Computed tomography and pattern reversal visual evoked potentials in chronic schizophrenic patients

Frequency-domain analysis of transient visual evoked potentials in schizophrenia

PURPOSE

Frequency-domain measures were applied to characterize neural deficits in individuals with schizophrenia using transient visual evoked potentials (tVEP). These measures were compared with conventional time-domain measures to elucidate underlying neurophysiological mechanisms and examine the value of frequency analysis.

METHODS

Four frequency bands of activity identified in previous work were explored with respect to magnitude (spectral power), timing (phase), a combined measure, magnitude-squared coherence (MSC), and compared to amplitudes and times of prominent deflections in the response.

RESULTS

Band 2 power/MSC (14-28 Hz) captured the major deflections in the waveform and its power predicted N75-P100 amplitude for patients and controls. Band 3 power/MSC (30-40 Hz) correlated highly with the earliest deflection (P60-N75), reflecting input to primary visual cortex (V1) and produced the largest magnitude effect. Phase of the 24th harmonic component predicted P100 peak time for patients and controls and yielded the largest group difference. Cluster analyses including time- and frequency-domain measures identified subgroups of patients with differential neurophysiological effects. A small but significant difference in visual acuity was found between groups that appears to be neurally based: Acuity (range 0.63-1.6) was not correlated with any tVEP measures in controls nor with input timing to V1 (P60 peak time) in patients, but was correlated with later tVEP measures in patients. All but two of the patients were on antipsychotic medication: Medication level (chlorpromazine equivalents) was correlated negatively with tVEP time measures and positively with certain magnitude measures yielding responses similar to controls at high levels.

CONCLUSIONS

Overall, frequency-domain measures were shown to be objective and recommended as an alternative to conventional, subjective time-domain measures for analyzing tVEPs and in distinguishing between groups (patients vs. controls and patient subgroups). The findings implicated a loss of excitatory input to V1 in schizophrenia. Acuity as measured in the current study reflected disease status, and medication level was associated with improved tVEP responses. These novel tVEP techniques may be useful in revealing neurophysiological processes affected in schizophrenia and as a clinical tool.

Visual sensory processing deficits in Schizophrenia and their relationship to disease state

CONTEXT

Visual Evoked Potential (VEP) abnormalities have been a fairly consistent finding in patients with schizophrenia, and it has been suggested that electrophysiological markers of early sensory processing may be useful as trait markers for the illness, and for development as potential diagnostic measures.

OBJECTIVE

Clear amplitude reductions in the occipital P1 component of the VEP (approximately 100 ms), have been repeatedly demonstrated in patients with schizophrenia. Here, we investigated whether the extent of this deficit was related to age, clinical symptoms, medication status and length of illness, in a large cohort of ethnically homogenous patients.

DESIGN, SETTING AND PARTICIPANTS

VEP responses to simple isolated-check stimuli were examined in 52 DSM-IV diagnosed patients with schizophrenia, and compared with responses from 26 healthy age-matched control subjects. Using high-density electrical scalp recordings, we assessed the integrity of the visual P1 component across the two groups. This study was conducted at St.Vincent's Psychiatric Hospital in Fairview, Dublin, Ireland.

RESULTS

Substantially reduced P1 amplitude was demonstrated in the patient group compared to controls. The deficit was not linked to age, length of illness or medication status. A small positive correlation, accounting for about 11% of the variance, was found between P1 amplitude and clinical symptoms scales (BPRS and SANS). In addition, we found that a slightly later (~110 ms) fronto-central component was relatively increased in the patient group, and was inversely correlated with the occipital P1 amplitude in the patients, but not in the healthy control subjects.

CONCLUSIONS

Our findings clearly demonstrate a deficit in early visual processing in patients with schizophrenia (with a large effect size; Cohen's d = 0.7) that is unrelated to chronicity. The results are consistent with recent findings showing that the P1 deficit is endophenotypic of the disorder and related to genetic risk factors rather than the disease process itself.

A new dimension of sensory dysfunction: stereopsis deficits in schizophrenia

BACKGROUND

Schizophrenia is a neurocognitive disorder with a wide range of cognitive and sensory impairments. Early visual processing has been shown to be especially impaired. This article investigates the integrity of binocular depth perception (stereopsis) in schizophrenia.

METHODS

Seventeen schizophrenia patients and 19 healthy control subjects were compared on the Graded Circles Stereo Test. Results of stereoacuity were compared between patients and control subjects using t test.

RESULTS

Schizophrenia patients demonstrated significantly (p = .006) reduced stereoacuity (mean = 142 arcseconds) versus control subjects (mean = 55 arcseconds). At the normative level for adults, patients performed below chance.

CONCLUSIONS

These findings demonstrate an impairment of binocular depth perception and further confirm deficits of early visual processing in schizophrenia. Findings are discussed in context of magnocellular/dorsal stream processing with implications for visual processing and cognitive deficits.

Impairments in generation of early-stage transient visual evoked potentials to magno- and parvocellular-selective stimuli in schizophrenia

OBJECTIVE

Patients with schizophrenia demonstrate significant impairments of early visual processing, potentially implicating dysfunction of the magnocellular visual pathway. The present study evaluates transient visual evoked potential (tVEP) responses to stimuli biased toward the magnocellular (M) or parvocellular (P) systems in patients with schizophrenia vs. normal volunteers first to evaluate relative contributions of M and P systems to specific tVEP components in schizophrenia and, second, to evaluate integrity of early M and P processing in schizophrenia.

METHODS

Seventy-four patients with schizophrenia and schizoaffective disorder were compared with 59 control subjects using separate stimuli to assess the tVEP response to M, P and mixed M/P conditions. Stimuli were biased toward M vs. P processing by manipulation of chromatic and achromatic contrast. C1, P1, N1 and P2 components were compared between patients and controls. All subjects showed 20/32 vision or better.

RESULTS

Waveforms were obtained to low contrast (M), chromatic contrast (P) and high contrast (mixed M/P) stimuli in both patients and controls. C1 was present to P and mixed M/P stimuli. Patients showed a significant reduction in amplitude and an increase in latency of the C1 component. P1 was elicited primarily by M and mixed M/P stimuli, whereas N1 was elicited primarily by P and mixed M/P stimuli. Patients showed reductions in both P1 and N1 amplitudes across conditions. However, only reductions in P1 amplitude survived covariation for between group differences in visual acuity. Further, P1 amplitude reductions in the M condition correlated with a proxy measure of global outcome.

CONCLUSIONS

M- and P-selective stimuli elicit differential components of the tVEP. Patients with schizophrenia show significant reductions in response even to simple visual stimuli. Deficits, particularly within the M system, may correlate significantly with global outcome and level of community functioning.

SIGNIFICANCE

Whereas deficits in high-order cognitive processing have been extensively documented in schizophrenia, integrity of early-stage sensory processing has been studied to a lesser degree. The present findings suggest that deficits in early-stage visual processing are significantly related to overall clinical outcome in schizophrenia. Further, between-group differences in visual acuity may influence VEP results, even for subjects with 'normal' vision (20/32 or better).

Quantitative electrophysiological characteristics and subtyping of schizophrenia

Quantitative descriptors of resting electroencephalogram (EEG) (QEEG) and event-related potentials (QERP) to visual and auditory stimuli were obtained from normal subjects and 94 chronic schizophrenic patients on medication, 25 chronic schizophrenics off medication, and 15 schizophrenics with no history of medication. These schizophrenic groups showed a high incidence of neurometric features that were significantly deviant from normative values. Multivariate discriminant analysis using these features successfully separated the schizophrenic patients from normals with high accuracy in independent replication. The data from the medicated group were subjected to cluster analysis. Newly developed algorithms were used for objective selection of the most effective set of variables for clustering and the optimum number of clusters to be sought. Five clusters were obtained, containing roughly equivalent proportions of the sample with markedly different QEEG profiles. The whole sample was then classified into these clusters. Each cluster contained patients both on and off medication, but patients who had never been medicated were classified into only three of these clusters. No significant clinical or demographic differences were found between members of the five clusters; however, clear differences in QERP profiles were seen. These results are described in detail and possible physiological and pharmacological implications are discussed.

Magnetic resonance imaging in schizophrenia: relationship with clinical measures

Relationships were examined between clinical features of schizophrenia and cerebrospinal fluid (CSF) volume in brain obtained by magnetic resonance imaging (MRI) in a sample of 59 patients. The volumes of the cerebral hemispheres and CSF were measured with a computer program designed to separate reliably neural tissue from CSF. The CSF to cranial volume ratios were related to history, symptom profile and outcome functioning. Earlier age of onset was associated with higher sulcal CSF ratio, r = -0.40. The anatomic measures were unrelated to symptom severity. However, patient subtypes differed in the laterality of measures. Higher left hemispheric ratios were seen in patients with severe negative symptoms, and left predominance of ventricular relative to sulcal ratios was associated with the presence of hallucinations and delusions. The results suggest that while higher CSF is related to earlier age of onset, the clinical symptoms are more related to its lateralization. This is consistent with the hypothesis that schizophrenia is a lateralized brain disease.

The short-term course of familial and nonfamilial schizophrenic-spectrum disorder

This study was designed to determine if familial and nonfamilial forms of schizophrenia show a different short-term illness course. Sixteen familial and 22 nonfamilial schizophrenics were evaluated on three occasions at regular 6-month intervals over an 18-month period. The familial and nonfamilial groups were compared for differences in positive and negative symptoms of psychosis and interpersonal and occupational role functioning. The data show that familial schizophrenics experience significantly higher levels of positive symptoms of psychosis and significantly worse occupational role functioning. Significant time by family history interactions indicates that the negative symptoms and interpersonal role functioning of the familial schizophrenics changed over the course of follow-up while remaining stable over time in the nonfamilial group. These data provide preliminary support for the hypothesis that familial schizophrenics show a higher degree of impairment during follow-up than nonfamilial schizophrenics.

Family history and brain morphology in schizophrenia: an MRI study

This study examined neuroanatomical differences between male schizophrenic patients with a family history of psychosis (n = 16) and those without such a history (n = 15). Intracranial area, cerebral area, ventricular size, and cortical atrophy were assessed using magnetic resonance imaging (MRI). Third ventricular enlargement was more prevalent in patients than controls (n = 15). Familial and nonfamilial patients differed significantly. Reduced cranial and cerebral areas without ventricular enlargement characterized familial patients, whereas nonfamilial patients showed marked lateral ventricular enlargement without a reduction in cranial/cerebral size.

Visual evoked potential correlates of positive/negative symptoms in schizophrenia

Previous studies of schizophrenic patients have found evoked potential (EP) correlates of clinical symptomatology, including EP differences between subtypes of schizophrenia. In the current study, 14 medicated male schizophrenics underwent flash visual evoked potentials (VEP) and were clinically rated for positive and negative symptoms. We tested the hypothesis that positive symptoms would be associated with VEP latency reduction and negative symptoms with latency prolongation. Patients were divided into predominantly positive symptom and predominantly negative symptom groups using a combination of positive and negative symptom ratings. Patients with predominantly positive symptoms exhibited reduced latencies when compared with predominantly negative symptom patients. Similarly, significant negative correlations between positive symptom ratings and P200 latency variables were found. Correlations between negative symptom measures and P200 latencies (in the opposite direction) were also noted, but were less significant. These relationships persisted when confounders were statistically controlled for. The results are consistent with previous findings of evoked potential correlates of clinical symptomatology, especially those finding EP latency correlates of psychosis severity and affective blunting. The findings are discussed in relationship to concepts relevant to psychosis, including arousal, sensory gating, and the dopamine hypothesis.

Choice of comparison group and findings of computerised tomography in schizophrenia

The literature indicates that whether or not schizophrenic patients are reported to have significant lateral ventricular enlargement depends on control, and not schizophrenic-group values. This discrepancy does not result from differences in age, the ratio of males to females, the number of control subjects used in each study, or whether control groups are comprised of normal subjects or medical patients. However, medical-patient controls tend to have smaller ventricles than do normal individuals. Thus, we assessed lateral- and third-ventricle size and the degree of cortical atrophy in 30 normal volunteers, 30 medical patients, and 30 chronic schizophrenic patients. The use of a medical control group seemed to result in underestimates of ventricle and sulcal size in the normal population and, therefore, overestimates of these values in schizophrenic groups.

Tomografia cerebral computadorizada e esquizofrenia: revisão crítica da literatura

Vários estudos sobre tomografia cerebral computadorizada (CT) relatam alteração da estrutura cerebral em esquizofrenia. A grande variação da prevalência e da localização das anomalias pode estar relacionada à heterogenidade da amostra estudada, à escolha das medidas de CT ou ao uso de diferentes critérios diagnósticos. Apesar de alguns achados contraditórios, parece estabelecido que um subgrupo de pacientes esquizofrênicos apresenta atrofia cerebral discreta ou moderada; esse subgrupo se caracterizaria por apresentar cronicidade da doença, pior resposta ao tratamento neuroléptico e pela presença de outros sinais de disfunção cerebral difusa, como distúrbios neuropsicológicos, anormalidades no EEG e «soft signs» neurológicos. Sinais de atrofia na CT foram observados em pacientes esquizofrênicos jovens, no primeiro surto psicótico, indicando que o desenvolvimento das anomalias estruturais não é conseqüência do tratamento ou da cronicidade da doença. Nos diferentes estudos, pacientes com atrofia apresentaram menor carga genética (história familiar para a esquizofrenia) e se observou com maior freqüência história de complicações na gestação, no parto e trauma craniano nos primeiros anos do desenvolvimento. Em face da possibilidade de que doentes esquizofrênicos com atrofia cerebral formem um subgrupo homogêneo quanto à clínica e à etiopatologia da doença, é importante identificar e estudar as alterações da CT e caracterizar esse subgrupo de pacientes.

Ventriculomegaly in schizophrenia: is the choice of controls important?

The issue of adequate controls for the study of ventriculomegaly in schizophrenia has been explored initially by Andreasen et al. (1982), who proposed that healthy volunteers, a group with presumably smaller ventricles than medical controls, be considered the optimal comparison group in this area of research. Recently, Smith and Iacono (1986) suggested that group differences may appear to be greater when controls who are patients are used, as a result of the systematic exclusion of medical patients with large though normal ventricles. We conducted a meta-analysis of 37 studies of lateral ventriculomegaly in schizophrenia to clarify this issue. The results indicate that the average effect size in studies with healthy controls does not differ significantly from that obtained in studies employing medical, neurological, or psychiatric (nonpsychotic) controls. Thus, any group without gross neurological damage or severe psychopathology may be used for establishing ventriculomegaly in schizophrenia.