Prospective de l'espace habité

190 p., ref. bib. : 17 p.3/

Visuospatial biases in complex regional pain syndrome: disentangling the role of visual vs. proprioceptive input

Complex regional pain syndrome (CRPS) is usually characterized by sensory, motor, trophic and autonomic symptoms, but cognitive deficits have also been increasingly recognized as being part of the symptomatology in an important subset of patients over the last few years. These deficits would affect the patients’ ability to mentally represent, perceive and use their affected limb. Importantly, it has recently been shown that deficits in spatial perception are not limited to stimuli applied on the body surface and the perception of the body, but that they can also extend to stimuli presented in external space, i.e., visual ones. More precisely, CRPS patients seemed to pay less attention to visual stimuli presented in the same side of space as the affected limb, and especially those presented close to the limb. However, the exact mechanisms underlying these deficits have yet to be elucidated, such as a possible dissociation between an explanation in terms of visual or proprioceptive input. Indeed, it is not clear whether the observed visuospatial biases depend on the actual sight of the limbs, i.e. the visual perception of the proximity between the visual stimuli and the affected limb. We investigate this question using a visual temporal order judgement (TOJ) task in upper-limb CRPS patients, which is classically used to investigate mechanisms of spatial attention. Patients report which of two visual stimuli presented with various inter-stimulus time intervals has been perceived first. The pairs of visual stimuli, fixed on either a wooden or a transparent board, are presented just above the patients’ hands, one stimulus close to either hand. The visual stimuli and the hands are thus always placed in the same position, but the hands and their proximity to the visual stimuli are either unseen or seen, depending on the use of the wooden or the transparent board, respectively. Preliminary results (N= 12) indicate that, as compared to the condition in which the hands are seen, the deficits in perceiving visual stimuli presented close to the affected hand are reduced when the hands are not seen, i.e. when the proximity between external stimuli and the affected hand is not visually perceived anymore. This preliminary result ascribes a predominant role to visual input about the body and its surrounding space for the development of cognitive deficits in CRPS. This finding is of particular importance since it has been proposed that acting on distorted visuospatial perception could potentially be efficient to treat chronic pain in CRPS. However, understanding the exact mechanisms by which rehabilitation of visuospatial abilities could possibly influence sensorimotor symptoms in CRPS firstly requires clarifying how and under which conditions the perception of external space can be affected by pain