Reduction in cerebral activation after right hemisphere stroke

Destruction or disconnection of specific neuronal structures or failure to activate those structures may impair brain function. Because the right hemisphere seems dominant for mediating arousal, which is an important determinant of the capacity for cerebral activation, we predicted that subjects with right hemisphere damage would have a greater reduction in the capacity for cerebral activation than subjects with left hemisphere damage. A paradigm requiring that two simple tasks be performed singly and simultaneously was used to assess the capacity for activation. Subjects with right hemisphere damage had significantly greater impairment in the capacity for cerebral activation than subjects with left hemisphere damage. This impairment may partly explain the associations between right hemisphere damage and decreased ability to perform certain analytic and linguistic tasks.     

Dyslexic adolescents: evidence of impaired visual and auditory language processing associated with normal lateralization and visual responsivity.

The questions of whether chronically dyslexic adolescent suffer any deficits of simple language stimulus processing or are less left hemisphere dominant than normal reading controls were addressed. The dyslexics were chosen for clarity of their specific reading problem and were older than dyslexics previously studied with lateralizing tests. Tasks administered in Experiment I were unilateral and bilateral tachistoscopic work recognitions and a tachistoscopic recognition report-time task for single lateralized letter stimuli. Experiment II, conducted a year later, readministered these tasks with modifications, and added dichotic digits and motor reaction time-stimulus detection tasks. It was concluded that right handed, chronic dyslexics: (1) possess left hemisphere language specialization; (2) show normal interhemispheric processing delays for single letter stimuli; (3) are, unlike nondyslexis but equally poor-reading Ss, clearly impaired in their efficiency of visual and auditory processing of simple language stimuli; (4) possess clear auditory memory deficits for verbal material; and (5) may possess an additional deficit of left hemisphere visual association area function.     

Right Hemisphere Language Dominance in a Right-Handed Patient with Late-Onset Seizures

Right hemisphere language dominance is rare in right-handed individuals and usually the result of language transfer associated with early left hemisphere pathology. We studied a 33-year-old right-handed man, with a normal MRI scan, who developed left frontal lobe seizures at age 15 years. Language lateralization testing by intracarotid amobarbital injection and dichotic listening showed the patient to be strongly right hemisphere language dominant. The clinical features of this patient do not fit the profile of pathology-induced language transfer, but instead suggest that he was right hemisphere language dominant before developing seizures. This case underscores the importance of language lateralization testing in patients who are candidates for seizure surgery, even if they are strongly right-handed and have late-onset seizures, features usually associated with left hemisphere language dominance. One implication is that the incidence of right hemisphere language dominance in the right-handed population may be underestimated.     

Right-hand superiority for throwing but not for intercepting

In humans, the organization of movements performed by both upper limbs, relies significantly on a left hemisphere "praxis" system that also subsumes speech function. Right hand preference may also be an expression of this left hemisphere dependence, arising from the preferential connections of the right hand to the left hemisphere. Consequently, a manual task that maximizes the spatial complexity of a target (presumably engaging right hemisphere mechanisms), while concurrently minimizing motor-programming demands, was expected to yield a diminished disparity in preference and performance between the hands. Left and right hand accuracy were measured independently for two motor tasks in 48 normal right-handed university students. In the first task, darts were thrown overhand at a stationary target. For the second task, subjects were asked to use the open hand to block (but not catch) projectiles launched at varying trajectories and velocities. ANOVA yielded a significant Hand x Task interaction, in which the left hand did not differ from the right hand in intercepting ability, but was significantly less accurate than the right hand for throwing. A sex difference favouring males was found for both tasks; this difference was not reducible to differences in physique or athleticism.     

Intracarotid amobarbital procedure and prediction of postoperative memory in patients with left temporal lobe epilepsy and hippocampal sclerosis

PURPOSE: Although temporal lobe epilepsy (TLE) patients with dominant hemisphere hippocampal sclerosis generally have good cognitive outcome after anterior temporal lobectomy (ATL), a minority of patients experience at least mild post-ATL decline on one or more standardized measures of episodic and semantic memory. The goal of this investigation was to determine whether memory outcome in this group could be predicted from preoperative intracarotid amobarbital procedure (IAP) recognition memory scores. METHODS: Data from 22 left TLE patients were studied retrospectively. All were left hemisphere language dominant and had IAP scores for each hemisphere, a significant degree of pathology-confirmed left hippocampal sclerosis (HS+), and no positive MRI findings other than atrophy. Cognitive outcome status was represented by the number of pre- to post-ATL declines across three tests, as defined by 90th percentile Reliable Change Index (RCI) criteria. RESULTS: Only 14% of the sample exhibited decline on more than one memory test. Low right IAP (left hemisphere injection) scores and relatively high preoperative cognitive ability and age at surgery predicted a greater risk of post-ATL memory decline. CONCLUSIONS: A minority of left TLE HS+ patients experience at least a mild degree of RCI-defined decline in episodic or semantic memory after ATL. The right hemisphere IAP memory score, which reflects the functional reserve of the contralateral hemisphere, can help predict the risk of postoperative memory decline for TLE patients in whom HS+ is likely based on the presence of hippocampal atrophy on MRI or early age of seizure onset.     

Imaging language networks before and after anterior temporal lobe resection: results of a longitudinal fMRI study

Purpose: Anterior temporal lobe resection (ATLR) controls seizures in up to 70% of patients with intractable temporal lobe epilepsy (TLE) but, in the language dominant hemisphere, may impair language function, particularly naming. Functional reorganization can occur within the ipsilateral and contralateral hemispheres. We investigated reorganization of language in left‐hemisphere–dominant patients before and after ATLR; whether preoperative functional magnetic resonance imaging (fMRI) predicts postoperative naming decline; and efficiency of postoperative language networks. Methods: We studied 44 patients with TLE due to unilateral hippocampal sclerosis (24 left) on a 3T GE‐MRI scanner. All subjects performed language fMRI and neuropsychological testing preoperatively and again 4 months after left or right ATLR. Key Findings: Postoperatively, individuals with left TLE had greater bilateral middle/inferior frontal fMRI activation and stronger functional connectivity from the left inferior/middle frontal gyri to the contralateral frontal lobe than preoperatively, and this was not observed in individuals with right TLE. Preoperatively, in left and right TLE, better naming correlated with greater preoperative left hippocampal and left frontal activation for verbal fluency (VF). In left TLE, stronger preoperative left middle frontal activation for VF was predictive of greater decline in naming after ATLR. Postoperatively, in left TLE with clinically significant naming decline, greater right middle frontal VF activation correlated with better postoperative naming. In patients without postoperative naming decline, better naming correlated with greater activation in the remaining left posterior hippocampus. In right TLE, naming ability correlated with left hippocampal and left and right frontal VF activation postoperatively. Significance: In left TLE, early postoperative reorganization to the contralateral frontal lobe suggests multiple systems support language function. Postoperatively, ipsilateral recruitment involving the posterior hippocampal remnant is important for maintaining language, and reorganization to the contralateral hemisphere is less effective. Preoperative left middle frontal activation for VF was predictive of naming decline in left TLE after ATLR.     

Semantic priming by pictures and words in the cerebral hemispheres

In order to determine whether pictures would act as more effective semantic primes than words in the right cerebral hemisphere, automatic semantic activation in intact hemispheres was studied with primed GO-NOGO lexical decision tasks by presenting word-word and picture-word pairs to the left visual field (right hemisphere) or to the right visual field (left hemisphere). Response times in Experiment 1 showed that categorically related targets (e.g., TABLE-BED) were primed only in the right visual field after both word and picture primes. Experiment 2 found that picture primes activated the representations of the corresponding written names in both visual fields. These observations suggest that the range of automatic semantic activation is larger in the left than in the right hemisphere. The results implicate that semantic categories may be organized in a different fashion in the left than the right hemisphere.     

Reaction times of four year old children to monaurally presented verbal stimuli: some evidence for right-hemisphere linguistic function

Previous studies of cerebral dominance in children have provided information about the relative superiority of the left hemisphere over the right for language processing. The present study, however, assessed the absolute capacity of each hemisphere's ability for analyzing auditory-verbal stimuli in a group of young children (mean age = 4.0). Twenty-four normally developing children (12 males and 12 females) responded to monaurally presented verbal stimuli with their right and left hands at separate times. The results were consistent with an efficiency model of neurolinguistic organization, suggesting that the childrens' minor hemisphere was actively processing verbal information in the presence of a dominant left hemisphere.     

The dynamic nature of language lateralization: effects of lexical and prosodic factors

In dichotic listening, a right ear advantage for linguistic tasks reflects left hemisphere specialization, and a left ear advantage for prosodic tasks reflects right hemisphere specialization. Three experiments used a response hand manipulation with a dichotic listening task to distinguish between direct access (relative specialization) and callosal relay (absolute specialization) explanations of perceptual asymmetries for linguistic and prosodic processing. Experiment 1 found evidence for direct access in linguistic processing and callosal relay in prosodic processing. Direct access for linguistic processing was found to depend on lexical status (Experiment 2) and affective prosody (Experiment 3). Results are interpreted in terms of a dynamic model of hemispheric specialization in which right hemisphere contributions to linguistic processing emerge when stimuli are words, and when they are spoken with affective prosody.     

Differential effects of left and right cerebral vascular accidents on language competency.

While language facility was once considered to be the sole province of the "dominant" left hemisphere, clinical and experimental findings suggest the right hemisphere plays an equally important role in many language tasks. To elucidate differential hemispheric language processes, Right Hemisphere Language Battery and Western Aphasia Battery data from left (LHD) and right (RHD) hemisphere cerebral vascular accident (CVA) patients and controls were subjected to multivariate discriminant analysis. The highly significant group differences and overall 95% classification rate obtained confirms the utility of the dependent measures in differential diagnosis. Results suggest CVA patients experience disparate language deficits, with the LHD group experiencing concordant-convergent language deficits and the RHD group displaying discordant-divergent deficits that interfere with the receptive and expressive language skills necessary for successful social discourse.     

A dissociation between the representation of tool-use skills and hand dominance: insights from left- and right-handed callosotomy patients

The overwhelming majority of evidence indicates that the left cerebral hemisphere of right-handed humans is dominant both for manual control and the representation of acquired skills, including tool use. It is, however, unclear whether these functions involve common or dissociable mechanisms. Here we demonstrate that the disconnected left hemispheres of both right- and left-handed split-brain patients are specialized for representing acquired tool-use skills. When required to pantomime actions associated with familiar tools (Experiment 2), both patients show a right-hand (left hemisphere) advantage in response to tool names, pictures, and actual objects. Accuracy decreases as stimuli become increasingly symbolic when using the left hand (right hemisphere). Tested in isolation with lateralized pictures (Experiment 3), each patient's left hemisphere demonstrates a significant advantage over the right hemisphere for pantomiming tool-use actions with the contralateral hand. The fact that this asymmetry occurs even in a left-handed patient suggests that the left hemisphere specialization for representing praxis skills can be dissociated from mechanisms involved in hand dominance located in the right hemisphere. This effect is not attributable to differences at the conceptual level, as the left and right hemispheres are equally and highly competent at associating tools with observed pantomimes (Experiment 4).     

Ipsilesional versus contralesional neglect depends on attentional demands

Right hemisphere injuries often produce contralesional hemispatial neglect (CN). In contrast to CN, some patients with right hemisphere damage can also show so-called ipsilesional neglect (IN). Previous reports found that patients tend to show IN on line bisection tasks but CN on other tasks such as target cancellation. To learn why these two tasks induce different spatial biases in patients with right hemisphere injury, conventional (i.e. solid) line bisection was compared with two novel bisection tasks consisting of horizontally aligned strings of characters. The subjects' task was to mark a target character that was at or closest to the true midpoint of the simulated line. Four of the 5 patients showed a dissociation whereby IN occurred for solid lines while CN was observed on character lines. The two patients assessed with an antisaccade paradigm showed a "visual grasp" for leftward stimuli. The present results suggest that neglect on line bisection may reflect two opposing forces, an approach behavior or "visual grasp" toward left hemispace and an attentional bias toward right hemispace.     

Apraxia of the left limbs in a case of callosal disconnection: the contribution of medial frontal lobe damage

A 40 year old right-handed woman suffered hemorrhage from an anterior cerebral artery aneurysm. CT scan showed destruction of the anterior two thirds of the corpus callosum, both cingulate gyri, and the white matter underlying the medial frontal lobes. The left limbs displayed apraxia on verbal command, in imitation, and in actual object use. There were antagonistic actions of both hands, and the patient accused her left hand of disobeying her. We interpret the leftsided apraxia as resulting from a lack of interhemispheric transfer combined with a deficit in ipsilateral motor control stemming from damage to the left supplementary motor area. Right frontal lobe damage may have impaired the motor learning capacity of the right hemisphere and thus its ability to compensate for the lack of left hemisphere motor control.     

Modulation of spatial bias in the dual task paradigm: evidence from patients with unilateral parietal lesions and controls

Lateral attentional bias is common after unilateral brain damage. It has sometimes been proposed that lateral bias is increased by concurrent cognitive demands, perhaps because of lost top-down compensation. However, an important limitation of previous studies is the sole use of right hemisphere patients. Here we employed a dual task paradigm to measure spatial bias on a visual task while manipulating demands of a concurrent auditory task. Bias was examined in patients with left or right parietal lesions and controls. In Experiment 1 the addition of either a non-spatial or spatial auditory task led to a rightward shift in visual bias. This same rightward shift occurred in controls, left parietals and right parietals. Experiment 2 examined whether the participant's response hand affected their bias. In addition, it attempted to distinguish between the hypothesis that modulatory effects are strongly dependent on lateralization of the concurrent task, and the hypothesis that dual tasks cause a general rightward shift. Response hand was found to have no effect on spatial bias. In addition, bias did not differ between left hemisphere (verbal) and right hemisphere (pitch) concurrent tasks, though the trend was for a smaller rightward shift with the verbal task. Our results show that dual tasks do not exacerbate patients' underlying deficits; instead they cause a global shift in attention to the right. This shift may resemble general rightward shifts that have previously been linked to reduced arousal.     

Sources of between-subjects variability in perceptual asymmetries: a meta-analytic review.

A number of studies have reported correlations between subjects' asymmetry scores on left and right hemisphere specialized tasks. In this paper we report the results of meta-analyses performed on these correlations. Results showed positive correlations between subjects' asymmetry scores on left and right hemisphere specialized tasks in both modalities (asymmetry scores were computed as R-L for both left and right hemisphere specialized tasks). Thus, in both modalities, some of the between-subjects variability in asymmetry scores appears to reflect non-stimulus specific individual differences in perceptual asymmetry. For the visual asymmetry tasks, results also showed that the subjects' asymmetry scores on left and right hemisphere specialized tasks were more highly correlated under conditions of bilateral than unilateral input. This finding suggests that bilateral tasks may be more sensitive to "characteristic perceptual asymmetry" than unilateral tasks.     

Inference in right hemisphere damaged individuals' comprehension: The role of sustained attention

The ability to make inferences for the purposes of comprehension is considered an important factor in pragmatic ability. In this experimental group study with stroke patients, the ability to make inferences and its associations with sustained attention and verbal working memory were explored. A group of 14 left‐hemisphere‐damaged individuals had more difficulty with tasks requiring the ability to revise inferences than a matched control group. Their results on those tasks tended to be associated with verbal working memory capacity. A group of 14 right‐hemisphere‐damaged (RHD) individuals also had problems in revising inferences, but their results were associated with sustained attention. In addition, the RHD subjects had problems in making inferences about characters' attitudes or motives. A lack of significant differences in results on tasks between the groups of brain damaged individuals indicate that comprehension of complex information might be impaired post stroke, irrespectively of whether the damage is to the left or right hemisphere. The results suggest that sustained attention, whilst not being a solitary sufficient factor, might somehow be involved in comprehension problems related to RHD. Implications for further research and clinical management of these sometimes subtle problems are discussed.     

Processing of facial blends of emotion: support for right hemisphere cognitive aging

Clinical research on facial emotions has focused primarily on differences between right and left hemiface. Social psychology, however, has suggested that differences between upper versus lower facial displays may be more important, especially during social interactions. We demonstrated previously that upper facial displays are perceived preferentially by the right hemisphere, while lower facial displays are perceived preferentially by the left hemisphere. A marginal age-related effect was observed. The current research expands our original cohort to include 26 elderly individuals over age 62. Fifty-six, strongly right-handed, healthy, adult volunteers were tested tachistoscopically by flashing randomized facial displays of emotion to the right and left visual fields. The stimuli consisted of line drawings displaying various combinations of emotions on the upper and lower face. The subjects were tested under two conditions: without attend instruction and with instructions to attend to the upper face. Based on linear regression and discriminant analyses modeling age, subject performance could be divided into two distinct groups: Young (< 62 years) and Old (> 62 years). Without attend instructions, both groups robustly identified the emotion displayed on the lower face, regardless of visual field presentation. With instructions to attend to the upper face, the Old group demonstrated a markedly decreased ability to identify upper facial displays, compared to the Young group. The most significant difference was noted in the left visual field/right hemisphere. Our results demonstrate a significant decline in the processing of upper facial emotions by the right hemisphere in older individuals, thus providing partial support for the right hemisphere hypothesis of cognitive aging. The decreased ability to perceive upper facial displays coupled with age-related deficits in processing affective prosody may well cause impaired psychosocial competency in the elderly.     

Lateralisation of spatial processing and age

Studies assessing spatial ability suggest right hemisphere specialisation for coordinate spatial processing and left hemisphere specialisation for categorical spatial processing. With regard to healthy ageing, spatial abilities may be affected selectively, with right hemisphere based coordinate processes being more vulnerable to age-related decline, but previous research has been inconsistent. In the present study, age and hemispheric specialisation of categorical and coordinate spatial abilities were explored. Testing 56 right-handed younger and older participants clearly showed a left hemisphere advantage for the categorical task and a right hemisphere advantage for the coordinate spatial task, for both age groups combined. Older adults were slower to process information and make a spatial judgement; nevertheless, the neural specialisation underlying spatial abilities seems to have remained consistent with age.     

Reading direction and spatial neglect

Many American and European investigators have reported that hemispatial neglect is more frequent and more severe after right than left hemisphere lesions. This hemispheric asymmetry may be due to biological asymmetries, learned behavior, or both. Readers of European languages, unlike readers of Semitic languages, scan from left to right. Learned rightward scanning may increase the unilateral neglect associated with right hemisphere lesions and reduce the severity of neglect associated with left hemisphere lesions. To learn if hemispheric asymmetries of neglect are influenced by learned scanning behavior, we used line bisection and cancellation tasks to study patients with unilateral stroke who read only a Semitic or European language before the age of fifteen. We found that independent of reading direction, unilateral neglect was more commonly associated with right than left hemisphere lesions. After right hemisphere damage right to left readers bisected lines closer to center than left to right readers, but on the cancellation test readers of European languages did not perform differently than readers of Semitic languages. These findings suggest that whereas learned scan direction may influence the severity of neglect when measured by line bisection, these learned directional scans cannot fully account for the observed hemisphere asymmetries of neglect. They also suggest that the line bisection test is more influenced by the direction of scanning than is the cancellation test.     

Pseudoneglect on a cancellation task

The "pseudoneglect" phenomenon initially described by Bowers and Heilman (1980) was examined in the context of a cancellation task. Normal subjects were administered cancellation tasks under a high arousal condition with target and foils which were intended to activate left hemisphere (verbal) processes or right hemisphere (spatial) processes. Significant right lateralized inattention was present on the spatial stimuli. The verbal stimuli failed to produce significant lateralized inattention, although it produced moderate left inattention among right-handed males. The results are consistent with literature identifying the right hemisphere as dominant for attention.