Anatomical predictors of recovery from visual neglect after prism adaptation therapy

Abstract

Prism adaptation (PA) is a non-invasive and convenient technique to rehabilitate visual neglect, but for unknown reasons it is not effective in all patients. Chronic persistent neglect is associated with inter-hemispheric white matter disconnection [1] . Patients-based studies and functional imaging studies report involvement of cortico-ponto-cerebellar pathway in PA mechanism. This network is a potential inter-hemispheric pathway [2] , and might therefore compensate for interhemispheric disconnection in neglect. Here we hypothesize that PA improves left neglect by facilitating inter-hemispheric communication through modulation of cortico-ponto-cerebellar pathways. If so, then the integrity of these pathways should predict patients’ response to PA. We used diffusion MRI to assess the relationships between PA-induced neglect recovery and microstructural integrity of white matter in 12 patients with unilateral strokes in the right hemisphere and chronic neglect. Voxelwise statistical analysis of the fractional anisotropy (FA) data was carried out using Tract-Based Spatial Statistics [3] . Consistent with our hypothesis, we found specific damage to fronto-ponto-cerebellar pathways in non-responder patients. Also, white matter alteration in the left undamaged hemisphere was associated with lack of improvement. Our findings suggest that PA can ameliorate signs of left visual neglect by improving inter-hemispheric communication through enhanced activity of fronto-ponto-cerebellar pathways. In particular, signals processed in the right cerebellum (spatial realignment) and in the left posterior parietal cortex (strategic calibration) might converge on left prefrontal areas, which receive from both the fronto-parietal superior longitudinal fasciculus and the fronto-ponto-cerebellar pathways.