Asymmetrical effects of neuroleptics on psychotic patients' performance of a tactile discrimination task

Visual field processing in paranoid and non-paranoid schizophrenics

The hypothesis that paranoid and non-paranoid schizophrenics are differentially associated with unilateral hemisphere dysfunction was tested on 12 paranoid and 12 non-paranoid schizophrenics, as well as on 24 affective patients and 24 normal controls. The subjects were presented for 150 ms with series of digit-pairs and open rings to the left or right visual fields. Overall recognition of digits and localization of gaps in the rings were better for the right than for the left visual field. However, performance of the paranoid and non-paranoid schizophrenics was relatively poorer in response to the right and left visual field stimuli, respectively. Since these data do not correspond to the findings obtained in the auditory modality, they were interpreted as indicating modality-specific associations of paranoid schizophrenia with left hemisphere dysfunction, and of non-paranoid schizophrenia with right hemisphere dysfunction.

Abnormal lateralization in schizophrenia: empirical evidence for an integrated model

Cerebral deficits in schizophrenia have been associated either with left hemisphere dysfunction, or with impairment in interhemispheric transfer. To test the relative efficacy of the two hypotheses, 63 right-handed subjects (24 paranoid schizophrenics, 21 nonparanoid schizophrenics, and 18 normal controls) were given two auditory lateral tasks: identification of dichotically delivered tonal sequences and digit sets. As the data analyses showed, more correct responses were given by the normal controls than by the patients, and by males than by females. Generally, report (especially from the ear reported second) was better from the right than from the left ear. This right ear advantage (which was more consistent in males than in females) was abnormally large for the paranoid schizophrenics who showed on both tests, relative to normal subjects, a slight decrement in right ear report and a significant decrement in left ear report. The data were interpreted as indicating left hemisphere dysfunction and structural callosal damage in paranoid schizophrenics.

Asymmetrical olfactory acuity and neuroleptic treatment in schizophrenia

Uni-rhinal olfactory acuity in schizophrenia was investigated in two experiments. The first assessed the presence of a predicted atypical asymmetry of nostril laterality and the second assessed the effect of antipsychotic treatment on the asymmetry. Although olfactory identification impairment has been well documented in schizophrenia, olfactory acuity has been neglected. This may be an oversight as cerebral structures of the mesial temporal lobe important to olfactory perception have often been implicated in the pathophysiology of schizophrenia and it is thus reasonable to postulate a primary impairment of olfactory acuity in schizophrenia. In addition, unmedicated patients with schizophrenia have exhibited asymmetrical laterality favouring the right over the left hemisphere in studies of visual, haptic, and auditory perception, and the few published prospective treatment studies have suggested a reversal of this asymmetry with first generation neuroleptic treatments. In experiment 1 a generalization of the perceptual asymmetry to olfactory acuity was examined by measurement of n-butanol olfactory thresholds with the Connecticut Chemosensory Perception Exam (CCPE) in an unmedicated sample of 17 patients with schizophrenia and 17 age, gender, and handedness matched normal controls. The patient sample showed an asymmetrical impairment of the left nostril that was not apparent in the normal control sample. In experiment 2, the CCPE was administered to a new sample of 10 patients with schizophrenia before and after neuroleptic treatment. The asymmetry observed in experiment 1 was replicated, and the relative advantage of the right nostril shifted to a relative advantage of the left nostril over the course of 8weeks of treatment. Results are discussed in relation to cerebral aspects of schizophrenia and potential implications to cognitive change from treatment.

Neuropsychological performance in chronic schizophrenia in response to neuroleptic dose reduction

The effect of 80%-90% neuroleptic dose reductions on neuropsychological function in schizophrenic and schizoaffective patients was examined in a prospective study. A neuropsychological battery was administered in the week prior to neuroleptic reduction followed by retesting at least 6 weeks postreduction. Patients were retested only if they did not relapse after reduction. The design allowed neuropsychological changes due to neuroleptic medications to be assessed independently of general clinical change. Neuropsychological performance was generally stable and unchanging. However, there was a trend toward significant improvement on a dichotic digits task based in improvement in left ear accuracy. Negative symptoms diminished after reduction. Compared with a normal control group, schizophrenics' initial laterality index showed a significantly exaggerated right ear advantage (REA); after reduction, the REA was no longer different from controls. The findings indicate that neuropsychological changes in a small sample of older nonrelapsing chronic schizophrenics are modest. The data suggest that neuroleptics may impair right hemisphere functions in some patients.

Laterality in schizophrenia. A reaction time study

A laterality study in schizophrenia was carried out by measuring reaction time (RT) in a baseline condition and while subjects were engaged in a concurrent task. In the baseline condition, a clinical measure of psychoticism was associated with differential slowing with the right hand in schizophrenic dextrals but not in a control group of affective dextrals. The concurrent task suppressed the effect of psychoticism on RT performance. The results suggest that left-hemisphere deficits in schizophrenia are state dependent, and so not necessarily due to cortical dysfunction.