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Biomedical subjects

B A Clementz

Publications and source records attributed to B A Clementz.

At least 37 records · Page 2Linked to original sources
PubMed1997

The effect of fixation condition manipulations on antisaccade performance in schizophrenia: studies of diagnostic specificity.

This series of studies evaluated (1) hypotheses that poor antisaccade performance is attributable to confounding variables (e.g., visual attention deficits, incomplete understanding of task demands) and (2) the specificity of poor antisaccade performance to schizophrenia. In addition to self-correcting errors before being cued to do so, schizophrenia patients also showed the expected saccadic reaction time changes to fixation condition manipulations: decreased latencies for gap and increased latencies for overlap trials. These data suggest that schizophrenia patients are adequately engaged in and understand the antisaccade task. Schizophrenia patients made fewer correct antisaccade responses than other psychiatric patients (obsessive-compulsive and bipolar disorder) and normal subjects. The first-degree relatives of schizophrenia patients also generated a decreased proportion of correct antisaccade responses compared with normal subjects. For schizophrenia patients who performed below the range of normal subjects, 26% of their relatives also performed below the normal range. Conversely, patients who performed normally did not have a single poor-performing relative. These data suggest that increased antisaccade error rates may index a liability for schizophrenia within a subset of families.

Adult↗
PubMed1997

Characteristics of open- and closed-loop smooth pursuit responses among obsessive-compulsive disorder, schizophrenia, and nonpsychiatric individuals.

Twenty obsessive-compulsive disorder patients and comparison samples of 20 schizophrenia and 20 nonpsychiatric individuals were presented with (a) a step-ramp task designed to measure smooth pursuit initiation and (b) a regular ramp task designed to measure steady-state tracking performance. Obsessive-compulsive disorder and non-psychiatric individuals had statistically similar pursuit reaction time and average eye accelerations during the open-loop interval. They also had similar closed-loop performance. Schizophrenia patients, however, had delayed pursuit reaction times and reduced eye acceleration during the last 60 ms of the open-loop interval. These findings suggest that brain regions supporting smooth pursuit performance are unimpaired among obsessive-compulsive disorder patients. Furthermore, the deficits found in the schizophrenia patients replicate and extend the results of previous smooth pursuit studies.

Adult↗
PubMed1996

The ability to produce express saccades as a function of gap interval among schizophrenia patients.

The ability to produce "express saccades" is associated with adequate functioning of saccadic burst cells in the superior colliculus. Saccadic burst cells appear to be under the inhibitory control of both the collicular and the dorsolateral frontal fixation systems. Twenty schizophrenia patients and 20 nonpsychiatric subjects were presented a saccade task that included five different gap intervals (0, 100, 200, 300, and 400 ms) between fixation point offset and peripheral target onset (at +/-4 degrees). All subjects generated the highest frequency of express saccades in trials with a gap interval of 200 ms. Schizophrenia patients had an increased frequency of express saccades across gap intervals, especially for targets presented in the right visual field. The groups did not differ in the percentages of anticipatory saccades or saccadic amplitudes. These results suggest that schizophrenia patients' saccadic burst cells in the superior colliculus are functioning adequately, but may be consistent with dysfunction of dorsolateral frontal cortex and/or its interconnecting subcortical circuitry.

Humans↗
PubMed1996

Timing and amplitude of saccades during predictive saccadic tracking in schizophrenia.

Schizophrenia patients have ocular motor abnormalities. It has been hypothesized that these abnormalities are associated with frontal eye field pathology. If so, schizophrenia patients should have difficulties decreasing saccadic reaction times in response to predictably moving targets. To evaluate the frontal eye field hypothesis, 25 schizophrenic and 26 nonpsychiatric subjects completed predictive saccadic tracking tasks. The groups demonstrated equivalent decreases in saccadic reaction times over consecutive trials. Schizophrenia patients, however, had faster reaction times and shorter amplitude saccades than nonpsychiatric subjects. The shorter amplitude saccades were made regardless of reaction time, perhaps an antipsychotic medication effect. The reaction time results are unlikely to be an effect of treatment with antipsychotic medication and are inconsistent with the hypothesis that schizophrenia patients have frontal eye field pathology.

Adult↗
PubMed1996

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.

Adult↗
PubMed1996

Ocular-motor delayed-response task performance among schizophrenia patients.

Twenty schizophrenia patients and 20 nonpsychiatric subjects were presented with an ocular-motor delayed-response task. Schizophrenia patients generated fewer memory-guided saccades which were characterized by increased latency and decreased gain relative to the nonpsychiatric subjects. In addition, the patients generated an increased frequency of reflexive (made to the initial cue) and anticipatory (made during the delay period) errors. The results are most consistent with hypothesized pathology of prefrontal cortex among schizophrenia patients.

Adult↗
PubMed1996

Ocular motor responses to unpredictable and predictable smooth pursuit stimuli among patients with obsessive-compulsive disorder.

This study was conducted to evaluate the smooth pursuit system functioning of patients with obsessive-compulsive disorder (OCD). For Study 1, 12 subjects with OCD and 12 nonpsychiatric subjects were administered 9-deg-per-sec ramp stimuli to elicit smooth pursuit eye movements. Consistent with a previous report, patients with OCD did not significantly differ from nonpsychiatric subjects on pursuit gain, or frequency of corrective and intrusive saccades. Patients with OCD, however, had smaller catch-up saccades during smooth pursuit than nonpsychiatric subjects. For Study 2, 12 subjects with OCD and 12 nonpsychiatric subjects were administered 2 different triangle wave stimuli with target velocities of 12 (0.2 Hz) deg per sec and 24 (0.4 Hz) deg per sec. Subjects with OCD and nonpsychiatric subjects did not significantly differ on any variable in the slow target velocity condition. When following 24-deg-per-sec targets, however, patients with OCD had significantly lower pursuit gain than the nonpsychiatric subjects. Results from Study 1 and 2 are consistent with the hypothesis that patients with OCD have a modest smooth pursuit deficit that is elicited only while following faster velocity targets.

Adult↗
PubMed1995

Abnormality of smooth pursuit eye movement initiation: specificity to the schizophrenia spectrum?

Schizophrenia patients have a deficiency of smooth pursuit eye movement initiation. We addressed whether this deficit is specifically related to a predisposition for schizophrenia. Thirty-two relatives of schizophrenia patients, eight schizotypals, 13 psychiatric comparison, and 33 nonpsychiatric subjects were assessed on smooth pursuit initiation. The nonpsychiatric subjects had significantly higher eye accelerations than did subjects in the other three groups, who did not significantly differ. The relatives were subdivided into three groups: (a) those with a schizophrenia spectrum disorder (n = 4) performed similarly to the schizotypals; (b) those with a major depression history (n = 7) were similar to the psychiatric comparison subjects; and (c) those with no psychiatric history differed from the nonpsychiatric subjects only on 30 degrees/s targets. There was also a significant relationship between offspring and parent eye accelerations to 30 degrees/s targets (r = .476). These results suggest that pursuit initiation deficits may be associated with a nonspecific, genetically transmitted neurological abnormality among schizophrenia spectrum disorder subjects.

Adult↗
PubMed1995

Internal consistency reliability of resting EEG power spectra in schizophrenic and normal subjects.

The reliability of resting electroencephalogram (EEG) power spectra was assessed for 49 normal and 44 schizophrenic subjects. We specifically examined internal consistency reliability to determine how much EEG data are necessary to ensure small measurement error. Twenty-one 8-s epochs of resting EEG were collected from each subject from site Cz. Epochs containing artifacts or blinks were eliminated. Power was computed in the bands delta (0.125-3 Hz), theta (3.125-8 Hz), alpha (8.125-13 Hz), beta1 (13.125-20 Hz) beta 2 (20.125-25 Hz) and beta 3 (25.125-30 Hz). Internal consistency was computed using coefficient alpha (Cronbach, 1951). Results for both groups indicated that eight artifact-free epochs of data were sufficient to give a coefficient alpha value of around .9. The schizophrenic and normal groups did not differ with respect to coefficient alpha. The proportion of artifacts in the data from the schizophrenics indicated that to obtain eight artifact-free epochs from members of each group, 40% more data would be required from the schizophrenics.

Adult↗
PubMed1994

Eye tracking dysfunction in schizophrenia: characterization of component eye movement abnormalities, diagnostic specificity, and the role of attention.

To characterize oculomotor components and diagnostic specificity of eye tracking abnormalities in schizophrenia, we examined a large consecutively admitted series of psychotic patients and matched controls. The most common abnormality in schizophrenic patients was low gain (slow) pursuit eye movements (47% of cases). Pursuit and saccadic eye movement abnormalities were no more severe in schizophrenic Ss than in those with affective psychoses, except that high rates of catch-up saccades were unique to schizophrenic Ss (17% of cases). These findings indicate that impaired pursuit eye movements are a major cause of eye tracking impairments in schizophrenia, that tracking dysfunctions commonly occur in affective psychoses, and that markedly high rates of catch-up saccades during eye tracking may be specific to schizophrenia.

Adult↗
PubMed1994

Resting EEG in first-episode and chronic schizophrenia.

We examined the frequency characteristics of the electroencephalogram (EEG) in 102 schizophrenic patients (44 first-episode and 58 chronic patients) and 102 normal comparison subjects. EEGs of schizophrenic patients had more delta (1-3 Hz) and theta (3.125-8 Hz) activity and less alpha (8.125-13 Hz) activity than normal comparison subjects. There were no significant differences in the EEG frequency composition of first-episode and chronic patients. Because first-episode and chronic patients were characterized by different disorder durations and treatment histories, the similarity of their EEGs suggests that EEG abnormalities are stable characteristics of schizophrenia and are not treatment-related epiphenomena. A principal components analysis of EEG power bands identified an augmented low frequency-diminished alpha component and a beta component. Schizophrenic patients had significantly higher scores on the augmented low frequency-diminished alpha component than did normal comparison subjects, and there was no significant group difference in scores on the beta component. The findings of this investigation suggest that EEG abnormalities in schizophrenia reflect aspects of brain dysfunction.

Acute Disease↗
PubMed1994

Smooth pursuit in schizophrenia: abnormalities of open- and closed-loop responses.

A sample of 29 schizophrenia patients and 27 nonpsychiatric subjects were tested on measures of open- and closed-loop smooth-pursuit performance. Rashbass step-ramps were used to measure pursuit latency and open-loop gain. Regular ramps were used to calculate frequency and amplitude of both catch-up saccades and square-wave jerks, frequency of anticipatory saccades, and steady-state gain. Schizophrenia patients demonstrated lower open-loop gain than did nonpsychiatric subjects, an effect that was accentuated at faster target velocities. They also showed reduced steady-state gain, but only to 30 degrees/s right-moving targets. There was no evidence of saccadic abnormalities during smooth pursuit among the schizophrenia patients. These patients generated fewer square-wave jerks than did nonpsychiatric subjects for 10 degrees /s left-moving targets. These results suggest an abnormality of smooth-pursuit initiation among patients with schizophrenia.

Adult↗
PubMed1994

Resting EEG in first-episode schizophrenia patients, bipolar psychosis patients, and their first-degree relatives.

We evaluated the resting electroencephalogram (EEG) of 50 first-episode schizophrenia patients and 55 of their relatives, 31 first-episode bipolar patients and 35 of their relatives, and 113 nonpsychiatric subjects and 42 of their relatives. The frequency characteristics of the EEG showed moderate stability for a subgroup of these subjects (n = 106) who were tested twice, approximately 9 months apart. Both the schizophrenia and bipolar patients showed a generalized pattern of increased delta and theta and decreased alpha activity. The bipolar patients demonstrated additional right hemisphere activity that was not present among the schizophrenia patients and nonpsychiatric subjects, a finding consistent with hypotheses concerning nondominant hemisphere involvement in the regulation of elated mood. The schizophrenia patients' female relatives and/or relatives with affective disorders and the bipolar patients had significantly reduced peak alpha frequencies. This finding may be related to reduced information processing capacity among these subjects.

Adolescent↗
PubMed1994

Saccadic system functioning among schizophrenia patients and their first-degree biological relatives.

In Study 1, 30 schizophrenia Ss and 27 nonpsychiatric comparison Ss were presented with a fixation task, a visually guided reflexive saccade (prosaccade) task, a predictive tracking task (0.4-Hz square wave), and an antisaccade task. The 2 groups did not differ on either the fixation or prosaccade tasks. Schizophrenia Ss had an increased number of errors on the antisaccade task and had decreased rightward visually guided saccade amplitudes during the predictive tracking task. In Study 2, 13 psychiatric comparison Ss and 32 first-degree biological relatives of the schizophrenia Ss were compared with the schizophrenia Ss and a larger and older sample of nonpsychiatric Ss (n = 33) on the predictive tracking and antisaccade tasks. The groups did not differ on predictive saccadic tracking. The schizophrenia Ss and their first-degree biological relatives made more errors on the antisaccade task than both the nonpsychiatric and psychiatric comparison groups (who did not significantly differ). Results are consistent with the notion that dysfunction of dorsolateral prefrontal cortex, caudate nucleus, or both is related to liability for schizophrenia.

Adult↗
PubMed1994

Handedness in first-episode psychotic patients and their first-degree biological relatives.

We evaluated the handedness of 58 schizophrenia patients and 54 of their relatives, 23 patients with major depression with psychosis and 24 of their relatives, 36 patients with bipolar psychosis and 33 of their relatives, and 119 nonpsychiatric subjects and 42 of their relatives. Computerized tomography measures were also available for a subset of the psychotic patients. The schizophrenia patients were significantly more left-handed than any of the other groups, and increased sinistrality was also associated with larger lateral ventricle to brain area ratios. The relatives of the schizophrenia patients did not significantly differ on handedness from either the relatives of the affective psychosis patients or the nonpsychiatric subjects. Our findings do not support the notion that left-handedness in schizophrenia is genetically influenced. More research with larger family member data sets is warranted to further explore this possibility.

Adolescent↗
PubMed1993

Mixture analysis of pursuit eye-tracking dysfunction in schizophrenia.

Results of two recent studies suggest that a distinct subgroup of schizophrenic patients and their relatives have particularly deviant eye tracking. Such heterogeneity could be of considerable importance, as it may indicate significant pathophysiologic or etiologic heterogeneity in schizophrenia. An analysis of 101 consecutive-admission schizophrenic patients confirmed the existence of two distinct subgroups of patients with higher and lower levels of spatial [root mean square (RMS)] eye-tracking error. However, there was no heterogeneity in the disturbance of pursuit eye movements. Anticipatory saccades, which by definition add very large amounts of spatial tracking error, were more frequent in the "high" RMS error group. Rates of anticipatory saccades were similar in the "low" RMS error patient group and normal controls, and there was no heterogeneity in the expression of anticipatory saccades. Apparent heterogeneity in global indices of eye-tracking impairment in schizophrenia appears to be a measurement artifact reflecting the powerful influence of anticipatory saccades on global performance indices, rather than true heterogeneity in the expression of any specific eye movement abnormality.

Adolescent↗