The right hemisphere involvement in the processing of morphologically derived words

It is widely documented that the left hemisphere is dominant in all complex linguistic tasks, including the processing of inflectional morphology. Both in Italian and in other languages, patients with brain damage with a selective deficit in derivational morphology have never been reported. Here we present the unusual case of two patients with very similar right-hemisphere lesions, who in the absence of aphasic disorders showed a selective inability in producing derivational morphology. Although both patients were unimpaired in producing verb infinitives, they both showed a selective deficit in producing nouns derived from verbs. This difficulty was not present in deriving nouns from other grammatical categories, such as adjectives. Interestingly, both patients mostly substituted the derived noun with the past participle of the verb. This pattern of results documents for the first time a right-hemisphere contribution in the domain of derivational morphology.     

Unilateral spatial neglect: a dramatic but often neglected consequence of right hemisphere damage

INTRODUCTION: Unilateral Spatial Neglect (USN) is a common consequence of right brain damage. In the most severe cases, behavioral signs of USN can last several years and compromise patients' autonomy and social rehabilitation. These clinical facts stress the need for reliable procedures of diagnosis and rehabilitation. STATE OF THE ART: The last 3 decades have witnessed an explosion of studies on USN, which raises issues related to complex cognitive activities such as mental representation, spatial attention and consciousness. USN is probably a heterogeneous syndrome, but some of its underlying mechanisms might be understood as an association of disorders of spatial attention. A bias of automatic orienting towards right-sided objects seems typical of left USN. Afterwards, patients find it difficult to disengage their attention in order to explore the rest of the visual scene. Neglected objects are sometimes processed in an "implicit" way. PERSPECTIVES: The development of behavioural paradigms and of neuroimaging techniques and their application to the study of USN has advanced our understanding of the functional mechanisms of attention and spatial awareness, as well as of their neural bases. A number of new procedures for rehabilitation have recently been proposed. CONCLUSION: The present review describes the clinical presentation of USN, its anatomical basis and some of possible accounts of different aspects of neglect behavior. Results of computer simulations and of rehabilitation techniques are also presented with implications for the functioning of normal neurocognitive systems.     

The role of the right hemisphere in contextual inference

The present report describes two experiments involving dichotic presentation of sentences which have been electronically altered to render all verbal content indecipherable while leaving the melodic structure of the sentences intact. In both experiments, right-handed subjects produced a significant left ear advantage in identifying the situational context portrayed by the sentences. Left-handers produced no significant ear differences. The left ear advantage on this task was unrelated to the direction or magnitude of subject's ear advantage on a standard CV dichotic task.     

A role for the left hemisphere in spatial processing

This study extended our recently reported evidence of a left hemisphere (LH) contribution to spatial processing on standard visuospatial tasks. The present investigation compared performance on these standard tasks with that on 'purer' experimental tasks. Two tasks of line orientation, two of shape rotation and a shape matching task were administered to 50 men with stable unilateral post-Rolandic missile injuries and 32 control subjects. A LH deficit was found on the standard task of line orientation but not the 'purer' task, suggesting that the LH plays a role in eliminating extraneous information, presented only in the standard test. As for shape rotation, the LH group was impaired on both tasks. On the shape matching task, both experimental groups were significantly slower than control subjects. It is proposed the LH makes an important contribution to mental rotation and the understanding of Euclidean geometrical shapes.     

The role of vision in spatial representation

A complex link exists between vision and unilateral spatial neglect (USN). Firstly, USN is not a perceptual deficit, secondly, USN is not necessarily accompanied by a visual deficit and finally, USN can be observed in non-visual modalities as well as in mental spatial imagery. This apparent supramodality of USN stands in sharp contrast to the fact that neglect signs are often more severe and more durable in the visual than in other sensory modalities (Chokron et al., 2002). The influence of vision on spatial representation has rarely been studied. In the present study we assessed six right brain-damaged patients suffering from left USN on two tasks involving spatial representations: a clock-drawing task and a drawing from memory task in two experimental conditions, with and without visual control. We confirm that even in mental imagery, the absence of visual feedback may decrease and even suppress left neglect signs (Bartolomeo and Chokron, 2001b; 2002). Since vision is largely involved in the orientation of attention in space, suppressing visual control could reduce the magnetic attraction towards the right ipsilesional hemispace and in this way could allow a re-orientation of attention towards the left neglected hemispace. We discuss the theoretical and therapeutic implications of these findings.     

The right hemisphere fails to orient to the negative valence of visually presented words

To assess cerebral functional asymmetry for accessing the meaning of emotional words, native English speakers were asked to make lexical decisions to emotional words, neutral words and nonwords briefly flashed in their left or right visual field, that is, perceived by their right or left visual cortex, respectively. Emotionally negative words had an overall probability of occurrence of 12.5% in each visual field and were expected to elicit a P3b event-related potential modulation indexing shifts of attention. Emotionally negative words elicited a P3b when perceived by the left visual cortex but failed to trigger such attention-related response when perceived by the right hemisphere. The results suggest relative insensitivity on the part of the right hemisphere in registering the negative emotional valence of written words.     

Aphasic reading and writing: possible evidence for right hemisphere participation

Aphasic patients performed two tasks, reading aloud and writing to dictation. In both tasks, success was positively correlated to the emotionality, the imageability and the frequency of the target words. In addition, the patients made more semantic Also, the relative difficulty of words was similar for aphasic patients to read and for normal male subjects to recognize in the left visual field. These results suggest that the performance of the aphasic patients on these language tasks were mediated in part by the right hemisphere.     

The role of the right hemisphere in processing negative sentences in context

Given a pattern consisting of x1, x2,..., xn similar elements and y1, which is perceived as different from the former, it is more plausible to assert that y is not x rather than to assert that x is not y (Wason, J. verb. Learn verb. Behav. 4, 7-11, 1965). In order to appreciate such a difference, the entire set has to be considered. Right-hemisphere brain-damaged patients were submitted to a series of visually presented patterns, each pattern consisting of seven similar items and one dissimilar item. Their task was to complete a statement referring to a single element of each pattern. Statements were either simple affirmative or negative sentences. Errors and reaction times were recorded. Patients with a right-hemisphere injury were found to be insensitive to the plausible-implausible dimension in completing negative sentences. It is hypothesized that right-hemisphere brain-damaged patients are less adequate in this task because they are less capable in putting each element into the visual context.     

Egocentric frame of reference: its role in spatial bias after right hemisphere lesions.

The reference shift hypothesis of unilateral neglect holds that spatial bias in left neglect stems from a rightward deviation of patients' egocentric frame of reference (ER). Twenty five unselected right brain-damaged patients participated in a straight-ahead pointing task to assess the position of their ER (Experiment 1). A rightward ER shift emerged only in the subgroup of patients with extensive parietal lesions. In Experiment 2, we found that the position of the ER did not predict the outcome of various visuospatial neglect tests (r = 0.07 to 0.27). In Experiment 3, no significant positive correlation emerged between the ER position and visual (r = 0.26) or tactile (r = -0.48) extinction. Two further experiments examined the relationships between the ER position and patients' performance on a reaction time test of directional motor bias (Experiment 4), and on a test of response times to lateralised visual stimuli (Experiment 5). Results showed that the ER position did not predict the distribution of accuracy scores or response times in either task (Experiment 3: accuracy: r = 0.06; response times: r = 0.16; Experiment 4: accuracy: r = 0.09; response times: r = 0.04). We concluded that the position of the ER plays no crucial role in the behavioural consequences of spatial bias induced by right hemisphere lesions.     

The role of the right hemisphere in the aetiology of the depressive disorders

Many differences between the hemispheres have been observed, from the gross anatomical level to differences in dendritic structure or neurotransmitter distribution. Analytic reasoning and language functions such as grammar and vocabulary are often lateralized to the left hemisphere of the brain. The right cerebral hemisphere plays a special role in tasks involving the direction of spatial attention, recognition of faces, perception, possibly generation of affect and affective prosody. Depression is associated with many different cognitive impairments e.g. in the domains of working memory and executive functions as well as interpersonal and social cognition problems. Little is known about the relationship between cognitive and affective deficits in depression. Researchers have hypothesised that the laterality of brain damage may facilitate the expression of emotional or affective disturbances. The aim of the study is to describe the role of the right hemisphere in the aetiology of depressive disorders.     

Metaphors and verbal creativity: The role of the right hemisphere

Ample research suggests that the right cerebral hemisphere plays a central role in verbal creativity as well as in novel metaphor comprehension. The aim of the present study was to directly examine the relation between verbal creativity and right hemisphere involvement during novel metaphor comprehension. Thus 30 healthy adults were asked to fill in the Hebrew version of the Remote Association Test to assess their level of creativity. In addition, reaction times and error rates were measured while these participants performed a semantic judgement task on two word expressions presented in a divided visual field paradigm. The word pairs comprised four types of semantic relations: novel metaphors, conventional metaphors, literal word pairs, and meaningless word pairs. Correlations were conducted to assess the relation between level of creativity and processing of the four pair types in the two cerebral hemispheres. The main finding was of a significant negative correlation between degree of creativity and reaction times to novel metaphor processing in the right hemisphere, thus supporting the involvement of this cerebral hemisphere in both tasks. Results are discussed in light of linguistic theories and recent neuroscientific evidence regarding relative hemispheric involvement during semantic processing.     

Metaphors and verbal creativity: The role of the right hemisphere

Ample research suggests that the right cerebral hemisphere plays a central role in verbal creativity as well as in novel metaphor comprehension. The aim of the present study was to directly examine the relation between verbal creativity and right hemisphere involvement during novel metaphor comprehension. Thus 30 healthy adults were asked to fill in the Hebrew version of the Remote Association Test to assess their level of creativity. In addition, reaction times and error rates were measured while these participants performed a semantic judgement task on two word expressions presented in a divided visual field paradigm. The word pairs comprised four types of semantic relations: novel metaphors, conventional metaphors, literal word pairs, and meaningless word pairs. Correlations were conducted to assess the relation between level of creativity and processing of the four pair types in the two cerebral hemispheres. The main finding was of a significant negative correlation between degree of creativity and reaction times to novel metaphor processing in the right hemisphere, thus supporting the involvement of this cerebral hemisphere in both tasks. Results are discussed in light of linguistic theories and recent neuroscientific evidence regarding relative hemispheric involvement during semantic processing.     

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.     

The role of the right hemisphere in form perception and visual gnosis organization

Peculiarities of series of picture interpretations and Rorschach test results in patients with unilateral benign hemispheric tumours are discussed. It is concluded that visual perception in the right hemisphere has hierarchic structure, i.e., each successive area from the occipital lobe towards the frontal having a more complicated function. Visual engrams are distributed over the right hemisphere in a manner similar to the way the visual information is recorded in holographic systems. In any impairment of the right hemisphere a tendency towards whole but unclear vision arises. The preservation of lower levels of visual perception provides for clear vision only of small parts of the image. Thus, confabulatory phenomena arises, which are specific for right hemispheric lesions.     

Unilateral right cerebral representation of reading in a familial left-hander

Several recent hypotheses of cerebral functional organization in natural left-handers hold that language, including reading, is localized either unilaterally in the left hemisphere or bilaterally, but not unilaterally in the right hemisphere. A case of alexia without agraphia in a left-hander with an infarct in the right occipital lobe and splenium of the corpus callosum is reported. That a permanent and complete alexia resulted from a single, right hemisphere lesion indicated that reading was completely lateralized to that hemisphere. The case demonstrates that in some natural left-handers language functions can be unilaterally represented in the right hemisphere.     

Inhibitory processes and spatial bias after right hemisphere damage

Patients with lesions in the right hemisphere often show signs of unilateral neglect for the left side of space. Even in the absence of these signs, however, when exploring a visual scene these patients show an initial orientation of their attention towards the right side (Gainotti, D'Erme, & Bartolomeo, 1991). Some patients might be able to compensate for this spatial bias by actively inhibiting the rightward orientation after its occurrence; as a result, they would be capable of extending their exploration to the left part of space. However, due to conflicting demands on the same resource pool, a rightward bias in these patients is expected to reappear or be enhanced when inhibitory mechanisms are used to avoid producing prepotent but inappropriate responses. Eighteen normal controls and 40 right brain-damaged (RBD) patients (17 showing signs of left neglect, 23 without neglect) performed two reaction time tasks requiring manual motor responses to lateralised visual stimuli. In one task, trials in which a motor response was to be withheld (catch trials) were also presented. Regardless of whether they had neglect, patients responded more slowly to left-sided than to right-sided events in both tasks. The presence of catch trials further increased this rightward bias in patients without signs of neglect, but not in neglect patients, consistent with the hypothesis that RBD patients may use inhibitory processes to compensate for spatial bias.     

The right hemisphere is not unitary in its role in aphasia recovery

Neurologists and aphasiologists have debated for over a century whether right hemisphere recruitment facilitates or impedes recovery from aphasia. Here we present a well-characterized patient with sequential left and right hemisphere strokes whose case substantially informs this debate. A 72-year-old woman with chronic nonfluent aphasia was enrolled in a trial of transcranial magnetic stimulation (TMS). She underwent 10 daily sessions of inhibitory TMS to the right pars triangularis. Brain activity was measured during picture naming using functional magnetic resonance imaging (fMRI) prior to TMS exposure and before and after TMS on the first day of treatment. Language and cognition were tested behaviorally three times prior to treatment, and at 2 and 6 months afterward. Inhibitory TMS to the right pars triangularis induced immediate improvement in naming, which was sustained 2 months later. fMRI confirmed a local reduction in activity at the TMS target, without expected increased activity in corresponding left hemisphere areas. Three months after TMS, the patient suffered a right hemisphere ischemic stroke, resulting in worsening of aphasia without other clinical deficits. Behavioral testing 3 months later confirmed that language function was impacted more than other cognitive domains. The paradoxical effects of inhibitory TMS and the stroke to the right hemisphere demonstrate that even within a single patient, involvement of some right hemisphere areas may support recovery, while others interfere. The behavioral evidence confirms that compensatory reorganization occurred within the right hemisphere after the original stroke. No support is found for interhemispheric inhibition, the theoretical framework on which most therapeutic brain stimulation protocols for aphasia are based.