Positron emission tomography and subcortical glucose metabolism in schizophrenia

Our previous observation of a disturbed subcortical-to-cortical gradient of activity in schizophrenia was further elucidated by examining glucose metabolism in three subcortical structures: lenticular nucleus, caudate nucleus, and thalamus. Local cerebral glucose metabolism was determined with 18F-fluorodeoxyglucose using positron emission tomography (PET) in a sample of 20 unmedicated schizophrenics and 18 normal volunteers. Repeated evaluations were performed for 12 schizophrenics following treatment with psychotropic medications and for 11 controls. Unmedicated schizophrenics had lower cortical and caudate absolute metabolic rates. Subcortical-to-cortical ratios for the lenticular nucleus and thalamus were increased in schizophrenics compared with controls, reflecting a preservation of activity in these structures relative to decreased cortical metabolism. When patients were grouped by length of medication-free period before the initial study, there was a trend for patients who had been medication free less than 6 months to have higher subcortical ratios. However, there were no consistent effects of medication in the subsample of patients whose PET studies were repeated following treatment. The results demonstrate relative hypermetabolism in structures implicated in dopamine pathways. An understanding of the physiological significance of this finding awaits the combined measurement of metabolic activity and neuroreceptors in schizophrenics.

Intraneuronal and extracellular neurofibrillary tangles exhibit mutually exclusive cytoskeletal antigens

We examined the possibility that neurofibrillary tangles (NFTs) were heterogeneous in postmortem hippocampus from 22 patients with or without senile dementia of the Alzheimer type. Intraneuronal NFTs and extracellular, or "ghost," NFTs were recognized in situ by only one or the other of two monoclonal antibodies. The first monoclonal antibody, RMO87, stained only intraneuronal NFTs and is specific for phosphate-dependent epitopes in tau and the two high molecular weight neurofilament proteins. The second monoclonal antibody, 2.2B10, is specific for glial fibrillary acidic protein, and it stained only the RMO87-negative extracellular NFTs. Treatment of sections with alkaline phosphatase or sodium dodecyl sulfate, and the isolation of NFTs from hippocampus, did not expose RMO87 binding sites in extracellular NFTs. These observations indicate that neurofilament-like and tau-like epitopes can be lost from NFTs in situ, and that at least two populations of morphologically and immunochemically distinct NFTs exist.

The reproducibility of the 133Xe inhalation technique in resting studies: task order and sex related effects in healthy young adults

Repeated applications of the 133Xe inhalation technique for measuring regional CBF (rCBF) were made during consecutive resting conditions in a sample of young healthy subjects. Subjects were grouped by order and by sex [nine had resting studies as the initial two measurements in a series of four measurement (six men, three women) and six had these measurements later (two men, four women)]. Three flow parameters were examined: f1 (fast flow) and IS (initial slope) for gray matter CBF, and CBF-15 for mean CBF (gray and white matter over 15-min integration), as well as w1, the percentage of tissue with fast clearing characteristics. With all groups combined, there were no significant differences between the two resting measurements, and high test-retest correlations were obtained for the flow parameters and w1. Analyses by order and sex grouping revealed, for the flow parameters, significant interactions of test-retest difference with order. Repeated initial studies showed reduced CBF from the first to second measurement, whereas resting studies performed later in the series showed no reduction. Interactions for test-retest difference with sex indicated that reduced CBF in serial measures was more pronounced for women. No hemispheric or regional specificity to account for these effects was found. Correction for PaCO2 differences did not alter these results. The results resemble data regarding habituation effects measured for other psychophysiologic measures, and suggest that reduction in CBF for consecutive measurements made on the same day may reflect habituation. This underscores the importance of controlling for effects of habituation on serial measurements of CBF and metabolism.

Regional cerebral blood flow in stroke: hemispheric effects of cognitive activity

Regional cerebral blood flow (rCBF) was measured with the xenon-133 inhalation technique in 15 patients with unilateral cerebral infarction and 12 matched controls. Measurements were performed during a standard resting baseline condition and during the performance of standardized verbal analogies and spatial line orientation tasks. Resting and activated CBF were lower in patients than in controls, and there were differences in the hemispheric pattern of activated CBF. Control subjects replicated earlier findings of asymmetric increase in CBF for the cognitive tasks, whereas patients showed abnormalities in lateralized CBF changes consistent with side of infarction. These findings underscore the utility of cognitive challenges in the study of rCBF in stroke. This can lead to an experimental paradigm in clinical studies of the relation between behavioral deficits and regional brain dysfunction and may also improve the utility of CBF measurements in clinical settings.

Age and regional cerebral blood flow at rest and during cognitive activity

The relationship between age and regional cerebral blood flow (rCBF) activation for cognitive tasks was investigated with the xenon Xe 133 inhalation technique. The sample consisted of 55 healthy subjects, ranging in age from 18 to 72 years, who were studied during rest and during the performance of verbal analogy and spatial orientation tasks. The dependent measures were indexes of gray-matter rCBF and average rCBF (gray and white matter) as well as the percentage of gray-matter tissue. Advanced age was associated with reduced flow, particularly pronounced in anterior regions. However, the extent and pattern of rCBF changes during cognition was unaffected by age. For the percentage of gray matter, there was a specific reduction in anterior regions of the left hemisphere. The findings suggest the utility of this research paradigm for investigating neural underpinnings of the effects of dementia on cognitive functioning, relative to the effects of normal aging.

The effect of anxiety on cortical cerebral blood flow and metabolism

The relation between anxiety and cortical activity was compared in two samples of normal volunteers. One group was studied with the noninvasive xenon-133 inhalation technique for measuring cerebral blood flow (CBF) and the other with positron emission tomography (PET) using 18Flurodeoxyglucose (18FDG) for measuring cerebral metabolic rates (CMR) for glucose. The inhalation technique produced less anxiety than the PET procedure, and for low anxiety subjects, there was a linear increase in CBF with anxiety. For higher anxiety subjects, however, there was a linear decrease in CBF with increased anxiety. The PET group manifested a linear decrease in CMR with increased anxiety. The results indicate that anxiety can have systematic effects on cortical activity, and this should be taken into consideration when comparing data from different procedures. They also suggest a physiologic explanation of a fundamental behavioral law that stipulates a curvilinear, inverted-U relationship between anxiety and performance.

Regional brain function in schizophrenia. I. A positron emission tomography study

Local cerebral glucose metabolism was determined with 18-F-fluorodeoxyglucose using positron emission tomography in a sample of 12 unmedicated schizophrenics and 12 matched normal controls. The data were analyzed for absolute metabolic rates and region/whole-brain ratios using the cortical-subcortical, antero-posterior, and laterality dimensions. Lobar areas within cortical regions were also compared. Across groups, subcortical metabolism was higher than cortical metabolism. Patients had lower metabolism, cortically and subcortically, and a steeper subcortical to cortical gradient. Patients with higher scores on the Brief Psychiatric Rating Scale had higher absolute metabolism and higher left relative to right hemispheric metabolism than did patients with lesser severity. The results did not show "hypofrontality" in schizophrenia. These findings provide some support for cerebral dysfunction in schizophrenia and indicate the need for further examination of the cortical-subcortical dimension.

Regional brain function in schizophrenia. II. Repeated evaluation with positron emission tomography

Cerebral glucose metabolism was measured twice in a sample of 15 schizophrenics and eight controls, using positron emission tomography (PET) with 18-F-fluorodeoxyglucose. Studies were separated by three to 33 weeks. Patients were unmedicated during the first study, and the majority were receiving neuroleptics during the second study. There were no changes from study 1 to study 2 in average whole-brain metabolic rates, regional cortical activity, or the gradient of subcortical to cortical activity. The steeper subcortical to cortical gradient in schizophrenics, present in the first study, persisted in the second. Changes in this gradient were uncorrelated with changes in clinical status. Laterality (right-left) was stable across studies, and changes toward higher right relative to left hemispheric metabolism were correlated with clinical improvement. The results support the hypothesis of abnormal hemispheric activity in schizophrenia and implicate the subcortical-cortical gradient as another dimension that merits further exploration.

Contralateral and ipsilateral control of fingers following callosotomy

The extent of ipsilateral control of the distal limbs is not documented. In this experiment visuo-motor control of fingers was investigated in two callosotomy patients. A substantial amount of ipsilateral control was evident, especially for the left hand fingers. Ipsilateral control of the right hand was evident for the thumb and index fingers, but not for the other fingers. Left hand fingers did not vary significantly in degree of ipsilateral control.

Brain function in psychiatric disorders. III. Regional cerebral blood flow in unmedicated schizophrenics

Regional cerebral blood flow (rCBF) was measured during resting baseline and the performance of a verbal and a spatial task in 19 unmedicated schizophrenics and 19 matched controls. Abnormalities in rCBF were evident in schizophrenics both for resting and activated measures. Resting flows were higher in the left hemisphere for schizophrenics, supporting the hypothesis of left hemispheric overactivation. This effect was stronger in the more severely disturbed patients. The pattern of rCBF changes during activation with the verbal and spatial tasks was also different in schizophrenics. Laterality of flow changes further supported the hypothesis of left hemispheric overactivation. Furthermore, whereas normals had greater increase in flow for the spatial than the verbal task, schizophrenics showed the reverse pattern. This effect also was more pronounced in the severely disturbed patients. Comparison with an earlier sample of medicated schizophrenics suggested that neuroleptics restore symmetry of resting flows before they produce symptomatic relief. Medication did not affect the abnormalities in pattern of rCBF changes during activation with cognitive tasks.

Brain function in psychiatric disorders. II. Regional cerebral blood flow in medicated unipolar depressives

Regional cerebral blood flow was measured during resting baseline and the performance of a verbal and a spatial task in 14 medicated depressives and 25 matched controls. Overall resting flows did not differ, nor were there hemispheric or anteroposterior differences between patients and controls for resting flows. Differences between patients and controls were evident during cognitive activity, and the effects were different for male and female patients. Depressed female patients had higher than normal flows in all conditions, whereas depressed male patients had lower than normal resting flows, which increased to normal during cognitive activity. Their anterior flows increased for the verbal task but not for the spatial task.

Hemispheric control of the writing hand: the effect of callosotomy in a left-hander

We report a case of a left-hander with left hemispheric language. After callosotomy, he could use the left hand to write only random letters and digits, and he became right-handed for writing. Therefore, writing by left-handers with left hemispheric language dominance may be accomplished by transcallosal transmission of the linguistic content from the left hemisphere to the right.

Brain function in psychiatric disorders. I. Regional cerebral blood flow in medicated schizophrenics

We measured regional cerebral blood flow during resting baseline and the performance of verbal and spatial tasks in 15 medicated schizophrenics and 25 matched controls. Patients did not differ from controls in resting flows but showed different blood-flow changes during task performance. Controls replicated earlier findings in normal subjects: flow increased during task performance, and the hemispheric increase was greater in the left for the verbal and in the right for the spatial task. In contrast, patients showed no flow asymmetry for the verbal task and greater left hemispheric increase for the spatial task. The latter finding is consistent with the hypothesis that schizophrenia is associated with left hemispheric overactivation for spatial tasks. In addition, schizophrenic women had unusual flow changes in that their highest flow increase was for the verbal task.

Mutism as a consequence of callosotomy

Transient mutism has been reported following commissurotomy and callosotomy. The cause for this mutism is unknown. A case of mutism following callosotomy is presented, and the preoperative and postoperative data on neurological, physiological, and psychological functioning are discussed. The data suggest that the mutism is not caused by general intellectual deterioration, cortical lesion, or peripheral damage affecting speech production. The syndrome may result from severing interhemispheric connections in cases where both hemispheres are required for speech production.

A cognitive-motor network demonstrated by positron emission tomography

The rate of local cerebral glucose metabolism was measured in subjects receiving a verbal (n = 4) and a spatial (n = 4) task. The verbal task produced greater metabolism in Wernicke's area relative to the right hemispheric homotopic region, whereas the spatial task produced greater metabolic activity in the right hemispheric homotopic region. Broca's area and its right hemisphere counterpart showed symmetrical activity during the verbal task, but there was a significant asymmetry to the right during the spatial task. Lateralized task effects were also obtained in the frontal eye fields, supporting a hypothesized neural network linking cognitive activity with motor orientation.

Hemispheric asymmetries in processing emotional expressions

Three experiments are reported on visual field asymmetries in the perception of emotional expressions on the face. In experiment I full faces expressing six different emotions were presented unilaterally for exposure durations, allowing the subject to judge whether the facial expression was positive or negative. Right-handed subjects judged all expressions except happiness as more negative when presented in the left visual field (LVF). This effect was smaller for left-handers and was absent in left-handers who use the non-inverted writing posture. In experiment II subjects were presented with happy, sad and "mixed" chimeric faces, projected to each visual field, for durations allowing only the detection of the existence of a face. LVF presentations produced greater differential rating of emotional valence for the three types of stimuli. In experiment III chimeric faces containing happy and sad expressions were presented unilaterally for durations allowing the subject to perceive the existence of two expressions on the face. The subjects were required to decide whether the mood expressed in the face was predominantly negative or positive. RVF presentations resulted in a bias toward positive judgments. These results indicate right hemispheric superiority for the perception and processing of emotional valence and a left hemispheric perceptual bias toward positive aspects of emotional stimuli.

Positron emission tomography in two cases of childhood epileptic encephalopathy (Lennox-Gastaut syndrome)

Two patients with childhood epileptic encephalopathy were studied by positron emission tomography before and after corpus callosotomy. Preoperatively, both patients showed in the temporal lobe unilateral hypometabolism that is characteristic of interictal epileptic foci. Postoperatively, the first patient had no seizures by the time of scanning, and his temporal lobe metabolism was bilaterally symmetric. Seizure control in the second patient did not improve by the time of scanning, and unilateral temporal hypometabolism persisted. This finding suggests a temporal lobe focus in two patients with Lennox-Gastaut syndrome.

Sex and handedness differences in cerebral blood flow during rest and cognitive activity

Cognitive activity resulted in increased flow of blood to the cerebral hemispheres. The increase was greater to the left hemisphere for a verbal task and greater to the right hemisphere for a spatial task. The direction and degree of hemispheric flow asymmetry were influenced by sex and handedness, females having a higher rate of blood flow per unit weight of brain, and females and left-handers having a greater percentage of fast-clearing tissue, presumably gray matter.

Cognitive concomitants of hemispheric dysfunction in schizophrenia

Forty-eight schizophrenics (24 paranoids, 24 nonparanoids) and 24 matched controls (12 men and 12 women in each group) were asked to detect the differences between 30 pairs of altered pictures presented successively (15 pairs) and simultaneously (15 pairs) in a counterbalanced order. Overall performance, as measured by reaction time and response quality, was better for controls than for schizophrenics. However, schizophrenics, like right hemisphere brain-damaged patients who presumably rely on their left hemisphere, reacted faster in the successive presentation procedure while the controls reacted equally fast in both conditions. These results support the hypothesis that schizophrenics tend to overactivate their left dysfunctional hemisphere. Twenty-four depressed patients, tested in the same procedure, showed a pattern of results similar to that of controls, suggesting that the results obtained for schizophrenics are not a general characteristic of psychosis.

Motoric laterality imbalance in schizophrenia. A possible concomitant of left hemisphere dysfunction

Two hundred schizophrenics were compared to 200 normal controls on a measure of laterality that included handedness, footedness, and eye dominance scales. Schizophrenics showed more left-sidedness on the laterality score. The established relationship between motoric and cognitive aspects of functional brain asymmetry, found in neurological and normal populations, suggests that the leftward tendency of schizophrenics may be manifested in cognitive and conative functions as well. These results seem to corroborate previous findings indicating that schizophrenia might be related to left hemisphere dysfunction. No relationship was found between handedness and eye dominance either in the schizophrenic or the normal groups. This finding questions the assumption that eyedness-handedness nonconcordance is a pathological sign.

Conjugate lateral eye movements as an index of hemispheric activation

Right handers moved their eyes leftward when solving spatial problems and rightward for verbal problems when the questioner sat behind them. When facing the questioner, the same subjects moved their eyes predominantly in only one direction, either right or left, regardless of problem type. The results indicate that the cerebral hemispheres, though specialized for problem type, are also preferentially activated within the same individuals.