Associations and dissociations of transitive and intransitive gestures in left and right hemisphere stroke patients

The study investigated performance on pantomime and imitation of transitive and intransitive gestures in 80 stroke patients, 42 with left (LHD) and 38 with right (RHD) hemisphere damage. Patients were also categorized in two groups based on the time that has elapsed between their stroke and the apraxia assessment: acute–subacute (n = 42) and chronic (n = 38). In addition, patterns of performance in apraxia were examined. We expected that acute–subacute patients would be more impaired than chronic patients and that LHD patients would be more impaired than RHD patients, relative to controls. The hemisphere prediction was confirmed, replicating previous findings. The frequency of apraxia was also higher in all LHD time post-stroke groups. The most common impairment after LHD was impairment in both pantomime and imitation in both transitive and intransitive gestures. Selective deficits in imitation were more frequent after RHD for transitive gestures but for intransitive gestures they were more frequent after LHD. Patients were more impaired on imitation than pantomime, relative to controls. In addition, after looking at both gesture types concurrently, we have described cases of patients who suffered deficits in pantomime of intransitive gestures with preserved performance on transitive gestures. Such cases show that the right hemisphere may be in some cases critical for the successful pantomime of intransitive gestures and the neural networks subserving them may be distinct. Chronic patients were also less impaired than acute–subacute patients, even though the difference did not reach significance. A longitudinal study is needed to examine the recovery patterns in both LHD and RHD patients.     

The different types of limb apraxia errors made by patients with left vs. right hemisphere damage

Limb apraxia errors were compared among normal controls and right- or left-hemisphere-damaged patients as they imitated gestures with the ipsilateral hand. Both brain-damaged groups made similar errors on nonrepresentative and representative/intransitive movements. In contrast for pretended object use movements (transitive), the left-hemisphere-damaged group made more arm position and classical body-part-as-object errors while the right hemisphere group made as many partial errors and more less-primitive, body-part-as-object errors than the left-hemisphere-damaged group. These results help explain why a certain percentage of right-hemisphere-damaged patients are labeled apraxic, but also suggest that the left hemisphere is more important for integrating intrapersonal space and the “representation” of extrapersonal space.     

Contextual mood priming following left and right hemisphere damage

This research examined the influence of mood-congruent and mood-incongruent contexts on recognizing affective prosody after brain damage. Predictions stemmed from an associative network theory of learning and memory. Thirty-three male subjects, 11 each in right hemisphere damaged (RHD), left hemisphere damaged (LHD), and normal control groups judged moods from the prosody of semantically neutral phrases. In one task, the prosodic stimulus phrases were judged in isolation. In another task, the phrases were preceded by short paragraphs which were either congruent or incongruent in emotional tone with the prosodic stimuli. These paragraphs were designed to prime specific mood choices. As anticipated, LHD subjects' prosodic mood recognition was more accurate when given congruent rather than incongruent affective contexts. Congruent contexts facilitated, and incongruent contexts disrupted, their prosodic mood judgments to the same extent as normals. RHD subjects showed a partial context decrement. They were less accurate than normal or LHD subjects in the congruent condition, and were unaffected by incongruent contexts. When given congruent biasing paragraphs, however, RHD subjects did experience facilitation on a par with that found for the other groups, indicating spared sensitivity to certain contextual factors. The distinction between automatic and effortful processes is offered as a potential explanation for the RHD group's pattern of performance.     

Task demands and limb apraxia in stroke

The present study was designed to examine the frequency and severity of apraxia in patients with left- or right-hemisphere stroke in both pantomime and imitation conditions and to compare the frequency of apraxia in each stroke group across the three patterns of apraxia described in Roy's model (Roy, 1996). Ninety-nine stroke patients and 15 age-matched healthy adults performed eight transitive gestures to pantomime and to imitation. Gestural performance was quantified as accuracy on five performance dimensions; a composite score, an arithmetic combination of the five performance dimensions, was used as an index of the overall accuracy. Analyses revealed a comparable proportion of patients in each stroke group were classified as apraxic in the imitation condition, but a higher proportion of left stroke patients were apraxic in the pantomime condition. The severity of apraxia in each stroke group and the performance dimensions affected were, however, comparable. Analyses of the patterns of apraxia (pantomime alone, imitation alone or apraxia in both conditions) revealed a higher frequency of apraxia in both stroke groups for the pattern reflecting apraxia in both conditions, indicating that a disruption at the movement execution stage of gesture performance was most common.     

Patterns of limb apraxia in primary progressive aphasia

Primary progressive aphasia (PPA) is a syndrome characterized by a progressive language deficit without other dementia features for at least two years (). Other deficits that are likely to co-exist with aphasia, such as apraxia, have only been investigated in a few case studies and only at a rudimentary level for the most part. In this study we investigate the frequency and severity of apraxic deficits in PPA patients. Ten PPA patients and twelve aged-matched healthy adults performed eight transitive gestures to pantomime and to imitation. Gesture performance was measured along five movement dimensions and a composite score based on the arithmetic mean of the five dimensions was calculated. Overall, PPA patients performed worse than controls with both pantomime and imitation. Furthermore, individual comparisons revealed that out of the three apraxia patterns described by (pantomime alone, imitation alone, or apraxia in both conditions), the most frequent pattern in PPA patients was apraxia in both conditions. This result corresponds with previous findings in populations of stroke and Alzheimer's patients. Considering the occurrence of apraxia in this population, this study supports the idea that a comprehensive apraxia assessment should be administered in cases of PPA.     

Right hemispatial neglect: frequency and characterization following acute left hemisphere stroke

The frequency of various types of unilateral spatial neglect and associated areas of neural dysfunction after left hemisphere stroke are not well characterized. Unilateral spatial neglect (USN) in distinct spatial reference frames have been identified after acute right, but not left hemisphere stroke. We studied 47 consecutive right handed patients within 48h of left hemisphere stroke to determine the frequency and distribution of types of right USN using cognitive testing and MRI imaging. The distribution of USN types was different from the previously reported distribution following acute right hemisphere stroke. In this left hemisphere stroke population, allocentric neglect was more frequent than egocentric neglect.     

Language acquisition following hemidecortication: Linguistic superiority of the left over the right hemisphere

The language development of three 9- and 10-year-old children possessing only a right or a left hemisphere was studied. Surgical removal of one brain half antedated the beginning of speech, so each child has acquired speech and language with only one hemisphere. Different configurations of language skill have developed in the two isolated hemispheres: phonemic and semantic abilities are similarly developed but syntactic competence has been asymmetrically acquired. In relation to the left, the right brain half is deficient in understanding auditory language, especially when meaning is conveyed by syntactic diversity; detecting and correcting errors of surface syntactic structure; repeating stylistically permuted sentences; producing tag questions which match the grammatical features of a heard statement; determining sentence implication; integrating semantic and syntactic information to replace missing pronouns; and performing judgments of word interrelationships in sentences. Language development in an isolated right hemisphere, even under seizure-free conditions, results in incomplete language acquisition.     

Morphologic agrammatism following a right hemisphere stroke in a dextral patient.

There is evidence of two major components of grammatic function in the brain: (1) morphologic, probably based in the postcentral perisylvian cortex, encompassing the selection of individual words and inflectional endings according to the rules of grammar; and (2) syntactic, probably based in the frontal lobes, encompassing construction of the overall structure of a sentence (syntax) to match the concept being considered. We present a stroke patient with impaired morphology but, unlike Broca's aphasics, relative sparing of syntax. He omitted 43% of articles, 40% of complementizers, 20% of pronouns, 27% of semantically marked prepositions, 43% of purely grammatic prepositions, and 22% of auxiliary verbs, but his average sentence length was 9.8 words and 64% of his sentences contained embedded clauses. He frequently intermingled two sentences to convey a given concept, juxtaposing words in grammatically unacceptable ways. This intermingling may represent either a grammatic "conduite d'approche," or a failure of the filtering function of a defective morphologic processor. His great difficulty in completing syntactic frames suggests that a more general form of the processes underlying grammatic morphology may play an important role in phrase structure generation.     

Progressive dysfluency associated with right hemisphere disease

A late onset progressive dysfluency following a right hemisphere stroke occurred in a 62-year-old male. Dysfluency was characterized by pronounced word and phrase reiterations, and sound and syllable reiterations to a lesser degree. Spontaneous speech was significantly more dysfluent than oral reading and repetition. Recitation and singing were minimally dysfluent. Reiterations were accompanied by reduced vocal loudness and increased rate of speech. Reiterations occurred in initial, medial, and final sentence position. Secondary symptoms such as facial grimacing were absent. In contrast to acquired cortical stuttering which is characterized by a preponderance of sound and syllable sentence initial repetitions, dysfluency was more closely characteristic of palilalia. The dysfluency occurred as a symptom of a diffuse nonspecific subcortical projection system defect related to massive infarction in the right middle cerebral artery distribution with associated atrophy.     

Severe stuttering associated with right hemisphere lesion

Following a right hemisphere stroke, a right-handed, 50-year-old male experienced a permanent dysfluency characterized by phoneme and syllable reiterations and, to a lesser extent, word and phrase reiterations. The reiterations occurred in initial, medial, and final positions and for all sentence elements (e.g., subject nouns, object nouns, verbs, modifiers). There was a notable loss of verbal automatisms (poems, songs, etc.). The patient's symptoms conform to the acquired stuttering syndrome described by A. Helm, R. Butler, and D.F. Benson (1978, Neurology, 28, 1159-1165).     

Homotopic language reorganization in the right hemisphere after early left hemisphere injury

Speech production is inextricably linked to speech perception, yet they are usually investigated in isolation. In this study, we employed a verbal-repetition task to identify the neural substrates of speech processing with two ends active simultaneously using functional MRI. Subjects verbally repeated auditory stimuli containing an ambiguous vowel sound that could be perceived as either a word or a pseudoword depending on the interpretation of the vowel. We found verbal repetition commonly activated the audition-articulation interface bilaterally at Sylvian fissures and superior temporal sulci. Contrasting word-versus-pseudoword trials revealed neural activities unique to word repetition in the left posterior middle temporal areas and activities unique to pseudoword repetition in the left inferior frontal gyrus. These findings imply that the tasks are carried out using different speech codes: an articulation-based code of pseudowords and an acoustic-phonetic code of words. It also supports the dual-stream model and imitative learning of vocabulary.     

Writing with the right hemisphere

We studied writing abilities in a strongly right-handed man following a massive stroke that resulted in virtually complete destruction of the language-dominant left hemisphere. Writing was characterized by sensitivity to lexical-semantic variables (i.e., word frequency, imageability, and part of speech), semantic errors in writing to dictation and written naming, total inability to use the nonlexical phonological spelling route, and agrammatism in spontaneous writing. The reliance on a lexical-semantic strategy in spelling, semantic errors, and impaired phonology and syntax were all highly consistent with the general characteristics of right hemisphere language, as revealed by studies of split-brain patients and adults with dominant hemispherectomy. In addition, this pattern of writing closely resembled the syndrome of deep agraphia. These observations provide strong support for the hypothesis that deep agraphia reflects right hemisphere writing.     

When left means right: an explanation of the left cradling bias in terms of right hemisphere specializations

Previous research has indicated that 70-85% of women and girls show a bias to hold infants, or dolls, to the left side of their body. This bias is not matched in males (e.g. deChateau, Holmberg & Winberg, 1978; Todd, 1995). This study tests an explanation of cradling preferences in terms of hemispheric specialization for the perception of facial emotional expression. Thirty-two right-handed participants were given a behavioural test of lateralization and a cradling task. Females, but not males, who cradled a doll on the left side were found to have significantly higher laterality quotients than right cradlers. Results indicate that women cradle on the side of the body that is contralateral to the hemisphere dominant for face and emotion processing and suggest a possible explanation of gender differences in the incidence of cradling.     

Imagery and verbal encoding in left and right hemisphere damaged patients

Neuropsychological aspects of imaginal and verbal encoding in memory were explored in two forced-choice recognition memory experiments with patients suffering from left and right anterior cerebral hemisphere damage. In the first experiment stimulus type and rate of presentation were varied. Predictions of patient performance based on the hypothesis that left anterior hemisphere pathology impairs verbal memory coding and right anterior hemisphere pathology impairs imaginal coding were confirmed. In a second recognition memory experiment for pictures of common objects, system-specific (imaginal or verbal) interference and distractor effects were demonstrated by analyzing the effects of interpolated tasks and the nature of false-recognition errors.     

Profiles of right hemisphere language and speech following brain bisection

A variety of language tasks were administered to two patients who had undergone staged callosal section in an effort to control otherwise intractable epilepsy. Right hemisphere lexical capacity varied and preliminary results suggest that the case displaying greater semantic power also possessed some syntactic competence. This same case (V.P.) was also capable of expressive language from the right hemisphere. This rare capacity allowed for fresh observations on the dynamic interactions of conscious control that occur in this kind of patient.     

Remembering 1500 pictures: the right hemisphere remembers better than the left

We hypothesized that the right hemisphere would be superior to the left hemisphere in remembering having seen a specific picture before, given its superiority in perceptually encoding specific aspects of visual form. A large set of pictures (N=1500) of animals, human faces, artifacts, landscapes, and art paintings were shown for 2s in central vision, or tachistoscopically (for 100ms) in each half visual field, to normal participants who were then tested 1-6 days later for their recognition. Images that were presented initially to the right hemisphere were better recognized than those presented to the left hemisphere. These results, obtained with participants with intact brains, large number of stimuli, and long retention delays, are consistent with previously described hemispheric differences in the memory of split-brain patients.     

Narrative comprehension in adults with right and left hemisphere brain-damage: theme organization.

The effects of delayed presentation of a central theme on the comprehension and interpretation of narratives were investigated in adults with right and left hemisphere brain-damage and normal individuals. The performance of subgroups of the subjects with right and left hemisphere brain-damage also was examined. Right hemisphere brain-damaged groups with anterior and posterior lesions were significantly less accurate and identified significantly fewer central themes when central theme presentation was delayed until the end of a narrative than when the theme was presented at the beginning. Subjects with anterior right hemisphere brain-damage produced significantly more embellishments and confabulations than subjects with posterior damage and non-brain-damaged controls, regardless of theme condition. The performance of non-brain-damaged subjects and subjects with fluent and nonfluent aphasia was unaffected by the organization of the central theme in the narratives.     

Prosodic facilitation in the resolution of syntactic ambiguities in subjects with left and right hemisphere damage

The purpose of this study was to determine if prosody facilitates the comprehension of sentences containing temporary syntactic ambiguities in control, and left (LHD) and right hemisphere damaged (RHD) subjects. To test for effects of prosodic facilitation, sentences were created where prosodic boundaries coincided with (cooperating), were absent (baseline), or conflicted (conflicting) with syntactic boundaries in three response times (RTs) experiments. Despite differences in overall RTs and response accuracy for each group, all three groups responded faster and more accurately to sentences in the cooperating than in the baseline and conflicting conditions across experiments, indicating that prosody facilitates syntactic parsing in brain-damaged subjects just as it does with normal control subjects. Results are discussed in relation to psycholinguistic theories of syntactic parsing and neurolinguistic theories of hemispheric specialization in processing the acoustic properties of prosodic structures.