Anna Berti

When Far Becomes Near: Remapping of Space by Tool Use

Far (extrapersonal) and near (peripersonal) spaces are behaviorally defined as the space outside the hand-reaching distance and the space within the hand-reaching distance. Animal and human studies have confirmed this distinction, showing that space is not homogeneously represented in the brain. In this paper we demonstrate that the coding of space as far and near is not only determined by the hand-reaching distance, but it is also dependent on how the brain represents the extension of the body space. We will show that when the cerebral representation of body space is extended to include objects or tools used by the subject, space previously mapped as far can be remapped as near. Patient P.P., after a right hemisphere stroke, showed a dissociation between near and far spaces in the manifestation of neglect. Indeed, in a line bisection task, neglect was apparent in near space, but not in far space when bisection in the far space was performed with a projection lightpen. However, when in the far space bisection was performed with a stick, used by the patient to reach the line, neglect appeared and was as severe as neglect in the near space. An artificial extension of the patients body (the stick) caused a remapping of far space as near space.

The anatomy of anosognosia for hemiplegia: a meta-analysis.

Anosognosia for hemiplegia is the denial of the contralesional motor deficits that may follow brain damage. Although this disturbance has been reported in the neurological literature since the beginning of the last century, only few longitudinal studies have addressed the issue of the anatomical substrate of the disorder. Here we present a comprehensive review of the literature on anosognosia for hemiplegia from 1938 to 2001, taking into account some of its clinical, epidemiological and anatomical aspects. In particular, an attempt has been made to identify the intra-hemispheric lesion locations most frequently associated to the denial behaviour. Our review shows that anosognosia for hemiplegia most frequently occurs in association to unilateral right-sided or bilateral lesions of different brain areas (cortical and/or subcortical). It seems to be equally frequent when the damage is confined to frontal, parietal or temporal cortical structures, and may also emerge as a consequence of subcortical lesions. Interestingly, the probability of occurrence of anosognosia is highest when the lesion involves parietal and frontal structures in combination, if compared to other combinations of lesioned areas. This pattern of lesions suggests the existence of a complex cortico-subcortical circuit underlying awareness of motor acts that, if damaged, can give raise to the anosognosic symptoms.

Levels of processing for visual stimuli in an "extinguished" field.

Volpe et al. (Nature 282, 722, 1979 [19]) described an experimental study of four patients with parietal tumours who were able to judge whether two simultaneous stimuli were identical or different, even when they were unable to name the stimulus contralateral to their brain injury. We report the case of another patient, E.M., in whom we have investigated this phenomenon further. E.M. had undergone a right temporal lobectomy to prevent recurrent seizures. She could correctly name photographs of objects presented in isolation to either the left or right visual field, at 150 msec exposure (although she was impaired for single objects on the left at 10 msec exposures). She was able to judge correctly whether two simultaneous objects on the left and right had the same or different names, even though she was often unable to name the object on the left. These judgements remained above chance when same-name pairs of stimuli showed the same object but seen from two different viewpoints, or even when they showed visually dissimilar exemplars of the same name category. This implies that the patient based her same-different judgements on categorical information about the pair of objects, even though she was often unable to name the contralateral object.

Dyschiria. An Attempt at its Systemic Explanation

It is argued, in this chapter, that unilateral neglect is still in need of a systemic explanation. The working hypothesis is then suggested that unilateral neglect has remained conceptually isolated within a syndrome of which it may constitute the most common, but not the exclusive nor even the necessary component. A theoretical neural model of an analog subserving both sensory and mental representation in the visuo-spatial domain is outlined. Depending on relatively minor changes in its location within the same functional unit, a circumscribed failure of the analog may involve neglect or misrepresentation of one side of space, thus lending theoretical support to our working hypothesis. The term dyschiria is proposed for the syndrome of hemispatial neglect-misrepresentation as a late tribute to H. Zingerle, who many years ago, in one of his papers which was a forerunner of this subject, employed this term.

‘Moving’ a paralysed hand: bimanual coupling effect in patients with anosognosia for hemiplegia

Selective neurological impairments can shed light on different aspects of motor cognition. Brain-damaged patients with anosognosia for hemiplegia deny their motor deficit and believe they can still move the paralysed limb. Here we study, for the first time, if the anomalous subjective experience that their affected hand can still move, may have objective consequences that constrain movement execution with the opposite, intact hand. Using a bimanual motor task, in which anosognosic patients were asked to simultaneously trace out lines with their unaffected hand and circles with their paralysed hand, we found that the trajectories of the intact hand were influenced by the requested movement of the paralysed hand, with the intact hand tending to assume an oval trajectory (bimanual coupling effect). This effect was comparable to that of a group of healthy subjects who actually moved both hands. By contrast, brain-damaged patients with motor neglect or actual hemiplegia but no anosognosia did not show this bimanual constraint. We suggest that anosognosic patients may have intact motor intentionality and planning for the plegic hand. Rather than being merely an inexplicable confabulation, anosognosia for the plegic hand can produce objective constraints on what the intact hand does.

Modular structure of awareness for sensorimotor disorders : Evidence from anosognosia for hemiplegia and anosognosia for hemianaesthesia

In the present paper, we shall review clinical evidence and theoretical models related to anosognosia for sensorimotor impairments that may help in understanding the normal processing underlying conscious self-awareness. The dissociations between anosognosia for hemiplegia and anosognosia for hemianaesthesia are considered to give important clinical evidence supporting the hypothesis that awareness of sensory and motor deficits depends on the functioning of discrete self-monitoring processes. We shall also present clinical and anatomical data on four single case reports of patients selectively affected by anosognosia for hemianaesthesia. The differences in the anatomical localization of lesions causing anosognosia for hemiplegia and anosognosia for hemianaesthesia are taken as evidence that cerebral circuits subserving these monitoring processes are located in separate brain areas, which may be involved both in the execution of primary functions and the emergence of awareness related to the monitoring of the same functions. The implications of these findings for the structure of conscious processes shall be also discussed.

Nonconscious Reading? Evidence From Neglect Dyslexia

In this study we present evidence which supports the view that reading mechanisms, if implicit assessed, are available also in the presence of a severe deficit of spatial awareness. A Stroop-like task was performed by a right brain-damaged patient affected by severe extrapersonal neglect and neglect dyslexia. In reading words and color words, the patient showed the usual pattern of neglect errors; omission, substitution and addition errors. However, when asked to name the colors in which color words were written, naming time was found to be affected by the meaning of those words he was not able to read correctly. The pattern of results in MD and in a group of normal subjects, who performed a modified version of the Stroop test performed by MD, have been interpreted as evidence of MDs implicit reading of the left-hand letters of color words during the Stroop test. The theoretical implications of this finding are discussed. Moreover, the comparison between the performance of MD and the performance of another group of normal subjects suggested that implicit processing in MD was carried out at a lower level of efficiency than in normals.

The left inferior frontal gyrus is crucial for reading the mind in the eyes: Brain lesion evidence

Deficit in the ability to understand and predict the mental states of others is one of the central features of traumatic brain injury (TBI), leading to problems in social-daily life such as social withdrawal and the inability to maintain work or family relationships. Although several functional neuroimaging studies have identified a widely distributed brain network involved in the Reading the Mind in the Eyes Test (RMET), the necessary brain regions engaged in this capacity are still heavily debated. In this study, we combined the RMET with a whole-brain voxel-based lesion symptom mapping (VLSM) approach to identify brain regions necessary for adequate RMET performance in a large sample of patients with penetrating TBI (pTBI). Our results revealed that pTBI patients performed worse on the RMET compared to non-head injured controls, and impaired RMET performance was associated with lesions in the left inferior frontal gyrus (IFG). Our findings suggest that the left IFG is a key region in reading the mind in the eyes, probably involved in a more general impairment of a semantic working memory system that facilitates reasoning about what others are feeling and thinking as expressed by the eyes.

Understanding Motor Awareness Through Normal and Pathological Behavior

Data on patients with localized brain damage and on neurologically intact subjects show that normal motor control depends on the functionality of a chain of neurobiological events. These events, through the activation of internal representations of the desired, predicted, and actual condition of ones body with respect to the external world, contribute to the construction of conscious knowledge of voluntary actions and to self-awareness.

Embodiment of an alien hand interferes with intact-hand movements

Summary Can we fully incorporate into our body schema the body parts of others, altering our sense of ownership [1]? And, to what extent, given the tight link between body and motor representations, does an altered sense of body-ownership affect motor awareness [2] and the sense of agency [3,4]? The new study we report here demonstrates that a body part of one individual can become so deeply embedded in anothers sensory-motor circuits as to have objective effects on the latters motor execution. Indeed, we found, in right-brain-damaged hemiplegic patients who identified another persons hand as belonging to themselves, significant interference effects of the alien hand movements on the actual movements of their own intact hand.