A cognitive-motor network demonstrated by positron emission tomography

Functional brain imaging in neuropsychology over the past 25 years

OBJECTIVE

Outline effects of functional neuroimaging on neuropsychology over the past 25 years.

METHOD

Functional neuroimaging methods and studies will be described that provide a historical context, offer examples of the utility of neuroimaging in specific domains, and discuss the limitations and future directions of neuroimaging in neuropsychology.

RESULTS

Tracking the history of publications on functional neuroimaging related to neuropsychology indicates early involvement of neuropsychologists in the development of these methodologies. Initial progress in neuropsychological application of functional neuroimaging has been hampered by costs and the exposure to ionizing radiation. With rapid evolution of functional methods-in particular functional MRI (fMRI)-neuroimaging has profoundly transformed our knowledge of the brain. Its current applications span the spectrum of normative development to clinical applications. The field is moving toward applying sophisticated statistical approaches that will help elucidate distinct neural activation networks associated with specific behavioral domains. The impact of functional neuroimaging on clinical neuropsychology is more circumscribed, but the prospects remain enticing.

CONCLUSIONS

The theoretical insights and empirical findings of functional neuroimaging have been led by many neuropsychologists and have transformed the field of behavioral neuroscience. Thus far they have had limited effects on the clinical practices of neuropsychologists. Perhaps it is time to add training in functional neuroimaging to the clinical neuropsychologist's toolkit and from there to the clinic or bedside. (PsycINFO Database Record

Development of abbreviated eight-item form of the Penn Verbal Reasoning Test

The ability to reason with language is a highly valued cognitive capacity that correlates with IQ measures and is sensitive to damage in language areas. The Penn Verbal Reasoning Test (PVRT) is a 29-item computerized test for measuring abstract analogical reasoning abilities using language. The full test can take over half an hour to administer, which limits its applicability in large-scale studies. We previously described a procedure for abbreviating a clinical rating scale and a modified procedure for reducing tests with a large number of items. Here we describe the application of the modified method to reducing the number of items in the PVRT to a parsimonious subset of items that accurately predicts the total score. As in our previous reduction studies, a split sample is used for model fitting and validation, with cross-validation to verify results. We find that an 8-item scale predicts the total 29-item score well, achieving a correlation of .9145 for the reduced form for the model fitting sample and .8952 for the validation sample. The results indicate that a drastically abbreviated version, which cuts administration time by more than 70%, can be safely administered as a predictor of PVRT performance.

Individual differences in verbal abilities associated with regional blurring of the left gray and white matter boundary

Blurring of the cortical gray and white matter border on MRI is associated with normal aging, pathological aging, and the presence of focal cortical dysplasia. However, it remains unclear whether normal variations in signal intensity contrast at the gray and white matter junction reflect the functional integrity of subjacent tissue. This study explores the relationship between verbal abilities and gray and white matter contrast (GWC) in healthy human adults. Participants were scanned at 3 T MRI and administered standardized measures of verbal expression and verbal working memory. GWC was estimated by calculating the non-normalized T1 image intensity contrast above and below the cortical gray/white matter interface. Spherical averaging and whole-brain correlational analyses were performed. Sulcal regions exhibited higher contrast compared to gyral regions. We found a strongly lateralized and regionally specific profile with reduced verbal expression abilities associated with blurring in left hemisphere inferior frontal cortex and temporal pole. Reduced verbal working memory was associated with blurring in widespread left frontal and temporal cortices. Such lateralized and focal results provide support for GWC as a measure of regional functional integrity and highlight its potential role in probing the neuroanatomical substrates of cognition in healthy and diseased populations.

Manipulation of frontal brain asymmetry by cognitive tasks

The purpose of the present study was to evaluate whether verbal fluency tasks may specifically induce relatively greater left than right hemispheric activation in the dorsolateral prefrontal cortex. The effectiveness of the manipulation was evaluated by EEG, which was recorded during performance of the verbal fluency task and during two control conditions, i.e., a baseline condition without cognitive demands, and a mental arithmetic task, respectively. The results demonstrate that the desired effect can only be achieved in individuals with good performance on the verbal fluency task. Good and poor performers do not only differ in lateral asymmetry, but also in the most affected region within the prefrontal cortex. Whereas good performers show relatively increased activation in the cortical region and hemisphere putatively most specialized for this kind of task (i.e., the left dorsolateral frontal cortex), poor performers show a marked shift of frontopolar asymmetry to the right.

Neural mechanisms associated with attention to temporal synchrony versus spatial orientation: an fMRI study

Previous neuropsychological and functional imaging studies have suggested that the right hemisphere is crucially involved in spatial cognition. By contrast, much less is known about the putative left hemisphere specialization for aspects of temporal cognition. Accordingly, we studied with functional magnetic resonance imaging the neural mechanisms underlying attention to stimulus onset synchrony or orientational congruence with identical pairs of geometric figures. In each trial, two rhombuses were presented, each 4 degrees peripheral to a central fixation cross, in the left and right visual hemifields. In half of the trials, subjects were asked to judge and indicate via button presses whether the rhombuses appeared simultaneously. In the other half of the trials, subjects indicated whether the orientation of the rhombuses was the same (Factor 1, task, temporal synchrony, orientation). In half of the trials, subjects responded with their right hand and in the other half with their left hand (Factor 2, hand, right, left). Data were analyzed using SPM99 and a random-effects model. Attention to orientation differentially activated right temporo-occipital cortex. Attention to stimulus onset synchrony activated left anterior superior temporal gyrus, left inferior parietal cortex, left medial frontal gyrus, and right operculum. Activation of right temporo-occipital cortex for attention to stimulus orientation is in good agreement with previous functional neuroimaging studies of stimulus orientation. More importantly, activation of a predominantly left-hemispheric network with attention to stimulus onset synchrony extends the results of previous functional imaging, psychophysical, and neuropsychological studies of temporal processing.

Brain activity during simulated deception: an event-related functional magnetic resonance study

TheGuilty Knowledge Test (GKT) has been used extensively to model deception. An association between the brain evoked response potentials and lying on the GKT suggests that deception may be associated with changes in other measures of brain activity such as regional blood flow that could be anatomically localized with event-related functional magnetic resonance imaging (fMRI). Blood oxygenation level-dependent fMRI contrasts between deceptive and truthful responses were measured with a 4 Tesla scanner in 18 participants performing the GKT and analyzed using statistical parametric mapping. Increased activity in the anterior cingulate cortex (ACC), the superior frontal gyrus (SFG), and the left premotor, motor, and anterior parietal cortex was specifically associated with deceptive responses. The results indicate that: (a) cognitive differences between deception and truth have neural correlates detectable by fMRI, (b) inhibition of the truthful response may be a basic component of intentional deception, and (c) ACC and SFG are components of the basic neural circuitry for deception.

Vascular dementia: a cognitive SPET-CBF activation study

OBJECTIVE

We investigated the pattern of regional cerebral blood flow (rCBF) responses to a cognitive task in vascular patients with and without dementia.

METHOD

We studied 8 controls and 18 vascular patients by quantitative rCBF assessed by (133)Xe inhalation method and SPET, both at rest and during a cognitive figure recognition task. Eight were mildly demented and 10 were nondemented vascular patients. According to their task performance, 12 patients were classified as 'good performers' (GPs) and 6 patients as 'poor performers' (PPs).

RESULTS

Vascular patients activated a larger number of brain areas than controls. No differences were observed between controls, nondemented and mildly demented patients in the pattern of rCBF activation. GPs presented a lower mean percentage of rCBF increase than either controls or PPs. GPs had lower values than PPs in the left temporal, parietal and occipital regions and in the right posterior cingulate and occipital regions.

CONCLUSIONS

These data suggest that vascular patients may functionally compensate for vascular damage by activating more brain areas than controls do and, consequently, by increasing the rate of regional activation.

Neural modeling and functional brain imaging: an overview

This article gives an overview of the different functional brain imaging methods, the kinds of questions these methods try to address and some of the questions associated with functional neuroimaging data for which neural modeling must be employed to provide reasonable answers.

An fMRI study of sex differences in regional activation to a verbal and a spatial task

Sex differences in cognitive performance have been documented, women performing better on some phonological tasks and men on spatial tasks. An earlier fMRI study suggested sex differences in distributed brain activation during phonological processing, with bilateral activation seen in women while men showed primarily left-lateralized activation. This blood oxygen level-dependent fMRI study examined sex differences (14 men, 13 women) in activation for a spatial task (judgment of line orientation) compared to a verbal-reasoning task (analogies) that does not typically show sex differences. Task difficulty was manipulated. Hypothesized ROI-based analysis documented the expected left-lateralized changes for the verbal task in the inferior parietal and planum temporal regions in both men and women, but only men showed right-lateralized increase for the spatial task in these regions. Image-based analysis revealed a distributed network of cortical regions activated by the tasks, which consisted of the lateral frontal, medial frontal, mid-temporal, occipitoparietal, and occipital regions. The activation was more left lateralized for the verbal and more right for the spatial tasks, but men also showed some left activation for the spatial task, which was not seen in women. Increased task difficulty produced more distributed activation for the verbal and more circumscribed activation for the spatial task. The results suggest that failure to activate the appropriate hemisphere in regions directly involved in task performance may explain certain sex differences in performance. They also extend, for a spatial task, the principle that bilateral activation in a distributed cognitive system underlies sex differences in performance.

Changes in brain activity during motor learning measured with PET: effects of hand of performance and practice

The aim of this study is to assess brain activity measured during continuous performance of design tracing tasks. Three issues were addressed: identification of brain areas involved in performing maze and square tracing tasks, investigation of differences and similarities in these areas related to dominant and nondominant hand performance, and most importantly, examination of the effects of practice in these areas. A total of 32 normal, right-handed subjects were instructed to move a pen with the dominant right hand (16 subjects) or nondominant left hand (16 subjects) continuously through cut-out maze and square patterns with their eyes closed during a 40-s positron emission tomography (PET) scan to measure regional blood flow. There were six conditions: 1) holding the pen on a writing tablet without moving it (rest condition); 2) tracing a maze without practice; 3) tracing the same maze after 10 min of practice; 4) tracing a novel maze; and tracing an easily learned square design at 5) high or 6) low speed. To identify brain areas generally related to continuous tracing, data analyses were performed on the combined data acquired during the five tracing scans minus rest conditions. Areas activated included: primary and secondary motor areas, somatosensory, parietal, and inferior frontal cortex, thalamus, and several cerebellar regions. Then comparisons were made between right- and left-hand performance. There were no significant differences in performance. As for brain activations, only primary motor cortex and anterior cerebellum showed activations that switched with hand of performance. All other areas, with the exception of the midbrain, showed activations that were common for both right- and left-hand performance. These areas were further analyzed for significant conditional effects. We found patterns of activation related to velocity in the contralateral primary motor cortex, related to unskilled performance in right premotor and parietal areas and left cerebellum, related to skilled performance in supplementary motor area (SMA), and related to the level of capacity at which subjects were performing in left premotor cortex, ipsilateral anterior cerebellum, right posterior cerebellum and right dentate nucleus. These findings demonstrate two important principles: 1) practice produces a shift in activity from one set of areas to a different area and 2) practice-related activations appeared in the same hemisphere regardless of the hand used, suggesting that some of the areas related to maze learning must code information at an abstract level that is distinct from the motor performance of the task itself.

The effects of unilateral forced nostril breathing on cognitive performance

This study describes the effects of 30 minutes of unilateral forced nostril breathing on cognitive performance in 51 right-handed undergraduate psychology students (25 males and 26 females). A verbal analogies task modeled after the Miller Analogies and SAT Tests was used as a test of left-hemispheric performance and mental rotation tasks based on the Vandenburg and Kuse adaptation of Shepard and Metzler's tests were used as spatial tasks for testing right-hemispheric performance. Spatial task performance was significantly enhanced during left nostril breathing in both males and females, p = .028. Verbal task performance was greater during right nostril breathing, but not significantly p = .14. These results are discussed in comparison to other cognitive and physiological studies using unilateral forced nostril breathing. This yogic breathing technique may have useful application in treating psychophysiological disorders with hemispheric imbalances and disorders with autonomic abnormalities.

Reliability of regional cerebral blood flow activation to cognitive tasks in elderly normal subjects

The assessment of cerebral blood flow (CBF) using noninvasive 133Xe techniques provides an indirect measurement of cortical metabolic activity. The utility of this method in longitudinal clinical studies depends on the stability and reproducibility of resting and activated flow measures. We evaluated CBF in a sample of 16 elderly normal subjects (aged 54-73 years) at rest and during task performance in two sessions separated by an average of 9 weeks. Resting global CBF was lower in the second session, a finding consistent with the known effects of habituation previously reported. Regionally specific activated CBF did not change with repeated measurements. The results provide evidence that the 133Xe technique is reliable and of potential utility in evaluating the effect of the natural course of brain disease, as well as the effects of therapeutic interventions on brain activity.

Decreases in frontal and parietal lobe regional cerebral blood flow related to habituation

We previously reported decreased mean CBF between consecutive resting conditions, ascribed to habituation. Here we address the regional specificity of habituation over three consecutive flow studies. Regional CBF (rCBF) was measured in 55 adults (12 right-handed men, 12 right-handed women, 14 left-handed men, 17 left-handed women), with the 133Xe inhalation technique, during three conditions: resting, verbal tasks (analogies), and spatial tasks (line orientation). Changes in rCBF attributable to the cognitive tasks were eliminated by correcting these values to a resting equivalent. There was a progressive decrease in mean rCBF over time, reflecting habituation. This effect differed by region, with specificity at frontal (prefrontal, inferior frontal, midfrontal, superior frontal) and inferior parietal regions. In the inferior parietal region, habituation was more marked in the left than the right hemisphere. Right-handers showed greater habituation than did left-handers. There was no sex difference in global habituation, but males showed greater left whereas females showed greater right hemispheric habituation. The results suggest that habituation to the experimental setting has measurable effects on rCBF, which are differently lateralized for men and women. These effects are superimposed on task activation and are most pronounced in regions that have been implicated in attentional processes. Thus, regional decrement in brain activity related to habituation seems to complement attentional effects, suggesting a neural network for habituation reciprocating that for attention.

Influence of lateral gaze on electroencephalographic spectral power

The effects of maintaining lateral gaze (as opposed to looking straight ahead) on electroencephalographic spectral power were tested in 12 right handed male subjects during eye opening (EO) and eye closure (EC). Our working hypothesis, based on Kinsbourne's paradigm, was that maintaining right lateral gaze activates the left hemisphere while maintaining left lateral gaze activates the right hemisphere, this activation resulting in a reduction in the spectral power over the hemisphere in question. Results showed that the variations in spectral power involved mainly the alpha frequency band. In the EC condition, the results were consistent with our working hypothesis: right lateral gaze produced a marked reduction in left hemispheric spectral power. In the EO condition, alpha power was constantly higher in the right hemisphere whether lateral gaze was maintained to the right or to the left. This can possibly be due to an attentional effect. Results are discussed with regard of the type of alpha rhythm and of the activation of cortical oculomotor centres. They shed light on the controversy concerning the existence of specific EEG correlates of cognitive activity, which preferentially involve each of the cerebral hemispheres.

Metabolic impairment in human amnesia: a PET study of memory networks

Human amnesia is a clinical syndrome exhibiting the failure to recall past events and to learn new information. Its "pure" form, characterized by a selective impairment of long-term memory without any disorder of general intelligence or other cognitive functions, has been associated with lesions localized within Papez's circuit and some connected areas. Thus, amnesia could be due to a functional disconnection between components of this or other neural structures involved in long-term learning and retention. To test this hypothesis, we measured regional cerebral metabolism with 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and positron emission tomography (PET) in 11 patients with "pure" amnesia. A significant bilateral reduction in metabolism in a number of interconnected cerebral regions (hippocampal formation, thalamus, cingulate gyrus, and frontal basal cortex) was found in the amnesic patients in comparison with normal controls. The metabolic impairment did not correspond to alterations in structural anatomy as assessed by magnetic resonance imaging (MRI). These results are the first in vivo evidence for the role of a functional network as a basis of human memory.

Lateral preference and neuropsychological correlates of schizotypy

A battery of 11 schizotypy questionnaires was administered to 316 male undergraduates. The scores of the 266 white subjects were subjected to a principal components analysis, and 73 subjects scoring at the upper and lower ends of the factor score distribution based on the first unrotated component were recalled for neuropsychological testing. The battery of neuropsychological tests consisted of four tests of motoric performance, four subtests from the Wechsler Adult Intelligence Scale-Revised, the conjugate lateral eye movement test, and a lateral preference questionnaire. Subjects high on schizotypy did not differ from low scorers on overall neuropsychological performance or performance asymmetries. High scorers did show a sinistral shift in hand and foot preference and more crossed dominance compared with controls. Asians scored significantly higher than whites on several schizotypy scales, raising the question of a possible ethnic bias in these measures.

Mapping the functional neuroanatomy of the intact human brain with brain work imaging

The recent development of noninvasive methods for measuring local rates of energy metabolism or blood flow in the brain has made it possible to investigate functional neuroanatomy in healthy human subjects. The best of these methods, high resolution measurement of regional cerebral blood flow (rCBF) with positron emission tomography (PET), provides a precision of anatomical localization that far exceeds that attainable with human brain lesion studies. Moreover, the study of healthy subjects avoids possible confounding effects of brain lesions, such as compensatory reorganization of brain function. PET-rCBF studies have already identified several cortical areas involved in higher-order visual processing, indicating that functional neuroimaging may yield a map of human visual cortex analogous to maps that have been developed by vision research in nonhuman primates. PET-rCBF studies of imagery and language demonstrate the potential of functional neuroimaging to map regions of human cortex that perform functions that cannot be studied so easily in nonhuman primates or perform functions that humans do not share with other species.

Cerebrocerebellar relationship during behavioral activation: a PET study

The effect of behavioral activation on cerebral and cerebellar glucose metabolism was studied in normal subjects when performing either a verbal memory task or a tactile somatosensory task. Each subject was also studied in a resting state control condition, either 1 h earlier or later than the activation task. Compared to the resting state, both tasks produced asymmetrical metabolic activation, which was opposite in direction within the cerebral and cerebellar hemispheres. In both tasks, the difference of activation of CMRglc in the right and left hemispheres in the cerebellum was negatively correlated with that in the sensory-motor region. This apparently coupled metabolic activation of one cerebellum and areas within the opposite cerebral hemisphere represents the inverse of the crossed cerebellar diaschisis phenomenon commonly observed when a vascular lesion affects one cerebral hemisphere and hypometabolism occurs in the opposite cerebellum. Because these correlations were selective and concordant with known anatomical connections, and were found in two different tasks, they suggest strong functional connections between these specific brain regions.

Impaired metabolic activation in Alzheimer's disease: a PET study during continuous visual recognition

Regional cerebral metabolic rate of glucose (rCMRGl) was studied in 21 patients with probable Alzheimer's disease (AD) and nine age-matched normal controls by positron emission tomography (PET) of 2(18F)-fluoro-deoxy-D-glucose (FDG) at rest and during stimulation with a continuous visual recognition task. While global metabolism at rest was comparable in both groups, rCMRGl in the temporo-parietal junction area, the mid-temporal and the frontal cortex was typically decreased in the AD patients. The continuous visual recognition task adapted to the individual performance capacity increased the global metabolic rate in the controls by 21 +/- 18%, while in the AD patients the metabolic change (5.7 +/- 11.1%) during activation was significantly weaker (P = 0.023). Due to the tasks chosen the activation of rCMRGl in both groups was most prominent in the visual cortex and the temporo-parietal association areas, although the recognition task additionally involved widespread brain structures with varying rCMRGl. A significant correlation was found between rCMRGl in areas usually severely affected by AD pathology, e.g. the temporo-parietal cortex, and GDS scores, and became stronger during metabolic activation. Neither at rest nor during stimulation was there a relationship between the rCMRGl of structures usually less involved in AD, e.g. the sensorimotor cortex, and the severity of dementia as assessed by the global deterioration scale (GDS). From these results it can be concluded that metabolic rate at rest reflects the extent of morphologic damage, while PET studies during activation indicate the brain's reserve capacity to respond to functional tasks. Since metabolism in AD patients during activation is more severely impaired than at rest, PET studies during functional tests could help in the selection of patients with a potential to benefit from therapeutic intervention.

Brain single photon emission computed tomography: newer activation and intervention studies

Single-photon emission computed tomography (SPECT) regional cerebral blood flow (rCBF) findings using non-xenon 133 tracers in combination with activation and intervention techniques are reviewed. Examination of the currently available data indicates that it is possible to detect the effects of a variety of activations and interventional procedures using SPECT rCBF with non-xenon 133 tracers. There are still many issues to be resolved before SPECT can reach the level of sophistication attained by xenon 133 and positron emission tomography in studying rCBF during activation or intervention. However, research to date indicates that SPECT rCBF studied with tracers other than xenon 133 has an excellent potential for increasing the ability to differentiate normal and pathological states.

Line orientation judgment in normal elderly and subjects with dementia of Alzheimer's type

Ninety-five normal controls divided into three subgroups (55-64 yrs, 65-74 yrs, and 75-84 yrs) and 11 subjects with early dementia of Alzheimer's type (DAT) were given a line orientation judgment task (Benton, Varney, & Hamsher, 1978). No difference appeared between the three control subgroups in global score but the difference between controls and DAT subjects was significant. However, some DAT subjects had a global score overlapping the scores of controls. Error types were also analyzed. Results of this analysis showed that some errors appeared in all subjects, normal and DAT, while others were specific to DAT subjects. It was speculated that these error types were a manifestation of a deeper visuospatial deficit, revealing a major problem of the DAT in spatial organization. Thus, this study suggests that an analysis of the error types observed in the line orientation judgment task may be helpful in differentiating normal elderly from early DAT.

Augmentation of auditory evoked potentials in somatization disorder

Sensory input regulation was examined in terms of augmenting/reducing of auditory evoked potentials in 10 patients with somatization disorder (8 males and 2 females) and 10 age- and sex-matched normal controls. The slope of P1-N1 amplitude change as a function of stimulus intensity was greater in patients compared with controls, suggesting an enhanced central nervous system response to sensory input. Taken together with previous findings of a failure to habituate to incoming stimuli in a similar group of patients, and evidence obtained in somatizers of both over-responding to background stimuli in a simple tone-discrimination task and enhanced parietal activation during selective attention, this finding suggests disturbances in the processes of attention and in the regulation of afferent stimuli in somatization disorder, and may help explain the multiple and chronic complaints characteristic of patients with the disorder.

Conjugate lateral eye movements: a second look

It has been suggested that conjugate lateral eye movements (CLEM) are related to cerebral lateralization. Two types of research have developed: studies examining individual differences (hemisphericity) and studies examining the type of questions used to elicit eye movements (hemispheric specialization). In a 1978 review, Ehrlichman and Weinberger questioned the notion that CLEM is related to cerebral lateralization, particularly with regard to individual differences. However, since their review, a substantial number of studies have been published which are pertinent to the validity of CLEM. The following paper reviewed the validity of CLEM through three avenues, neurophysiological evidence, relationships with other measures of laterality and relation to spatial and verbal stimuli. Overall, it was concluded that there is sufficient evidence to support the CLEM model. Converging evidence from studies on EEG, electrical stimulation, ablation, brain damage, sodium amytal testing, blood flow, positron emission tomography, dichotic listening, and visual half fields was found to be, for the most part, supportive. The results for verbal and spatial task performance were mixed. Studies examining verbal abilities or a verbal to spatial comparison were generally supportive. The findings for spatial abilities alone were more equivocal. Evidence on question-type was found to be weak but positive, with about half the studies showing the predicted asymmetry and the other half reporting nonsignificant results. The implications of an interaction between hemisphericity or characteristic arousal and hemispheric specialization were also discussed.

Directed drug distribution: adding controlled brain activity to a drug

Environmental factors can alter the state of an organism so as to influence the response to drugs. This fact is widely recognized even though the responsible mechanisms are difficult to understand and control. The capacity of environmental influences to alter local drug pharmacokinetics is rarely considered. Drug localization and resulting action within the brain are influenced by vascular blood flow factors, local concentration differences in competing neurohumours, and receptor density. These are all frequently asymmetrically represented in the brain and drug effects are correspondingly laterality dependent. Attention to regional brain pharmacokinetics and the influence of environment on regional blood flow, local neurohumor concentration, and receptor density represents an untapped opportunity to enhance the desired effect of a centrally active drug at its site of action without enhancing general systemic toxicity. Combined pharmacotherapy and psychotherapy may result in superior therapeutic responses. Psychotherapy is a potential tool deliberately to manipulate environmental factors that influence physiological and physical chemical parameters that determine drug disposition.

Visual hemispace differences reflect hemisphere asymmetries

The relationship between the representation of the extracorporeal visual hemispace and the contralateral hemisphere has been investigated by presenting visual stimuli foveally either in the right or in the left hemispace. In a lexical decision task (Exp. 1) and a face-familiarity decision task (Exp. 2) lateral asymmetries very similar to those obtained using the divided visual field technique have been found. These results suggest that under particular circumstances the hemispace representation in the contralateral hemisphere overrides the retinal representation. Finally, it was found that in a lexical decision task performance with stimuli in the right hemispace was very similar to that with stimuli in a central position. The physiological and adaptive meaning of this phenomenon is discussed.

Focal right temporo-occipital blood flow changes associated with judgment of line orientation

Focal cerebral blood flow changes for judgment of line orientation were determined using the 133Xe inhalation technique with 18 normal right-handed male subjects. Measurements were made during three conditions in the same session: a line orientation task, a sensorimotor control task, and normal rest. Blood flow changes attributable to the judgment of line orientation were found for the measure f1 at a detector centered over the right temporo-occipital region. For the measure IS this activation was significant in the temporo-occipital region in both hemispheres but significantly greater in the right hemisphere. For f1 the change in blood flow and for IS the percent change in blood flow in the right temporo-occipital region attributable to judgment of line orientation decreased as performance on the line orientation task improved.

Right hemisphericity of Australian aboriginal children. II: Conjugate lateral eye movements

Right-handed Aboriginal and White Australian children were compared in Greater Sydney areas having substantial Aboriginal subpopulations. The 45 Aboriginal children showed significantly higher percentages of leftward conjugate lateral eye movements than did the 82 White children for two sets of 17 questions: the WISC-R Similarities test and an original set of questions. A relative right-hemisphericity of the Aboriginal children on the level of hemispheric activation is inferred, which complements the earlier finding of a right-hemisphericity of these same children on the level of performance of lateralized cognitive tests.

Conjugate lateral eye movements and cognitive mode: blindness as a control for visually-induced oculomotor effects

The relationship between lateral eye movement directionality and type of cognitive task was investigated in a single blind subject with septo-optic dysplasia. Results from an 80-item test showed that rightward eye movements were significantly associated with verbal tasks and leftward eye movements with spatial tasks. As visual influences on oculomotor behaviour were eliminated, the findings suggested that lateralized eye movements might have arisen as a consequence of asymmetrical activation of cognitive origin triggering the frontal eye field orienting mechanism.

The transmission of information in natural systems

An isomorphism of information storage and transmission in natural systems is presented. First, a structural and functional dichotomy found in the control centres of the predominant systems in the physical, biological and psychological realms is outlined. The dichotomy of control is shown to allow for an intrinsic balance between the preservation of a system's information, on the one hand, and its alteration and usage, on the other. It is then shown that the mechanisms of communication between the control centre elements are isomorphic among these diverse systems. That is, the transmission of information from one control element to another entails its "double-inversion", which allows for the retrieval of the information in its original form by means of a second transfer process. This mechanism of information transmission leads to novel conclusions concerning the nature of the "brain code".