Some failures of intermanual and cross-lateral transfer in chronic schizophrenia

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.

Hemispheric cooperation--a crucial factor in schizophrenia? Neurophysiological evidence

Previous behavioural studies have demonstrated evidence for impaired interhemispheric cooperation in schizophrenia patients. The present study uses event-related brain potentials (ERPs) and source localisations to investigate the neurophysiological mechanisms underlying hemispheric cooperation. Fourteen schizophrenia patients and 15 healthy controls performed a lexical decision task on words and pseudowords presented tachistoscopically either unilaterally to the right or left visual field or bilaterally, with two identical copies, one in each visual field. Behavioural results confirmed earlier findings that healthy controls exhibit a significant bilateral redundancy gain (BRG) for words, which is absent for pseudowords. Schizophrenia patients failed to show the bilateral redundancy gain for words, consistent with a deficit in interhemispheric information exchange. ERPs revealed a significant increase in amplitude approximately 180 ms after stimulus onset, occurring specifically for words in the bilateral stimulation condition. This neurophysiological correlate of the behavioural BRG was absent in patients. Source localisation using minimum norm estimates demonstrated BRG-related enhanced activity in the left temporal cortex for healthy controls, but not schizophrenia patients. Interestingly, behavioural and ERP data indicated a clear left-hemispheric laterality for word processing in healthy participants as well as in patients. Our findings provide behavioural and neurophysiological evidence for reduced interhemispheric cooperation in schizophrenia which may be due to impaired transfer of information from the right to the left hemisphere.

Right hemispheric dysfunction in schizophrenia

This study uses the Poffenberger (1912) paradigm, which compares the difference between "crossed" (stimuli and motor response areas are contralateral) and "uncrossed" (stimuli and motor response areas are ipsilateral) conditions to estimate interhemispheric transfer time. Simple reaction time (RT) was recorded to stimuli presented to the left visual field (LVF), right visual field (RVF), or bilaterally (BVF) in individuals with schizophrenia (n = 10) and controls (n = 14), who responded using either the left or right hand. While the results provide no evidence for differences between the groups in information transfer between the hemispheres, the schizophrenia group were significantly slower to respond to LVF stimuli, suggesting right hemisphere dysfunction.

Broad-Perspective Perceptual Disorder of the Right Hemisphere

Traditional accounts of right-posterior brain injury describe a syndrome of low-level perceptual sequelae producing marked acute dependency and transient safety concerns. The syndrome is also held to spare cognition and to carry a generally favorable long-term prognosis. The present paper reviews publications and anecdotal data that challenge this picture. Recent theoretical expositions and empirical studies stipulate three major cognitive functions of the right posterior association cortex: processing novel input, guiding reactions to emergencies, and anticipating consequences. Appearing benign after acute recovery, the impairment of these processes produces vocational, social and marital dysfunctions that increase as a function of chronicity, ultimately becoming more broadly disabling than focal injuries in other cortical loci. The unique symptom picture and serious implications suggest that the long-term syndrome should be labeled (Broad-Perspective Perceptual Disorder) and incorporated in future clinical taxonomies, underscoring the need for extraordinary long-term assistance and specialized therapeutics. Procedures for assessment and differential diagnosis are outlined.

Lateralized Lexical Decision in Schizophrenia: Hemispheric Specialization and Interhemispheric Lexicality Priming

Reports of left-hemisphere dysfunction and abnormal interhemispheric transfer in schizophrenia are mixed. The authors used a unified paradigm, the lateralized lexical decision task, to assess hemispheric specialization in word recognition, hemispheric error monitoring, and interhemispheric transfer in male, right-handed participants with schizophrenia (n=34) compared with controls (n=20). Overall, performance and error monitoring were worse in patients. However, patients like controls showed left-hemisphere superiority for lexical processing and right-hemisphere superiority for error monitoring. Only patients showed selective-interhemispheric lexicality priming for accuracy, in which performance improved when the lexical status of target and distractor stimuli presented to each hemifield was congruent. Results suggest that schizophrenia is associated with impaired monitoring and with increased interhemispheric automatic information transfer rather than with changed hemispheric specialization for language or error monitoring.

A study of transcallosal inhibition in schizophrenia using transcranial magnetic stimulation

A considerable body of imaging research has demonstrated morphological changes in the corpus callosum (CC) of patients with schizophrenia. Transcranial magnetic stimulation (TMS) allows the possibility for the in vivo investigation of a variety of aspects of brain function including the spread of information across the CC. We aimed to investigate whether patients with schizophrenia demonstrate abnormalities of transcallosal inhibition (TCI), a TMS parameter measured with both single and paired pulse experiments. 25 patients with DSM-IV schizophrenia and 20 normal volunteers participated in the study. Electromyographic (EMG) recordings from the bilateral abductor pollicis brevis (APB) muscle were made during focal TMS stimulation to the motor cortex. Experimental paradigms were utilised to measure both the timing and degree of the effect of TCI. The patient group demonstrated a reduction in the degree of TCI at rest and during a sustained muscle contraction. TCI commenced at the same time in the patient and the control group but was of prolonged duration in the patient group although the length of TCI correlated with medication dose. Patients with schizophrenia demonstrate a reduction in the degree of TCI that appeared independent of medication dose. The latency of TCI is not altered in the patient group suggesting that cortical inhibitory mechanisms, rather than corpus callosal ones, are likely to be the cause of these TCI alterations.

Reduced interhemispheric transmission in schizophrenia patients: evidence from event-related potentials

Interhemispheric transfer was investigated in 14 schizophrenia patients and 15 age- and sex-matched healthy controls in a lateralized lexical decision task. Words and pseudowords were tachistoscopically presented either to the left or to the right visual hemifield. Event-related potentials were determined from a 65-channel electroencephalogram. Information transfer between hemispheres was assessed by the interhemispheric transmission time (IHTT), the N1-latency difference between ipsilateral and contralateral hemisphere.Controls, but not schizophrenia patients showed significantly faster IHTT from the right to the left hemisphere for words, while IHTT from the left to the right hemisphere did not differ between groups and stimuli. These findings are interpreted in terms of a deficit in schizophrenia to transfer verbal information from the right to the left hemisphere via the corpus callosum.

Bilateral transfer deficit in schizophrenia: a trait marker

Schizophrenic patients who had shown improvement over a 6-week treatment period were tested for their bilateral transfer of skill with a mirror-drawing task. Compared with first degree relatives and normal control subjects, patients showed a significant deficit in bilateral transfer of skills in terms of response accuracy both before and after treatment. These findings indicate that the deficit is an enduring functional loss in schizophrenia.

Impaired interhemispheric integration in brain oxygenation and hemodynamics in schizophrenia

We examined 38 patients with chronic schizophrenia to find and qualify disturbances in interhemispheric integration in brain oxygen metabolism and hemodynamics during a psychological task. A group of thirty-eight age- and sex-matched healthy volunteers were monitored as controls. Multi channel near-infrared (NIR) spectrophotometry was used to observed real-time alterations in cerebral oxygenation in areas of both hemispheres of the forebrain adjacent to the forehead during the mirror drawing task (MDT). In response to MDT normal volunteers showed distinct and well-integrated patterns of changes in oxygenated hemoglobin Hb, deoxygenated Hb, and blood volume total Hb. On the other hand, half the schizophrenics showed dysregulated patterns between hemispheres which never appeared in normal volunteers. Certain schizophrenic symptoms may be related to defective interhemispheric integration.

Bilateral transfer deficit in schizophrenia

Right-handed chronic schizophrenics, left-handed normals, and right-handed normals were tested on a measure of bilateral transfer of motor skill in contralateral hands. Schizophrenics compared with normals showed significantly poor bilateral transfer of skill in terms of errors committed; the group difference was nonsignificant in terms of response time. Results suggested a breakdown in perceptual-motor coordination in schizophrenia.

Schizophrenia: a disease of interhemispheric processes at forebrain and brainstem levels?

The evidence is convincing that each human cerebral hemisphere is capable of human mental activity. This being so, every normal human thought and action demands either a consensus between the two hemispheres, or a dominance of one over the other, in any event integrated into a unity of conscious mentation. How this is achieved remains wholly mysterious, but anatomical and behavioral data suggest that the two hemispheres, and their respective bilateral, anatomical-functional components, maintain a dynamic equilibrium through neural competition. While the forebrain commissures must contribute substantially to this competitive process, it is emphasized in this review that the serotonergic raphé nuclei of pons and mesencephalon are also participants in interhemispheric events. Each side of the raphé projects heavily to both sides of the forebrain, and each is in receipt of bilateral input from the forebrain and the habenulo-interpeduncular system. A multifarious loop thus exists between the two hemispheres, comprised of both forebrain commissural and brainstem paths. There are many reasons for believing that perturbation of this loop, by a variety of pathogenic agents or processes, probably including severe mental stress in susceptible individuals, underlies the extraordinarily diverse symptomatology of schizophrenia. Abnormality of features reflecting interhemispheric processes is common in schizophrenic patients; and the 'first rank' symptoms of delusions or hallucinations are prototypical of what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is focused primarily through, the raphé serotonergic system, that plays such a fundamental role in consciousness, in dreaming, in response to psychotomimetic drugs, and probably in movement, and even the trophic state of the neocortex. This system is also well situated to control the dopaminergic neurons of the ventral tegmental area, thus relating to the prominence of dopaminergic features in schizophrenia; and the lipofuscin loading and intimate relation with blood vessels and ependyma may make neurons of the raphé uniquely vulnerable to deleterious agents.

Agenesis of the corpus callosum and schizophrenia: a case report

Clinical, radiological and neuropsychological findings in the first reported case of schizophrenia with complete agenesis of the corpus callosum are described. Although causal inferences were made difficult by the co-existence of a left frontotemporal cyst and a family history of affective disorder, some theories of the role of callosal dysfunction in schizophrenia require revision in the light of this case.

Corpus callosum function in schizophrenia: a neuropsychological assessment of interhemispheric information processing

Impaired corpus callosum function has been reported in schizophrenia. We measured intra- and interhemispheric visual information processing in 16 schizophrenic patients and 16 matched controls. Although the schizophrenics performed worse between than within cerebral hemispheres, this pattern was similar to that of the normal controls. Schizophrenics do not show particular dysfunction of the corpus callosum.

A model of brain function: its implications for psychiatric research

Much current research in psychiatry proceeds in the absence of an integrated model of brain function. It is based instead on the effort to relate clinical syndromes to single, localised abnormalities in the brain. Such an approach is inconsistent with existing data, inadequate for linking research findings with clinical practice, and, probably, fundamentally misdirected. A model of brain function is presented that is based on Luria's notion of cerebral functional systems and on the proposition that the neural substrates of emotion are those processes that integrate different brain regions. Some of the implications of this model for research are discussed.

A controlled magnetic resonance imaging study of corpus callosum thickness in schizophrenia

Two previous postmortem studies reported an increased thickness of the corpus callosum in schizophrenic patients compared to psychiatric controls. We report an in vivo study of the corpus callosum in schizophrenic patients (n = 38) and healthy controls (n = 41) using magnetic resonance (MR) brain imaging. A significant increase in mean callosal thickness was found in the middle and anterior, but not the posterior, parts of the callosal body. However, when the patients and controls were compared by gender and handedness, schizophrenic men were found not to differ from control men in callosal thickness, regardless of handedness, whereas schizophrenic women were found to have a highly significant increase in callosal middle and anterior thickness compared to control women. The data suggest that increased callosal thickness in schizophrenia is gender related, a factor that is not considered by postmortem studies. The implications of increased callosal dimensions in female schizophrenics are discussed.

Biological substrates of schizophrenia

Schizophrenia is increasingly believed to represent a group of organic disorders which primarily, although not exclusively, affect the central nervous system. Our purpose is to review a representative sample of twentieth-century literature which speaks to the biological substrates of the syndrome. Subjects reviewed include genetic and environmental contributions to the onset of illness, early and recent findings of gross structural anomalies, and apparent histopathological alterations in cerebral cortex, cerebellar vermis, limbic system, and brain stem, as well as problems of cerebral asymmetry. Data from a diverse group of electrophysiological studies reveal several promising correlates of these areas of investigation. Despite the inconsistent nature of the findings to date, several themes have begun to emerge, including patterns of hypofrontal/hyperparietal regional cerebral flow and glucose utilization, left hemispheric dysfunction, and deficits of interhemispheric information processing. The interpretation and significance of these emerging patterns remains unclear and must await more profound insights into the nature of normal and abnormal cerebral function.

A histological study of the corpus callosum in chronic schizophrenia

As a followup to a post-mortem study of the brains of schizophrenic and control subjects where the corpus callosum was found to be significantly thicker anteriorly in early onset compared to late onset schizophrenia, histological sections of 18 schizophrenic, 7 manic-depressive, and 11 medical/surgical control subjects were prepared using a stain for glia and a stain for callosal fibers. A quantitative study of the concentration of glial cells and interhemispheric callosal fibers revealed no difference between groups. A neuropathologist unaware of the tissue origin rated the histological sections for gliosis. There was significantly more severe gliosis in the callosi of the late onset schizophrenics compared to early onset schizophrenics as well as the control group. These preliminary findings suggesting callosal pathology are discussed, and the need for further studies is stressed.