Arnaud Saj

Subjective Visual Vertical in Pitch and Roll in Right Hemispheric Stroke

Background and Purpose— Patients with right hemispheric stroke usually present an anticlockwise deviation of the subjective visual vertical (SVV) in the frontal (roll) plane. However, the occurrence of a similar disorder in the sagittal (pitch) plane has never been assessed. We investigated the subjective visual vertical in both planes in those patients. Methods— Eight patients, 4 with spatial neglect (N+) and 4 without neglect (N−), were compared with 4 healthy participants (C). They sat facing a luminous bar adjustable in rotation, either in the roll or in the pitch plane, and had to orient it in a vertical position, in the dark. Results— Compared with N− (−0.1°) and C (+1.1°) groups, N+ patients presented with a significant backward deviation (−4.5°) of the SVV in pitch. In accordance with other studies, they also showed a significant anticlockwise deviation (−8.8°) of the SVV in roll, as compared with N− (−1.9°) and C (+0.4°) subjects. This was associated with an opposite trunk deviation in both planes. Conclusions— While confirming the anticlockwise deviation already reported in the frontal plane, we showed for the first time to our knowledge a backward deviation of the SVV in neglect patients, which has to be put in relation with their balance disorders.

The visual vertical in the pusher syndrome: influence of hemispace and body position.

AbstractThe subjective visual vertical (SVV) was investigated in right brain–damaged (RBD) patients with pusher syndrome (PS) which is thought to stem from an erroneous perception of body orientation. The participants, sitting or lying, had to align a luminous rod with gravity. The task was performed in darkness with the rod centred to the body, or placed in the left (neglected) or in the right hemispace. The error, negligible in the control group (+0.3°; n = 6) and mild in the nonneglect non–pusher patients (–1.8°; n = 6), was clearly clockwise in the pusher neglect patients (N+P+; +7.2°; n = 4), but anticlockwise in the non–pusher neglect patients (–6.6°; n = 6). In both neglect groups, error was greater when the rod was in the left space. In N+P+ patients, the performance was strongly affected by posture (lying: +5.2°; sitting: +9.2°). Intra–individual variability was also much greater in this group. This study confirms the contralesional deviation of SVV in RBD patients without PS and suggests the presence of an opposite bias in RBD patients affected by PS.

Prism adaptation enhances activity of intact fronto-parietal areas in both hemispheres in neglect patients.

Unilateral spatial neglect involves a failure to report or orient to stimuli in the contralesional (left) space due to right brain damage, with severe handicap in everyday activities and poor rehabilitation outcome. Because behavioral studies suggest that prism adaptation may reduce spatial neglect, we investigated the neural mechanisms underlying prism effects on visuo-spatial processing in neglect patients. We used functional magnetic resonance imaging (fMRI) to examine the effect of (right-deviating) prisms on seven patients with left neglect, by comparing brain activity while they performed three different spatial tasks on the same visual stimuli (bisection, search, and memory), before and after a single prism-adaptation session. Following prism adaptation, fMRI data showed increased activation in bilateral parietal, frontal, and occipital cortex during bisection and visual search, but not during the memory task. These increases were associated with significant behavioral improvement in the same two tasks. Changes in neural activity and behavior were seen only after prism adaptation, but not attributable to mere task repetition. These results show for the first time the neural substrates underlying the therapeutic benefits of prism adaptation, and demonstrate that visuo-motor adaptation induced by prism exposure can restore activation in bilateral brain networks controlling spatial attention and awareness. This bilateral recruitment of fronto-parietal networks may counteract the pathological biases produced by unilateral right hemisphere damage, consistent with recent proposals that neglect may reflect lateralized deficits induced by bilateral hemispheric dysfunction.

‘The anatomy underlying acute versus chronic spatial neglect’ also depends on clinical tests

Sir, We would like to make a few comments on the interesting paper recently published in Brain by Karnath et al. (2011). We were impressed by the careful assessment of spatial neglect during acute and chronic phase, which was combined with a solid voxel-wise lesion symptom mapping technique in a series of 54 patients with right-hemisphere stroke. Anatomical data indicated that lesions in the superior and middle temporal gyri, the basal ganglia, as well as the inferior occipitofrontal fasciculus are responsible for spatial neglect in both acute and chronic phases. We also had the opportunity to evaluate 69 patients with right brain lesions longitudinally. Our patients were admitted after a first right-hemisphere stroke (mean delay: 7.5 ± 14.6 days), at a mean age of 64.95 ± 14.6 years. Mean delay between the acute and chronic phase was 350.21 ± 184.7 days. These demographic data are comparable with the patients of Karnath et al . (2011). Neglect was considered as present when patients failed at least two out of eight tests (Table 1)—unlike diagnoses based on two out three tests in Karnath et al . (2011). In the acute phase, 31 patients had neglect (45%). In the chronic phase, 17 of these 31 neglect patients still showed a significant impairment (55%). Using the same voxel-wise lesion mapping as Karnath et al . (2011), we found partly different results, particularly in the acute phase (detailed below). However, we believe that major differences in the findings may depend on the clinical measures used to define neglect, since this syndrome may include heterogeneous symptoms. View this table: Table 1 Neuropsychological results on paper and pencil tests. All scores were calculated as described in Verdon et al . (2010) Bowen et al . (1999) reported that the frequency of occurrence of neglect in patients with right brain damage may vary considerably and …

Patients With Left Spatial Neglect Also Neglect the “Left Side” of Time

Previous research suggests that people construct mental time lines to represent and reason about time. However, is the ability to represent space truly necessary for representing events along a mental time line? Our results are the first to demonstrate that deficits in spatial representation (as a function of left hemispatial neglect) also result in deficits in representing events along the mental time line. Specifically, we show that patients with left hemispatial neglect have difficulty representing events that are associated with the past and, thus, fall to the left on the mental time line. These results demonstrate that representations of space and time share neural underpinnings and that representations of time have specific spatial properties (e.g., a left and a right side). Furthermore, it appears that intact spatial representations are necessary for at least some types of temporal representation.

Neuroanatomy of space, body, and posture perception in patients with right hemisphere stroke.

Objective: To specify the neuroanatomical correlates of biases in the representations of the gravitational vertical (subjective vertical [SV]) and body axis (subjective straight ahead [SSA]), as well as postural difficulties, in patients with hemispheric stroke. Methods: The analysis focused on right hemisphere lesions in 21 neglect patients and 21 non-neglect patients (using MRIcro software) and related performance in 2 experimental tasks (SV and SSA) and a clinical balance assessment. Voxel-based lesion-symptom mapping was used to highlight brain areas in which lesions best explained the severity of task biases (p < 0.01). Results: The bias in the representation of body orientation was found to be strongly related to lesions of the anterior parietal cortex and the middle part of the superior temporal gyrus. The SV errors were associated with more widespread lesions of the posterior parietal and temporal cortices. Imbalance was preferentially associated with lesions of the posterior insula and the adjacent temporoparietal cortex. Conclusion: This study evidenced a cortical dissociation for body-centered and gravitational representations biases, which may reflect the differential involvement of these brain regions in spatial information processing. The lesions involved in representation biases (especially of the SV) and postural difficulties overlapped to some extent in the temporoparietal, superior temporal, and posterior insular regions of the cortex.

Straight ahead in spatial neglect: Evidence that space is shifted, not rotated

The egocentric reference appears to be altered in neglect patients, as evidenced by an ipsilesional error when pointing straight ahead. In this study, patients with right brain damage used a horizontal rod to show this straight-ahead direction. There was a systematic rightward translation of the rod, and no clockwise rotation occurred in five of six neglect patients. The results suggest a preferential rightward translation of space representation in neglect.

Effect of Posture on the Perception of Verticality in Neglect Patients

Background and Purpose— The anticlockwise (ACW) deviation of the visual and visuohaptic subjective verticals (SVs), known to occur in patients with right hemisphere lesion, is amplified by spatial neglect (N). These patients have only been assessed when sitting. We investigated the hypothesis that postural changes modulate visuohaptic SV deviation. Methods— Eight patients presenting with a right hemisphere lesion and spatial N were compared with 6 matched control subjects (C). In the dark, they had to rotate a luminous rod to put it at the vertical in 4 conditions: (1) sitting with plantar sole support; (2) sitting without plantar sole support; (3) sitting with legs extended on a support; and (4) supine position. Results— N patients showed a significant ACW deviation (−4.5°) of the SV compared with C subjects (+0.01°). The effect of body position depended on the group (P=0.022) because changes had definite effects in the N but not in the C group. In fact, the former showed a reduction of the ACW deviation, from the first to the fourth condition. Conclusions— Although the possible role of plantar and leg somaesthetic inputs remains to be thoroughly investigated, the modulation of gravitational inputs at trunk or vestibular level influences the SV deviation in N patients. This has to be put in relation with the modulation of N signs reported by other authors when passing from the sitting to the supine position.

Asymmetrical effects of unilateral right or left amygdala damage on auditory cortical processing of vocal emotions

Significance The human voice is a major source for auditorily communicated social signals. The voice in general, and emotional cues embedded in vocalizations in particular, receive enhanced decoding in sensory cortical areas of the auditory system. This enhanced cortical decoding is assumed to be remotely driven by the amygdala, which responds to socially and emotionally meaningful stimuli. Here, we tested for the first time, to our knowledge, how damage to either the left or right amygdala impairs the cortical processing of human voices and vocal affect. Amygdala damage generally leads to reduced cortical processing of human voices in the hemisphere corresponding to the side of the amygdala damage, whereas only left amygdala damage impaired the cortical processing of vocal affect. We tested whether human amygdala lesions impair vocal processing in intact cortical networks. In two functional MRI experiments, patients with unilateral amygdala resection either listened to voices and nonvocal sounds or heard binaural vocalizations with attention directed toward or away from emotional information on one side. In experiment 1, all patients showed reduced activation to voices in the ipsilesional auditory cortex. In experiment 2, emotional voices evoked increased activity in both the auditory cortex and the intact amygdala for right-damaged patients, whereas no such effects were found for left-damaged amygdala patients. Furthermore, the left inferior frontal cortex was functionally connected with the intact amygdala in right-damaged patients, but only with homologous right frontal areas and not with the amygdala in left-damaged patients. Thus, unilateral amygdala damage leads to globally reduced ipsilesional cortical voice processing, but only left amygdala lesions are sufficient to suppress the enhanced auditory cortical processing of vocal emotions.

Where is the “straight ahead” in spatial neglect?

We investigated the subjective straight-ahead (SSA) projection of body-midline parts (head and trunk) in patients with neglect and patients with nonneglect, using a method disentangling lateral shift and lateral tilt components of the bias. Patients with neglect showed a similar counterclockwise SSA tilt for each body part and an ipsilesional lateral shift, more severe for the trunk than for the head. Thus, neglect results in a tilt of the body midline representation.