some impairments in duration discrimination and the precision with which they reproduced the intervals on the estimation task, particularly the shorter 400 ms interval. The most severe impairments tended to occur in the comorbid ADHD+RD group. No impairments were found on the frequency discrimination task. ADHD participants also displayed significant intra-individual variability in their performance on the estimation task. Finally, short-term and working memory, estimated full-scale IQ, and teacher report of hyperactivity/impulsivity were found to differentially predict performance on the time perception measures in the adolescent clinical sample.

CONCLUSIONS

Deficits in duration discrimination, duration estimation, and intra-individual performance variability may have cascaded effects on the temporal organisation of behaviour in children and adolescents with ADHD and ADHD+RD.

fMRI evidence that the neural basis of response inhibition is task-dependent

Event-related fMRI was used to investigate the hypothesis that neural activity involved in response inhibition depends upon the nature of the response being inhibited. Two different Go/No-go tasks were compared-one with a high working memory load and one with low. The 'simple' Go/No-go task with low working memory load required subjects to push a button in response to green spaceships but not red spaceships. A 'counting' Go/No-go task (high working memory load) required subjects to respond to green spaceships as well as to those red spaceships preceded by an even number of green spaceships. In both tasks, stimuli were presented every 1.5 s with a 5:1 ratio of green-to-red spaceships. fMRI group data for each task were analyzed using random effects models to determine signal change patterns associated with Go events and No-go events (corrected P< or =0.05). For both tasks, Go responses were associated with signal change in the left primary sensorimotor cortex, supplementary motor area (SMA) proper, and anterior cerebellum (right>left). For the simple task, No-go events were associated with activation in the pre-SMA; the working memory-loaded 'counting' task elicited additional No-go activation in the right dorsolateral prefrontal cortex. The findings suggest that neural contributions to response inhibition may be task dependent; the pre-SMA appears necessary for inhibition of unwanted movements, while the dorsolateral prefrontal cortex is recruited for tasks involving increased working memory load.

Altered control of visual fixation and saccadic eye movements in attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is characterized by the overt symptoms of impulsiveness, hyperactivity, and inattention. A frontostriatal pathophysiology has been hypothesized to produce these symptoms and lead to reduced ability to inhibit unnecessary or inappropriate behavioral responses. Oculomotor tasks can be designed to probe the ability of subjects to generate or inhibit reflexive and voluntary responses. Because regions of the frontal cortex and basal ganglia have been identified in the control of voluntary responses and saccadic suppression, we hypothesized that children and adults diagnosed with ADHD may have specific difficulties in oculomotor tasks requiring the suppression of reflexive or unwanted saccadic eye movements. To test this hypothesis, we measured eye movement performance in pro- and anti-saccade tasks of 114 ADHD and 180 control participants ranging in age from 6 to 59 yr. In the pro-saccade task, participants were instructed to look from a central fixation point toward an eccentric visual target. In the anti-saccade task, stimulus presentation was identical, but participants were instructed to suppress the saccade to the stimulus and instead look from the central fixation point to the side opposite the target. The state of fixation was manipulated by presenting the target either when the central fixation point was illuminated (overlap condition) or at some time after it disappeared (gap condition). In the pro-saccade task, ADHD participants had longer reaction times, greater intra-subject variance, and their saccades had reduced peak velocities and increased durations. In the anti-saccade task, ADHD participants had greater difficulty suppressing reflexive pro-saccades toward the eccentric target, increased reaction times for correct anti-saccades, and greater intra-subject variance. In a third task requiring prolonged fixation, ADHD participants generated more intrusive saccades during periods when they were required to maintain steady fixation. The results suggest that ADHD participants have reduced ability to suppress unwanted saccades and control their fixation behavior voluntarily, a finding that is consistent with a fronto-striatal pathophysiology. The findings are discussed in the context of recent neurophysiological data from nonhuman primates that have identified important control signals for saccade suppression that emanate from frontostriatal circuits.

Ocular motor behavior of children with neurofibromatosis 1

Patients with neurofibromatosis 1 show neurocognitive deficits including abnormal visuospatial performance, but oculomotor behavior has not been studied. We recorded saccades in neurofibromatosis 1 and normal children, ages 6 to 12 years. Patients showed increased latency and diminished amplitude to more eccentric targets for both visually guided and memory-guided saccades. Subtracting the latencies of visually guided saccades from memory-guided saccades produced no differences between groups. For predictive saccades (0.5 Hz), patients with neurofibromatosis 1 generated fewer anticipatory saccades than normal subjects, but patients with neurofibromatosis 1 made more direction errors in an antisaccade task. Patients with neurofibromatosis 1 show saccade abnormalities that are not easily ascribed to dysfunction within single cortical areas. Rather, the findings likely reflect (1) partial involvement of different components of a widely distributed cerebral network that controls saccades, (2) impaired visuomotor maturation in a brain abnormal early in development, and (3) excessive gamma-aminobutyric acid-mediated inhibition, which could influence basal ganglia pathways that modulate superior colliculus activity.

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.

Control of volitional and reflexive saccades in Tourette's syndrome

We hypothesized that Tourette's syndrome (TS) patients would display abnormal control of saccades because of overlap between brain areas suspected in TS pathophysiology and those involved saccade control. Subjects were required to look toward (pro-saccade) or away from (anti-saccade) a visual target. Saccadic reaction times were elevated among TS subjects in all tasks. The occurrence of reflexive pro-saccades in the immediate anti-saccade task was normal, suggesting that the ability to inhibit reflexive saccades was not impaired in TS. However, timing errors (eye movements made prior to GO signal in delayed saccade tasks) were increased in TS indicating that ability to inhibit or delay planned motor programs is significantly impaired in TS.

Development of pro- and antisaccades in children with attention-deficit hyperactivity disorder (ADHD) and healthy controls

To date, the investigation of the antisaccade task, a simple test of "executive functions," in children with ADHD has yielded inconsistent results. The present study aimed at contributing to this issue by (a) the investigation of a large sample of carefully diagnosed ADHD patients aged 7-15 years, and (b) the analyses of differential age effects in patients and controls. Healthy control children were pairwise matched with patients (N = 46; age = 136 +/- 24 months) for age and gender, and did not significantly differ in IQ. Horizontal pro- and antisaccades were elicited under the 200-ms gap and overlap conditions (blocks of 100 trials each). Overall, patients exhibited (a) augmented pro- and antisaccadic reaction times, (b) augmented error rates (antitasks), (c) augmented proportions of early responses (all conditions), and (d) reduced proportions of express saccades under the prosaccadic gap condition. The greater decline in anti- as compared to pro-SRT with increasing age that characterized controls was missing in patients. Confirming Barkley's (1997) neuropsychological theory of ADHD, these results altogether point to alterations in "executive functions" in ADHD patients that are presumably supported by frontal lobe structures, in particular the lateral prefrontal cortex and the frontal eye fields.

Inhibitory processes in adults with persistent childhood onset ADHD

The theory that attention-deficit/hyperactivity disorder (ADHD) stems from a deficit in an executive behavioral inhibition process has been little studied in adults, where the validity of ADHD is in debate. This study examined, in high-functioning young adults with persistent ADHD and a control group, 2 leading measures of inhibitory control: the antisaccad task and the negative priming task. ADHD adults showed weakened ability to effortfully stop a refle ve or anticipated oculomotor response but had normal ability to automatically suppress irrelevant information. Results suggest that an inhibitory deficit in ADHD is confined to effortful inhibition of motor response, that antisaccade and negative priming tasks index distinct inhibition systems, and that persistence of ADHD symptoms into adulthood is associated with persistence of executive motor inhibition deficits.

Oculomotor abnormalities in boys with tourette syndrome with and without ADHD

OBJECTIVE

To assess saccadic eye movements in boys with Tourette syndrome (TS) with and without attention-deficit hyperactivity disorder (ADHD), comparing performance with that of an age-matched group of male controls.

METHOD

Three different saccade tasks (prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and execution of eye movements, including motor response preparation, response inhibition, and working memory. The study included 14 boys with TS without ADHD (TS-only), 11 boys with TS and ADHD (TS+ADHD), and 10 male controls.

RESULTS

Latency of prosaccades was prolonged in boys with TS (both with and without ADHD) compared with controls. Variability in prosaccade latency was greater in the groups of boys with TS+ADHD compared with both the TS-only and control groups. Response inhibition errors on both the antisaccade task (directional errors) and memory-guided saccade task (anticipatory errors) were increased in boys with TS+ADHD compared with those with TS-only. There were no significant differences among the three groups in accuracy of memory-guided saccades.

CONCLUSIONS

Oculomotor findings suggest that TS is associated with delay in initiation of motor response as evidenced by excessive latency on prosaccades. Signs of impaired response inhibition and variability in motor response appear to be associated with the presence of ADHD.

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.

Is ADHD a disinhibitory disorder?

Attention deficit hyperactivity disorder (ADHD) is widely theorized to stem from dysfunctional inhibitory processes. However, the definition of inhibition is imprecisely distinguished across theories. To clarify the evidence for this conception, the author relies on a heuristic distinction between inhibition that is under executive control and inhibition that is under motivational control (anxiety or fear). It is argued that ADHD is unlikely to be due to a motivational inhibitory control deficit, although suggestions are made for additional studies that could overturn that conclusion. Evidence for a deficit in an executive motor inhibition process for the ADHD combined type is more compelling but is not equally strong for all forms of executive inhibitory control. Remaining issues include specificity to ADHD, whether inhibitory problems are primary or secondary in causing ADHD, role of comorbid anxiety and conduct disorder, and functional deficits in the inattentive ADHD subtype.

Oculomotor abnormalities in attention deficit hyperactivity disorder: a preliminary study

BACKGROUND

Prevailing hypotheses suggest that attention deficit hyperactivity disorder (ADHD) is secondary to dysfunction of motor intentional systems mediated by prefrontal circuitry. Oculomotor paradigms provide a mechanism for examining and localizing dysfunction at the interface between movement and cognition.

OBJECTIVE

Three different saccade tasks (reflexive or prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and the execution of eye movements, including motor response preparation, response inhibition, and working memory.

METHODS

The study included 19 children with ADHD, divided into two groups: a group of 8 children on methylphenidate at the time of testing and a group of 11 children not taking any psychoactive medication. Results from the two groups were compared with those from 25 age- and gender-matched normal control children.

RESULTS

Both groups of children with ADHD made significantly more directional errors than did controls on the antisaccade task and significantly more anticipatory errors than did controls on the memory-guided saccade task, findings that are consistent with deficits in response inhibition. There were no significant differences in prosaccade latency, although unmedicated children with ADHD showed significantly greater variability in latency on the prosaccade task than did controls. On the memory-guided saccade task there were no significant differences in saccade accuracy; however, unmedicated children with ADHD showed longer saccade latency than did either controls or medicated children with ADHD.

CONCLUSIONS

Oculomotor findings suggest that deficits in prefrontal functions, in particular response inhibition, contribute to behavioral abnormalities observed in ADHD. Findings also suggest that the administration of methylphenidate is associated with improvements in the consistency of motor response. Although there were no observed improvements in response inhibition with methylphenidate, conclusions await a design in which subjects complete testing both on and off medication.

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

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 degrees 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.

Eye movement task measures inhibition and spatial working memory in adults with schizophrenia, ADHD, and a normal comparison group

Schizophrenia and attention deficit/hyperactivity disorder (ADHD) are both associated with deficits in inhibition and working memory, although in ADHD the working memory deficit is hypothesized to be secondary to the inhibitory deficit. This similarity in cognitive processes has been paralleled by similarities across the two groups in the performance of working memory and inhibition tasks. The delayed oculomotor response task is an alternative task, which may allow greater separation of working memory from inhibitory components, and thus its use may provide additional information on primary vs. secondary deficits in these disorders. Ten young adult ADHD sufferers, 10 schizophrenic subjects, and 10 normal subjects were matched on age, gender, and education. Eye movements were recorded during delayed oculomotor response tasks with 1- and 3-s delays. Both the ADHD and the schizophrenic subjects demonstrated dis-inhibition (an increased percentage of premature saccades); however only schizophrenic subjects demonstrated an impaired working memory (decreased spatial accuracy of the remembered saccade). The results are consistent with the hypothesis that working memory is a primary deficit in schizophrenia, but secondary to the inhibitory deficit in ADHD.

Executive function oculomotor tasks in girls with ADHD

OBJECTIVE

To assess executive function in girls with attention-deficit/hyperactivity disorder (ADHD) using oculomotor tasks as possible trait markers for neurobiological studies.

METHOD

Thirty-two girls aged 6 to 13 years with DSM-IV ADHD and 20 age-matched, normal control girls were tested on a variety of oculomotor tasks requiring attention, working memory, and response inhibition, which included smooth pursuit, delayed response, and go-no go tasks.

RESULTS

Girls with ADHD performed the delayed response task correctly on 32% of trials as measured by number of memory-guided saccades, in contrast to 62% of trials for control subjects (p = .0009). Patients made twice as many commission errors to no go stimuli (p = .0001) and 3 times as many intrusion errors (saccades in the absence of go or no go stimuli; p = .004) during the go-no go task compared with controls. Smooth pursuit performance was statistically equivalent across subject groups. Repeated testing in a subgroup of 15 patients revealed substantial practice effects on go-no go performance.

CONCLUSIONS

The data confirm that girls with ADHD exhibit impairments in executive function, as has been reported in boys, implying a similar pathophysiology of ADHD in both sexes. However, practice effects may limit the utility of the oculomotor go-no go task for some neurobiological studies.

On inhibition/disinhibition in developmental psychopathology: views from cognitive and personality psychology and a working inhibition taxonomy

Disinhibition is a common focus in psychopathology research. However, use of inhibition models often is piecemeal, lacking an overarching taxonomy of inhibitory processes. The author organizes key concepts and models pertaining to different kinds of inhibitory control from the cognitive and temperament/personality literatures. Within the rubrics of executive inhibitory processes, motivational inhibitory processes, and automatic attentional inhibition processes, 8 kinds of inhibition are distinguished. Three basic temperament traits may address key executive and motivational inhibitory processes. Future developmental psychopathology research should be based on a systematic conceptual taxonomy of the kinds of inhibitory function relevant to a given disorder. Such an approach can clarify which inhibition distinctions are correct and which inhibition deficits go with which disorders.

Exploratory eye movements to pictures in childhood-onset schizophrenia and attention-deficit/hyperactivity disorder (ADHD)

We investigated exploratory eye movements to thematic pictures in schizophrenic, attention-deficit/hyperactivity disorder (ADHD), and normal children. For each picture, children were asked three questions varying in amount of structure. We tested if schizophrenic children would stare or scan extensively and if their scan patterns were differentially affected by the question. Time spent viewing relevant and irrelevant regions, fixation duration (an estimate of processing rate), and distance between fixations (an estimate of breadth of attention) were measured. ADHD children showed a trend toward shorter fixations than normals on the question requiring the most detailed analysis. Schizophrenic children looked at fewer relevant, but not more irrelevant, regions than normals. They showed a tendency to stare more when asked to decide what was happening but not when asked to attend to specific regions. Thus, lower levels of visual attention (e.g., basic control of eye movements) were intact in schizophrenic children. In contrast, they had difficulty with top-down control of selective attention in the service of self-guided behavior.

Exploratory eye movements to pictures in childhood-onset schizophrenia and attention-deficit/hyperactivity disorder (ADHD)

We investigated exploratory eye movements to thematic pictures in schizophrenic, attention-deficit/hyperactivity disorder (ADHD), and normal children. For each picture, children were asked three questions varying in amount of structure. We tested if schizophrenic children would stare or scan extensively and if their scan patterns were differentially affected by the question. Time spent viewing relevant and irrelevant regions, fixation duration (an estimate of processing rate), and distance between fixations (an estimate of breadth of attention) were measured. ADHD children showed a trend toward shorter fixations than normals on the question requiring the most detailed analysis. Schizophrenic children looked at fewer relevant, but not more irrelevant, regions than normals. They showed a tendency to stare more when asked to decide what was happening but not when asked to attend to specific regions. Thus, lower levels of visual attention (e.g., basic control of eye movements) were intact in schizophrenic children. In contrast, they had difficulty with top-down control of selective attention in the service of self-guided behavior.

Components of visual search in childhood-onset schizophrenia and attention-deficit/hyperactivity disorder

This study tested the hypotheses that visual search impairments in schizophrenia are due to a delay in initiation of search or a slow rate of serial search. We determined the specificity of these impairments by comparing children with schizophrenia to children with attention-deficit hyperactivity disorder (ADHD) and age-matched normal children. The hypotheses were tested within the framework of feature integration theory by administering children tasks tapping parallel and serial search. Search rate was estimated from the slope of the search functions, and duration of the initial stages of search from time to make the first saccade on each trial. As expected, manual response times were elevated in both clinical groups. Contrary to expectation, ADHD, but not schizophrenic, children were delayed in initiation of serial search. Finally, both groups showed a clear dissociation between intact parallel search rates and slowed serial search rates.

The antisaccade: a review of basic research and clinical studies

The ability to suppress reflexive responses in favor of voluntary motor acts is crucial for everyday life. Both abilities can be tested with an oculomotor task, the antisaccade task. This task requires subjects to suppress a reflexive prosaccade to a flashed visual stimulus and instead to generate a voluntary saccade to the opposite side. This article reviews what is currently known about the neural structures and processes which are involved in the performance of this task. Current data show that a variety of brain lesions, neurological diseases and psychiatric disorders result in errors, i.e. prosaccades towards the stimulus, in this task. Brain imaging studies have shown that a widely distributed cortical and subcortical network is active during the generation of antisaccades. These findings are discussed and the potential of the antisaccade task for diagnostic purposes is evaluated.

Do hyperactive children have motor organization and/or execution deficits?

Hyperactive children have been described as motorically clumsy. To explore the validity of this assertion, an experiment using the additive factor method was designed to examine motor organization and execution in hyperactive children. Four groups of boys aged 7 to 8 years took part in the study: (1) a pure hyperactive (HA) group, N=20; (2) a pure conduct-disordered (CD) group, N=18; (3) a mixed hyperactive/conduct-disordered (HA+CD) group, N=12; (4) a normal (N) control group, N=22. While the small sample size precluded a definitive conclusion, the results indicated that neither HA nor CD children showed any motor organization or execution deficit in a simple sequential key-tapping task. Given previous findings indicating that hyperactive children show deficits in more complex motor coordination skills, the generalizability of our negative results needs to be examined on other more complex tasks.

Working memory in childhood-onset schizophrenia and attention-deficit/hyperactivity disorder

We investigated verbal and spatial working memory in participants with childhood-onset schizophrenia (N=13), attention-deficit/hyperactivity disorder (ADHD; N=31) and age-matched normal children (N=27). The ages of the participants ranged from 9 to 20 years, with an average age of approx. 14 in all groups. Diagnoses were based on structured interviews (Kiddie-Schedule for Affective Disorders and Schizophrenia) with the children and their parents and made using DSM-III-R criteria. Verbal working memory was assessed by the highest number of digits recalled in forward and backward order on the Digit Span subtest of the Wechsler Intelligence Scale. Results showed that normal children recalled more digits than schizophrenic and ADHD children, who did not differ. Spatial working memory was assessed with the Dot Test of Visuospatial Working Memory: The children were presented with a dot on a page for 5 s and asked to mark its location on a blank page immediately after presentation or 30 s later. A distracter task was used during the delay to prevent verbal rehearsal. The average distance between the target dot and the child's mark in the 30-s condition was shorter for normal than for schizophrenic and ADHD children, who did not differ. Thus, both schizophrenic and ADHD children showed deficits in verbal and spatial working memory. These results suggest that in both disorders, the capacity of the sensory buffers may be diminished, and/or the availability and allocation of resources to the central executive may be limited.

Inhibitory dysfunction in hyperactive boys

Recent evidence suggests that the main deficit in childhood hyperactivity is in frontal lobe-mediated self-regulative functions such as inhibitory control. Hyperactives have consistently been shown to perform poorly on the stop task, which is a laboratory measurement of inhibitory control. This study was aimed at extending knowledge about inhibitory processes involved in the hyperactive's performance on this task. For this purpose, the performance of 11 pervasive hyperactives was compared to the performance of normal children on two stop tasks which differed from each other in the contingency of timing of the stop signal. In Stop1 stop signals were internally related, i.e. presented at time intervals after onset of the response stimulus, whereas in Stop2 stop signals were externally related, i.e. presented at time intervals related to the subject's own go-process. Both tasks were modifications of the classical stop task in modality of the stop signal visual instead of auditory and in event rate, which was half-shortened. The aim of this study was: (a) to replicate the findings of deficient inhibitory functions in hyperactive children in the stop task in spite of modifications in modality and event rate; and (b) to elucidate (dis)similarities of stopping processes or of group differences in these stopping processes triggered by stop delays related either to external or to internal processes. Hyperactive children were less efficient than controls in inhibiting their motor response in both versions of the stop task. independent of whether the stop signals were externally or internally related. Furthermore, the go-process of the hyperactives was more variable and erratic in both tasks. Thus, the results strengthen the effectiveness of stop tasks in distinguishing hyperactive from normal children.

Familial transmission of two independent saccadic abnormalities in schizophrenia

Difficulties with inhibiting inappropriate responses, i.e. disinhibition, and problems with spatial memory are both presumed to be a part of the phenotypic expression of the genetic risk for schizophrenia. Schizophrenic probands are impaired on saccadic eye movement tasks which require (a) response inhibition to prepotent stimuli and (b) generation of an accurate response to a remembered or calculated spatial location, but it is unknown how these deficits are inherited. Sixteen schizophrenic probands, their 32 parents, and two normal control groups completed a delayed oculomotor response and an antisaccade task. The parents with a positive ancestral family history for chronic psychosis (n = 8) were presumed to be more likely than their family history-negative spouses to be genetic carriers for schizophrenia. Probands and their positive family history parents had more failures of response inhibition than did normal control groups. However, it was the probands and their negative family history spouses who demonstrated impaired accuracy of the remembered- or antisaccades. Disinhibition may be closely tied to a specific genetic risk for schizophrenia. However, a second familial factor related to the maintenance or manipulation of spatial information may also contribute to the genetic risk of the full clinical disorder.

Relationships between neuropsychological and oculomotor measures in schizophrenia patients and normal controls

Establishing the relationship between oculomotor and neuropsychological impairments might facilitate a more coherent description of schizophrenia-associated neurocognitive deficits. Therefore, we assessed several aspects of neuropsychological and oculomotor function in 25 medicated schizophrenia patients and 24 age-matched controls. Neuropsychological tasks included the Wisconsin Cart Sort Test (WCST), the Trail Making Test (TMT), the Rey Auditory Verbal Learning Test, and finger tapping speed. Oculomotor functions assessed included smooth pursuit, initiation of smooth pursuit, predictive pursuit, fixation, visually guided saccades, remembered saccades, and antisaccades. Among the schizophrenia patients, predictive pursuit performance correlated significantly with finger tapping (dominant hand), TMT (both parts), and one WCST measure (categories completed). The only other significant correlation among the schizophrenia patients was between antisaccade performance and part A of the TMT. Perseverative errors during the WCST and antisaccade performance were the only measures significantly correlated among the normals. Closely related neurocognitive deficits may be responsible for impairments in TMT, WCST, predictive pursuit, and antisaccade performance in schizophrenia.

Inhibition and attention deficit hyperactivity disorder

This paper updates the author's earlier hypothesis that Attention Deficit Hyperactivity Disorder (ADHD) reflects underactivity in Gray's Behavioral Inhibition System. Five areas of research are reviewed: (1) studies using the stop-signal task, (2) studies of errors of commission, (3) a study of inhibition indexed by eye movements, (4) a neuroimaging study of the corpus callosum, and (5) a study on the prediction of response to methylphenidate. Data from the many different dependent variables in these studies are interpreted as supporting disinhibition as a core deficit in ADHD.

Smooth pursuit eye movements in childhood-onset schizophrenia: comparison with attention-deficit hyperactivity disorder and normal controls

Abnormalities of the smooth pursuit eye movements of adults with schizophrenia have been well described. We examined smooth pursuit eye movements in schizophrenic children, contrasting them with normal and attention-deficit hyperactivity disorder (ADHD) subjects, to determine whether there is continuity of eye movement dysfunction between childhood- and adult-onset forms of schizophrenia. Seventeen schizophrenic children with onset of illness by age 12, 18 ADHD children, and 22 normal children were studied while engaged in a smooth pursuit eye tracking task. Eye tracking variables were compared across the three groups. Schizophrenic children exhibited significantly greater smooth pursuit impairments than either normal or ADHD subjects. Within the schizophrenic group, there were no significant relationships between eye tracking variables and clinical variables, or ventricular/brain ratio. Childhood-onset schizophrenia is associated with a similar pattern of smooth pursuit abnormalities to that seen in later-onset schizophrenia.