Examining the relationship between degree of handedness and degree of cerebral lateralization for processing facial emotion.

This paper examines the relationship between degree of handedness and degree of cerebral lateralization on a task of processing positive facial emotion in right-handed individuals. Three hundred and thirteen right-handed participants (157 women) were given two behavioral tests of lateralization: a handedness questionnaire and a chimeric faces test. Two further handedness measures were taken: familial lefthandedness and writing posture. Regression analysis showed that both degree of handedness and sex were predictive of degree of lateralization. Individuals who were strongly right-handed were also more strongly lateralized to the right hemisphere for the task. Men were more strongly lateralized than women. Data were reanalyzed for men and women separately. The relationship between handedness and lateralization remained for men only. Neither familial left-handedness nor writing posture were associated with cerebral lateralization for men or women. The results suggest a positive relationship between degree of handedness and degree of cerebral lateralization, and further that there is a sex difference in this relationship. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Choosing sides: The left and right of the normal brain.

One view of brain organization holds that the left cerebral hemisphere controls language processes, while the right hemisphere deals with various nonverbal activities such as visuospatial tasks. It is argued that a substantial proportion of the population deviates from this modal model, and that the investigation of individual differences in brain organization through careful studies of neurologically intact Ss is critical to the understanding of cerebral function. Deviations from the modal model are seen as normal and genetically determined, rather than pathological in origin. It is suggested that different functions, such as handedness, language, and visuospatial ability, are lateralized by relatively independent mechanisms, and therefore can be dissociated. Evidence for a positive relation between brain lateralization and cognitive ability is presented. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial distribution of responses to simple and complex sounds in the primary auditory cortex

The basic functional organization of the cat primary auditory cortex is discussed as it is revealed by electrophysiological studies of the distribution of elementary receptive field (RF) parameters. RFs of cortical neurons have been shown to vary considerably from neuron to neuron; additionally, specific RF properties vary independently. Furthermore, some of the RF properties are nonhomogeneously distributed across the auditory cortex and can be interpreted as forming "maps" that represent specific stimulus information in a topographic way. Accordingly, the functional organization of the primary auditory cortex is interpreted as a series of superimposed independent parameter maps. The consequences of such a layout for the spatial and temporal coding of pure tones and speech sounds is illustrated and ramifications for the interpretation of far-field event-related potentials are discussed.     

Predicting reading performance from neuroimaging profiles: The cerebral basis of phonological effects in printed word identification.

This study linked 2 experimental paradigms for the analytic study of reading that heretofore have been used separately. Measures on a lexical decision task designed to isolate phonological effects in the identification of printed words were examined in young adults. The results were related to previously obtained measures of brain activation patterns for these participants derived from functional magnetic resonance imaging (fMRI). The fMRI measures were taken as the participants performed tasks that were designed to isolate orthographic, phonological, and lexical-semantic processes in reading. Individual differences in the magnitude of phonological effects in word recognition, as indicated by spelling-to-sound regularity effects on lexical decision latencies and by sensitivity to stimulus length effects, were strongly related to differences in the degree of hemispheric lateralization in 2 cortical regions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Handwriting posture and cerebral organization: How are they related?

Since J. Levy and M. Reid (see PA, Vols 57:5149 and 61:12570) first reported an association between handwriting posture and cerebral lateralization, a number of studies related to this issue have appeared in the literature. There is currently a great deal of controversy regarding the nature of the association between handwriting posture and brain organization. It is argued that this controversy loses much of its force when clinical data regarding functional lateralization in left-handers are taken into account. The relevant background on brain organization in left-handers, Levy and Reid's findings and studies related to their findings, and Levy and Reid's speculations with respect to possible interpretations of their data and research bearing on those speculations are reviewed and discussed. (2 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suppressed UDP-galactose: ceramide galactosyltransferase and myelin protein mRNA in twitcher mouse brain

To investigate the role of temporal processing in language lateralization, we monitored asymmetry of cerebral activation in human volunteers using positron emission tomography (PET). Subjects were scanned during passive auditory stimulation with nonverbal sounds containing rapid (40 msec) or extended (200 msec) frequency transitions. Bilateral symmetric activation was observed in the auditory cortex for slow frequency transitions. In contrast, left-biased asymmetry was observed in response to rapid frequency transitions due to reduced response of the right auditory cortex. These results provide direct evidence that auditory processing of rapid acoustic transitions is lateralized in the human brain. Such functional asymmetry in temporal processing is likely to contribute to language lateralization from the lowest levels of cortical processing.     

Genetic features of the spatial organization of the human cerebral cortex

The within-pair similarity of the topographical maps of the spatial synchronization of the cerebral cortical potentials was studied in 11 pairs of monozygotic twins and 20 genetically unrelated subjects in the resting state and during four types of intellectual activity. It was demonstrated that the degree of similarity of the topographical maps is higher in the resting state in the monozygotic twins than in the genetically unrelated subjects. No frequency band of the EEG which exerts a special influence on the formation of the high degree of similarity of the spatial synchronization of the potentials was found. The maximal similarity in the topographical maps of the monozygotic twins is observed in the anterior regions of the left hemisphere and in the temporoparietal regions of the right. Differences between groups are recorded in both regions; however they are especially distinct in the right hemisphere. The data obtained make it possible to draw an inference regarding the influence of a genetic factor not only on individual components of the EEG (which had been previously demonstrated by a number of authors), but also on the systemic organization of the cortical processes. The right-hemispheric activity apparently relates to the most controllable genetic processes. The results of the analysis of the similarity of topographical maps during various types of activity confirm this: the coefficient of similarity reaches the level of significance in the majority of pairs of monozygotic twins only in a "right-hemispheric" test (simultaneous analysis of nonverbal material).     

Measuring degree of cerebral lateralization in children as a function of age.

Discusses the indices of the degree of cerebral lateralization given by J. C. Marshall et al (see record 1975-30869-001) in the context of developmental experiments. These indices are the differences in the number of correct responses when information is presented to the right and left perceptual fields divided by either the total number of correct responses or by the total number of errors, according to whether proportional accuracy across the perceptual fields is above or below .5. Marshall et al argued that these measures are unconstrained by an S's overall level of accuracy. However, it is shown for hypothetical developmental experiments, in which error rates tend to decrease as a function of age, that the Marshall et al indices are arbitrarily related to changes in the efficiency of the hemispheres. The indices indicate developmental increases in lateralization, although the difference between the hemispheres remains constant and even in some circumstances where the difference decreases. It is argued that the use of the Marshall et al index either prejudges the issue or results in relationships that are difficult to predict on any substantive theory of cerebral lateralization. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in mental abilities, hemispheric lateralization, and rate of physical growth at adolescence.

Tested the hypothesis that sex differences in verbal and spatial abilities are related to sex differences in rates of physical maturation and that this relationship is mediated by variation in the organization of higher cortical functions. 40 males and 40 females, ranging in age from 10-16 yrs, were tested on 3 verbal measures (including the Digit Symbol subtest of the WISC and the Word Fluency subtest of the Primary Mental Abilities Test), 3 spatial measures (including the Block Design subtest of the WISC and a modified version of the Embedded Figures Test), and a dichotic test of phoneme identification. Late-maturing Ss of both sexes performed better than early maturers on tests of spatial ability, but the groups did not differ on tests of verbal ability. Among older Ss, the late maturers of both sexes showed greater hemispheric lateralization than early maturers. Sex differences on the ability measures, although in the predicted direction, did not reach significance. Results are discussed with respect to the relationship between hemispheric organization of function and mental abilities and the relationship between maturational rate and lateralization. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Salivary testosterone concentrations in left-handers: An association with cerebral language lateralization.

The level of testosterone exposure in early brain development may influence the direction or degree of cerebral language lateralization. Possible links between individual differences in testosterone levels and patterns of speech representation were investigated in 180 healthy young adults (97 left handed, 83 right handed) using the Fused Dichotic Words Test (T. Halwes, 1991). Among left-handed participants, significantly higher testosterone concentrations were observed in individuals with a left-ear advantage on dichotic listening than in individuals with a right-ear advantage. Among right-handed participants, the pattern of group differences in testosterone tended to be reversed, resulting in a statistically significant interaction. Results extend prior findings by S. D. Moffat and E. Hampson (see record 1996-03260-006) and raise the possibility that higher testosterone is associated with patterns of brain organization in which speech and praxic functions are lateralized to the same hemisphere. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A computer simulation study of cortical imaging from scalp potentials

In this paper, computer simulation studies were conducted to test the feasibility of imaging brain electrical activity from the scalp electroencephalograms. The inhomogeneous three-concentric-sphere head model was used to represent the head volume conductor. Closed spherical dipole layers, consisting of several thousand uniformly distributed dipoles, were used to reconstruct the cortical potential maps corresponding to neuronal sources located inside the brain. Simulation results indicate that the present procedure can image both cortical and deep sources, and for the cortical sources, a spatial resolution as high as 1.2 cm can be achieved.     

Sexually-dimorphic patterns of cortical asymmetry, and the role for sex steroid hormones in determining cortical patterns of lateralization

Cortical asymmetry varies in degree and direction. Sex differences exist for both dimensions of asymmetry: males tend to exhibit more accentuated asymmetries and stronger right hemisphere dominance compared with females, while females typically exhibit more diffuse lateralization patterns and greater left hemisphere bias compared with males. The following review considers the effects of sex steroid hormones on the sexual dimorphism of cortical lateralization patterns in human and nonhuman animals. Several excellent papers exist which consider sexual dimorphism in cortical asymmetries for morphological, physiological or functional asymmetries alone. This paper attempts to consider influences of sex steroid hormones on cortical lateralization in a framework that includes morphology, physiology and function. Converging evidence from studies that incorporate varying methodologies and theoretical backgrounds indicates that sex steroid hormones are important for influencing cortical asymmetry. Although a mechanism has not yet been identified, testosterone is the most likely candidate to influence cortical dominance.     

Imaging neuroscience: principles or maps?

This article reviews some recent trends in imaging neuroscience. A distinction is made between making maps of functional responses in the brain and discerning the rules or principles that underlie their organization. After considering developments in the characterization of brain imaging data, several examples are presented that highlight the context-sensitive nature of neuronal responses that we measure. These contexts can be endogenous and physiological, reflecting the fact that each cortical area, or neuronal population, expresses its dynamics in the context of interactions with other areas. Conversely, these contexts can be experimental or psychological and can have a profound effect on the regional effects elicited. In this review we consider experimental designs and analytic strategies that go beyond cognitive subtraction and speculate on how functional imaging can be used to address both the details and principles underlying functional integration and specialization in the brain.     

Cortical pathways to the mammalian amygdala

The amygdaloid nuclear complex is critical for producing appropriate emotional and behavioral responses to biologically relevant sensory stimuli. It constitutes an essential link between sensory and limbic areas of the cerebral cortex and subcortical brain regions, such as the hypothalamus, brainstem, and striatum, that are responsible for eliciting emotional and motivational responses. This review summarizes the anatomy and physiology of the cortical pathways to the amygdala in the rat, cat and monkey. Although the basic anatomy of these systems in the cat and monkey was largely delineated in studies conducted during the 1970s and 1980s, detailed information regarding the cortico-amygdalar pathways in the rat was only obtained in the past several years. The purpose of this review is to describe the results of recent studies in the rat and to compare the organization of cortico-amygdalar projections in this species with that seen in the cat and monkey. In all three species visual, auditory, and somatosensory information is transmitted to the amygdala by a series of modality-specific cortico-cortical pathways ("cascades") that originate in the primary sensory cortices and flow toward higher order association areas. The cortical areas in the more distal portions of these cascades have stronger and more extensive projections to the amygdala than the more proximal areas. In all three species olfactory and gustatory/visceral information has access to the amygdala at an earlier stage of cortical processing than visual, auditory and somatosensory information. There are also important polysensory cortical inputs to the mammalian amygdala from the prefrontal and hippocampal regions. Whereas the overall organization of cortical pathways is basically similar in all mammalian species, there is anatomical evidence which suggests that there are important differences in the extent of convergence of cortical projections in the primate versus the nonprimate amygdala.     

Inverse relationship between the size of pattern reversal visual evoked potentials from the left brain and the degree of left-hand preference in left-handed normal subjects: importance of the left brain

The relation of the degree of left-hand preference to pattern reversal visual evoked potentials (VEPs) from right and left brain was studied in male left-handers. The degree of the left-hand preference was assessed by the Waterloo Handedness Questionnaire. Visual stimuli consisted of black and white checkerboard patterns generated on a TV screen. VEPs were simultaneously recorded from occipital leads of the right and left hemispheres. The degree of left-hand preference was found to be inversely and significantly related to size of VEPs only from left brain, not from right brain. That is, the conduction time, amplitude, duration, and area of N1-P1 waves linearly decreased as the degree of left-hand preference increased. These results were in accord with the testosterone hypothesis of cerebral lateralization, but not compatible with the right shift theory of handedness. It was concluded that visuomotor control by the left brain would be the main biological correlate of left-hand preference with regard to sensorimotor and cognitive functions.     

Electroencephalographic signs of compensatory reactions following stroke with location of the focus in the right and left cerebral hemispheres

The authors studied 41 patients with acute disorders of cerebral circulation, a focus in the right hemisphere and 14 with foci in the left hemisphere. The traits of compensatory reactions were studied according to the background and functional EEG, depending upon the severity, stage, localization and lateralization of focal vascular brain lesions. The authors indicate to a rigidity of clinical and EEG changes in patients with right hemispheric localization of the focus which is explained by the authors by disturbances of the higher cortical functions in these patients.     

Optical imaging reveals the functional architecture of neurons processing shape and motion in owl monkey area MT

We have used optical imaging based on intrinsic signals to explore the functional architecture of owl monkey area MT, a cortical region thought to be involved primarily in visual motion processing. As predicted by previous single-unit reports, we found cortical maps specific for the direction of moving visual stimuli. However, these direction maps were not distributed uniformly across all of area MT. Within the direction-specific regions, the activation produced by stimuli moving in opposite directions overlapped significantly. We also found that stimuli of differing shapes, moving in the same direction, activated different cortical regions within area MT, indicating that direction of motion is not the only parameter according to which area MT of owl monkey is organized. Indeed, we found clear evidence for a robust organization for orientation in area MT. Across all of MT, orientation preference changes smoothly, except at isolated line- or point-shaped discontinuities. Generally, paired regions of opposing direction preference were encompassed within a single orientation domain. The degree of segregation in the orientation maps was 3-5 times that found in direction maps. These results suggest that area MT, like V1 and V2, has a rich and multidimensional functional organization, and that orientation, a shape variable, is one of these dimensions.     

Finding parametric representations of the cortical sulci using an active contour model

The cortical sulci are brain structures resembling thin convoluted ribbons embedded in three dimensions. The importance of the sulci lies primarily in their relation to the cytoarchitectonic and functional organization of the underlying cortex and in their utilization as features in non-rigid registration methods. This paper presents a methodology for extracting parametric representations of the cerebral sulcus from magnetic resonance images. The proposed methodology is based on deformable models utilizing characteristics of the cortical shape. Specifically, a parametric representation of a sulcus is determined by the motion of an active contour along the medial surface of the corresponding cortical fold. The active contour is initialized along the outer boundary of the brain and deforms toward the deep root of a sulcus under the influence of an external force field, restricting it to lie along the medial surface of the particular cortical fold. A parametric representation of the medial surface of the sulcus is obtained as the active contour traverses the sulcus. Based on the first fundamental form of this representation, the location and degree of an interruption of a sulcus can be readily quantified; based on its second fundamental form, shape properties of the sulcus can be determined. This methodology is tested on magnetic resonance images and it is applied to three medical imaging problems: quantitative morphological analysis of the central sulcus; mapping of functional activation along the primary motor cortex and non-rigid registration of brain images.     

Simultaneous glutamate and perfusion fMRI responses to regional brain stimulation

Functional magnetic resonance imaging (fMRI) rests on the assumption that regional brain activity is closely coupled to regional cerebral blood flow (rCBF) in vivo. To test the degree of coupling, cortical brain activity was locally stimulated in rats by reversed microdialysis infusion of picrotoxinin, alphagamma-aminobutyric acid-A antagonist. Before and during the first 30 minutes of infusion, simultaneous fMRI (rCBF) and neurochemical (interstitial glutamate concentration) measures of brain activity were highly correlated (r = 0.83). After 30 minutes of picrotoxinin-induced stimulation, glutamate levels decreased but rCBF remained elevated, suggesting that additional factors modulate the relationship between neuronal neurotransmitters and hemodynamics at these later stages.