In this commentaryI evaluate the claim made byKeenan, Nelson, OÕConnor, and Pascual-Leone (2001) that since self-recognition results from right hemispheric activity, self-awareness too is likely to be produced by the activity of the same hemisphere. This reasoning is based on the assumption that self-recognition represents a valid operationalization of self-awareness; I present two views that challenge this rationale. Keenan et al. also support their claim with published evidence relating brain activityand self-awareness; I closelyexamine their analysis of one specific (...) review of literature and conclude that it appears to be biased. Finally, recent research suggests that inner speech (which is associated with left hemispheric activity) is linked to self-awareness—an observation that further casts doubt on the existence of a right hemispheric self-awareness. Ó 2002 Elsevier Science (USA). All rights reserved. (shrink)

The human brain is divided into two hemispheres, right and left, that are joined by a thick ‘cable’ of neural fibres called the corpus callosum. It has long been observed that injury to the left hemisphere in the average adult damages speech, speech comprehension, and reading, and causes paralysis on the right side of the body. Injury to the right hemisphere, on the other hand, seems to leave linguistic capabilities intact, but causes paralysis on the (...) left side of the body. These observations have given rise to the twin concepts of contralaterality of hemispheric control and cognitive specialization of hemispheric function. As far back as the nineteenth century, it was recognized that the left hemisphere’s specialty was language. Pioneering British neurologist John Hughlings Jackson asserted in 1868 that the left hemisphere was the ‘leading side’ in most people, responsible for the control of speech and will. In the decade of the 1940s, French neurologist Henry Hecaen and British psychologist Oliver Zangwill demonstrated that the right hemisphere, far from being passive, controlled visuospatial processing. (shrink)

The present study was designed to explore the relationship between self-reported dissociative experiences and performance in tasks eliciting right-hemisphere processing load. Thirty-four participants performed a vigilance task in two conditions: with task-irrelevant negative-arousing pictures and task-irrelevant neutral pictures. Dissociation was assessed with the Dissociative Experience Scale. Consistent with theories positing right-hemisphere deregulation in high non-clinical dissociators, dissociative experiences correlated with greater vigilance decrement only in the negative picture condition. As both the vigilance task and negative picture (...) processing are right lateralized, this result provides support for a right-hemisphere dysfunction in high dissociators, at least in negative conditions. (shrink)

The existence of shoulder abduction (SA) and finger extension (FE) movement capacity shortly after stroke onset is an important prognostic factor, indicating favorable functional outcome for the hemiparetic upper limb. Here we asked whether variation in lesion topography affects these two movements in a similar or a distinct way, and whether lesion impact is similar or distinct for left and right hemisphere damage. SA and FE movements were examined in 77 chronic post-stroke patients using relevant items of the (...) Fugl-Meyer test. Lesion effects were analyzed separately for left and right hemispheric damage (LHD, RHD) patient groups using voxel-based lesion-symptom mapping. In the LHD group, SA and FE were affected only by damage to the cortico-spinal tract in its passage through the corona radiata. In contrast, following RHD, these two movements were affected not only by cortico-spinal tract damage but also by damage to white matter association tracts, the putamen and the insular cortex. In both groups, voxel clusters have been found where damage affected SA and also FE, along with voxels where damage affected only one of the two movements. The capacity to execute SA and FE movements following stroke is affected significantly by damage to shared and distinct voxels in the cortico-spinal tract in LHD patients and by damage to shared and distinct voxels in a larger array of cortical and subcortical regions in RHD patients. (shrink)

Using fMRI, we investigated how right temporal lobe gliomas affecting the posterior superior temporal sulcus alter neural processing observed during speech perception and production tasks. Behavioural language testing showed that three pre-operative neurosurgical patients with grade 2, grade 3 or grade 4 tumours had the same pattern of mild language impairment in the domains of object naming and written word comprehension. When matching heard words for semantic relatedness (a speech perception task), these patients showed under-activation in the tumour infiltrated (...) right superior temporal lobe compared to 61 neurotypical participants and 16 patients with tumours that preserved the right postero-superior temporal lobe, with enhanced activation within the (tumour-free) contralateral left superior temporal lobe. In contrast, when correctly naming objects (a speech production task), the patients with right postero-superior temporal lobe tumours showed higher activation than both control groups in the same right postero-superior temporal lobe region that was under-activated during auditory semantic matching. The task dependent pattern of under-activation during the auditory speech task and over-activation during object naming was also observed in eight stroke patients with right hemisphere infarcts that affected the right postero-superior temporal lobe compared to eight stroke patients with right hemisphere infarcts that spared it. These task-specific and site-specific cross-pathology effects highlight the importance of the right temporal lobe for language processing and motivate further study of how right temporal lobe tumours affect language performance and neural reorganisation. These findings may have important implications for surgical management of these patients, as knowledge of the regions showing functional reorganisation may help to avoid their inadvertent damage during neurosurgery. (shrink)

In this commentary I use recent empirical evidence and theoretical analyses concerning the importance of language and the meaning of self-recognition to reevaluate the claim that the right mute hemisphere in commissurotomized patients possesses a full consciousness. Preliminary data indicate that inner speech is deeply linked to self-awareness; also, four hypotheses concerning the crucial role inner speech plays in self-focus are presented. The legitimacy of self-recognition as a strong operationalization of self-awareness in the right hemisphere is (...) also questioned on the basis that it might rather tap a preexisting body awareness having little to do with an access to mental events. I conclude with the formulation of an alternative interpretation of commissurotomy according to self-awareness — a “complete” one in the left hemisphere and a “primitive” one in the right hemisphere. (shrink)

Attention and consciousness are two distinct neural processes which are intricately intertwined. However, there is asymmetry in the distribution of attentional abilities across the two hemispheres. The right hemisphere is asserted to be dominant for attentional abilities. Research suggests that the ventral frontoparietal cortex of the right hemisphere is dominant for exogenous attentional abilities, attention is phylogenetically more primitive than endogenous attention, and, compared to the left hemisphere, the right hemisphere is more adept (...) at abilities and functions that are of more primitive origin. This review explores the attentional abilities of the mute right hemisphere, the extent to which these may affect consciousness, and whether the unilateral dominance of the exogenous network influences consciousness. (shrink)

Chronic stroke survivors with severe contralesional arm paresis face numerous challenges to performing activities of daily living, which largely rely on the use of the less-affected ipsilesional arm. While use of the ipsilesional arm is often encouraged as a compensatory strategy in rehabilitation, substantial evidence indicates that motor control deficits in this arm can be functionally limiting, suggesting a role for remediation of this arm. Previous research has indicated that the nature of ipsilesional motor control deficits vary with hemisphere (...) of damage and with the severity of contralesional paresis. Thus, in order to design rehabilitation that accounts for these deficits in promoting function, it is critical to understand the relative contributions of both ipsilesional and contralesional arm motor deficits to functional independence in stroke survivors with severe contralesional paresis. We now examine motor deficits in each arm of severely paretic chronic stroke survivors with unilateral damage to determine whether hemisphere-dependent deficits are correlated with functional independence. Clinical evaluation of contralesional, paretic arm impairment was conducted with the upper extremity portion of the Fugl-Meyer assessment. Ipsilesional arm motor performance was evaluated using the Jebsen-Taylor Hand Function Test, grip strength, and ipsilesional high-resolution kinematic analysis during a visually targeted reaching task. Functional independence was measured with the Barthel Index. Functional independence was better correlated with ipsilesional than contralesional arm motor performance in the left hemisphere damage group [JTHFT: [r = −0.73, p = 0.017]; grip strength: [r = 0.64, p = 0.047]], and by contralesional arm impairment in the right hemisphere damage group [UEFM: [r = 0.66, p = 0.040]]. Ipsilesional arm kinematics were correlated with functional independence in the left hemisphere damage group only. Examination of hemisphere-dependent motor correlates of functional independence showed that ipsilesional arm deficits were important in determining functional outcomes in individuals with left hemisphere damage only, suggesting that functional independence in right hemisphere damaged participants was affected by other factors. (shrink)

We addressed the questions whether stimuli presented below the threshold of verbal awareness are nevertheless perceived and whether there are perceptual differences between the two cerebral hemispheres. Pictures of line drawn objects and animals were subliminally presented to each visual half-field for subsequent identification in a form as fragmented as possible. The performance of 40 healthy subjects was compared to that of 63 controls. Whereas identification performance after blank presentation in the experimental group did not differ from that of controls, (...) identification in a significantly more fragmented form was achieved after the presentation of the complete picture. This effect, however, occurred only after subliminal stimulation in the left visual field, i.e., of the right hemisphere. Our results show that pictures presented below the threshold of verbal awareness can be perceived, and that only the right hemisphere can perceive them and make use of the perception. It remains an open question whether this kind of hemispheric specialization represents a right hemisphere dominance for subliminal perception or reflects an inability of the left hemisphere to access and behaviorally use unaware percepts via fragmented picture identification, for which a right hemisphere advantage is known. (shrink)

Twenty-four aphasic and fifteen right brain-damaged subjects were compared on their ability to identify the objects whose use was depicted in a series of twenty videotaped pantomimes. Aphasics were inferior to right brain-damaged patients in inferring object use. Success was correlated with Performance IQ, but not with language measures. Analysis of movement features contributing to subjects' choices reveal speed of movement and object weight to be the most robust and hand shape and size to be the most fragile.