Long-term sensorimotor and therapeutical effects of a mild regime of prism adaptation in spatial neglect. A double-blind RCT essay

Abstract

Spatial neglect (SN) is commonly associated with poor functional outcome. Adaptation to a rightward optical deviation of vision has been shown to benefit to SN rehabilitation. The neurophysiological foundations and the optimal modalities of prism adaptation (PA) therapy however remain to be validated. This study is aimed at exploring the long-term sensory-motor, cognitive and functional effects produced by weekly PA sessions over a period of four weeks. A double-blind, monocentric randomized and controlled trial (RCT) was carried out. Twenty patients with left SN secondary to stroke were included, 10 in the "prism" group and 10 in the "control" group. The sensory-motor effects of PA were evaluated by measurement of manual and visual straight-ahead, and also by precision of pointing without visual feedback before and after each PA session. The functional independence measure (FIM) was evaluated before and at 1, 3 and 6 months after PA, while SN severity was assessed using the Behavioural Inattention Test (BIT) before and 6 months after PA. Before the intervention, only manual straight-ahead pointing constituted a reproducible sensory-motor measurement. During prism exposure, a questionnaire showed that not a single patient were aware of the direct effects of optical deviation on pointing movement performance. The sensory-motor after-effects produced by the PA produced a more rapid reduction of the rightward manual straight-ahead, which was secondarily followed by visual straight-ahead. These sensory-motor effects helped to clarify the action mechanisms of PA on SN. At the conclusion of the 6-month follow-up, the two groups showed similar improvement, indicating that a weekly PA session over 4 weeks was not sufficient to produce long-term functional benefit. This improvement was correlated with the evolution of visual straight-ahead, which can be proposed as a marker for patients outcome.

Pushing attention to one side: Force field adaptation alters neural correlates of orienting and disengagement of spatial attention

“…There were no significant correlations between the percentage of adaptation and changes in ERP amplitudes (all | r | < 0.11, all p > 0.58), see Supporting information Table S1 for complete correlation statistics). This lack of correlation is consistent with findings in the prism adaptation literature, where the size of motor after‐effects does not correlate with the degree of neglect improvement in patients (Pisella, Rode, Farnè, Boisson, & Rossetti, ; Rode et al., ; Sarri et al., ). Moreover, there is evidence that neglect patients typically show larger changes in spatial attention than healthy subjects despite comparable motor after‐effects (Jacquin‐Courtois et al., ).…”

“…In this case, a lateral bias in visual or proprioceptive representations of space following adaptation would seem unlikely to underpin attention effects. Prism adaptation requires the physical location of the limb to be laterally displaced with respect to visual target locations, and leads to substantial changes in the felt position of the limb and perception of visual straight ahead (for review see Newport & Schenk, ; Rode et al., ). Force field adaptation, by contrast, involves no mismatch between visual and physical space, and leads to limb position trajectories in late adaptation that hardly deviate from a straight path to visual targets.…”

Efficacy of home-based visuomotor feedback training in stroke patients with chronic hemispatial neglect

“…Alternatively, VFT may recruit spared dorsal visual stream regions located in the undamaged hemisphere contralateral to the hand used to perform the training. It is also possible that VFT and prism adaptation (Newport & Schenk, 2012;Rode et al, 2015) recruit similar sensorimotor processes. Similarly to what happens during prism adaptation, the patients correct their grasping position until successful performance is achieved (i.e., the rod is balanced), a process known as strategic recalibration in the prism literature (Newport & Schenk, 2012).…”

Anatomical predictors of successful prism adaptation in chronic visual neglect

“…After removal of the prisms, reaching initially deviates towards the left neglected side, and neglect eventually disappears. Unfortunately, neglect does not improve in all treated patients (Luauté et al, 2006;Rode et al, 2015;Rousseaux, Bernati, Saj, & Kozlowski, 2006;Saj, Cojan, Vocat, Luauté, & Vuilleumier, 2013), for unknown reasons (Barrett, Goedert, & Basso, 2012;Chokron, Dupierrix, Tabert, & Bartolomeo, 2007) . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 Drawing on our previous evidence suggesting a role for posterior callosal dysfunction in the chronic persistence of neglect (Lunven et al, 2015), we hypothesized that PA might improve neglect by facilitating compensation through the contribution of the left, undamaged hemisphere.…”

“…After removal of the prisms, reaching initially deviates towards the left neglected side, and neglect eventually disappears. Unfortunately, neglect does not improve in all treated patients [9][10][11][12] , for unknown reasons 13 .…”