Daniele Nico

The role of the right parietal lobe in anorexia nervosa.

BACKGROUND Patients with anorexia nervosa (AN) overestimate their size despite being severely underweight. Whether this misperception echoes an underlying emotional disturbance or also reflects a genuine body-representation deficit is debatable. Current measures inquire directly about subjective perception of body image, thus distinguishing poorly between top-down effects of emotions/attitudes towards the body and disturbances due to proprioceptive disorders/distorted body schema. Disorders of body representation also emerge following damage to the right parietal lobe. The possibility that parietal dysfunction might contribute to AN is suspected, based on the demonstrated association of spatial impairments, comparable to those found after parietal lesion, with this syndrome. METHOD We used a behavioral task to compare body knowledge in severe anorexics (n=8), healthy volunteers (n=11) and stroke patients with focal damage to the left/right parietal lobe (n=4). We applied a psychophysical procedure based on the perception, in the dark, of an approaching visual stimulus that was turned off before reaching the observer. Participants had to predict whether the stimulus would have hit/missed their body, had it continued its linear motion. RESULTS Healthy volunteers and left parietal patients estimated body boundaries very close to the real ones. Conversely, anorexics and right parietal patients underestimated eccentricity of their left body boundary. CONCLUSIONS These findings are in line with the role the parietal cortex plays in developing and maintaining body representation, and support the possibility for a neuropsychological component in the pathogenesis of anorexia, offering alternative approaches to treatment of the disorder.

Motor deficits and optokinetic stimulation in patients with left hemineglect

Optokinetic stimulation with left direction of the movement of luminous dots temporarily improved motor weakness of the left hand in two right-brain-damaged patients with left spatial hemineglect. Stimulation to the right had no effect. In two left-brain-damaged patients, optokinetic stimulation did not affect the right motor weakness, regardless of direction of the movement of the optokinetic stimuli. We suggest that in patients with left hemineglect, contralesional motor deficits have a neglect-related component, which, as other aspects of the neglect syndrome, may be improved by optokinetic stimulation. The mechanisms may include a temporary restoration of the spatial coordinates of bodily representations, pathologically distorted towards the side of the lesion.

Body and movement: Consciousness in the parietal lobes

A critical issue related to the notion of identity concerns our ability to discriminate between internally and externally generated stimuli. This basic mechanism likely relies on perceptual and motor information, and requires that both motor plans and the resulting activity be continuously mapped on a reliable body representation. It has been widely demonstrated that the parietal cortices of the two hemispheres play a crucial role, albeit differently specialized, in both monitoring internal representation of our own actions and sustaining body representation. Ample neuropsychological evidence indicates that while damage to the left parietal cortex affects the ability to generate and/or monitor an internal model of ones own movement, lesions of the right parietal lobe are largely responsible for severe perturbations of the internal representation of ones own body. In the present paper, we discuss the processes involved in body perception and self-recognition and propose a tentative model describing how the right and left parietal cortices contribute in integrating various sources of information to produce the unique, elementary experience of ones own body in motion. The ecological value of this process in constructing identity and autobiographical experience will be discussed.

Locomotor body scheme.

The concept of body schema has been introduced and widely discussed in the literature to explain various clinical observations and distortions in the body and space representation. Here we address the role of body schema related information in multi-joint limb motion. The processing of proprioceptive information may differ significantly in static and dynamic conditions since in the latter case the control system may employ specific dynamic rules and constraints. Accordingly, the perception of movement, e.g., estimation of step length and walking distance, may rely on a priori knowledge about intrinsic dynamics of limb segment motion and inherent relationships between gait parameters and body proportions. The findings are discussed in the general framework of space and body movement representation and suggest the existence of a dynamic locomotor body schema used for controlling step length and path estimation.

Left neglect dyslexia and the processing of neglected information.

A patient (ES) with a right fronto-temporo-parieto-occipital lesion, and left neglect dyslexia, is reported. ES performed reading and association tasks on written words, composed of two embedded words, one to the left and one to the right of the division point. The meaning of the whole stimulus differed from that of the embedded words, and could not be inferred from either of them. ES produced appropriate associations even to those stimuli on which she made neglect paralexic errors. This dissociation reflects a distinction between processes which use co-ordinate spatial systems and subserve perceptual awareness, impaired in hemineglect, and processes which do not. The latter analyse left-sided information to a large extent, without reaching awareness.

Detecting directional hypokinesia: The epidiascope technique

A new technique to detect directional hypokinesia is proposed.. Subjects with unilateral neglect were administered cancellation tests with an epidiascope used to dissociate visual input from motor output. Two different cancellation tasks were performed in order to compare this technique with the method devised by Tegner and Levander [Brain 114, 1943-1951, 1991]. No difference in detecting hypokinetic deficits was observed; however, our method was easier to perform and more suitable for clinical testing.

Different motor imagery modes following brain damage

In recent years, many researches have explored the relationship between overt and covert motor activity (i.e., mental simulation). Consistent evidence has been provided in favour of close similarities between the two functions, particularly based on behavioural and neuroimaging studies on healthy participants. Interestingly, literature on the pathological population remains largely controversial. Yet, a clear understanding of whether and how mental simulation is modified by overt motor disorders is far from a speculative question, especially in view of the increasing interest for the use of mental practice in motor rehabilitation. Here, we explored whether a single set of cognitive skills is applied while solving tasks that implicitly require mental simulation of an action, or whether alternative strategies might be elicited according to the imagers actual motor capabilities. For this purpose, we recruited a group of patients who suffered from a stroke affecting selectively either the right or the left hemisphere, responsible for motor impairments ranging in severity. We required them, and a group of age-matched healthy controls, to perform a task of simulated grasping, and two tasks involving handedness judgments (on hands and gloves, respectively). Dissociations were found between the performances of patients suffering from left versus right brain damage, according to the task and, interestingly, the actual state of the imagers motor capabilities. This finding suggests that motor imagery might include alternative mental strategies that are independent from the actual state of the motor system. We discuss how these mental operations are differently affected by motor impairment, and consider the implications of the present theoretical finding for neurorehabilitation.

Believing what you feel: Using proprioceptive feedback to reduce unilateral neglect

Unilateral spatial neglect declines when participants reach to grip the center of long metal rods compared with when they point to the perceived center, suggesting that visuomotor control systems are less affected by neglect than other representational systems (I. H. Robertson, D. Nico, & B. Hood, 1995). In this study, 16 participants with unilateral left neglect actually picked up rods, and we predicted short-term improvements in neglect because of induced conflict between a phenomenally symmetrical visual world on the one hand and a proprioceptively conveyed rightward-biased world on the other. With participants serving as their own controls, significant short-term improvements in neglect were found on 2 out of 4 neglect tasks after participants experienced proprioceptive feedback discrepant from the judgments they made on the basis of visual information alone.

Lack of orientation due to a congenital brain malformation: A case study

Topographical disorientation is usually described in patients who have lost the ability to orient themselves as a consequence of acquired focal brain damage. Here, we describe the case of a 20-year-old woman with a congenital brain malformation who has never been able to orient herself within the environment. We addressed in detail her ability to orient and navigate within the environment by administering a number of tasks in both ecological and experimental surroundings. The results indicate a complete inability to use any kind of strategy useful for orientation.

Horizontal space misrepresentation in unilateral brain damage I. Visual and proprioceptive-motor influences in left unilateral neglect

Patients with unilateral neglect can misperceive horizontal distances in the contralesional space as being shorter than equivalent ipsilesional ones. We evaluated the visual and motor-proprioceptive components of space misrepresentation through a distance reproduction task performed both with and without visual guidance. Four groups of right brain damaged patients (neglect with hemianopia (N+H+), neglect with inferior quandrantanopia (N+Q+), neglect without hemianopia (N+H-) and patients without neglect or hemianopia (N-H-)) and one group of healthy controls (C) performed the line bisection task and reproduced horizontal distances either by setting the endpoints or by doubling the length of a line in the contralesional or ipsilesional space. The doubling length task was administered in three different conditions: (a) visuomotor (the patient draws the line in free vision); (b) visual (by sight the patient guides the examiner drawing the line); (c) proprioceptive-motor (the patient is blindfolded and manually inspects and extends the horizontal distance subtended by the line). Compared to C and N-H- patients, only N+H+ patients exhibited a significant ipsilesional shift in line bisection. N+H+ patients showed the most severe contralesional-overextension/ipsilesional-underextension asymmetry in the endpoint, visuomotor and visual line extension task. In the proprioceptive-motor condition no asymmetry was found and N+H- showed greater overextension on both sides of space. In N+H-, brain damage was mainly centered in central-frontal cortex and basal ganglia. These findings re-emphasize the relevance of damage to visual retinotopically organized representations of space in the genesis of horizontal space misrepresentation of neglect patients and suggest the possible association of a non-lateralized defective processing of proprioceptive-motor information with unilateral neglect.