Biomedical subjects

Deborah L Levy

Publications and source records attributed to Deborah L Levy.

11 recordsLinked to original sources

PubMed2006

Bipolar and schizophrenic patients differ in patterns of visual motion discrimination.

BACKGROUND: Since Kraepelin's early distinction between bipolar disorder and schizophrenia, it has been assumed that these disorders represent two different pathophysiological processes, although they share many clinical symptoms. Previous studies showed that velocity discrimination, a sensitive psychophysiological measure of the visual motion system, is deficient in schizophrenia. Here we examined whether the motion processing impairment found in schizophrenia also occurs in bipolar disorder. METHODS: We compared 16 bipolar patients, 25 schizophrenic patients, and 25 normal controls on a velocity discrimination task. We measured the psychophysical threshold for velocity discrimination and contrast detection (as a control task) in all subjects. RESULTS: Bipolar patients showed normal velocity discrimination thresholds at intermediate velocities, the range in which velocity cues dominate velocity discrimination, and at low velocities. Schizophrenic patients, however, showed elevated velocity discrimination thresholds at intermediate and low velocities. At higher velocities, both bipolar and schizophrenic patients showed elevated thresholds. All subjects showed normal contrast detection thresholds. CONCLUSIONS: Normal velocity discrimination in the intermediate range of velocity indicates unimpaired motion processing in bipolar disorder. The abnormal velocity discrimination of both schizophrenic and bipolar patients at higher velocities may reflect impaired temporal processing rather than impaired motion processing per se. These results suggest that the pathophysiological processes of bipolar disorder and schizophrenia diverge at the stage of visual motion processing, a sensory component mediated primarily in the extrastriate cortex.

Adolescent↗

PubMed2004

Antisaccade performance in biological relatives of schizophrenia patients: a meta-analysis.

Poor performance on the antisaccade (AS) task has been interpreted as a potential indicator of genetic liability that may enhance the power of linkage studies of a multidimensional phenotype for schizophrenia. Every study has replicated the finding of significantly worse performance in schizophrenia patients regardless of which specific antisaccade paradigm was employed. In some studies involving a standard version of the antisaccade task, relatives of schizophrenia patients made an increased number of errors, but in other studies that used this same paradigm, relatives of schizophrenia patients did not differ from controls. In this paper, we report the results of a meta-analysis on studies that used the standard antisaccade paradigm. The meta-analysis shows that those studies that reported large effect sizes and statistically significant differences between relatives of schizophrenia patients and controls used inclusion/exclusion criteria that were not symmetrical between the two groups, whereas those studies that reported small and nonsignificant differences between relatives of schizophrenia patients and controls used symmetrical inclusion/exclusion criteria. Specifically, studies that applied stricter psychopathology exclusion criteria to controls than to relatives of schizophrenia patients had larger effect sizes than studies that applied comparable exclusion criteria to both groups, suggesting that antisaccade performance is compromised by psychopathology in general rather than by schizophrenia per se. Since symmetrical inclusion/exclusion criteria between relatives of schizophrenia patients and controls are essential for a genetic analysis, and those studies that did apply symmetrical criteria had small effect sizes, the available data suggest that poor antisaccade performance is unlikely to be useful in identifying clinically unaffected carriers of genes for schizophrenia.

Genotype↗

PubMed2004

Linkage of eye movement dysfunction to chromosome 6p in schizophrenia: additional evidence.

Establishing the genetics of physiological traits associated with schizophrenia may be an important first step in building a neurobiological bridge between the disease phenotype and its genetic underpinnings. One of the best known of the traits associated with schizophrenia is a disorder of smooth pursuit eye tracking (ETD), which is present in 50-80% of schizophrenia patients. ETD is more than three times more prevalent in the families of a schizophrenia patient than is schizophrenia itself. Arolt et al. [1999] estimated LOD scores for ETD of 2.85 for D6S282 and 3.70 for D6S271, two markers on 6p21.1, as well as obtaining an indication of possible linkage for schizophrenia. Our sample comprised two large families in Denmark. Markers in the region that was implicated by the study of Arolt et al. [1996, 1999] were analyzed as part of a genome scan using the "latent trait (L.T.) model" for the co-transmission of schizophrenia and ETD that we had previously fitted to segregation analysis data from Norway. We obtained a LOD score of 2.05 for D6S1017, a marker within 3 cM of the positive markers obtained by Arolt et al. [1996, 1999]. We regard our results as independent evidence supporting the findings of Arolt et al. [1996, 1999] and also as support for the L.T. model as a way of combining the traits ETD and schizophrenia.

Case-Control Studies↗

PubMed2004

Transitive inference in schizophrenia: impairments in relational memory organization.

Transitive inference (TI) describes a fundamental operation of relational (e.g., explicit) memory organization [Eichenbaum, H., Cohen, N.J., 2001. From Conditioning to Conscious Recollection: Memory Systems of the Brain. Oxford Univ. Press]. Here we investigate TI in schizophrenia (SZ), a neurocognitive disorder associated with explicit but not implicit memory dysfunction. SZ patients and healthy controls were trained on a series of learned discriminations that were hierarchically organized (A>B, B>C, C>D, and D>E). They were then tested on each training pair and two novel "inference" pairs: AE, which can be evaluated without consideration of hierarchical relations, and BD, which can only be evaluated by hierarchical relations. SZ patients and controls successfully learned the training pairs and correctly responded to the nonrelational AE pairs. However, SZ patients were less accurate than controls in responding to the relational BD pairs, consistent with the hypothesis that higher-level memory processes associated with relational memory organization are impaired in SZ. The results are discussed with respect to the relational memory model and candidate neuro-cognitive mechanisms of TI.

Adult↗

PubMed2004

Lexical competition and spoken word identification in schizophrenia.

Schizophrenia (SZ) is a disorder associated with dysfunction of the neural substrate involved in lexical processing, the superior temporal lobe (STL). We examined whether the detrimental effects of lexical competition on word identification are exaggerated in SZ. The results showed that SZ patients were less able than controls to identify words coming from high lexical competitor environments (i.e., high density and high frequency lexical neighborhoods). They did not differ from controls, however, in identifying words coming from low lexical competitor environments (i.e., low density and low frequency lexical neighborhoods). Further, when SZ patients misidentified high competitor words, the erroneously reported words were of a significantly higher frequency than those reported by controls when they misidentified high competitor words (i.e., the HF misidentification bias). Identification accuracy for high competitor words negatively correlated with amount of thought disorder, and the HF misidentification bias positively correlated with the lifetime frequency and severity of auditory hallucinations, the latter of which serving as presumed independent measures of STL dysfunction in SZ.

Adult↗

PubMed2004

Compromised late-stage motion processing in schizophrenia.

BACKGROUND: Visual motion processing is compromised in schizophrenia, as shown in deficient velocity discrimination. Processing of motion signals comprises progressive stages along the geniculate-striate-extrastriate-cortex pathway. Based on neurophysiologic and brain lesion studies, a velocity discrimination deficit can implicate early-stage motion processing if it is contrast-dependent or late-stage motion processing if it is contrast-independent. METHODS: To determine which stage underlies the deficient velocity discrimination in schizophrenia, we examined the effects of visual contrast on velocity discrimination. We measured velocity discrimination thresholds in schizophrenia patients (n = 34) and normal control subjects (n = 17) at both low and high contrasts, using each subject's contrast detection threshold to equate contrast levels. RESULTS: Schizophrenia patients showed poor velocity discrimination that improved little with high contrast, whereas normal control subjects showed enhanced velocity discrimination with increased contrast. CONCLUSIONS: The finding that the velocity discrimination deficit in schizophrenia is independent of contrast modulation implicates the later, rather than the earlier, stages of motion processing, which is mediated in the extrastriate cortex.

Adult↗

PubMed2004

The antisaccade task and neuropsychological tests of prefrontal cortical integrity in schizophrenia: empirical findings and interpretative considerations.

To date, every published study of the antisaccade task has replicated the finding that schizophrenia patients make an increased number of errors. This finding has been interpreted as support for frontal and/or basal ganglia dysfunction in schizophrenia, primarily because neurological patients with pathology in these brain regions also make large numbers of errors on the antisaccade task. Here, we compared the performance of schizophrenia patients and nonpsychiatric controls on an antisaccade task and on two neuropsychological tests, the Wisconsin Card Sorting Test, which is assumed to tap frontal lobe functioning, and the interference condition of the Stroop Test, which is thought to tap dorsolateral prefrontal cortex/anterior cingulate functioning. We examined the pattern of intercorrelations among these tasks. Schizophrenia patients made significantly more errors on the antisaccade task, made more perseverative errors and achieved fewer categories on the Wisconsin Card Sorting Test, and were significantly slower during the interference condition of the Stroop Test than were nonpsychiatric controls. Antisaccade errors were significantly correlated with interference performance on the Stroop in schizophrenia patients and in controls, but were not significantly correlated with the measures of Wisconsin Card Sorting Test performance in either group. The pattern of intercorrelation suggests that these tasks should not be thought of as representing a unitary variable of "frontal cortical integrity". Although aspects of these tasks tap the ability to inhibit prepotent responses, each task is also behaviorally complex. The multifaceted nature of these tasks makes it difficult to isolate which brain regions are part of the network underlying the specific act of inhibiting a prepotent response (for example, the reflexive saccade toward the novel peripheral target) and which regions participate in aspects of task performance that are related to non-inhibitory components (for example, executing an antisaccade). A broadly distributed network is undoubtedly involved in both processes. Parsing the various components of cognitively complex tasks may help to clarify both the specific behaviors that are anomalous and their underlying neural substrates. We also address the complexity of inferring localized brain dysfunction in schizophrenia patients based on seemingly analogous behavioral deficits in neurological populations.

Journal Article↗

PubMed2003

Antisaccade performance is abnormal in schizophrenia patients but not in their biological relatives.

Numerous studies have replicated the finding that schizophrenia patients make an increased number of errors on an antisaccade task. Some studies have reported that relatives of schizophrenia patients also make an increased number of antisaccade errors, a finding that has been interpreted to support the usefulness of compromised antisaccade performance as an index of genetic liability for schizophrenia. We examined performance on an antisaccade task in schizophrenia patients, nonpsychiatric controls, first-degree relatives of schizophrenia patients and first-degree relatives of nonpsychiatric controls. Schizophrenia patients made significantly more errors than did nonpsychiatric controls, but relatives of schizophrenia patients did not differ from relatives of controls or from all controls. Increased antisaccade errors on the standard version of the antisaccade task are associated with schizophrenia, but do not seem to be a co-familial trait for schizophrenia.

Adult↗

PubMed2003

Effects of typical, atypical, and no antipsychotic drugs on visual contrast detection in schizophrenia.

OBJECTIVE: Visual contrast detection has been reported in some studies to be normal in schizophrenia patients, but in other studies impairments have been reported. Because contrast detection in the visual processing system is mediated by dopamine, and because the pharmacotherapy of schizophrenia involves blocking dopamine postsynaptic receptor sites, the authors investigated the effects of dopamine-blocking antipsychotic drugs on visual contrast detection in schizophrenia. METHOD: Visual contrast detection thresholds were measured in healthy subjects and schizophrenia patients receiving typical and atypical antipsychotic drugs; a two-alternative, forced-choice psychophysical method was used. Also included were six patients receiving no antipsychotic treatment as well as clinically unaffected first-degree relatives of the schizophrenia patients. RESULTS: Patients receiving atypical antipsychotic drugs showed unimpaired visual contrast detection, those given typical antipsychotic drugs exhibited higher visual contrast detection thresholds, and the unmedicated schizophrenic patients showed visual contrast detection thresholds significantly below those of healthy subjects. CONCLUSIONS: Dopamine modulation via D(2) receptor blockade affects sensory processes in schizophrenia, shifting visual contrast detection from hypersensitivity in the unmedicated state to normal and even to hyposensitive levels. Thus, antipsychotic drug treatment may account for the inconsistent reports concerning visual contrast detection in schizophrenia.

Adult↗

PubMed2002

Idiom processing in schizophrenia: literal implausibility saves the day for idiom priming.

Schizophrenia patients have difficulty processing nonliteral forms of discourse such as idiomatic expressions. We hypothesized that schizophrenia patients would show impaired idiom processing for literally plausible idioms (e.g., kick the bucket) but not for literally implausible idioms (e.g., be on cloud nine). Thirty-two patients and 36 controls listened to sentences containing literally plausible and implausible idioms and made lexical decisions about idiom-related or literal-related targets. Schizophrenia patients showed reduced priming for literally plausible idioms but intact priming for literally implausible idioms compared with controls. Both groups showed evidence of literal word priming. These results are consistent with the notion that schizophrenia patients make normal use of context under conditions that minimize the need for controlled processing.

Adult↗

PubMed2002

Spatial and object working memory impairments in schizophrenia patients: a Bayesian item-response theory analysis.

This study reports evidence that schizophrenia patients are significantly impaired in both spatial and object (shape) working memory. A 3-s delay between exposure and recall of targets was used and Bayesian item-response theory was applied to compensate for the tasks' differential difficulty while simultaneously taking account of missing data from participant attrition. Weaker evidence was found that in schizophrenia both domains are equally impaired on average, that spatial and object working memory appear to be more highly correlated with each other in the schizophrenia population than in the normal population, and that schizophrenia patients show greater variability in spatial than object working memory performance.

Adult↗