Deficits of hierarchical predictive coding in left spatial neglect.

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 deficits following right brain damage.

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.

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.

The dynamic nature of the sense of ownership after brain injury. Clues from asomatognosia and somatoparaphrenia.

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, body temperature and sense of body ownership: a potential link? Insights from a single case study".

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.

Updating impairments and the failure to explore new hypotheses following right brain damage.

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.

Perception of active head rotation in patients with severe left unilateral spatial neglect.

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.

Radial bisection of words and lines in right-brain-damaged patients with spatial neglect.

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.

Co-speech hand movements during narrations: What is the impact of right vs. left hemisphere brain damage?

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 spatial side of somatoparaphrenia: a case study.

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.

Cingulate neglect in humans: disruption of contralesional reward learning in right brain damage.

Motivational valence plays a key role in orienting spatial attention. Nonetheless, clinical documentation and understanding of motivationally based deficits of spatial orienting in the human is limited. Here in a series of one group-study and two single-case studies, we have examined right brain damaged patients (RBD) with and without left spatial neglect in a spatial reward-learning task, in which the motivational valence of the left contralesional and the right ipsilesional space was contrasted. In each trial two visual boxes were presented, one to the left and one to the right of central fixation. In one session monetary rewards were released more frequently in the box on the left side (75% of trials) whereas in another session they were released more frequently on the right side. In each trial patients were required to: 1) point to each one of the two boxes; 2) choose one of the boxes for obtaining monetary reward; 3) report explicitly the position of reward and whether this position matched or not the original choice. Despite defective spontaneous allocation of attention toward the contralesional space, RBD patients with left spatial neglect showed preserved contralesional reward learning, i.e., comparable to ipsilesional learning and to reward learning displayed by patients without neglect. A notable exception in the group of neglect patients was L.R., who showed no sign of contralesional reward learning in a series of 120 consecutive trials despite being able of reaching learning criterion in only 20 trials in the ipsilesional space. L.R. suffered a cortical-subcortical brain damage affecting the anterior components of the parietal-frontal attentional network and, compared with all other neglect and non-neglect patients, had additional lesion involvement of the medial anterior cingulate cortex (ACC) and of the adjacent sectors of the corpus callosum. In contrast to his lateralized motivational learning deficit, L.R. had no lateral bias in the early phases of attentional processing as he suffered no contralesional visual or auditory extinction on double simultaneous tachistoscopic and dichotic stimulation and detected, with no exception, single contralesional visual and auditory stimuli. In a separate study, we were able to compare L.R. with another RBD patient, G.P., who had a selective lesion in the right ACC, in the adjacent callosal connections and the medial-basal prefrontal cortex. G.P. had no contralesional neglect and displayed normal reward learning both in the left and right side of space. These findings show that contralesional reward learning is generally preserved in RBD patients with left spatial neglect and that this can be exploited in rehabilitation protocols. Contralesional reward learning is severely disrupted in neglect patients when an additional lesion of the ACC is present: however, as demonstrated by the comparison between L.R. and G.P. cases, selective unilateral lesion of the right ACC does not produce motivational neglect for the contralesional space.

(Un)awareness of unilateral spatial neglect: a quantitative evaluation of performance in visuo-spatial tasks.

Right-brain-damaged patients with unilateral spatial neglect are usually unaware (anosognosic) about their spatial deficits. However, in the scientific literature there is a lack of systematic and quantitative evaluation of this kind of unawareness, despite the negative impact of anosognosia on rehabilitation programs. This study investigated anosognosia for neglect-related impairments at different clinical tasks, by means of a quantitative assessment. Patients were tested in two different conditions (before and after execution of each task), in order to evaluate changes in the level of awareness of neglect-related behaviours triggered by task execution. Twenty-nine right-brain-damaged patients (17 with left spatial neglect) and 27 neurologically unimpaired controls entered the study. Anosognosia for spatial deficits is not pervasive, with different tasks evoking different degrees of awareness about neglect symptoms. Indeed, patients showed a largely preserved awareness about their performance in complex visuo-motor spatial and reading tasks; conversely, they were impaired in evaluating their spatial difficulties in line bisection and drawing from memory, showing over-estimation of their performance. The selectivity of the patients' unawareness of specific manifestations of spatial neglect is further supported by their preserved awareness of performance at a linguistic task, and by the absence of anosognosia for hemiplegia. This evidence indicates that discrete processes are involved in the aware monitoring of cognitive and motor performance, which can be selectively compromised by brain damage. Awareness of spatial difficulties is supported by a number of distinct components, and influenced by the specific skills required to perform a given task.

Arousal responses to noxious stimuli in somatoparaphrenia and anosognosia: clues to body awareness.

A complex brain representation of our body allows us to monitor incoming sensory stimuli and plan actions towards the external world. A critical element of such a complex representation is the sense of ownership towards our own body parts. Brain damage may disrupt this representation, leading to the striking neuropsychological condition called somatoparaphrenia, that is, the delusion that one's own limbs belong to someone else. The clinical features characterizing somatoparaphrenia are well known, however, physiological clues of the level at which this condition may disrupt sensory functions are unknown. In the present study we investigated this issue by measuring the anticipatory skin conductance response to noxious stimuli approaching either the affected or the intact body side in a group of patients with somatoparaphrenia (n=5; three females, age range=66-84), and in a group of patients with anosognosia for sensory deficits, i.e. preserved ownership but decreased awareness of somatosensory deficit, (n=5; one female, age range=62-81 years) and in a group of purely hemiplegic patients (n=5; two females, age range=63-74 years) with no deficits of ownership or sensory awareness. Results show that anticipatory skin conductance responses to noxious stimuli directed to the contralesional hand are significantly reduced as compared to noxious stimuli directed to the ipsilesional hand in patients with somatoparaphrenia. By contrast a non-reduced anticipatory skin conductance response was observed in control participants as well as in patients affected by anosognosia for the somatosensory deficit and in patients affected by pure motor deficits. Furthermore, a pain anticipation response was always measured when the stimuli were directed towards the ipsilesional, unaffected hand in all groups. Our results show for the first time that the delusions shown by somatoparaphrenic patients are associated with an altered physiological index of perceptual analysis. The reduced response to sensory threats approaching the body suggests a deep detachment of the affected body part from the patient's body representation. Conversely, normal reactions to incoming threats are found in the presence of impaired sensory awareness but intact body ownership, supporting the notion that representation of the body may be affected at different levels following brain damage.

Exploring the effects of ecological activities during exposure to optical prisms in healthy individuals.

Prism adaptation improves a wide range of manifestations of left spatial neglect in right-brain-damaged patients. The typical paradigm consists in repeated pointing movements to visual targets, while patients wear prism goggles that displace the visual scene rightwards. Recently, we demonstrated the efficacy of a novel adaptation procedure, involving a variety of every-day visuo-motor activities. This "ecological" procedure proved to be as effective as the repetitive pointing adaptation task in ameliorating symptoms of spatial neglect, and was better tolerated by patients. However, the absence of adaptation and aftereffects measures for the ecological treatment did not allow for a full comparison of the two procedures. This is important in the light of recent findings showing that the magnitude of prism-induced aftereffects may predict recovery from spatial neglect. Here, we investigated prism-induced adaptation and aftereffects after ecological and pointing adaptation procedures. Forty-eight neurologically healthy participants (young and aged groups) were exposed to rightward shifting prisms while they performed the ecological or the pointing procedures, in separate days. Before and after prism exposure, participants performed proprioceptive, visual, and visual-proprioceptive tasks to assess prism-induced aftereffects. Participants adapted to the prisms during both procedures. Importantly, the ecological procedure induced greater aftereffects in the proprioceptive task (for both the young and the aged groups) and in the visual-proprioceptive task (young group). A similar trend was found for the visual task in both groups. Finally, participants rated the ecological procedure as more pleasant, less monotonous, and more sustainable than the pointing procedure. These results qualify ecological visuo-motor activities as an effective prism-adaptation procedure, suitable for the rehabilitation of spatial neglect.

Avaliação da prosódia emocional em adultos com lesão de hemisfério direito / Emotional prosody assessment in adults with right brain damage

Uma lesão de hemisfério direito pode gerar alterações comunicativas, comprometendo habilidades dos processamentos discursivo, pragmático-inferencial, léxico-semântico e prosódico (nos níveis compreensivo e expressivo). Uma das sequelas que vem sendo estudadas é a disprosódia. No entanto, o conhecimento sobre os instrumentos de avaliação para seu diagnóstico ainda é restrito. Este artigo visa a apresentar uma revisão sistemática sobre os instrumentos de avaliação da prosódia emocional em estudos de pessoas com lesão de hemisfério direito. Fez-se uma busca de resumos nas bases SciELO, LILACS e PubMed, com as palavras-chave "hemisfério", "direito", "prosódia" e "emocional". Encontraram-se 14 estudos apenas na base PubMed. A maioria utiliza tarefas experimentais, com pouca frequência de testes padronizados, sendo que seis investigações tiveram a participação de um mesmo pesquisador. Ressalta-se o caráter relativamente recente e incipiente dos estudos internacionais sobre a avaliação de déficits prosódicos após lesão cerebral direita, havendo uma importante lacuna nacional nessa área de diagnóstico neuropsicológico(AU)

A right hemisphere brain damage can cause communicative impairments, compromising skills in discursive, pragmatic-inferential, lexical-semantic, and prosodic (at the comprehensive and expressive levels) processing. One of the sequelae which has been studied is dysprosody. However , the knowledge of the assessment instruments for its diagnosis is yet uncertain. The aim of this article is to present a systematic review on the emotional prosody assessment instruments in studies of people with right hemisphere brain damage. Abstracts were searched for in SciELO, Lilacs and PubMed databases, using the keywords "right", "hemisphere", "emotional" and "prosody". 14 studies were found only in Medline database. Most of them use experimental tasks, with standardized tests being less frequent, and six investigations were conducted by the same researcher. The relatively recent and incipient nature of the international studies on the assessment of prosodic deficits after right hemisphere brain damage must be highlighted, as well as an important national gap in this field of neuropsychological diagnosis(AU)

Avaliação da prosódia emocional em adultos com lesão de hemisfério direito / Emotional prosody assessment in adults with right brain damage

Uma lesão de hemisfério direito pode gerar alterações comunicativas, comprometendo habilidades dos processamentos discursivo, pragmático-inferencial, léxico-semântico e prosódico (nos níveis compreensivo e expressivo). Uma das sequelas que vem sendo estudadas é a disprosódia. No entanto, o conhecimento sobre os instrumentos de avaliação para seu diagnóstico ainda é restrito. Este artigo visa a apresentar uma revisão sistemática sobre os instrumentos de avaliação da prosódia emocional em estudos de pessoas com lesão de hemisfério direito. Fez-se uma busca de resumos nas bases SciELO, LILACS e PubMed, com as palavras-chave "hemisfério", "direito", "prosódia" e "emocional". Encontraram-se 14 estudos apenas na base PubMed. A maioria utiliza tarefas experimentais, com pouca frequência de testes padronizados, sendo que seis investigações tiveram a participação de um mesmo pesquisador. Ressalta-se o caráter relativamente recente e incipiente dos estudos internacionais sobre a avaliação de déficits prosódicos após lesão cerebral direita, havendo uma importante lacuna nacional nessa área de diagnóstico neuropsicológico.

A right hemisphere brain damage can cause communicative impairments, compromising skills in discursive, pragmatic-inferential, lexical-semantic, and prosodic (at the comprehensive and expressive levels) processing. One of the sequelae which has been studied is dysprosody. However , the knowledge of the assessment instruments for its diagnosis is yet uncertain. The aim of this article is to present a systematic review on the emotional prosody assessment instruments in studies of people with right hemisphere brain damage. Abstracts were searched for in SciELO, Lilacs and PubMed databases, using the keywords "right", "hemisphere", "emotional" and "prosody". 14 studies were found only in Medline database. Most of them use experimental tasks, with standardized tests being less frequent, and six investigations were conducted by the same researcher. The relatively recent and incipient nature of the international studies on the assessment of prosodic deficits after right hemisphere brain damage must be highlighted, as well as an important national gap in this field of neuropsychological diagnosis.