Asymmetrical effects of unilateral cortical suction lesions: Behavioral characterization.

Assessed behavioral effects of unilateral frontocortical suction lesions in the right and left hemispheres in 24 male Sprague-Dawley rats, using a computerized activity monitoring system. Lesions of the right frontal cortex produced postoperative hyperactivity consisting of increases in the total distance traveled, average distance per movement, and average speed of movement. Vertical, rotational, and stereotypic measures were not changed. Ss receiving left hemisphere lesions did not differ from sham-operated controls on any behavioral variable. The lateralized hyperactivity resulting from lesions of the right frontal cortex was confined to increased length and speed of horizontal movement and did not appear to represent a generalized increase in all components of spontaneous activity. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lactate formation from [U-13C]aspartate in cultured astrocytes: compartmentation of pyruvate metabolism

Sixteen subjects naive to biofeedback learned lateralised interhemispheric control of slow cortical potentials (SCPs) across electrode sites F3-F4 during three sessions of visual electroencephalograph (EEG) biofeedback. Subjects were required to generate slow negativity shifts either towards the left or the right hemisphere in sixty pseudorandomly ordered trials per session. Group 1 (n = 8) were told to use emotional strategies in the task (positive emotions for left hemisphere activation, negative emotion for right hemisphere activation), group 2 received no guidance. Both groups received feedback in the form of an on-screen rocket-ship, initially centrally placed, which rose to indicate an increase in left hemisphere negativity (relative to the right hemisphere) and fell to indicate an increase in right hemisphere negativity (relative to the left hemisphere). A 2 x 3 x 3 x 2 ANOVA (group x session x block x trial) showed no performance differences between the strategy and no strategy groups. Both groups learned to produce correct direction shifts in the final third of each session during both trial types (P < 0.001). The no strategy group showed a particularly strong within session learning effect (P < 0.0037) with poor performance in the early part of the sessions, and strong shifts at the end. Subjects high on withdrawal showed stronger rightward shifts in keeping with right hemisphere involvement in behavioural withdrawal. This is the first demonstration of self regulation of interhemispheric frontal asymmetry.     

Cold water stress abolishes hyperactivity produced by cortical suction lesions without altering noradrenergic depletion.

Through the 30-day postoperative period following focal right hemisphere cortical suction lesions, lesioned and sham-operated control male Sprague-Dawley rats were placed in cold water for 5 min either 4 times at weekly intervals, once during the 1st postoperative week, or not at all. Results indicate different effects of the swim on lesioned and control Ss. Stress at weekly intervals produced hyperactivity in controls but weekly stress in lesioned Ss blocked the development of their expected hyperactivity. A single stress experience occurring 1 wk postoperatively was also sufficient to block the development of hyperactivity in lesioned Ss. Stress, although affecting behavior, did not alter the pattern of norepinephrine depletions in lesioned Ss. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of stimulation of the lateral hypothalamus on the spike trains of the rabbit neocortical neurons

Cross- and autocorrelation histograms of the impulse activity of the visual and sensorimotor cortical neurons were plotted before and after stimulation of the right (RH) and left lateral hypothalamus (LH) which provoked food motivation reactions. Reorganization in correlated activity of neocortical neurons was more expressed after the LH than the RH stimulation. Only after the LH stimulation the number of neuronal pairs with co-related activity in the left hemisphere increased by 41% and some order of priority appeared in the neuronal discharges. The visual neurons discharged after the sensorimotor ones with delays up to 120 ms. The conclusion was drawn that cortical interhemispheric asymmetry of electrical activity during hunger was associated with unequal operation of the right and left lateral hypothalamus.     

Spiroperidol reinstates asymmetries in neglect in rats recovered from left or right dorsomedial prefrontal cortex lesions.

The role of dopaminergic mechanisms in spontaneous behavioral recovery from cortical neglect was examined in rats that received lesions of either the left or the right dorsomedial prefrontal cortex (PCm, also referred to as AGm). Neglect was assessed by rating the degree of head orientation to visual, auditory, or tactile stimuli. Following behavioral recovery, separate groups received 0.03, 0.05, 0.07, or 0.10 mg/kg spiroperidol or the vehicle. In accordance with the lateralization of neglect typically seen postsurgery, spiroperidol dose-dependently reinstated contralesional neglect in left PCm operates and ipsilesional neglect in right PCm operates. Neglect was reinstated by spiroperidol in right PCm operates at lower doses than in left PCm operates. Also, only right PCm operates demonstrated asymmetrical bilateral dose-dependent neglect. Spiroperidol did not produce neglect in unilaterally brain-damaged control subjects. The results indicate that dopaminergic mechanisms may underlie spontaneous recovery from cortical neglect and that these mechanisms are asymmetrical in left and right PCm operates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of letter and picture naming resulting from callosal disconnection

BACKGROUND: Detailed mapping of the corpus callosum for functional fractionation in humans remains incomplete. OBJECTIVE: To examine separable interhemispheric transfer of visual information by callosal fibers, especially in the splenium. METHODS: We examined callosal disconnection signs in a 14-year-old boy with a lesion confined to the posterior part of the splenium and reviewed reported cases with callosal lesions. RESULTS AND CONCLUSION: The patient presented with left hemialexia as the only manifestation of callosal disconnection syndrome. The only difficulty demonstrated was in reading aloud or copying letters, which were presented tachistoscopically to the left visual field, with his right hand. He could copy letters presented to his left visual field with his left hand, however. Therefore, left hemialexia was not due to hemiamblyopia or hemineglect. There was no anomia for pictures and colors in the left visual field. MRI revealed that the lesion was limited to the ventroposterior end of the splenium. Review of 40 reported patients with callosal lesions suggests that the anterior to middle part of the splenium is involved in transferring picture information from the language-nondominant hemisphere to the language-dominant hemisphere and that the ventroposterior part is involved in transferring letter information.     

Left hemispheric neuronal heterotopia: a PET, MRI, EEG, and neuropsychological investigation of a university student

A 21-year-old left-handed medical student had a prominent unilateral cerebral cortical malformation due to an ontogenetic migration disorder. We performed neuropsychological studies, EEG, T1- and T2-weighted and proton-density MRI, and positron emission tomography (PET) (under both the resting condition and neuropsychological activation). Neuropsychological testing revealed normal intelligence and generally normal memory functioning but selective deficits in tests of verbal fluency and spatial-figural relationships. Proton-density and T2-weighted MRI revealed extensive left cortical heterotopia that included parts of the Wernicke area. PET under the resting condition revealed a small interhemispheric difference with slightly reduced glucose metabolism in the left temporoparietal cortical zone. An activation PET (with the patient performing a verbal fluency test) resulted in a normal overall increase in metabolism but marked deviations in cortical areas. The highest activity changes were in the Broca and Wernicke areas of the right hemisphere, and there was very little activation in those regions of the left hemisphere that were expected to respond well to the activation--the temporal, parietal, and temporo-occipital cortical zones. We conclude that there can be large compensations for unilateral heterotopia.     

Spatial relationships of electrical activity during reproduction of verbal signals in children

The study of intercentral correlations of the brain biopotentials in five-to six year old children revealed considerable differences in the spatial distribution of interrelations of the neocortex projection and associative zones during reproduction of familiar and unfamiliar words. Reproduction of familiar words was accompanied by the greatest enhancement of interrelations of associative structures (infraparietal, frontal areas and Broca speech centre) with projection zones of the motor and acoustic analysers in the left hemisphere, while reproduction of unfamiliar words was attented with closer connections of the projection motor zone with the temporal and the anterior associative (frontal and speech) zones in the right hemisphere. The facts obtained testify to the existence of the interhemispheric asymmetry and to the different involvement of the neocortex projection and associative zones in the organization of motor speech in children.     

Interhemispheric Interaction During Global-Local Processing in Mathematically Gifted Adolescents, Average-Ability Youth, and College Students.

Interhemispheric interaction in mathematically gifted (MG) adolescents, average-ability (AA) youth, and college students (CS) was examined by presenting hierarchical letter pairs in 3 viewing conditions: (a) unilaterally to the right hemisphere (RH), (b) unilaterally to the left hemisphere (LH), or (c) bilaterally, with 1 member of the pair presented to each hemisphere simultaneously. Participants made global-local, match-no-match judgments. For the AA and CS, the LH was faster for local matches and the RH for global matches. The MG showed no hemispheric differences. Also, AA and CS were slower on cooperative compared with unilateral trials, whereas the MG showed the opposite pattern. These results suggest that enhanced interhemispheric interaction is a unique functional characteristic of the MG brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive dominance and functional asymmetry of brain

Rapid environmental changes lead to formation of adaptive dominance which makes the body search for biologically appropriate reactions under the new conditions. This changes in fundamental properties of the brain, like memory, emotions, hemispheric functional asymmetry by ensuring optimization of the processing of a drastically increased flow of signals. The order of information processing is determined by its significance for the body. Selection of new and emotiogenic signals first activates by changes in cortical-subcortical relationships, the left hemisphere and the right hemisphere isolate new and emotiogenic information, respectively. Subsequent inversion of hemispheric dominance, i.e. the prevalence of right hemispheric functions provides construction of a new programme of the body's interaction with the altered environment. This may be possible as it is the right hemisphere that predominantly regulates emotional, humoral, and endocrine regulation. At this stage of adaptation, there is an increase in interhemispheric integration which eventually restores the initial interhemispheric relationships. The newly recovered dominance of the left hemisphere ensures not only an effective reproduction of the formed programme, but organizes a leading reflection of reality.     

Spindle frequency activity in the sleep EEG: individual differences and topographic distribution

Focal magnetic transcranial stimulation (TCS) is employed for mapping of the motor cortical output to abductor digiti minimi (ADM) muscle. The aim of this study was to evaluate the interhemispheric asymmetries in normals. Motor maps were obtained through motor evoked potentials (MEPs) recordings from ADM muscle in 20 healthy subjects in right and left hemispheres TCS. Measurement of several indexes such as excitability threshold, MEPs amplitude, MEPs latency, and silent period duration did not show differences between the hemispheres. Moreover, no interhemispheric asymmetries were found when the amplitude ratio values were analyzed. The hand motor cortical area, as represented by the number of responsive sites (3.6 vs. 3.5) and the "hot spot" site localization presented a fairly symmetrical organization. Absolute values displayed a relatively wide intersubject variability, while their interhemispheric differences were extremely restricted. This observation can offer a new tool in diagnosing and following up neurological disorders affecting the central motor system, mainly for those concerning monohemispheric lesions.     

The decoding of emotional concepts in patients with focal cerebral lesions

The effects of focal brain lesions on the decoding of emotional concepts in facial expressions were investigated. Facial emotions are hierarchically organized patterns comprising (1) structural surface features, (2) discrete (primary) emotional categories and (3) secondary dimensions, such as valence and arousal. Categorical decoding was measured using (1) selection of category labels and selection of the named emotion category; (2) matching one facial expression with two choice expressions. Dimensional decoding was assessed by matching one face with two different expressions with regard to valence or arousal. 70 patients with well documented cerebral lesions and 15 matched hospital controls participated in the study. 27 had left brain damage (LBD; 10 frontal, 10 temporal, 7 parietal); 37 had right brain damage (RBD; 15 frontal, 11 temporal, 11 parietal). Six additional patients had lesions involving both frontal lobes. Right temporal and parietal lesioned patients were markedly impaired in the decoding of primary emotions. The same patients also showed a reduced arousal decoding. In contrast to several patients with frontal and left hemisphere lesions, emotional conceptualization and face discrimination was not independent in these groups. No group differences were observed in valence decoding. However, right frontal lesions appeared to interfere with the discrimination of negative valence. Moreover, a distraction by structural features was noted in RBD when facial identities were varied across stimulus and response pictures in matching tasks with differing conceptual load. Our results suggest that focal brain lesions differentially affect the comprehension of emotional meaning in faces depending on the level of conceptual load and interference of structural surface features.     

The effect of goal-subgoal conflict on planning ability after frontal- and temporal-lobe lesions in humans

Twenty-one patients with unilateral prefrontal cortical neurosurgical lesions (11 left and 10 right) and 38 patients with unilateral temporal lobectomy (19 left and 19 right) were compared to 44 matched control subjects on their performance on the 3-D Computerized Tower of Hanoi (3-D CTOH) test. The problems were split into those with or without a significant goal-subgoal conflict determined by whether the correct first move in each problem took the subject apparently away or towards the final goal state. The left frontal lesion and right temporal lobectomy groups were significantly impaired on problems with goal-subgoal conflicts. In the left frontal group, this deficit was confined to earlier four-move problems, whereas the right temporal group showed a more general deficit on later five-move problems. The left frontal lesion deficit is explained in terms of an inability to inhibit the response compatible with achieving a final goal, whereas the impairment in the right lesion group was related to a specific impairment in spatial memory.     

Callosal involvement in a lateralized stroop task in alcoholic and healthy subjects.

To investigate the role of interhemispheric attentional processes, 25 alcoholic and 28 control subjects were tested with a Stroop match-to-sample task and callosal areas were measured with magnetic resonance imaging. Stroop color-word stimuli were presented to the left or right visual field (VF) and were preceded by a color cue that did or did not match the word's color. For matching colors, both groups showed a right VF advantage; for nonmatching colors, controls showed a left VF advantage, whereas alcoholic subjects showed no VF advantage. For nonmatch trials, VF advantage correlated with callosal splenium area in controls but not alcoholic subjects, supporting the position that information presented to the nonpreferred hemisphere is transmitted via the splenium to the hemisphere specialized for efficient processing. The authors speculate that alcoholism-associated callosal thinning disrupts this processing route. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal and spatial context memory in patients with focal frontal, temporal lobe, and diencephalic lesions

Patients with focal frontal, temporal lobe, or diencephalic lesions were investigated on measures of temporal (recency) and spatial (position) context memory, after manipulating exposure times to match recognition memory for targets (pictorial stimuli) as closely as possible. Patients with diencephalic lesions from an alcoholic Korsakoff syndrome showed significant impairment on the temporal context (recency) task, as did patients with frontal lesions penetrating the dorsolateral frontal cortex, according to MRI (and PET) evidence. Patients with temporal lobe lesions showed only a moderate (non-significant) impairment on this task, and patients with medial frontal lesions, or large frontal lesions not penetrating the dorsolateral cortical margins, performed as well as healthy controls at this task. On the spatial context memory task, patients with lesions in the temporal lobes showed significant impairment, and patients with right temporal lesions performed significantly worse than patients with left temporal lesions. Patients with diencephalic lesions showed only a modest (non-significant) impairment on this task, and the frontal lobe group performed normally. When a group of patients with temporal lobe lesions resulting from herpes encephalitis were examined separately, an identical pattern of results was obtained, the herpes group being significantly impaired on spatial memory and showing a trend towards impairment for temporal context memory. There were strong correlations between anterograde memory quotients and context memory performance (despite the use of an exposure time titration procedure) and a weak association in the frontal group with one frontal/executive task [corrected] (card-sorting perservations). It is predicted that correlations between temporal context memory and frontal/executive tasks will be greater in samples of patients all of whom have frontal lesions invading the dorsolateral cortical margin.     

Apoptosis signaling by death receptors

How do stimulus size and item number relate to the magnitude and direction of error on center estimation and line cancellation tests? How might this relationship inform theories concerning spatial neglect? These questions were addressed by testing twenty patients with right hemisphere lesions, eleven with left hemisphere lesions and eleven normal control subjects on multiple versions of center estimation and line cancellation tests. Patients who made large errors on these tests also demonstrated an optimal or pivotal stimulus value, i.e., a particular size center estimation test or number of lines on cancellation that either minimized error magnitude relative to other size stimuli (optimal) or marked the boundary between normal and abnormal performance (pivotal). Patients with right hemisphere lesions made increasingly greater errors on the center estimation test as stimuli were both larger and smaller than the optimal value, whereas those with left hemisphere lesions made greater errors as stimuli were smaller than a pivotal value. In normal subjects, the direction of errors on center estimation stimuli shifted from the right of true center to the left as stimuli decreased in size (i.e., the crossover effect). Right hemisphere lesions exaggerated this effect, whereas left hemisphere lesions diminished and possibly reversed the direction of crossover. Error direction did not change as a function of stimulus value on cancellation tests. The demonstration of optimal and pivotal stimulus values indicates that performances on center estimation and cancellation tests in neglect are only relative to the stimuli used. In light of other studies, our findings indicate that patients with spatial neglect grossly overestimate the size of small stimuli and underestimate the size of large stimuli, that crossover represents an "apparent" shift in error direction that actually results from normally occurring errors in size perception, and that the left hemisphere is specialized for one aspect of size estimation, whereas the right performs dual roles.     

Interhemispheric transfer in children with early-treated phenylketonuria

Phenylketonuria (PKU) is a genetic disorder of amino acid metabolism that is associated with brain catecholamine depletion and deficient myelination. Although neuropsychological deficits have been documented in children with early-treated PKU (ETPKU), no study to date has examined possible effects of impaired myelination in this population. In the present study, interhemispheric transfer time was assessed for 14 children with ETPKU, 22 children with attention deficit-hyperactivity disorder, and 48 normal children, using a manual reaction time paradigm previously validated with callosal agenesis patients (Milner, 1982). Children with ETPKU demonstrated slowed interhemispheric transfer from the left to the right hemisphere as compared with the two other groups. The magnitude of slowing was correlated with age and phenylalanine levels at birth. Results support the hypothesis that abnormal myelination disrupts the development of interhemispheric connections in ETPKU, and suggest that left hemisphere projections may be particularly susceptible to such disruption.     

Bilateral neuropathologic changes in a child with hemimegalencephaly

Evaluation of a 7-month-old girl with developmental delay and intractable seizures revealed hemispheric asymmetry and an enlarged right cerebral hemisphere. Because of a history of seizures refractory to medical therapy, she was admitted for right hemispherectomy, but died of complications of surgery. Postmortem brain examination revealed asymmetric enlargement of the right cerebral hemisphere but no gross abnormalities in the left hemisphere. Microscopic examination demonstrated bilateral neuropathologic changes consistent with severe cortical dysplasia in the right cerebral hemisphere and mild cortical dysplasia in the left. Although white matter abnormalities in the unaffected hemisphere have been reported in hemimegalencephaly, bilateral cortical abnormalities, not reported previously in patients with hemimegalencephaly, may account for the varied clinical outcome with medical therapy or after hemispherectomy.     

Evidence for anatomical but not functional asymmetry in the hemidecorticate rat.

Studied 51 male Long-Evans rats with unilateral ablation of the left or right cerebral neocortex or left or right hippocampus using a battery of tests of spatial orientation, motor coordination, and social behavior, including Morris water task, radial arm maze, feeding, narrow beam traversing, puzzle latches, hoarding, grooming, nest building, running wheel activity, male–male interaction, and shock-induced aggression. Comparison of the brains of operated and control Ss confirmed previous suggestions that the right hemisphere of the rat is bigger and may have different connections than the left hemisphere. Despite the morphological asymmetries, comparison of the behavior of Ss with right and left hemidecortication and right and left hippocampal lesions failed to show a single instance of functional asymmetry in the rat brain. These behavioral results contrast with previous reports of functional asymmetry in the control of activity, orientation, and rotation. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Asymmetry of the interhemispheric visuomotor integration in callosal agenesis

We measured visuomotor responses following the Poffenberger paradigm in an acallosal boy, without other detectable neural defects. In this task crossed and uncrossed RT reflect the time of intra- and interhemispheric integration and the difference (CUD) estimates the interhemispheric transfer time. CUDs in the hemifields were largely asymmetrical in this subject, suggesting that visuomotor processing is extremely lengthened when the right hemisphere (RH) detects the light and the left hemisphere (LH) controls the motor output whereas it is very fast in the opposite direction. This asymmetry, which is present in comparable data available from the literature, may indicate the functional superiority of the LH in controlling the ipsilateral hand, as suggested by recent MRI findings.