Quantitative Assessment of Motor Neglect.

Background and Purpose: We used differential actigraphy as a novel, objective method to quantify motor neglect (a clinical condition whereby patients mimic hemiplegia even in the absence of sensorimotor deficits), whose diagnosis is at present highly subjective, based on the clinical observation of patients' spontaneous motor behavior. Methods: Patients wear wristwatch-like accelerometers, which record spontaneous motor activity of their upper limbs during 24 hours. Asymmetries of motor behavior are then automatically computed offline. On the basis of normal participants' performance, we calculated cutoff scores of left/right motor asymmetry. Results: Differential actigraphy showed contralesional motor neglect in 9 of 35 patients with unilateral strokes, consistent with clinical assessment. An additional patient with clinical signs of motor neglect obtained a borderline asymmetry score. Lesion location in a subgroup of 25 patients was highly variable, suggesting that motor neglect is a heterogenous condition. Conclusions: Differential actigraphy provides an ecological measure of spontaneous motor behavior, and can assess upper limb motricity in an objective and quantitative manner. It thus offers a convenient, cost-effective, and relatively automatized procedure for following-up motor behavior in neurological patients and to assess the effects of rehabilitation.

The anatomo-clinical picture of the pathological embodiment over someone else's body part after stroke.

Recently, a monothematic delusion of body ownership due to brain damage (i.e., the embodiment of someone else's body part within the patient's sensorimotor system) has been extensively investigated. Here we aimed at defining in-depth the clinical features and the neural correlates of the delusion. Ninety-six stroke patients in a sub-acute or chronic phase of the illness were assessed with a full ad-hoc protocol to evaluate the embodiment of an alien arm under different conditions. A sub-group of seventy-five hemiplegic patients was also evaluated for the embodiment of the movements of the alien arm. Fifty-five patients were studied to identify the neural bases of the delusion by means of voxel-based lesion-symptom mapping approach. Our results show that, in forty percent of the whole sample, simply viewing the alien arm triggered the delusion, but only if it was a real human arm and that was seen from a 1st person perspective in an anatomically-correct position. In the hemiplegic sub-group, the presence of the embodiment of the alien arm was always accompanied by the embodiment of its passive and active movements. Furthermore, the delusion was significantly associated to primary proprioceptive deficits and to damages of the corona radiata and the superior longitudinal fasciculus. To conclude, we show that the pathological embodiment of an alien arm is well-characterized by recurrent and specific features and might be explained as a disconnection deficit, mainly involving white matter tracts. The proposed exhaustive protocol can be successfully employed to assess stroke-induced disorders of body awareness, unveiling even their more undetectable or covert clinical forms.

A new clinical evaluation of asomatognosia in right brain damaged patients using visual and reaching tasks.

INTRODUCTION: The term asomatognosia refers to a unilateral disturbance of body ownership following a cerebrovascular incident. Patients with asomatognosia consider the contralesional limbs as missing or having disappeared from awareness. This neuropsychological disorder modifies body ownership in terms of perceptual experience, visual identification and sense of belonging of contralesional body parts. In the literature, asomatognosia is usually tested by using verbal scales. METHOD: In this study, we first developed a new test to assess asomatognosia that includes a visual identification task and a reaching task. We examined 16 healthy participants and 20 right brain damaged patients. The participants were asked to identify, reach and touch their left hand when positioned in peripersonal space, in presence of an extraneous hand (belonging to the examiner). We analyzed how the deficit is modulated by the reciprocal positions in space of the two limbs, the relationship with personal neglect and the anatomical correlate using a Voxel-based Lesion Symptom Mapping (VLSM) analysis with CT data. RESULTS: The results show that the asomatognosia cannot be simply considered as one of the many manifestations of personal neglect but should be taken into account as a "productive" disorder characterized by the misidentification of the own hand with an extraneous hand. The VLSM analysis of patients with asomatognosia revealed the involvement of the inferior and middle frontal lobe. CONCLUSIONS: The novel task that has been developed in the present study could be used as an objective tool to measure this specific disorder of body ownership or to uncover subclinical conditions of asomatognosia.

Anosognosia for hemianaesthesia: a voxel-based lesion-symptom mapping study.

Brain-damaged patients affected by hemianaesthesia (i.e., the loss of tactile sensibility on the contralesional side of the body) may deny their deficits (i.e., anosognosia for tactile deficits) even reporting tactile experience when stimuli are delivered on the impaired side. So far, descriptive analysis on small samples of patients reported that the insular cortex, the internal/external capsule, the basal ganglia and the periventricular white matter would subserve anosognosia for hemianaesthesia. Here, we aimed at examining in depth the anatomo-functional nature of anosognosia for hemianaesthesia by means of a voxelwise statistical analysis. We compared two groups of left hemiplegic patients due to right brain damages differing only for the presence/absence of anosognosia for left hemianaesthesia. Our findings showed a lesional cluster confined mainly to the anterior part of the putamen. According to the current anatomical evidence on the neural basis of sensory expectancies, we suggested that anosognosia for hemianaesthesia might be explained as a failure to detect the mismatch between expected and actual tactile stimulation.

Long-lasting amelioration of walking trajectory in neglect after prismatic adaptation.

In the present study we explored the effect of prismatic adaptation (PA) applied to the upper right limb on the walking trajectory of a neglect patient with more severe neglect in far than in near space. The patient was asked to bisect a line fixed to the floor by walking across it before and after four sessions of PA distributed over a time frame of 67 days. Gait path was analyzed by means of an optoelectronic motion analysis system. The walking trajectory improved following PA and the result was maintained at follow-up, 15 months after treatment. The improvement was greater for the predicted bisection error (estimated on the basis of the trajectory extrapolated from the first walking step) than for the observed bisection error (measured at line bisection). These results show that PA may act on high level spatial representation of gait trajectory rather than on lower level sensory-motor gait components and suggest that PA may have a long-lasting rehabilitative effect on neglect patients showing a deviated walking trajectory.

Temporal coupling due to illusory movements in bimanual actions: evidence from anosognosia for hemiplegia.

In anosognosia for hemiplegia, patients may claim having performed willed actions with the paralyzed limb despite unambiguous evidence to the contrary. Does this false belief of having moved reflect the functioning of the same mechanisms that govern normal motor performance? Here, we examined whether anosognosics show the same temporal constraints known to exist during bimanual movements in healthy subjects. In these paradigms, when participants simultaneously reach for two targets of different difficulties, the motor programs of one hand affect the execution of the other. In detail, the movement time of the hand going to an easy target (i.e., near and large), while the other is going to a difficult target (i.e., far and small), is slowed with respect to unimanual movements (temporal coupling effect). One right-brain-damaged patient with left hemiplegia and anosognosia, six right-brain-damaged patients with left hemiplegia without anosognosia, and twenty healthy subjects were administered such a bimanual task. We recorded the movement times for easy and difficult targets, both in unimanual (one target) and bimanual (two targets) conditions. We found that, as healthy subjects, the anosognosic patient showed coupling effect. In bimanual asymmetric conditions (when one hand went to the easy target and the other went to the difficult target), the movement time of the non-paralyzed hand going to the easy target was slowed by the 'pretended' movement of the paralyzed hand going to the difficult target. This effect was not present in patients without anosognosia. We concluded that in anosognosic patients, the illusory movements of the paralyzed hand impose to the non-paralyzed hand the same motor constraints that emerge during the actual movements. Our data also support the view that coupling relies on central operations (i.e., activation of intention/programming system), rather than on online information from the periphery.

Verbal commands help the execution of endogenous movements in anarchic hand.

Patients with anarchic hand (AH) syndrome exhibit involuntary but seemingly purposeful controlesional upper limb movements. Here we report on the case of a patient (AC) presenting with a right AH following a left medial frontal lesion. Previous literature indicated that endogenous movements, particularly in the presence of distractors, are impaired in AH, whereas exogenous movements are spared. In this study we examined exogenous and endogenous (or sequential) movements using a new experimental procedure. Our main aim was to investigate whether the ability to perform sequential movements improves under verbal command as anecdotally observed in patients with AH. Results showed that the performance of AC's right AH was impaired in sequential tasks and that this impairment was improved by verbal command. The observed reduction in errors in sequential tasks under external verbal command was coupled with a compensatory increase in response times.

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.

Bisecting lines with different tools in right brain damaged patients: the role of action programming and sensory feedback in modulating spatial remapping.

In a first experiment we studied, through a line bisection task, (a) the frequency of the selective disruption of far or near space representations in a group of 28 right brain-damaged patients and (b) the effect of tool use on line bisection error in far and near space in order to clarify whether the kind of action performed by the subject influences the extension of space representation, as suggested by previous studies. In a second experiment, carried out on two neglect patients, we asked whether the representation of "near" and "far" space depends on the sensory feedback during the execution of the action or whether it is independent on sensory feedback and more related to the action programmed as a consequence of the kind of tool used. Our data show (a) that dissociations between far and near space neglect are a frequent observation in right brain damaged patients and that most of these patients are able to recode space representations when tools change the spatial relation between the agent's body and the target object; (b) that spatial remapping can be elicited by the kind of action associated to the tool used and by the sensory feedback (either visual or proprioceptive) available during the execution of the task. In particular, presence of tactile proprioceptive feedback elicited remapping of far space into near space, whereas absence of visual feedback induced remapping of near space into far space.

Impairments of trunk movements following left or right hemisphere lesions: dissociation between apraxic errors and postural instability.

Stroke patients present with apraxic or postural deficits involving trunk movements. Praxis and posture control have been associated with the functions of the left and the right hemisphere, respectively. For the first time, in this study the occurrence of apraxic and postural components in trunk movement deficits following right and left hemisphere lesions were investigated in the same participants. Twenty-three patients with left (L/pt), 12 with right (R/pt) hemisphere lesion, and 30 healthy controls were evaluated with a 21-item test assessing the imitation of meaningless, symbolic and reaching movements presented twice on visual or proprioceptive modality. Erroneous, motor responses of the trunk were classified as postural (compensations to overcome stability or asymmetry deficits) or apraxic (execution errors not due to biomechanical constraints). Postural instability reactions were significantly more frequent among the R/pts, whilst apraxic responses were overwhelming within the L/pts. The findings are consistent with the view that the left hemisphere is dominant for praxis and suggest that this dominance be extended to trunk praxis. The results also support the hypothesis that trunk postures are coded in relation to the environment by a representational system. A widespread network, mainly sitting in the right hemisphere, subserves this postural system. The distinction between praxic and postural deficits in executing trunk movements should be kept in mind when evaluating trunk movement difficulties shown by stroke patients, in following up their recovery or when tailoring rehabilitation programmes.

Coding of far and near space during walking in neglect patients.

Previous studies have shown that far space can be remapped as near when reached by a stick that artificially prolongs the participants' personal space. In the present study, the authors asked whether a similar remapping occurs when far space is reached not by using a tool but by locomotion. Neglect patients showed more severe neglect in far than in near space in bisection tasks executed from different distances either by pointing to a target line with a projection light pen or by walking across the line. A kinematic study of the walking performance of one of those neglect patients showed that, contrary to the prediction of remapping during locomotion, the walking trajectories were rectilinear. The authors interpreted these results as evidence that in their patients-at least for short, linear trajectories-no remapping of space took place during locomotion. The location of far objects was coded at the beginning of the movement, and the error in the bisection computation was generated within the 1st representation that was activated.