The aim of this study was to investigate, in 114 stroke patients, the frequency of occurrence of a largely unknown neurological disorder, characterized by a postural imbalance due to a 'pushing away' reaction of the body towards the contralesional side of space, in function of hemispheric lesion localization and gender. The study also investigate the relation of this contraversive pushing with active movement, somatosensory perception deficits and, in particular, inattention of contralesional hemispace and body. The similarity of the presence of contraversive pushing and the syndrome of spatial hemineglect together with a gender-related differentiation suggest the existence of a "pusher syndrome", in which the pathophysiology points in the direction of a spatial higher-order processing deficit, related to spatial inattention, underlying the higher frequency and severity of contraversive pushing after right brain lesions.

We investigated the presence of postural abnormalities in a consecutive sample of stroke patients, with either left or right brain damage, in relation to their perceived body position in space. The presence or absence of posture-related symptoms was judged by two trained therapists and subsequently analysed by hierarchical classes analysis (HICLAS). The subject classes resulting from the HICLAS model were further validated with respect to posture-related measurements, such as centre of gravity position and head position, as well as measurements related to the postural body scheme, such as the perception of postural and visual verticality. The results of the classification analysis clearly demonstrated a relation between the presence of right brain damage and abnormalities in body geometry. The HICLAS model revealed three classes of subjects: The first class contained almost all the patients without neglect and without any signs of contraversive pushing. They were mainly characterised by a normal body axis in any position. The second class were all neglect patients but predominantly without any contraversive pushing. The third class contained right brain damaged patients, all showing neglect and mostly exhibiting contraversive pushing. The patients in the third class showed a clear resistance to bringing the weight over to the ipsilesional side when the therapist attempted to make the subject achieve a vertical posture across the midline. The clear correspondence between abnormalities of the observed body geometry and the tilt of the subjective postural and visual vertical suggests that a patient's postural body geometry is characterised by leaning towards the side of space where he/she feels aligned with an altered postural body scheme. The presence of contraversive pushing after right brain damage points in to a spatial higher-order processing deficit underlying the higher frequency and severity of the axial postural abnormalities found after right brain lesions.

In many paradigms of stimulation techniques aimed at reducing hemispatial neglect, somatosensory and proprioceptive stimulation are often interchanged, although the anatomical and functional pathways transmitting these signals are clearly different. Therefore, we have investigated the effects of one somatosensory stimulation technique, the cyclic pressure application (CPA), and have compared them with the effects of left transcutaneous electrical stimulation (TENS) on the expression of left hemispatial neglect in 13 stroke patients, as assessed by two visuospatial exploration tasks: the Star Cancellation task and Schenkenberg's Line Bisection task. In a first experiment, four treatment conditions were given: TENS, CPA, TENS + CPA, as well as a placebo condition. For each patient, the intensity of the TENS was determined, based on his/her conscious somatosensory threshold for the electrical impulses. In order to determine whether unconscious proprioceptive afferent information instead of exteroceptive somatosensory stimulation is a sufficient condition to improve hemispatial neglect, we carried out a second experiment, only with patients suffering from complete somatosensory loss. The effects of the different treatments were investigated, using the same sequence as for Experiment 1, but, this time, the applied intensity of TENS was manipulated over two conditions : (1) one in which the intensity of TENS stimulation was below the motor (proprioceptive) threshold and (2) one in which the intensity was determined following the degree of proprioceptive stimulation demonstrated by the point at which a visible muscle contraction during the stimulation could be elicited. The results demonstrated that proprioceptive-based TENS stimulation is a sufficient condition to reduce hemispatial neglect, even when a severe somatosensory loss was present.

We have systematically studied the subjective postural vertical (SPV) and the location of the centre of gravity (COG) in right brain damaged patients, classified according to the severity of their hemispatial neglect. The results indicate that the patients lean towards the side of space where they feel aligned with their ipsilesionally displaced SPV, resulting in a ipsilesional deviation of the COG. This displacement can be reduced by the effect of contralesionally applied transcutaneous electrical nerve stimulation (TENS). However, in the severe neglect patients, an increasing mismatch arose between the perceived body orientation and the direction of the gravitational force. The results indicate that this conflict is compensated by a contraversive shift of the COG towards the contraversive side in order to re-align the SPV with the gravitational vertical.

No abstract