Right brain-damaged patients with unilateral spatial neglect fail to explore the left side of space. Recent EEG and clinical evidence suggests that neglect patients might suffer deficits in predictive coding, i.e. in identifying and exploiting probabilistic associations among sensory stimuli in the environment. To gain direct insights on this issue, we focussed on the hierarchical components of predictive coding. We recorded EEG responses evoked by central, left-side or right-side tones that were presented at the end of sequences of four central tones. Left-side and right-side deviant tones produce a pre-attentive Mismatch Negativity that reflects a lower-order prediction error for the \'Local\' deviation of the tone at the end of the sequence. Higher-order prediction errors for the frequency of these deviations in the acoustic environment, i.e. \'Global\' deviation, are marked by the P3 response. We show that when neglect patients are immersed in an acoustic environment characterized by frequent left-side deviant tones, they display no pre-attentive Mismatch Negativity both for left-side deviant tones and infrequent omissions of the last tone, while they have Mismatch Negativity for infrequent right-side deviant tones. In the same condition, neglect patients show no P300 response to \'Global\' prediction errors for deviant tones, including those in the non-neglected right-side, and omissions. In contrast to this, when right-side deviant tones are predominant in the acoustic environment, neglect patients have pre-attentive Mismatch Negativity both for right-side deviant tones and infrequent omissions, while they display no Mismatch Negativity for infrequent left-side deviant tones. Most importantly, in the same condition neglect patients show enhanced P300 response to infrequent left-side deviant tones, notwithstanding that these tones evoked no pre-attentive Mismatch Negativity. This latter finding indicates that \'Global\' predictions are independent of \'Local\' error signals provided by the Mismatch Negativity. These results qualify deficits of predictive coding in the spatial neglect syndrome and show that neglect patients base their predictive behaviour only on statistical regularities that are related to the frequent occurrence of sensory events on the right side of space.

Visual working memory (VWM) involves the encoding and maintenance of visual information over time, with the requirement that object features be accurately bound to spatial locations. We and others have shown that damage to the right hemisphere leads to impaired spatial working memory. Here, we test the notion that right brain damage (RBD) may have consequences for domain general VWM. We had eight RBD patients and a group of healthy control participants perform a VWM task under different loads (1 to 3 items to recall) and spatial competition (high vs. low). All participants were asked to remember the colour of target items presented on the right side of space. Patients showed impaired encoding of information evident in poor precision of memory representations and increased guessing rates even at a set size of only one item. Our data suggests that VWM capacity is severely limited following RBD. Although five of the eight patients presented with neglect, it is not clear whether this deficit in VWM is unique to the syndrome. We suggest that future work should directly pit attention and VWM demands against one another in the same patients to determine whether the confluence of deficits in these domains is the critical determinant of the neglect syndrome. Regardless of the implications for the neglect syndrome, however, our data show that VWM deficits in RBD patients extend into non-spatial feature space.

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.
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.
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.
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.

The sense of ownership is the feeling that a body part belongs to ourselves. Brain damage may disrupt this feeling, leading to somatoparaphrenia (SP), i.e., the delusion that one\'s limbs belong to someone else. This delusional feeling is typically associated with profound motor and somatosensory deficits. We reviewed the cases of SP reported so far in the literature outlining the clinical and neuroanatomical profile of SP. We then investigated and reported three new peculiar cases of SP that allow new insights into the theoretical framework of this neuropsychological condition. We thus propose an innovative theoretical account that integrates previous evidence and the new cases described. We suggest that a defective update of the ongoing dynamic representation of the body finalised to perception and action, may be the key for the disownership feelings of patients with SP. The erroneous spatial representation of the limb contralateral to the lesion would have the logical consequence of delusional misattribution of the seen own arm.

The vestibular system plays a pivotal role in behavioural and physiological aspects of body representation. If on the one hand, the stimulation of the vestibular system in healthy subjects provokes body representation distortions, accompanied by a decrease of body temperature, on the other hand, in brain-damaged patients it transiently restores body representation disorders. So far, the physiological counterpart of such behavioural amelioration on patients has never been explored. Here we aimed at investigating body temperature variations following Caloric Vestibular Stimulation (CVS), in a patient affected by somatoparaphrenia who regained the sense of body part ownership after the stimulation. Results showed an increase in body temperature after CVS, which also correlated with the temporary restored sense of limb ownership. Our results support the idea that physiological signals are fundamental to maintain a coherent mental representation of the body.

We have shown recently that damage to the right hemisphere impairs the ability to update mental models when evidence suggests an old model is no longer appropriate. We argue that this deficit is generic in the sense that it crosses multiple cognitive and perceptual domains. Here, we examined the nature of this updating impairment to determine more precisely the underlying mechanisms. We had right (RBD, N = 12) and left brain damaged (LBD, N = 10) patients perform versions of our picture-morphing task in which pictures gradually morph from one object (e.g., shark) to another (e.g., plane). Performance was contrasted against two groups of healthy older controls, one matched on age (HCO-age-matched, N = 9) and another matched on general level of cognitive ability (HCO-cognitively-matched, N = 9). We replicated our earlier findings showing that RBD patients took longer than LBD patients and HCOs to report seeing the second object in a sequence of morphing images. The groups did not differ when exposed to a morphing sequence a second time, or when responding to ambiguous images outside the morphing context. This indicates that RBD patients have little difficulty alternating between known representations or labeling ambiguous images. Instead, the difficulty lies in generating alternate hypotheses for ambiguous information. Lesion overlay analyses, although speculative given the sample size, are consistent with our fMRI work in healthy individuals in implicating the anterior insular cortex as critical for updating mental models.

Unilateral spatial neglect is a common neurological syndrome following predominantly right hemisphere damage, and is characterized by a failure to perceive and report stimuli in the contralesional side of space. To test the reference shift hypothesis that contralesional spatial neglect in right-brain-damaged patients is attributed to a rightward deviation of the egocentric reference frame, we measured the final angular position to which controls and left-side neglect patients actively turned their head toward the left in response to a verbal instruction given from each of three locations-right, left, and front-in two conditions, with and without visual feedback. When neglect patients were asked to \"look straight ahead\", they deviated about 30° toward the right in the eyes-open condition. However, the rightward deviation was markedly reduced in the eyes-closed condition. Regardless of visual feedback, there was no significant difference between controls and neglect patients in the final angular position of active head rotation when the verbal instruction came from the subject\'s left or front side; however, the final angular position was significantly smaller in the neglect patients than in the controls when the verbal instruction was given from the right. These results support the contention that cervico-vestibular stimulation during active head rotation restores spatial remapping and sensori-motor correlations and so improves neglect without affecting the position of the egocentric reference; however, once left-side neglect patients respond to verbal instruction from the right side, they are unable to disengage attention from the hemispace, and the performance of head rotation is disturbed.

Persons with brain damage show deviant patterns of co-speech hand movement behaviour in comparison to healthy speakers. It has been claimed by several authors that gesture and speech rely on a single production mechanism that depends on the same neurological substrate while others claim that both modalities are closely related but separate production channels. Thus, findings so far are contradictory and there is a lack of studies that systematically analyse the full range of hand movements that accompany speech in the condition of brain damage. In the present study, we aimed to fill this gap by comparing hand movement behaviour in persons with unilateral brain damage to the left and the right hemisphere and a matched control group of healthy persons. For hand movement coding, we applied Module I of NEUROGES, an objective and reliable analysis system that enables to analyse the full repertoire of hand movements independent of speech, which makes it specifically suited for the examination of persons with aphasia. The main results of our study show a decreased use of communicative conceptual gestures in persons with damage to the right hemisphere and an increased use of these gestures in persons with left brain damage and aphasia. These results not only suggest that the production of gesture and speech do not rely on the same neurological substrate but also underline the important role of right hemisphere functioning for gesture production.

The bisection of lines positioned radially (with the two ends of the line close and far, with respect to the participant\'s body) has been less investigated than that of lines placed horizontally (with their two ends left and right, with respect to the body\'s midsagittal plane). In horizontal bisection, patients with left neglect typically show a rightward bias for both lines and words, greater with longer stimuli. As for radial bisection, available data indicate that neurologically unimpaired participants make a distal error, while results from right-brain-damaged patients with left spatial neglect are contradictory. We investigated the bisection of radially oriented words, with the prediction that, during bisection, linguistic material would be recoded to its canonical left-to-right format in reading, with the performance of neglect patients being similar to that for horizontal words. Thirteen right-brain-damaged patients (seven with left spatial neglect) and fourteen healthy controls were asked to manually bisect 40 radial and 40 horizontal words (5-10 letters), and 80 lines, 40 radial and 40 horizontal, of comparable length. Right-brain-damaged patients with spatial neglect exhibited a proximal bias in the bisection of short radial words, with the proximal part corresponding to the final right part of horizontally oriented words. This proximal error was not found in patients without neglect and healthy controls. For bisection, short radial words may be recoded to the canonical orthographic horizontal format, unveiling the impact of left neglect on radially oriented stimuli.

The perception of the bodily self in space is a composite cognitive function requiring a dynamic integrated brain mechanism. Somatoparaphrenia (SP), a delusional belief concerning the experienced disownership for the contralesional paralyzed arm, represents the disruption of such mechanism. In two experiments, we have investigated the alteration of limb disownership after spatial manipulations in a right-brain-damaged patient affected by chronic SP. In experiment 1 the patient\'s spatial attention was switched between the left and right sides of space. SP signs worsened when the patient was interviewed from the left compared to the right bedside. In the second experiment we showed the first systematic transient remission of SP using left caloric vestibular stimulation (CVS), a physiologic manipulation mainly acting on the spatial frame of reference. Taken together, these results shed further light on the spatial nuance of SP and on the importance of vestibular signals for the generation of a coherent body representation. Furthermore, our case study demonstrated the possibility of eliciting more severe SP signs if the patient is interviewed from the left bedside. Additionally, CVS applications may have an important impact on the rehabilitation of these symptoms.