Jacques Honoré

Improvement of The Motor Deficit of Neglect Patients Through Vestibular Stimulation: Evidence for A Motor Neglect Component

The effect of vestibular stimulation on motor performance has been studied comparatively in 2 groups of hemiplegic patients, one including 9 right brain-damaged patients (RBD) with neglect, the other 9 left brain-damaged patients (LBD) without neglect. In the RBD group, a transient but significant improvement of motor performance was observed following stimulation, although motor scores remained unchanged in two cases. Moreover, a temporary remission of personal neglect and anosognosia was obtained in 8 out of 9 patients. In contrast to the RBD group, the motor performance of the LBD group was not improved through vestibular stimulation, although a moderate improvement of force was noticed in one ambidextrous patient who had shown transient signs of neglect at the acute stage. These results suggest the participation of a motor neglect component in the motor deficit of neglect patients. The motor neglect component may be considered as one of the many manifestations of the neglect syndrome and, as such, can be improved by the sensory manipulations which presumably restore a conscious representation of the left side of space.

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.

Reduction of cutaneous reaction time by directing eyes towards the source of stimulation

Reaction time to expected lateral cutaneous stimulation was measured in Man when the eyes were directed (1) towards the stimulated area, (2) towards another point within the same hemispace and (3) towards the other hemispace. As performance was better in the first case, this suggests that compatible eye postural activity reinforces the effect of spatial attention.

Peripherally Presented Emotional Scenes: A Spatiotemporal Analysis of Early ERP Responses

Recent findings from event-related potentials (ERPs) studies provided strong evidence that cen- trally presented emotional pictures could be used to assess affective processing. Moreover, several studies showed that emotionally charged stimuli may automatically attract attention even if these are not consciously identified. Indeed, such perceptive conditions can be compared to those typical of the peripheral vision, particularly known to have low spatial resolution capacities. The aim of the present study was to characterize at behavioral and neural levels the impact of emotional visual scenes presented in peripheral vision. Eighteen participants were asked to categorize neutral and unpleasant pictures presented at central (0°) and peripheral eccentricities (−30 and +30°) while ERPs were recorded from 63 electrodes. ERPs were analysed by means of spatio-temporal principal component analyses (PCA) in order to evaluate influences of the emotional content on ERP components for each spatial position (central vs. peripheral). Main results highlight that affective modulation of early ERP components exists for both centrally and peripherally presented pictures. These findings suggest that, for far peripheral eccentricities as for central vision, the brain engages specific resources to process emotional information.

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.

Early brain-body impact of emotional arousal

Current research in affective neuroscience suggests that the emotional content of visual stimuli activates brain–body responses that could be critical to general health and physical disease. The aim of this study was to develop an integrated neurophysiological approach linking central and peripheral markers of nervous activity during the presentation of natural scenes in order to determine the temporal stages of brain processing related to the bodily impact of emotions. More specifically, whole head magnetoencephalogram (MEG) data and skin conductance response (SCR), a reliable autonomic marker of central activation, were recorded in healthy volunteers during the presentation of emotional (unpleasant and pleasant) and neutral pictures selected from the International Affective Picture System (IAPS). Analyses of event-related magnetic fields (ERFs) revealed greater activity at 180 ms in an occipitotemporal component for emotional pictures than for neutral counterparts. More importantly, these early effects of emotional arousal on cerebral activity were significantly correlated with later increases in SCR magnitude. For the first time, a neuromagnetic cortical component linked to a well-documented marker of bodily arousal expression of emotion, namely, the SCR, was identified and located. This finding sheds light on the time course of the brain–body interaction with emotional arousal and provides new insights into the neural bases of complex and reciprocal mind–body links.

Reward anticipation, cognition, and electrodermal activity in the conditioned monkey

In the present report, we examine electrodermal activity (skin conductance responses, SCRs) in monkeys trained to perform target-selection (TS) tests. In each test, the animal was presented in successive trials with the same two unequally rewarded targets on a touch screen. The probabilistic contingencies of the rewards associated with each target rendered the selection of the best difficult. Our findings revealed SCRs time-locked to the arm movements toward the rewarded targets, occurring after the target touches. Parameters of the SCRs were stable when the uncertainty of the choices and of the outcomes varied. The results support the hypothesis that the physiological processes indexed by the SCRs are the correlate of anticipatory appetitive behavior. In contrast, there is no evidence that the SCRs reflect cognitive processes associated with the detection of the best target.