Unilateral Left Hemisphere Lesions Research Articles

A dual task priming investigation of right hemisphere inhibition for people with left hemisphere lesions

BackgroundDuring normal semantic processing, the left hemisphere (LH) is suggested to restrict right hemisphere (RH) performance via interhemispheric suppression. However, a lesion in the LH or the use of concurrent tasks to overload the LH's attentional resource balance has been reported to result in RH disinhibition with subsequent improvements in RH performance. The current study examines variations in RH semantic processing in the context of unilateral LH lesions and the manipulation of the interhemispheric processing resource balance, in order to explore the relevance of RH disinhibition to hemispheric contributions to semantic processing following a unilateral LH lesion.MethodsRH disinhibition was examined for nine participants with a single LH lesion and 13 matched controls using the dual task paradigm. Hemispheric performance on a divided visual field lexical decision semantic priming task was compared over three verbal memory load conditions, of zero-, two- and six-words. Related stimuli consisted of categorically related, associatively related, and categorically and associatively related prime-target pairs. Response time and accuracy data were recorded and analyzed using linear mixed model analysis, and planned contrasts were performed to compare priming effects in both visual fields, for each of the memory load conditions.ResultsControl participants exhibited significant bilateral visual field priming for all related conditions (p < .05), and a LH advantage over all three memory load conditions. Participants with LH lesions exhibited an improvement in RH priming performance as memory load increased, with priming for the categorically related condition occurring only in the 2- and 6-word memory conditions. RH disinhibition was also reflected for the LH damage (LHD) group by the removal of the LH performance advantage following the introduction of the memory load conditions.ConclusionsThe results from the control group are consistent with suggestions of an age related hemispheric asymmetry reduction and indicate that in healthy aging compensatory bilateral activation may reduce the impact of inhibition. In comparison, the results for the LHD group indicate that following a LH lesion RH semantic processing can be manipulated and enhanced by the introduction of a verbal memory task designed to engage LH resources and allow disinhibition of RH processing.

A case of impaired verbalization but preserved gesticulation of motion events

In most cultures, most of the time, when people talk they gesture. We took advantage of a rare opportunity to explore the relation between the verbalization and gesticulation of motion events by studying Marcel, an English speaker with a unilateral left-hemisphere lesion affecting frontal, parietal, and temporal sectors of the perisylvian cortex. Marcel has intact semantic knowledge of the three major classes of words that are commonly used in English descriptions of motion events—specifically, concrete nouns, action verbs, and spatial prepositions—as well as intact syntactic knowledge of how these word classes are typically combined in the intransitive motion construction (e.g., The ball rolled down the hill). However, his ability to retrieve the lexical-phonological structures of these words is severely impaired. Despite this profound anomia, he is still remarkably skilled at producing iconic manual depictions of motion events, as demonstrated in two experiments involving spontaneous gestures and one experiment involving elicited gestures. Moreover, the structural characteristics of Marcel's gestures are clearly sensitive to the idiosyncratic meanings of English verbs and prepositions, and they may also be sensitive to the way motion events are syntactically packaged in the intransitive motion construction. These findings improve our understanding of how some brain-damaged individuals with severe aphasia but without manual apraxia can successfully employ gesture to augment the semantic content of their speech.

Hemispheric contributions to lexical ambiguity resolution in a discourse context: Evidence from individuals with unilateral left and right hemisphere lesions

In the present study, a cross-modal semantic priming task was used to investigate the ability of left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects to use a discourse context to resolve lexically ambiguous words. Subjects first heard four-sentence discourse passages ending in ambiguous words and after an inter-stimulus interval (ISI) of either 0 or 750 ms, made lexical decisions on first- or second-meaning related visual targets. NBD control subjects, at the 0 ms ISI, only activated contextually appropriate meanings, though significant effects, as a group, were only seen in second-meaning biased contexts. Surprisingly, at the 750 ms ISI, these subjects activated both appropriate and inappropriate meanings in first-meaning biased contexts. With respect to the LHD nonfluent aphasic patients, the majority activated first meanings regardless of context at the 0 ms ISI, though effects for the group were not significant. At the 750 ms ISI, these patients again activated first meanings regardless of context, with significant effects for the group only seen in first-meaning biased contexts. With regard to the RHD patients, the majority activated second meanings regardless of context at the 0 ms ISI and first meanings regardless of context at the 750 ms ISI, though, as a group, the effects were not significant. In light of our previous findings (Grindrod & Baum, 2003, submitted), the present data are interpreted as supporting the notion that damage to the left hemisphere disrupts either lexical access processes or the time course of lexical activation, whereas damage to the right hemisphere impairs the use of context and leads to activation of ambiguous word meanings based on meaning frequency.

Representations of the human body in the production and imitation of complex movements

Previous investigations suggest that there are at least three distinct types of representation of the human body. One representation codes structural information about body part location (body structural description), the second codes knowledge about body parts (body semantics or body image), and the third provides a dynamic mapping of the current positions of body parts relative to one another (body schema) (Buxbaum & Coslett, 2001; Schwoebel, Coslett, & Buxbaum, 2001; Sirigu, Grafman, Bressler, & Sunderland, 1991). In this study we used an influential "two route" model of gesture performance (Gonzalez Rothi, Ochipa, & Heilman, 1991) to derive predictions about the body representations expected to underlie the production and imitation of meaningful and meaningless movements. The relationships between these measures were examined in 55 patients with unilateral left-hemisphere lesions. Multiple regression analyses demonstrated that performance on body semantics and body schema tasks were significant and unique predictors of meaningful gesture performance, whereas the body schema measure alone predicted imitation of meaningless movements. Body structural descriptions did not enter into any of the models. These findings are consistent with performance of meaningful actions via a semantic route that accesses body semantics and other action knowledge, and performance of meaningless movements via a "direct" route that bypasses this information.

The left parietal and premotor cortices: motor attention and selection

It is well established that the premotor cortex has a central role in the selection of movements. The role of parts of the parietal cortex in movement control has proved more difficult to describe but appears to be related to the preparation and the redirection of movements and movement intentions. We have referred to some of these processes as motor attention. It has been known since the time of William James that covert motor attention can be directed to an upcoming movement just as visuospatial attention can be directed to a location in space. While some parietal regions, particularly in the right hemisphere, are concerned with covert orienting and the redirecting of covert orienting it may be useful to consider other parietal regions, in the anterior inferior parietal lobule and in the posterior superior parietal lobule, particularly in the left hemisphere, as contributing to motor attention. Such parts of the parietal lobe are activated in neuroimaging experiments when subjects covertly prepare movements or switch intended movements. Lesions or transcranial magnetic stimulation (TMS) affect the redirecting of motor attention. The difficulties apraxic patients experience when sequencing movements may partly be due to an inability to redirect motor attention from one movement to another. The role of the premotor cortex in selecting movements is also lateralized to the left hemisphere. Damage to left hemisphere movement selection mechanisms may also contribute to apraxia. If, however, it remains intact after a stroke then the premotor cortex may contribute to the recovery of arm movements. A group of patients with unilateral left hemisphere lesions and impaired movements in the contralateral right hand was studied. Functional magnetic resonance imaging showed that in some cases the premotor cortex in the intact hemisphere was more active when the stroke-affected hand was used. TMS in the same area in the same patients had the most disruptive effect on movements. In summary, patterns of motor impairment and recovery seen after strokes can partly be explained with reference to the roles of the parietal and premotor cortices in motor attention and selection.

Analysis of lexical-semantic processing and extensive neurological, electrophysiological, speech perception, and language evaluation following a unilateral left hemisphere lesion: Pure word deafness?

Background : Theoretical models of lexical-semantic processing that explicate the relationships between spoken word comprehension, repetition, and writing to dictation are discussed in relation to pure word deafness (PWD). Various theories relative to the neuroanatomical sites and pathophysiological/electrophysiological mechanisms that cause the speech perception deficit seen in PWD are reviewed, as well as case studies that have identified variables that facilitate comprehension of spoken language for individuals with PWD. Aims : A case study of an individual with an extensive and complex neurological history and a constellation of symptoms suggestive of PWD is presented. Extensive evaluation, including experimental tasks developed to test a theoretical lexical processing model, was undertaken to determine whether this case fitted the criteria for a diagnosis of PWD. Methods & Procedures : Extensive neurological, electrophysiological, speech perception, and language testing was undertaken to confirm site of lesion, assess neurophysiological processes underlying speech perception, and determine overall language status. Experimental tasks based on a lexical-semantic processing model assessed word and nonword repetition and writing to dictation under two conditions: presentation with and without facial cues. Outcomes & Results : MRI confirmed a lesion in the participant's left frontoparietal area. Electrophysiological measures indicated his auditory nerve and auditory brainstem functions were intact, middle latency response (MLR) was normal over his right hemisphere and absent over his left hemisphere, and a significant mismatch negativity (MMN) response was elicited by pitch, but not phonetic, differences. Speech perception testing indicated he had difficulty with spectral or spectro-temporal discrimination and combining phonological and semantic information, as well as decreased ability to use formant motion in sentence perception and to perceive speech in noise. Language testing revealed relatively intact spontaneous language production and reading comprehension. The participant's performance on experimental tasks indicated an effect of syllable length and presentation mode for both words and nonwords. That is, as the number of syllables increased, his performance decreased; however, repetition and writing to dictation reflected superior performance with facial cues regardless of word and nonword length when compared to presentation without cues. Relative to the lexical processing model, the participant's performance suggested impoverished phonetic processing in the auditory analysis system. Conclusions : The results of extensive evaluation revealed a selective impairment in acoustic phonetic perception that is consistent with a diagnosis of PWD. The findings of this study support other studies that have demonstrated that speech perception involves cortical areas other than the temporal lobes.

Pitch and Timing Abilities in Adult Left-Hemisphere-Dysphasic and Right-Hemisphere-Damaged Subjects

The production and perception of pitch and rhythm were tested in patients with acquired unilateral left-hemisphere (LH) lesions (and subsequent motor dysphasia, n = 13), patients with unilateral right-hemisphere (RH) lesions (n = 14), and normal age-matched controls. While the LH dysphasic subjects were not generally impaired on the production or perception of pitch, they were grossly impaired on the production and perception of rhythm. The RH subjects, in contrast, were impaired on measures of pitch perception and production, including the discrimination and production of single notes and of melodies. It is concluded that the two hemispheres differ in their specialization for the perception and production of pitch and rhythm.

Spatial localization in patients with unilateral posterior left or right hemisphere lesions.

In this study, perceptual and visuomotor spatial localization were examined in patients with unilateral right (RH) or left (LH) hemisphere lesions and in a group of control subjects. Perceptual localization was measured with a position-discrimination task; in the visuomotor localization task, subjects had to point to a visual target. Both tasks were investigated in conditions with or without background visibility and with central and peripheral targets. In the visuomotor task, hand visibility was also manipulated. In both tasks, targets were presented in the left and right visual hemifield. The perceptual task revealed impairments for both LH and RH patients in the contra-lateral visual hemifield. RH patients also revealed slightly larger impairments in conditions without a visual background. In the visuomotor task, the LH patients were not impaired, whereas the RH patients were impaired in conditions without hand visibility and/or background visibility. Hence, our data strengthen the idea that spatial localization is not a unitary function and that perceptual and visuomotor localization can be selectively impaired. We suggest that one of the important factors distinguishing between localization impairments in RH and LH patients might be absolute versus relative localization.

A Case of Prosopagnosia Following Moderate Closed Head Injury with Left Hemisphere Focal Lesion

This study describes a left handed woman with prosopagnosia following traumatic brain injury with a focal lesion confined to the left-posterior hemisphere. Few cases of prosopagnosia following unilateral left hemisphere lesions have previously been reported in the literature. Corrected visual acuity was 20/70 (binocular), color vision was intact on screening, and shape detection was borderline. Impairments in higher order visual perception were evident to varying degrees on nonfacial tasks. Matching of unfamiliar faces was very slow but accurate. A marked impairment in the ability to recognize familiar faces and learn new face-name associations was evident on experimental tasks relative to the performance of healthy control subjects. In contrast, identification of characteristics of faces (gender, age) and identification and matching of facial expressions were relatively preserved. We discuss the cognitive processing stages that appear to be disrupted using Bruce and Young's (1986) model of facial recognition and perception as a framework.

The Role of the Left Hemisphere in Verbal and Spatial Reasoning Tasks

Laterality of reasoning processes have long been a source of investigation. Differing formats of verbal and spatial reasoning tasks have meant it has not been possible to extricate true performance level from artefacts of input and output modalities. The Verbal and Spatial Reasoning Test (VESPAR) offers this opportunity, by virtue of matched sets of verbal and spatial inductive reasoning problems. Two series of 40 patients with unilateral left and right hemisphere lesions were tested on two verbal and two spatial subtests of the VESPAR, together with a battery of baseline tests. The performance of the left and right hemisphere lesion cases was compared with a normal standardisation sample. Whereas only the left hemisphere group failed the verbal sections, both left and right hemisphere groups failed the spatial sections. The influence of aphasia on spatial reasoning was considered to be an incomplete explanation for the failure of the left hemisphere group on the spatial sections. It is concluded that this investigation provides firmer evidence of a crucial role for the left hemisphere in both verbal and spatial abstract reasoning processes.

Lesion site patterns in severe, nonverbal aphasia to predict outcome with a computer-assisted treatment program.

To test whether lesion site patterns in patients with chronic, severe aphasia who have no meaningful spontaneous speech are predictive of outcome following treatment with a nonverbal, icon-based computer-assisted visual communication (C-ViC) program. Retrospective study in which computed tomographic scans performed 3 months after onset of stroke and aphasia test scores obtained before C-ViC therapy were reviewed for patients after receiving C-ViC treatment. A neurology department and speech pathology service of a Department of Veterans Affairs medical center and a university aphasia research center. Seventeen patients with stroke and severe aphasia who began treatment with C-ViC from 3 months to 10 years after onset of stroke. Level of ability to use C-ViC on a personal computer to communicate. All patients with bilateral lesions failed to learn C-ViC. For patients with unilateral left hemisphere lesion sites, statistical analyses accurately discriminated between those who could initiate communication with C-ViC from those who were only able to answer directed questions. The critical lesion areas involved temporal lobe structures (Wernicke cortical area and the subcortical temporal isthmus), supraventricular frontal lobe structures (supplementary motor area or cingulate gyrus 24), and the subcortical medial subcallosal fasciculus, deep to the Broca area. Specific lesion sites were also identified for appropriate candidacy for C-ViC. Lesion site patterns on computed tomographic scans are helpful to define candidacy for C-ViC training, and to predict outcome level. A practical method is presented for clinical application of these lesion site results in combination with aphasia test scores.

Differential patterns of language and motor reorganization following early left hemisphere lesion: a PET study.

There is extensive evidence for post-lesional plasticity in the language and motor domains. We examined possible domain-specific differences in reorganizational patterns, hypothesizing that interhemispheric reorganization would be predominantly homotopic for language, but predominantly nonhomotopic for motor control. Using oxygen 15-water positron emission tomography, regional cerebral blood flow was studied during rest, listening to sentences, repetition of sentences, and finger tapping of the right hand. Task-specific primary, secondary, and tertiary regions of interest were defined according to the degree of regional involvement in language/motor functions as documented in previous studies. Regional activations were compared within and across functional domains. Nine patients (aged 4-20 years) with unilateral left hemisphere lesion involving both the primary motor and perisylvian language cortices were studied. Two samples of healthy adults were included for additional comparisons. Hemispheric asymmetry of blood flow changes within regions of interest. As predicted, rightward asymmetry of activations in primary and secondary regions was stronger for language than for movement, but the expected inverse difference for tertiary regions (greater rightward asymmetry of motor activations) was not found. Within-domain comparisons showed that for listening to sentences, rightward asymmetry was strongest in primary and weakest in tertiary regions, whereas the inverse differences were found for movement. The findings suggest a greater potential for homotopic interhemispheric reorganization in the language than in the motor domain. Interhemispheric motor reorganization was generally limited.

Pattern of Neuropsychological Deficit at Age Five Years Following Neonatal Unilateral Brain Injury

The pattern of language deficit following left-hemisphere brain injury and visual/spatial deficit following right-hemisphere injury in an adult or older child is well recognized, but has been inconsistently reported following presumed neonatal brain injury. Our prospective study of 24 children at age 5 with documented neonatal unilateral brain injury lends support to the theory of hemisphere specialization at the time of birth. Twelve children who had unilateral left-hemisphere lesion were compared to 12 children with unilateral right-hemisphere lesion of similar timing and severity. Relative visual/spatial deficit following right-hemisphere lesion and receptive language deficit following left-hemisphere lesion were identified. Lateralized measures of grip strength, fine motor speed, and fine motor dexterity were not significantly different between the groups for either hand in this nonhemiparetic study sample. Only one child with a left-hemisphere lesion was left-handed, and only one child (right-lesion) had a hemiparesis.

Interaction between Tone and Intonation in Thai after Unilateral Brain Damage

Intonational characteristics of Thai sentences were used to evaluate fundamental frequency (F0) control in brain-damaged patients with unilateral left and right hemisphere lesions. Subjects (n= 41) included 9 young and 10 old normal adults, 12 right hemisphere patients, and 10 left hemisphere aphasic patients (7 fluent and 3 nonfluent). Sentences were comprised of six words, three of which were keywords occurring in sentence-initial, -medial, and -final positions. All 125 possible sequences of three of the five Thai tones (mid, low, falling, high, rising) were superimposed on monosyllabic keywords. Utterances were produced at a conversational speaking rate. AverageF0of keywords was analyzed as a function of sentence position, tone, and group. For both normal and brain-damaged speakers, results indicated that tones in sentence-final position were significantly lower inF0than in either sentence-initial or -medial position; falling and high tones were significantly higher inF0than mid, low, and rising tones. Findings are discussed in relation to issues pertaining to hemispheric specialization and the nature ofF0deficits in nonfluent and fluent aphasic patients.

Covert visual attention in schizophrenia spectrum personality disordered subjects: Visuospatial cuing and alerting effects

A recent study observed lateralized deficit in the disengagement of covert visual attention in schizophrenic patients. Subsequent attempts to replicate this finding have had mixed results. Differences in the neuroleptic treatment or other secondary factors associated with schizophrenia are some of the possible reasons for these inconsistent findings. In this study, we examined the ability to shift covert visual attention in neuroleptic-naive, schizophrenia spectrum personality disordered (SSPD; n = 35) subjects and normal controls ( n = 34) under a variety of spatial cuing and alerting conditions. We hypothesized that SSPD subjects would have difficulty with disengagement of covert visual attention from an invalidly cued left visual field when the target appeared in the right visual field in comparison to the normal subjects. As predicted, schizophrenia spectrum personality disordered subjects had significantly longer latencies for the right visual field invalid targets than normals ( p = .014). Under the remaining cue conditions, spectrum subjects performed normally. Consequently, the cost of left visual field invalid cueing for the right visual field target was significantly higher in spectrum personality subjects than in normals. The cost for the invalid right visual field cue and the benefits of valid cue in both fields were very similar in the two groups. The findings of an asymmetrical deficit in the disengagement and shift of covert visual attention in schizophrenia spectrum subjects are similar to the one's observed in patients with unilateral left hemisphere lesions.

Hierarchical Stimuli and Hemispheric Specialization: Two Case Studies

Local versus global visual processing was examined in two patients with massive unilateral left hemisphere lesions using a directed attention task involving hierarchical stimuli. Previous studies found an impressive global advantage in patients with posterior left hemisphere lesions on similar tasks. In addition, whereas patients with left inferior parietal lobule (IPL) lesions showed the global interference on local processing that is typically observed in normals, patients with lesions centered on the superior temporal gyrus (STG) demonstrated no interference. Paradoxically, our two patients who had complete destruction of both the left IPL and STG regions showed an overall local advantage due to local interference on global processing. We propose that following extensive left hemisphere damage, the isolated right hemisphere may be able to perform efficiently the type of processing usually ascribed to the left hemisphere (i.e., local). However, at least under certain conditions, this apparent functional plasticity seems to occur at the expense of the type of processing normally associated with the right hemisphere (i.e., global).

Speech Timing at the Sentence Level in Thai After Unilateral Brain Damage

The present study examined temporal characteristics of spoken sentences in Thai to evaluate timing control in brain-damaged patients with unilateral left and right hemisphere lesions. Subjects included 10 young and 10 old normal adults, 14 right hemisphere patients, and 2 left hemisphere nonfluent and 7 fluent aphasic patients. Utterances were produced at a conversational speaking rate. Duration measures were taken from wide-band spectrograms. Results indicated that left hemisphere patients exhibited abnormal timing on both absolute and relative timing measures, whereas right hemisphere patients did not. Among left hemisphere patients, fluent as well as nonfluent aphasics exhibited aberrant temporal patterns. Left hemisphere patients were also more variable than right hemisphere patients which, in turn, were more variable than normals in their production of sentences. In comparison to earlier findings on timing at segment and word levels, it was found that deficit profiles varied between fluent and nonfluent aphasics as a function of the size of the linguistic unit with nonfluent aphasics being affected at the segment, word, and sentence level but fluent aphasics affected at the sentence level only. Findings are discussed in relation to issues pertaining to hemispheric specialization and the nature of timing deficits in nonfluent and fluent aphasic patients.

Depression in secondary epilepsy: relation to lesion laterality.

Patients with epilepsy often have depressive disorders. This association may be particularly prominent in secondary epilepsy from a left hemisphere lesion. Among 1611 outpatients with epilepsy 272 patients were identified whose seizures originated from a structural brain lesion other than mesial temporal sclerosis. Sustained depressive disorders had occurred in 25 (9%) of these patients with secondary epilepsy. The depressed patients were compared with the remaining patients without depression with regard to location of lesion laterality and seizure variables. The only group difference was unilateral left hemisphere lesions in 58% of the patients with depression compared with only 21% of the non-depressed patients (chi 2 = 10.4, p = 0.006). This finding supports the idea of a relation of depression with epileptogenic lesions in the left hemisphere.

Stop voicing in thai after unilateral brain damage

Abstract Word-initial bilabial stops (/b p ph/), alveolar stops (/d t th/), and velar stops (/k kh/) in Thai were produced by 20 normal adults (10 young, 10 old), 12 non-aphasic patients with unilateral right hemisphere lesions, and 17 aphasic patients with unilateral left hemisphere lesions (nine fluent, eight non-fluent). Voice onset time (VOT) was measured from broad-band spectrograms. Relative frequency distributions of VOT values indicated minimal or no overlap between homorganic stop consonants for normal speakers, only sporadic occurrences of overlap for right hemisphere speakers, slightly more overlap for left fluent speakers, and even more overlap for left non-fluent speakers. By group, mean VOTs of homorganic stop consonants differed for all groups except /d t/ for the left non-fluent. By voicing category, mean VOTs of /b d/ for the left non-fluent group were shorter than those of other groups, and mean VOT of /k/ was longer than those of other groups. Mean VOTs of /ph th kh/ for the old normal ...

Probe-Evoked Potential Findings Following Unilateral Left-Hemisphere Lesions in Children

An evoked potentials procedure that has repeatedly provided evidence of predominant right-hemisphere engagement during language tasks in recovered adult aphasics was applied to the study of 14 children with early unilateral left-hemisphere lesions and in 14 matched normal subjects. In contrast with the adult patients, the children with left-hemisphere lesions displayed the normal pattern of predominant left-hemisphere engagement in visuospatial tasks. These data suggest that language restitution and development following early lesions involves intrahemispheric rather than interhemispheric functional reorganization.