Perception of longitudinal body axis in patients with stroke: a pilot study.

BACKGROUND AND AIMS: To investigate the hypothesis that patients with a hemisphere stroke may perceive their longitudinal body axis (LBA) rotated in the frontal plane. This error in an egocentric frame of reference could be detrimental to posture, as tilted LBA would imply an unequal distribution of body mass about the true vertical. METHOD: 26 healthy subjects matched in age with 18 patients living with stroke participated in the study. The 18 patients were tested on average 80 days after a first left (n = 8) or right (n = 10) hemisphere stroke. Participants perceived their LBA by adjustments of the orientation of a luminous rod pivoting around a dorsonavel axis to the subjective direction of LBA. Participants were studied in the supine position to dissociate somaesthetic cues from graviceptive cues. RESULTS: Patients with stroke perceived their LBA rotated to the contralesional side in comparison with controls (p = 0.004). For all controls and 10 patients with stroke, the perceived LBA was very close to true LBA (mean (SD) 0.24 degrees (1.31 degrees)). For eight patients with stroke (six right stroke, two left stroke), the perceived LBA was rotated from true body orientation in the direction opposite to the lesioned side (range 3-9.5 degrees, mean 5.2 degrees). These eight patients provided similar estimates by tactile manipulation of the rod (without vision). The rotation of perceived LBA was more pronounced for right-hemisphere strokes. The magnitudes of perceptual rotations correlated with sensory loss, signs of spatial neglect and the degree of postural and gait disability. CONCLUSION: This is the first study showing that certain patients with a hemisphere stroke perceive their LBA rotated to the contralesional side. The consequences for perceptuomotor coordination have implications for their postural disorders.

Visual contribution to self-induced body sway frequencies and visual perception of male professional dancers.

We studied the degree of dependence on vision, for postural control and for perception, among male adult dancers and untrained subjects. First, body sways were analyzed on a free seesaw platform. Fast Fourier transform processing allowed spectral frequency analysis of the platform sways recorded by an accelerometer. Secondly, a visual dependence test, the rod and frame test (RFT) was used. Professional dancers were significantly more stable and less dependent on vision for postural control and for perception than untrained subjects. Presumably, professional dance training strengthens the accuracy of proprioceptive inputs and shifts sensorimotor dominance from vision to proprioception. For the dancers, there was interaction between the RFT visual dependence and the visual control of posture: the less visual-dependent they were for the RFT, the more stable they were in dynamic balance conditions.

Subjective vertical and postural activity.

Three experiments were conducted to test the effect of postural information, resulting from the active control of balance, on the perception of the vertical. Subjects were required to adjust a luminous rod in two different visual contexts: in the dark or within a tilted visual frame. In these experiments, postural activity was manipulated by placing observers either in a situation of slight postural imbalance (Experiment 1) or in a situation of postural immobilization (Experiment 2). In both situations performance was compared with a control condition in which subjects were standing upright freely (Experiment 1) or sitting unconstrained (Experiment 2). Results showed no main effect of active posture or of immobilization on the visual perception of the vertical. In the third experiment, subjects were supine with their Z body axis perpendicular to the plane of the luminous rod. Thus, body orientation relative to gravity was modified and motor activity reduced. In this position, the physical vertical was perceived quite accurately in a dark environment. Moreover, in the titled frame condition, the supine body position clearly improved vertical judgements. These results are discussed in relation to the ecological theory of orientation.

The role of neck afferents in subjective orientation in the visual and tactile sensory modalities.

We studied the influence of neck afferents on the perception of orientation. In Experiment 1, we investigated the effect of head tilt on the subjective vertical in both the visual and tactile modalities. The results showed that head tilt triggers an Aubert effect in the visual modality and a Müller effect in the tactile modality. Significant positive correlations between the two adjustment modalities were restricted to head tilt to the left. In Experiment 2, we investigated the role of neck afferents on tactile orientation in seated and supine positions. The results showed that, in the supine position, the tactile E-effect was twice as large as in the seated position. These experiments confirm that tactile perception of orientation is affected by neck afferents, and show that the influence of neck afferents is limited by relevant gravitational cues.

[A clinical rating scale for personality. Its validation through factor analysis in geriatrics (author's transl)]. / Echelle clinique d'évaluation de la personnalité. Validation par analyse factorielle en gériatrie.

A rating scale has been established in our department. It is used to assess different psychological aspects. It can be applied in treatment trials as well as to provide a descriptive study of personality or behaviour. 26 two-pole items at five levels are covered by this scale. A factor analysis was used to validate the scale on a population of old people in institutional care. This showed the scale evaluates one general factor and nine group factors: affective maturity, social ease, inhibition, social adaptation, anxiety depression, psychic well-being, psychopathic tendencies, extraversion and receptivity, guilt-feeling. To appreciate the effects of psychotropic drugs on behaviour, these ten factors can be grouped into three: a factor we can call "mental health", a factor of social adaptation, an affective-emotional factor.

Head orientation involvement in assessment of the subjective vertical during whole body tilt.

The aim of this research was to investigate the involvement of head tilt in the assessment of the subjective vertical during whole body tilt. For inclinations up to 28 degrees, it appears that the whole body tilt gives rise to more important deviations towards its direction (A-effect) than when the tilt was restricted to the head. A multiple regression analysis shows that errors in head-tilt condition partially account for the global errors observed in condition of whole body tilt. Other factors (relative to the degree of inclination) also played a role in the determination of the subjective vertical in whole body tilt but were less important than head tilt. These results are highly compatible with the assumption of head orientation as the major determinant in roll-tilt effects.

Strobe frequency in the rod and frame effect.

This experiment dealt with the role of strobe frequency on the rod and frame effect in frame-dependent and frame-independent subjects in light of the destabilizing effect of strobe lighting on body posture. Analysis showed that the frame effect was resistant to strobe illumination and was significantly stronger at 2 Hz than at 9 Hz. Since the stroboscopic effect was not related to the extent of the frame effect observed in normal light, there was no over-all dependence on the different components of the visual field (static and kinetic). Moreover, analysis of eye movements during stroboscopic exposure confirmed previous observation of a visual scanning style related to orienting activity.

Individual differences in the ability to identify, select and use appropriate frames of reference for perceptuo-motor control.

The causes of the interindividual differences (IDs) in how we perceive and control spatial orientation are poorly understood. Here, we propose that IDs partly reflect preferred modes of spatial referencing and that these preferences or "styles" are maintained from the level of spatial perception to that of motor control. Two groups of experimental subjects, one with high visual field dependency (FD) and one with marked visual field independency (FI) were identified by the Rod and Frame Test, which identifies relative dependency on a visual frame of reference (VFoR). FD and FI subjects were tasked with standing still in conditions of increasing postural difficulty while visual cues of self-orientation (a visual frame tilted in roll) and self-motion (in stroboscopic illumination) were varied and in darkness to assess visual dependency. Postural stability, overall body orientation and modes of segmental stabilization relative to either external (space) or egocentric (adjacent segments) frames of reference in the roll plane were analysed. We hypothesized that a moderate challenge to balance should enhance subjects' reliance on VFoR, particularly in FD subjects, whereas a substantial challenge should constrain subjects to use a somatic-vestibular based FoR to prevent falling in which case IDs would vanish. The results showed that with increasing difficulty, FD subjects became more unstable and more disoriented shown by larger effects of the tilted visual frame on posture. Furthermore, their preference to coalign body/VFoR coordinate systems lead to greater fixation of the head-trunk articulation and stabilization of the hip in space, whereas the head and trunk remained more stabilized in space with the hip fixed on the leg in FI subjects. These results show that FD subjects have difficulties at identifying and/or adopting a more appropriate FoR based on proprioceptive and vestibular cues to regulate the coalignment of posturo/exocentric FoRs. The FI subjects' resistance in the face of altered VFoR and balance challenge resides in their greater ability to coordinate movement by coaligning body axes with more appropriate FoRs (provided by proprioceptive and vestibular co-variance).

Water-level representation by men and women as a function of rod-and-frame test proficiency and visual and postural information.

In the water-level task, it has been repeatedly shown that, compared with men, women more often fail to represent the surface of a liquid as horizontal regardless of the tilt of the container. An attempt was made to reduce this robust gender gap through the manipulation of relevant upright references conveyed both by the position of the stimuli and the posture of the subject. It was reasoned that bringing the women to focus on such gravitational references through postural adjustment might help their performance equal that of men, thus shedding some light on the nature of the difficulty they experience in the standard setting. A lesser effect was anticipated among men. However, the results showed that, even after controlling for proficiency in the correlated visuospatial situation of the rod-and-frame test, the performance of men always surpassed that of women. Irrespective of gender, water-level representation on vertical sheets was unaffected by the subject's posture, whereas it improved when horizontal sheets were coupled with the most unstable posture. Whereas the persistence of the yet-unaccounted-for gender difference was underscored, the contributions of visual and postural cues issued at arm and full-body levels were discussed.

[Elaboration and standardization of a series of psychometric tests for old people (author's transl)]. / Mise au point et étalonnage d'une batterie d'épreuves psychométriques pour l'examen des personnes âgées

We had previously elaborated a series of psychometric tests for old people. The aim of this test series is to assess the effects of brain-stimulating drugs (vasodilatating drugs). A factorial analysis was then carried out which enables us to reduce the number of tests, on the one hand, and to indicate the most fundamental fields of activity in old people, on the other hand. Four factors were distinguished. They assess respectively: watchfulness, memory, fluidity, and precision in the task undertaken. These four factors are strongly correlated. This implies the presence of a general factor, close in kind to the first factor. Watchfulness, attention and concentration are, in fact, necessary but insufficient conditions for the performance of all cognitive activities. A total of 7 tests among the most representative of each factor were retained. They are described in detail: test conditions, instructions, scoring and standardization.

Position of the egocentric reference and performance in line bisection and subjective vertical estimation tasks.

Egocentric body coordinates such as the sagittal midline have been proposed to act as a reference for ballistic movements in extracorporeal space. Symmetrical functioning of the multiple neural structures processing sensory information would account for the normal sagittal position of the egocentric reference. According to this hypothesis a unilateral parietal lesion would induce a ipsilesional deviation which would prevent neglect patients from responding to stimuli that occur on that side. In this line of reasoning, an experimental manipulation of the position of the egocentric reference by way of a postural perturbation should have an effect on visuospatial tasks performance in normal subjects. Seventeen right-handed subjects were submitted in the dark to two visuomotor tasks: the adjustment of a luminescent rod to the vertical and the bisection of a luminescent line, either with the trunk and the head aligned at 0 degrees or with a 30 degrees trunk rotation to the right or to the left. Results revealed no significant effect of trunk rotation on the performance in both tasks. We discuss these findings and their implication for the understanding of the neglect syndrome.

The role of head-centric spatial reference with a static and kinetic visual disturbance.

A static or kinetic visual disturbance affects subjects' ability to estimate the direction of the gravitational vertical. This kind of error is increased by a head roll inclination. In two experiments, we combined head orientation with a static (Experiment 1: tilted frame) versus kinetic (Experiment 2: rotating disk) visual disturbance. The results showed that with a static visual disturbance, the increase of errors in the inclined head condition was mainly the consequence of a postural head effect like an Aubert effect. On the contrary, with a kinetic visual disturbance, it appears that the disk effect increases with head inclination. However, individual errors observed with the head inclined in front of a stationary disk were systematically correlated with the errors triggered by the same head inclination in front of a rotating disk. These observations confirm that the head axis spatial reference plays an important role in orientation perception, whatever the head position and the kind of visual display.

The properties of chimeric picornavirus IRESes show that discrimination between internal translation initiation sites is influenced by the identity of the IRES and not just the context of the AUG codon.

The internal ribosome entry segment (IRES) of picornaviruses consists of approximately 450 nt of 5'-untranslated region, terminating at the 3' end with an approximately 25 nt element consisting of an absolutely conserved UUUC motif followed by a more variable pyrimidine-rich tract and G-poor spacer, and finally an AUG triplet, which is considered to be the actual ribosome entry site. Events following entry at this site differ among picornaviruses: in encephalomyocarditis virus (EMCV) virtually all ribosomes initiate translation at this site (AUG-11); in foot-and-mouth-disease virus (FMDV), one-third of the ribosomes initiate at this AUG (the Lab site), and the rest at the next AUG 84 nt downstream (Lb site); and in poliovirus (PV), the AUG at the 3' end of the IRES (at nt 586 in PV type 1) is considered to be a silent entry site, with all ribosomes initiating translation at the next AUG downstream (nt 743). To investigate what determines this different behavior, chimeras were constructed with a crossover at the conserved UUUC motif: the body of the IRES, the sequences upstream of this UUUC motif, was derived from one species, and the downstream sequences from another. When the body of the FMDV or PV IRESes was replaced by that of EMCV, there was a marked increase in the absolute and relative frequency of initiation at the upstream AUG, the Lab site of FMDV and 586AUG of PV, respectively. In contrast, when the body of the EMCV IRES was replaced by that of PV, initiation occurred with no preference at three AUGs: the normal site (AUG-11), AUG-10 situated 8 nt upstream, and AUG-12, which is 12 nt downstream. Thus although the context of the AUG at the 3' end of the IRES may influence initiation frequency at this site, as was shown by improving the context of 586AUG of PV, the behavior of the ribosome is also highly dependent on the nature of the upstream IRES. Delivery of the ribosome to this AUG in an initiation-competent manner is particularly efficient and accurate with the EMCV IRES.

An internal ribosome entry segment promotes translation of the simian immunodeficiency virus genomic RNA.

The retroviral genomic RNA is the messenger for the synthesis of the group-specific antigen (gag) and polymerase precursors of the major structural proteins and enzymes of the virion. The 5'-untranslated leader of the simian immunodeficiency virus (SIV) genomic RNA is formed of highly structured domains involved in key steps of the viral life cycle. Thus, the presence of stable RNA structures between the 5'-cap and the gag start codon are thought to strongly inhibit scanning of a 43 S preinitiation ribosomal complex. This prompted us to look for an alternative to the canonical ribosome scanning. By using a standard bicistronic assay in the rabbit reticulocyte lysate, we show that the SIVmac 5'-leader contains an internal ribosome entry segment (IRES) and that gene expression driven by this IRES is stimulated upon cleavage of eukaryotic initiation factor 4G. Deletion analysis revealed that the sequence between the major splice donor and the gag AUG codon is required for IRES activity. DNA transfection and viral transduction experiments in both NIH-3T3 and COS-7 cells confirmed that translation driven by the SIV leader is IRES-dependent and thus insensitive to the immunosuppressant rapamycin. Identification of an IRES in SIV is of particular interest for the understanding of lentivirus replication and also for the design of novel lentiviral vectors suitable for gene transfer.

Selection of spatial frame of reference and postural control variability.

The present paper addresses the question of the possible links between perceptive visual field dependence-independence and the visual contribution to postural control. In our differential approach, visual field dependent (FD) and independent (FI) subjects were selected on the basis of their score in the Rod and Frame Test (subjective vertical). The hypothesis that we have tested is that the FD subjects use mainly visual cues for estimating not only their subjective vertical but also their body orientation and stability. Moreover, we have postulated that these subjects use mainly dynamic visual cues to control their postural stability. In the postural test, the selected subjects were instructed to stand in the sharpened Romberg position in darkness and under normal or stroboscopic illumination, in front of either a vertical or a tilted frame. Lateral head and body orientation and stability were measured. We found that: (1) all subjects leaned slightly towards the tilted frame (postural frame effect), and this was obtained on the basis of the static visual cues alone; (2) FD subjects were less stable than FI subjects, and their stability required the use of dynamic visual cues, mainly extracted from the vertical frame. In FI subjects, static visual cues may act as a complementary regulation, enhancing stability even with a strobe tilted frame. We thus demonstrate that visual field dependence interacts with the visual contribution to postural control.

Isotropic visual field effect on spatial orientation and egocentric localization.

The aim of this paper is to demonstrate the presence of a similar visual field effect on both spatial orientation and egocentric localization. A first experiment explored an orientation task (Visually Perceived Vertical or VPV determination) and compared the effects of a frame inclined either in the midfrontal plane (in this condition subjects assessed roll VPV) or in the median plane (subjects assessed pitch VPV) or in both combined planes (subjects assessed both roll and pitch VPV). A second experiment compared the frame effects specified above to the frame effect observed in an egocentric localization task (Visually Perceived Eye Level judgment) performed with a frame slanted in the median plane. The results showed that angular frame variations from -15 to +15 deg result in the same psychometric function for both orientation and localization tasks. In each experiment, correlations showed that individual differences occur in relation to an overall sensitivity to the visual field. Individual sensitivity may be accounted for by a ratio of visual to graviceptive information which remains constant whatever the perception plane (midfrontal or median plane) and whatever the task (spatial orientation or localization).