Comparison of the smooth eye tracking disorder of schizophrenics with that of nonhuman primates with specific brain lesions

A sensory-motor decoder that transforms neural responses in extrastriate area MT into smooth pursuit eye movements

Visual motion drives smooth pursuit eye movements through a sensory-motor decoder that uses multiple parallel neural pathways to transform the population response in extrastriate area MT into movement. We evaluated the decoder by challenging pursuit in monkeys with reduced motion reliability created by reducing coherence of motion in patches of dots. Our strategy was to determine how reduced dot coherence changes the population response in MT. We then predicted the properties of a decoder that transforms the MT population response into dot coherence-induced deficits in the initiation of pursuit and steady-state tracking. During pursuit initiation, decreased dot coherence reduces MT population response amplitude without changing the preferred speed at its peak. The successful decoder reproduces the measured eye movements by multiplication of 1) the estimate of target speed from the peak of the population response with 2) visual-motor gain based on the amplitude of the population response. During steady-state tracking, the decoder that worked for pursuit initiation failed to reproduce the paradox that steady-state eye speeds do not accelerate to the target speed despite persistent image motion. It predicted eye acceleration to target speed even when monkeys' eye speeds were steady at well below the target speed. To account for the effect of dot coherence on steady-state eye speed, we postulate that the decoder uses sensory-motor gain to modulate the eye velocity positive feedback that normally sustains perfect steady-state tracking. Then, poor steady-state tracking persists because of balance between eye deceleration caused by low positive feedback gain and acceleration driven by MT.NEW & NOTEWORTHY By challenging a sensory-motor system with degraded sensory stimuli, we reveal how the sensory-motor decoder transforms the population response in extrastriate area MT into commands for the initiation and steady-state behavior of smooth pursuit eye movements. Conclusions are based on measuring population responses in MT for multiple target speeds and different levels of motion reliability and evaluating a decoder with a biologically motivated architecture to determine the decoder properties that create the measured eye movements.

A sensory-motor decoder that transforms neural responses in extrastriate area MT into smooth pursuit eye movements

Visual motion drives smooth pursuit eye movements through a sensory-motor decoder that uses multiple parallel components and neural pathways to transform the population response in extrastriate area MT into movement. We evaluated the decoder by challenging pursuit in monkeys with reduced motion reliability created by reducing coherence of motion in patches of dots. Reduced dot coherence caused deficits in both the initiation of pursuit and steady-state tracking, revealing the paradox of steady-state eye speeds that fail to accelerate to target speed in spite of persistent image motion. We recorded neural responses to reduced dot coherence in MT and found a decoder that transforms MT population responses into eye movements. During pursuit initiation, decreased dot coherence reduces MT population response amplitude without changing the preferred speed at the peak of the population response. The successful decoder reproduces the measured eye movements by multiplication of (i) the estimate of target speed from the peak of the population response with (ii) visual-motor gain based on the amplitude of the population response. During steady-state tracking, the decoder that worked for pursuit initiation failed. It predicted eye acceleration to target speed even when monkeys' eye speeds were steady at a level well below target speed. We can account for the effect of dot coherence on steady-state eye speed if sensorymotor gain also modulates the eye velocity positive feedback that normally sustains perfect steadystate tracking. Then, poor steady-state tracking persists because of balance between deceleration caused by low positive feedback gain and acceleration driven by MT.

Sensorimotor transformation deficits for smooth pursuit in first-episode affective psychoses and schizophrenia

BACKGROUND

Smooth pursuit deficits are an intermediate phenotype for schizophrenia that may result from disturbances in visual motion perception, sensorimotor transformation, predictive mechanisms, or alterations in basic oculomotor control. Which of these components are the primary causes of smooth pursuit impairments and whether they are impaired similarly across psychotic disorders remain to be established.

METHODS

First-episode psychotic patients with bipolar disorder (n = 34), unipolar depression (n = 24), or schizophrenia (n = 77) and matched healthy participants (n = 130) performed three smooth pursuit tasks designed to evaluate different components of pursuit tracking.

RESULTS

On ramp tasks, maintenance pursuit velocity was reduced in all three patients groups with psychotic bipolar patients exhibiting the most severe impairments. Open loop pursuit velocity was reduced in psychotic bipolar and schizophrenia patients. Motion perception during pursuit initiation, as indicated by the accuracy of saccades to moving targets, was not impaired in any patient group. Analyses in 138 participants followed for 6 weeks, during which patients were treated and psychotic symptom severity decreased, and no significant change in performance in any group was revealed.

CONCLUSIONS

Sensorimotor transformation deficits in all patient groups suggest a common alteration in frontostriatal networks that dynamically regulate gain control of pursuit responses using sensory input and feedback about performance. Predictive mechanisms appear to be sufficiently intact to compensate for this deficit across psychotic disorders. The absence of significant changes after acute treatment and symptom reduction suggests that these deficits appear to be stable over time.

Fronto-cerebellar circuits and eye movement control: a diffusion imaging tractography study of human cortico-pontine projections

A possible role of the cerebellum in cognitive function might be revealed through its anatomical connections with specific regions of the cerebral cortex. To understand the kind of information transmitted between the cortex and cerebellum, we studied the connections from six subdivisions of frontal and prefrontal cortex using diffusion imaging tractography. Cortico-pontine fibers travel through the cerebral peduncles and reach the cerebellum by way of a synaptic link in the pontine nuclei. In 19 human data sets, we tracked connections between the cerebral peduncle and left hemispheric masks of the superior frontal gyrus (SFG), precentral gyrus (PcG), middle frontal gyrus (MFG), orbital frontal cortex, and two regions of inferior frontal gyrus, including pars opercularis and pars triangularis. Cortico-pontine fibers arose from the PcG, the caudal/medial SFG and a small region of the MFG in a majority of the subjects analyzed. While these regions do have known roles in cognitive and executive functions, all three are strongly associated with the planning and execution of eye movements. Connections from more ventral prefrontal cortex were negligible, indicating that these regions are only sparsely represented in the circuit. Based on this pattern of connectivity, it is likely that the prefrontal connections to the cerebellum are involved in covert motor operations and the control of eye movements.

Eye movement dysfunction in first-degree relatives of patients with schizophrenia: a meta-analytic evaluation of candidate endophenotypes

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.

Eye movement and visual motion perception in schizophrenia I: Apparent motion evoked smooth pursuit eye movement reveals a hidden dysfunction in smooth pursuit eye movement in schizophrenia

To date, smooth pursuit eye movement in schizophrenia has only been investigated using a target stimulus in continuous motion. However, smooth pursuit can also be evoked by an oscillating jumping dot that appears to be in apparent motion and although there is no continuous motion on the retinal surface this apparently moving stimulus can effortlessly elicit smooth-pursuit eye movement. In the first of two experiments smooth pursuit eye movement was evoked by target stimuli in continuous (real) motion at seven target velocities from 5.0 to 35.0 deg/s, and in a second experiment it was measured in response to an oscillating jumping dot in apparent motion at eight target velocities from 5.0 to 25.0 deg/s in a group with mixed-symptoms in schizophrenia and in a control group. The results of Experiment 1 provided no evidence for a dysfunction in continuous motion evoked smooth pursuit eye movement in the group with schizophrenia. However, following the removal of saccadic eye movements in smooth pursuit, the group with schizophrenia showed significantly lower smooth pursuit eye velocity at target velocities from 20.0 to 35.0 deg/s. The results of Experiment 2 revealed that apparent motion evoked smooth pursuit eye velocity in the group with schizophrenia was significantly lower in comparison with normal observers at all target velocities up to 25.0 deg/s with the inclusion or exclusion of saccadic eye movements. The findings demonstrate that overall smooth pursuit eye movement evoked in response to a continuous (real) motion target in the group with schizophrenia may nevertheless contain a hidden temporal resolution and integration dysfunction that is revealed when smooth pursuit eye movement is evoked in response to an oscillating jumping dot in apparent motion. The findings also demonstrate that normal smooth pursuit eye movement in normal observers can be made to resemble the dysfunctional smooth pursuit eye movement that is naturally found in some people with schizophrenia by using a target stimulus in apparent motion.

Evidence from increased anticipation of predictive saccades for a dysfunction of fronto-striatal circuits in obsessive-compulsive disorder

In obsessive-compulsive disorder (OCD), a dysfunction of neuronal circuits involving prefrontal areas and the basal ganglia is discussed that implies specific oculomotor deficits. Performance during reflexive and predictive saccades, antisaccades and predictive smooth pursuit was compared between patients with OCD (n=22), patients with schizophrenia (n=21) and healthy subjects (n=24). Eye movements were recorded by infrared reflection oculography. In both patient groups, higher frequencies of anticipatory saccades with reduced amplitudes in the predictive saccade task were observed. Additionally, reduced smooth pursuit eye velocity and increased frequencies of saccadic intrusions during smooth pursuit as well as increased error rates in the antisaccade task were demonstrated for patients suffering from schizophrenia. Patients with OCD and schizophrenia revealed different patterns of oculomotor impairment: whereas increased anticipation of predictive saccades provides evidence for a dysfunction of the circuit between the frontal eye field and the basal ganglia in both groups, results from the antisaccade task imply additional deficits involving the dorsolateral prefrontal cortex in schizophrenic patients. Furthermore, the cortical network for smooth pursuit (especially the frontal eye field) is also assumed to be disturbed in schizophrenia.

Eye tracking in schizophrenia: does the antisaccade task measure anything that the smooth pursuit task does not?

Smooth pursuit and antisaccade eye-tracking abnormalities have been proposed as endophenotypes for schizophrenia. However, it is not clear whether these tasks measure the same underlying abnormality. We hypothesised that these measures would be correlated. The association between smooth pursuit and antisaccade task performance was assessed in 50 schizophrenic patients, 80 unaffected first-degree relatives and 40 unaffected controls. Smooth pursuit measures included gain, number of saccades and a qualitative measure of smooth pursuit. The antisaccade distractibility error (ADE) score was the only measure of the antisaccade task. A significant correlation was found between reduced gain and an increased ADE score for all the subjects in the three groups combined. The total number of saccades was negatively correlated with the ADE score in the schizophrenic group, but positively in the relative group. Qualitative ratings of smooth pursuit correlated with the ADE score. Our results suggest that the antisaccade distractibility error score is related to gain and qualitative measures of smooth pursuit, although the relationship with number of saccades did not conform to this pattern. The finding may reflect a shared genetic liability, that affects both eye-tracking phenotypes. It is likely that both measures reflect frontal cortical dysfunction.

Smooth-pursuit eye movement and directional motion-contrast sensitivity in schizophrenia

Although the occurrence of visual processing and eye-movement disorders in schizophrenia have been widely recognized, their relationship with the symptoms of schizophrenia is less well understood. In two experiments the relationship between directional-motion processing and smooth-pursuit eye movement was investigated in normal observers and in groups with positive and negative symptoms in schizophrenia. The first experiment measured linear smooth-pursuit eye movement at six target velocities from 5.0 to 30.0 degrees s(-1) and the second experiment measured directional motion-contrast sensitivity at three spatial (1.0, 4.0 and 8.0 c/deg) and five temporal (0.75, 3.0, 6.0, 12.0 and 18.0 Hz) frequencies in the same groups of observers. No significant differences were found between the control and positive-symptom group in directional motion-contrast sensitivity and smooth-pursuit eye movements. In comparison, a relationship was found between a significant reduction in directional motion-contrast sensitivity and significantly reduced smooth-pursuit eye movement in the negative-symptom group and serves to further cleave the distinction between positive and negative symptoms in schizophrenia. The relationship between visual motion processing and pursuit eye movement in the negative-symptom group was explained by a disorder in directional motion processing that fails to fully engage the pursuit eye movement system and reduces smooth pursuit eye-velocity gain.

Response to unexpected target changes during sustained visual tracking in schizophrenic patients

BACKGROUND

Evidence supports an association between liability to schizophrenia and smooth-pursuit eye movement (SPEM) abnormalities. Knowledge of the biological mechanisms of SPEM abnormalities may provide critical insights into the etiology of schizophrenia. SPEM is elicited by sensory motor information from the movement of the object's image on the retina (retinal motion signal) and subsequent extraretinal motion signals. Previous studies suggest that a deficit in predictive responses to extraretinal motion signals may underlie the SPEM phenotype in schizophrenia. Data suggest that at-risk individuals for schizophrenia depend less on extraretinal and more on retinal motion signals to maintain pursuit than healthy individuals.

METHODS

We designed a pursuit task that employs unexpected changes in target direction during smooth pursuit. The unpredictable task is unique in that performance is expected to be better if the subject's response is biased towards retinal motion.

RESULTS

The study included 23 schizophrenia patients and 22 normal controls. Results showed that schizophrenia patients showed significantly superior performance (i.e. higher smooth pursuit gain) for a brief period after an unexpected change in target direction compared with healthy subjects.

CONCLUSION

Findings of superior performance by schizophrenic patients are interesting because they circumvent confounds of generalized deficits. These results provide further evidence of specific deficit in the predictive pursuit mechanism and over-reliance on retinal error signals to maintain pursuit in schizophrenia.

Smooth pursuit and antisaccade eye movements in siblings discordant for schizophrenia

Smooth pursuit eye movement (SPEM) and antisaccade deficits have been proposed as endophenotypes in the search for schizophrenia genes. We assessed these measures in 24 schizophrenia patients, 24 of their healthy siblings, and 24 healthy controls closely matched to the siblings. Between-group differences were assessed using a random effects regression model taking into account the relatedness between patients and siblings. Patients showed reduced SPEM gain, increased frequency of saccades during pursuit, increased antisaccade error rate, and reduced antisaccade gain compared to controls. Siblings performed intermediate, i.e. between patients and controls, on most measures, but were particularly characterised by reduced antisaccade gain. SPEM gain at one target velocity was significantly correlated between patients and siblings, highlighting the necessity of taking into account within-family correlations in the statistical analysis of between-group differences. It is concluded that subtle SPEM and antisaccade deficits are observed in clinically unaffected siblings of schizophrenia patients; these deficits may be useful markers of genetic liability to schizophrenia.

Syndromes of schizophrenia and smooth-pursuit eye movement dysfunction

There have been a number of studies on smooth pursuit eye movement (SPEM) dysfunction in schizophrenia. However, the association between SPEM dysfunction and particular clinical symptoms remains unclear. We examined SPEM dysfunction in relation to schizophrenic symptoms using both the positive/negative dichotomy and the three-syndrome model. Subjects included 78 patients with schizophrenia and 60 healthy control subjects. SPEM performance was indexed by root mean square error. Symptom profiles were assessed using the Positive and Negative Syndrome Scale (PANSS), and the three-primary syndromes were identified by factor analysis of PANSS ratings (Psychomotor poverty: deficit negative symptoms; Disorganization: defined primarily by thought disorder; and Reality distortion: hallucinations and delusions). Compared with controls, the schizophrenia group showed significant impairment in global SPEM function. The three-syndrome approach produced more specific findings than the dichotomous model. Of the three syndromes, only the Disorganization dimension showed a significant association with increased global SPEM dysfunction. The specificity of SPEM dysfunction to Disorganization was verified in comparisons among schizophrenia subgroups and the control group. By contrast, the general domains of positive and negative symptoms were both found to be modestly associated with SPEM dysfunction. The separation of positive and negative symptoms that contribute to Disorganization from those that define Reality Distortion and Psychomotor Poverty has revealed significant new associations between SPEM and schizophrenic symptoms. These findings are interpreted in light of the proposal that the Disorganization syndrome is the central form of pathology in schizophrenia.

Fixation stability in schizophrenia, bipolar, and control subjects

A few investigators have suggested that visual fixation abnormalities may serve as an endophenotype of liability for schizophrenia. However, the data are equivocal. Conflicting reports regarding the specificity of fixation deficits to schizophrenia may be attributable to methodological differences. Thirty-four schizophrenia patients, 20 bipolar patients, and 30 non-patient controls were presented targets for central fixation. Fixation was scored in terms of frequency of saccades as well as qualitative ratings. Analysis of variance on the number of saccades produced during fixation revealed that the three groups did not differ. Similarly, we observed that the schizophrenia patients did not differ from either bipolar patients or controls in terms of ratings of fixation quality. It appears that schizophrenia patients are not characterized by poor visual fixation. The findings are discussed in terms of the viability of visual fixation as a marker of schizophrenic diathesis, as well as possible implications for the analysis of schizophrenia patients' visual search performance.

Clinical and biological concomitants of resting state EEG power abnormalities in schizophrenia

BACKGROUND

This study investigated the clinical and biological concomitants of electroencephalogram power abnormalities in schizophrenia.

METHODS

We examined the power characteristics of resting electroencephalograms in 112 schizophrenic patients. Also collected were measures of psychotic symptomatology, brain morphology, ocular motor functioning, electrodermal activity, and nailfold plexus visibility. Seventy-eight nonschizophrenic psychosis patients (e.g., mood disorder patients with psychosis) and 107 nonpsychiatric control subjects were included for comparison.

RESULTS

Schizophrenic patients whose electroencephalograms were characterized by augmented low-frequency power and diminished alpha-band power had more negative symptoms, larger third ventricles, larger frontal horns of the lateral ventricles, increased cortical sulci widths, and greater ocular motor dysfunction compared with schizophrenic patients without these electroencephalogram characteristics. In nonschizophrenic psychosis patients, augmented low-frequency and diminished alpha-band powers failed to be associated with any clinical or biological indices.

CONCLUSIONS

Results suggest that clinical and biological concomitants of low-frequency and alpha-band power abnormalities in schizophrenia are unique, perhaps indicating the presence of thalamic and frontal lobe dysfunction.

Eye movement dysfunction as a biological marker of risk for schizophrenia

OBJECTIVE

Our aim was to review smooth pursuit eye movement (SPEM) studies in schizophrenia and groups at high risk for schizophrenia, with a view to evaluating the utility of SPEM dysfunction as a biological marker of risk for schizophrenia.

METHOD

Smooth pursuit eye movement studies, related saccade function and the unresolved issues in this area of schizophrenia research were addressed. The different perspectives on the trait marker status of SPEM dysfunction, provided by both high-risk studies and related developmental research were considered. Attention was also given to the relationship between eye movement dysfunction and symptom profiles.

RESULTS

Converging evidence points to the robust and specific nature of SPEM dysfunction in schizophrenia, and highlights the role of frontal lobe and a related network dysfunction. The vast majority of 'high risk' studies support the view that SPEM dysfunction is also genetically specific to schizophrenia, and is not simply due to the overt expression of this illness. Studies assessing SPEM in relation to symptomatology show an association with the Disorganisation syndrome in particular.

CONCLUSIONS

Evidence for the specificity of SPEM dysfunction to diagnosed schizophrenia, as well as to healthy individuals with a genetic vulnerability to schizophrenia, suggests that the SPEM task has efficacy as a test of gene carrier status in schizophrenia, and therefore as a trait marker of risk for schizophrenia. Future studies should seek to explore the relationships between SPEM and other eye movement dysfunctions (antisaccades, express saccades), in view of evidence that some of these dysfunctions also show specificity for schizophrenia.

Smooth pursuit eye movements to extra-retinal motion signals: deficits in patients with schizophrenia

In order to understand mechanisms underlying the smooth pursuit abnormality(ies) in schizophrenia, new methods, which independently evaluated predictive smooth pursuit responses to extra-retinal motion signals, were developed and tested. The study compared responses to only extra-retinal motion signals in normal volunteers (n = 25), and individuals with a chronic (n = 21) and a recent onset (n = 18) schizophrenia. Subject groups with chronic schizophrenia and recent onset schizophrenia had significantly poorer predictive pursuit than normal subjects in response to only extra-retinal motion signals. The poor predictive pursuit was evident even at low target velocity when the closed-loop pursuit gain was normal in patients with schizophrenia. Ten of the 18 recent onset patients were drug-free at the time of testing and had no or minimum previous exposure to anti-psychotic medications. Re-analyses of the data showed that on most measures of predictive pursuit, drug-free patients were not significantly different from patients who received anti-psychotic drug treatment. Both patient groups had significantly poorer predictive pursuit than normal subjects. These results suggest that a deficit in processing extra-retinal motion may underlie the abnormal smooth pursuit response in schizophrenia. At low target velocities, patients with schizophrenia were able to compensate for the low extra-retinal gain by increasing the gain of response to the retinal slip velocity. This indicates that patients were able to process retinal slip velocity and generate smooth pursuit eye movements, but experienced a specific deficit in processing and/or integrating extra-retinal motion information for the smooth pursuit response.

SPECT study of visual fixation in schizophrenia and comparison subjects

BACKGROUND

The consistent association of impaired eye movements and schizophrenia suggests a relationship between the neurobiology of the illness and visual pursuit systems. Visual fixation (VF), an eye "movement" task at zero velocity, is the simplest such abnormality in schizophrenia patients and their relatives.

METHODS

We used a VF task for a functional imaging study. Six neuroleptic-free schizophrenia patients and eight gender and mean age matched comparison subjects had SPECT scans with 20 mCi of Tc99-HMPAO, during VF on a simple blue line intersection. MEDX data saved in ANALYZE format for SPM 95 was used to generate paired t-test statistical data for display in Talairach space, with rCBF changes given as Z-scores.

RESULTS

Patients, compared to controls, had increased rCBF in both the parahippocampal gyrus (bilaterally) and in the right fusiform gyrus. They had decreased rCBF in the left frontal cortex, including medial and superior frontal gyri and anterior cingulate. Overall, compared to controls, patients had medial temporal lobe hyperperfusion along with left prefrontal hypoperfusion.

CONCLUSIONS

These findings are consistent with the hypothesized imbalance between the medial temporal and frontal lobes that is postulated for schizophrenia. It was of interest that the relative rCBF differences between schizophrenia patients and controls in this small sample were observable with this cognitively non-demanding visual fixation task.

Investigation of frontal lobe subregions in first-episode schizophrenia

The evidence for frontal lobe structural abnormalities in schizophrenia using magnetic resonance (MR) imaging has been mixed, but most studies used either single slice measures or total volumes of a single frontal region, neither of which is sensitive to potential volume differences in more specific subregions. This study employed reliable methods for parcellation of the frontal lobes from MR images based on the sulcal anatomy. Following a cytoarchitectonic theory that distinguishes dorsomedial (archicortically derived) from ventrolateral (paleocortically derived) frontal subregions, we measured the superior frontal gyrus, anterior cingulate gyrus, and orbital frontal region in 19 first-episode schizophrenia patients and 26 healthy comparison subjects. Results indicated that male patients had significantly larger right orbital frontal volume compared to their left orbital frontal volume and compared to healthy men. Among male patients larger right orbital frontal volume was significantly correlated with smaller right 'archicortical' (i.e. anterior cingulate and superior frontal gyri) volume. Furthermore, the ratio of right orbital frontal to right 'archicortical' volume was significantly and positively correlated with level of delusions among male patients. These findings suggest that there may be reciprocal controls on 'archicortical' and 'paleocortical' neurodevelopment among men with schizophrenia, and that larger paleocortical relative to archicortical volumes may be associated with increased delusions.

Hippocampal N-acetyl aspartate in unaffected siblings of patients with schizophrenia: a possible intermediate neurobiological phenotype

BACKGROUND

Shared neurobiological characteristics of patients with schizophrenia and their siblings may represent "intermediate phenotypes" that may more closely reflect the genetic susceptibility underlying this illness. We sought evidence of such phenotypes using magnetic resonance spectroscopy based on previously described regional abnormalities in levels of the neuronal marker N-acetyl-aspartate (NAA) in the hippocampal area and dorsolateral prefrontal cortex of patients with schizophrenia.

METHODS

We studied 47 schizophrenics, 60 unaffected siblings, and 66 healthy control subjects with long echo time multislice proton magnetic resonance spectroscopic imaging, primarily measuring NAA, creatine plus phosphocreatine (CRE), and choline-containing compounds.

RESULTS

Both patients and their unaffected siblings had significant reductions in hippocampal area NAA/CRE as compared with control subjects. As exploratory analyses, estimates of heritability were performed. Although quantitative correlation of hippocampal NAA between patients and sibs was low (likely reflecting measurement noise), qualitatively defined "low hippocampal NAA/CRE phenotypes" yielded relative risk estimates (lambda s) of between 3.8 and 8.8, suggesting this characteristic is heritable.

CONCLUSIONS

Our finding adds to the evidence that hippocampal abnormalities are associated with schizophrenia and may represent a novel biological phenotype for genetic studies of schizophrenia.

Eye tracking abnormalities in schizophrenia: evidence for dysfunction in the frontal eye fields

BACKGROUND

Eye tracking deficits are robust abnormalities in schizophrenia, but the neurobiological disturbance underlying these deficits is not known.

METHODS

To clarify the pathophysiology of eye tracking disturbances in schizophrenia, we tested 12 first-episode treatment-naive schizophrenic patients and 10 matched healthy individuals on foveofugal and foveopetal step-ramp pursuit tasks.

RESULTS

On foveopetal tasks, the initiation of pursuit eye movements was delayed in schizophrenic patients, and their steady-state pursuit gain was reduced particularly at slower target speeds (8 and 16 deg/sec). In foveofugal step-ramp tasks, their primary catch-up saccades were normal in latency and accuracy, but their postsaccadic pursuit in the first 100 msec after the primary catch-up saccade was significantly reduced even relative to their slow steady-state pursuit, especially during and immediately after an acute episode of illness.

CONCLUSIONS

These observations indicate that motion-sensitive areas in posterior temporal cortex provide sufficiently intact information about moving targets to guide accurate catch-up saccades, but that the sensory processing of motion information is not being used effectively for pursuit eye movements. Low-gain pursuit after the early stage of pursuit initiation suggests that the use of extraretinal signals about target motion (e.g., anticipatory prediction) only partially compensates for this deficit. The pattern of low-gain pursuit, impaired pursuit initiation, and intact processing of motion information for catch-up saccades but not pursuit eye movements, was consistent in the schizophrenic patients tested at five time points over a 2-year follow-up period, and implicates the frontal eye fields or their efferent or afferent pathways in the pathophysiology of eye tracking abnormalities in schizophrenia.

Deficits in smooth-pursuit eye movements after muscimol inactivation within the primate's frontal eye field

To evaluate smooth-pursuit (SP) function in the primate frontal eye field (FEF), microinjections of muscimol, a gamma-aminobutyric acid (GABA) agonist, were used to reversibly deactivate physiologically characterized sites in FEF. SP was severely impaired by deactivation at sites in the FEF's smooth eye movement region (FEFsem) located in the fundus and posterior bank of the macaque monkey's arcuate sulcus. These SP deficits were apparent immediately after the muscimol injection and persisted for several hours but recovered by the next day. SP was most drastically and consistently impaired for directions similar to the injected site's elicited smooth eye movement direction or to the optimal SP direction for its neuronal responses. Targets moving in these directions, usually ipsilateral to the injected hemisphere, were tracked primarily with saccades after the muscimol injection, the peak SP velocity being only 10-30% of preinjection velocity. SP in other directions, including contralateral, was less strongly affected. Initial SP acceleration in response to target motion onset was also significantly diminished, generally by approximately the same proportion as peak SP velocity. In contrast, saccades were largely unaffected by muscimol injections in FEFsem; nor was there an immediate effect on SP when control sites in the saccadic region of FEF (FEFsac) were deactivated, although a SP deficit often appeared 30-60 min after FEFsac injections, possibly reflecting diffusion of muscimol into neighboring FEFsem. These reversible SP deficits produced by muscimol inactivation within FEFsem are similar to permanent deficits caused by large aspiration lesions of FEF and indicate that inclusion of FEFsem is the critical factor determining whether FEF lesions impair SP. The severity of the reversible deficits found here indicates how extremely critical FEFsem is for normal highgain SP.

Psychobiological heterogeneity of familial and sporadic schizophrenia

BACKGROUND

Although schizophrenia is presumed to be heterogeneous, there has been limited success distinguishing familial from sporadic cases. We used psychobiological measures to examine heterogeneity, as they may be closer to neurobiology than symptoms. Smooth pursuit eye movement quality (SPEM) and dichotic listening (DL) tests to tones and words were used to assess hemispheric laterality asymmetry.

METHODS

Forty-six research unit patients participated in assessments of family history (FH) and physiological measures. FH was categorized by three exclusive groups: FH-1 patients had a chronic schizophrenia-related psychosis in a first-degree relative, FH-2 had it in second-degree relative, and FH-3 had no family member with a reoccurrence.

RESULTS

Analysis of variance showed a significant group difference for SPEM and DL tones. SPEM was significantly worse in all three schizophrenia groups than for the normal comparison subjects. Among the schizophrenia groups, the nonfamilial group (FH-3) had the worst SPEM quality, FH-2 had intermediate quality, and FH-1 had the best quality. Conversely, only the nonfamilials (FH-3) had normal right hemispheric lateralization for tones, whereas familials did not, and FH-2 again had intermediate values. The lateralization quotient for DL words did not significantly differ among the groups.

CONCLUSIONS

SPEM was affected most in sporadic, not familial schizophrenia, whereas dichotic listening was most affected in familial schizophrenia. This double dissociation supports the utility of the familial/sporadic distinction and suggests that etiological factors in different forms of schizophrenia may impact principally on distinct neurobiological substrates, despite similar patient phenomenology.

Delusional disorder and eye tracking dysfunction: preliminary evidence of biological and clinical heterogeneity

This study used eye tracking movement tests to examine the relationships between frontal field functions and clinical features. Smooth pursuit and voluntary saccadic eye movements were recorded and analyzed in 34 delusional disorder (DD) patients and in 40 normal subjects. The DD group differed significantly from the group of normal subjects in some eye tracking performances. As reported in our previous study (Gambini et al., 1993), DD patients showed abnormalities of voluntary saccadic eye movements. In this study, we also found abnormal smooth pursuit eye movements, indicating a cerebral dysfunction similar to those detected in schizophrenic patients. Moreover, normal smooth pursuit eye movement performance in DD patients was related to remitted depressive mood and probably to benefit from antipsychotic medications, thus supporting the idea of the biological and clinical heterogeneity of DD.

Reduced cognitive functions in a group of whiplash patients with demonstrated disturbances in the posture control system

Past studies examining whether or not cognitive changes actually have occurred as a result of a whiplash (WL) accident have produced varying results. The aim of this study was to identify possible cognitive dysfunctions in a group with persistent problems after whiplash due to injuries to the posture control system and related structures. The whiplash subjects (n = 23) were selected on the basis of their reduced gain in the Smooth Pursuit Neck Torsion test (SPNT). The WL group differed significantly from a closely matched control group on tests of learning and memory, and prolonged divided attention and concentration. After attempting to rule out other ways of interpreting these differences (such as pain, depression, medication, and premorbid health problems), these data were interpreted as lending support to the notion of a causal connection between the disturbed posture control system and some cognitive malfunctions.

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.

Saccades to moving targets in schizophrenia: evidence for normal posterior cortex functioning

People diagnosed with schizophrenia have abnormalities of smooth pursuit eye movement initiation that could be attributable to dysfunction of posterior cortical areas and/or the smooth pursuit regions of frontal cortex. To evaluate whether schizophrenia patients' pursuit initiation performance is most consistent with pre- or postrolandic neuropathology, 25 schizophrenia patients and 25 nonpsychiatric individuals were presented step-ramp stimuli moving either away from or toward the fovea. Schizophrenia and nonpsychiatric individuals did not differ on position error of saccades to moving targets, suggesting that the schizophrenia patients did not have general difficulty with motion perception. During the initial 100 ms of smooth pursuit, however, schizophrenia patients had significantly slower eye velocities than did nonpsychiatric individuals. These results suggest that schizophrenia patients' smooth pursuit abnormalities are not associated with neuropathology of posterior cortical areas.