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.     

Physiological responses to verbally inaccessible pictorial information in the left and right hemispheres.

The effects of brief pictorial information on transfer between the cerebral hemispheres were investigated through recordings of skin conductance responses. The stimuli had been judged previously as neutral, positive, or negative by an independent group of participants. The verbally accessible (VA) stimuli were neutral, whereas the brief, verbally inaccessible (VI) stimuli were positive or negative. The VA and VI stimuli were presented simultaneously, in the same visual half-field (intrahemispheric), or in the opposite visual half-field (interhemispheric). In a 3rd condition, there were only VA stimuli in either visual field. The right hemisphere was especially sensitive to negative VI presentations in both the inter- and intrahemispheric groups. The left hemisphere showed a corresponding sensitivity to positive stimuli, but only in the interhemispheric group. These findings confirm the hemispheric roles in mediating positive versus negative emotions and show that left-to-right transfer can take place without linguistic cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical priming in the cerebral hemispheres: automatic in the left hemisphere, postlexical in the right hemisphere?

Automatic and postlexical semantic processing in the cerebral hemispheres was studied by presenting categorically related but nonassociated word pairs (e.g., TABLE-BED) to the left visual field (LVF) or to the right visual field (RVF) in semantic priming experiments. Experiment 1 examined automatic priming across stimulus onset asynchronies (SOAs) of 165 and 750 ms with a low proportion of related pairs and a low nonword ratio, employing a GO-NOGO lexical decision task. In contrast to an earlier view that a larger range of meanings is automatically activated in the right than in the left hemisphere, priming was observed in the RVF/left hemisphere only. SOA did not exert any effects. In Experiment 2, postlexical semantic matching of the prime and the target was encouraged by requiring subjects to respond to both of them at the same time. Now there was priming in the LVF, suggesting that a postlexical matching process works in the right hemisphere. The earlier studies showing a right hemisphere advantage in categorical priming are reinterpreted according to the postlexical right hemisphere hypothesis.     

Encoding of geometric and landmark information in the left and right hemispheres of the avian brain.

Chicks were trained binocularly to find food buried under sawdust in the center of a square enclosure. When tested in an enclosure made larger or smaller in size, binocular and left-eyed chicks searched mainly on the basis of relative distance of the food from the enclosure walls, whereas right-eyed chicks searched on the basis of absolute distance. Moreover, binocular and left-eyed chicks relied mainly on global spatial information (i.e., distances from the walls), whereas right-eyed chicks also used information provided by visual landmarks. These results suggest that the right hemisphere of the avian brain (fed mostly by the left eye) is primarily concerned with encoding of relational spatial information, whereas the left hemisphere (fed mainly by the right eye) is concerned with absolute metric information, possibly as part of an encoding strategy based primarily on local (both spatial and nonspatial) cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Creativity and the cerebral hemispheres.

Comments on M. A. Dirkes's (see record 1979-24696-001) argument for fostering divergent (creative) thinking processes in the classroom, arguing that the notions of hemispheric differences used to support the argument are not strongly supported by research. Individual differences in hemispheric processing also create problems for Dirkes's argument. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual-task interference and the cerebral hemispheres.

It has been argued that dual-task interference is reduced when the 2 cerebral hemispheres can carry out the 2 tasks independently. Evidence for this idea has arisen from studies involving manipulations such as lateralized stimulation or response, or requiring mental operations believed to depend primarily on a particular hemisphere. However, these studies have typically involved a very limited degree of response uncertainty, which appears critical in producing the most extreme dual-task interference (the psychological refractory effect). Pairs of tasks with independent response uncertainty were examined, and various manipulations were used to promote hemispheric task separation. Dual-task interference was not modulated by these manipulations. It seems likely that response selection represents a central bottleneck, in the sense that this process cannot operate simultaneously and independently in the 2 hemispheres. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What is line bisection in unilateral spatial neglect? Analysis of perceptual and motor aspects in line bisection tasks

Various methods have been applied to study the physical properties of metal supported bilayer lipid membranes (s-BLM) and large unilamellar liposomes containing biotinylated phospholipids during the binding of IgG modified by avidin. Electrostriction method applied to s-BLM showed that addition of avidin-IgG (A-IgG) complex in a small concentration (0.2 mumol/l) resulted in an approximately twofold decrease of membrane capacitance, C, increase of elasticity modulus in direction perpendicular to the membrane plane, E perpendicular, by 5-20%, increase in intrinsic membrane potential, delta phi m, by approximately 30 mV, and an approximately 5-15% increase of the coefficient of dynamic viscosity, eta. The method of ultrasonic velocimetry showed that addition into the suspension of liposomes of unmodified IgG did not induce any changes in ultrasound velocity, while addition of A-IgG complex in a concentration range of 0-1 mumol/l led to an increase of the velocity number [u]. The plot of changes of [u] versus A-IgG concentration has a tendency to saturate at concentrations above 0.5 mumol/l, which suggests long-range interactions in the membrane induced by strong binding of A-IgG to the biotin sites on the membrane. Probably, this binding leads to a decrease of the coefficient of adiabatic compressibility of liposomes.     

Neurochemical asymmetry of human cerebral hemispheres

The study was concerned with cholinesterase activity and acetylcholine content in the cortical tissue of the human brain, obtained in autopsy and during neurosurgery. A symmetry of cholinesterase activity was found in paired cortical zones of the cutaneous analyser, while in the cortical substance of the motor analyser, its activity was asymmetrical. In the parietal cortex the acetylcholine content was almost equal on two sides; a tendency to its asymmetry was noted in the frontal area. These characteristics of interhemispheric transmitter-enzyme relations between symmetrical cortical centres seem to be a link in the mechanism underlying paired and asymmetrical activity of cortical areas of the cerebral hemispheres in humans.     

How and why do the two cerebral hemispheres interact?

Research on the anatomical bases of interhemispheric interaction, including individual differences in corpus callosum (CC) anatomy, is reviewed. These anatomical findings form the basis for the discussion of 2 major themes. The 1st considers interhemispheric transfer time (IHTT) and related issues. These include varieties of IHTT and possible directional asymmetries of IHTT. Evidence suggests that pathological variations in IHTT may have cognitive consequences. The 2nd involves conditions under which interhemispheric interaction is necessary and beneficial. The data suggest that when both hemispheres have some competence at a difficult task, there is a benefit to interhemispheric interaction. The role of the CC in the dynamic distribution of attention may be particularly relevant to this advantage. Throughout the article reference is made to individual differences and developmental changes associated with interhemispheric interaction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Image generation and processing of generated images in the cerebral hemispheres.

Recent computational models describing the contribution of the cerebral hemispheres to visual imagery have suggested an exclusive capacity of the left hemisphere to generate multipart images. A brief review of relevant findings indicates that the evidence presented in support of this suggestion is not entirely compelling; this prompted a reexamination of this issue in a lateral tachistoscopic study on normal adults. Sixteen subjects participated in two experiments in which they had to decide whether or not a lowercase letter contained a segment extending above or below the main body of the letter. This decision was made directly on lowercase letters in one experiment (perceptual task) and on their generated images in the other experiment (imagery task). The quality of the letters (clear or blurred) and the retinal eccentricity of stimulus presentation (small or large) were orthogonally manipulated. The perceptual task yielded no main effect of visual field but a significant interaction of visual field and letter quality. By contrast, the imagery task resulted in a left visual-field superiority but no interaction involving the visual fields—a departure from predictions based on current models of visual imagery. In addition, the pattern of results in the imagery task corresponded to that obtained with blurred letters in the perceptual task, suggesting limitations in spatial resolution of visual images. Implications of these results for models of cerebral lateralization and visual imagery are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The cerebral hemispheres cooperate to perform complex but not simple tasks.

Three experiments were designed to examine whether task complexity determines the degree to which a division of processing across the hemispheres (i.e., across-hemisphere processing) underlies performance when within- and across-hemisphere processing are equally possible. When task complexity was relatively low, performance in a midline condition that allowed for either within- or across-hemispheric processing resembled within-hemisphere performance (Experiments 1 and 2). However, when task complexity was high, performance in a midline condition (Experiments 1 and 2) and a lateralized condition, which also allowed for either within- or across-hemisphere processing (Experiment 3), resembled across-hemisphere performance. Results complement and extend prior work (e.g., M. T. Banich & A. Belger, see record 1990-30280-001) by indicating that the degree to which interhemispheric cooperation underlies performance changes with the complexity of the task being performed. This finding suggests that the hemispheres dynamically couple or uncouple their processing as a function of task complexity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Seeing and imagining in the cerebral hemispheres: A computational approach.

Visual recognition, navigation, tracking, and imagery are posited to share certain high-level processing subsystems. A theory of some of these subsystems is formulated, developed in light of an analysis of problems that must be solved by the visual system and the constraints on the solutions to these problems. Inferences about perceptual subsystems are used to develop a theory of how mental images are generated. Support for this theory is adduced from studies of split-brain patients and a review of relevant neuropsychological findings. A computational mechanism is developed to account for how visual function becomes lateralized in the brain; this mechanism is used to predict how the hypothesized processing subsystems become lateralized. Some critical tests of the theory of lateralization of perceptual processing subsystems are reported, and the theory is extended to account for the lateralization of image-transformation subsystems and is used to account for the almost ubiquitous variability evident in the neuropsychological literature on lateralization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Integration and interference in the cerebral hemispheres: relations with hemispheric specialization

The two hemispheres of the brain often perform complementary computations and make unique contributions to task performance. This study examines the interaction of linguistic (left hemisphere) and prosodic (right hemisphere) information in speech processing. An individual differences approach is used in which interference between linguistic and prosodic processes in a Stroop-like task is compared between individuals who process the two dimensions in opposite hemispheres (complementary specialization) vs. those who process both dimensions in the same hemisphere (noncomplementary specialization). Complementarity was not related to interference in any way. This finding is consistent with the hypothesis of Chiarello and Maxfield (1996) that interference is equivalent between and within hemispheres when it arises in a response selection stage.     

Differential effect of right and left vagal stimulation on right and left circumflex coronary arteries

In anasthetised, closed-chest dogs in complete heart block that were paced at a ventricular rate of 100 beats/min, vagal stimulation increased right coronary (RC) flow by 46% and conductance by 59%, but these increases were less than those measured in the left circumflex coronary (LCC) flow (66%) and conductance (80%). Both the right and left vagus nerves affected RC and LCC flow, the left vagus having the greater effect. The response to vagal stimulation is not limited at higher ventricular rates.     

Implicit and explicit memory retrieval within and across the disconnected cerebral hemispheres.

The authors report that the divided right and left cerebral hemispheres are both adept at priming, a type of implicit memory, and that subcortical routes can mediate implicit memory retrieval across the hemispheres. Two individuals with complete section of all forebrain commissures, L.B. and N.G., were given tests of recall and recognition (explicit memory) and stem-completion priming (implicit memory). The right and left hemispheres of N.G. and the left hemisphere of L.B. exhibited significant intrahemispheric priming. Interhemispheric priming was similar in extent to intrahemispheric priming. Under several intra- and interhemispheric conditions, significant implicit retrieval occurred in the face of abnormal explicit retrieval. Because all forebrain commissures had been severed in L.B. and N.G., interhemispheric priming was necessarily supported by subcortical structures. The observed dissociation between explicit and implicit memory performance indicates that the routes of interhemispheric transfer vary with type of memory retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)