Non-invasive modulation of post-stroke hemianopia: Influence of gray and white matter integrity
Poster No:
86
Submission Type:
Abstract Submission
Authors:
Monica Toba1,2, Nicole Macias3, Xavier Corominas-Teruel4, Corentin Gobatto5, Thomas Guenin4, Krishna Priya Radhakrishnan4, Alexia Potet4, Antoni VALERO-CABRE6
Institutions:
1Paris Brain Institute, Paris, France, 2LNFP University of Picardy Jules Verne, Amiens, France, 3Universitat Rovira i Virigili, Tarragona, Tarragona, 4Paris Brain Institute, Paris, Ile de France, 5Pitie Salpetriere Hospital, Paris, Ile de France, 6CNRS UMR 7225, Paris Brain Institute, Paris, Ile de France
First Author:
Monica Toba
Paris Brain Institute|LNFP University of Picardy Jules Verne
Paris, France|Amiens, France
Paris Brain Institute|LNFP University of Picardy Jules Verne
Paris, France|Amiens, France
Co-Author(s):
Introduction:
Homonymous lateral hemianopia (HLH) is a visual deficit following retro-chiasmal lesions in which conventional visual rehabilitation has shown poor effectiveness. We present interim analysis of visual perimetry and neuroimaging datasets from a pre-therapeutic, randomized cross-over, double-blind trial in HLH patients after a unilateral stroke. It assesses the ability of Transcranial Alternating Current Stimulation (tACS) to improve visual perception via the synchronization of dorsal attentional orienting systems [1, 2, 3]. We hypothesized a high degree of variability in visual outcomes and a strong influence of gray matter regions and white matter tracts (either spared or impacted by the stroke) subtending perceptual and attentional orienting abilities [4,5], following active tACS.
Methods:
A cohort of n=9 HLH patients (8 male & 1 female, age: 59±12 years old) without pre-existing severe ophthalmological disorders or contraindication to tACS and/or MRI, was recruited at least 3 months after a stroke, for this study. A group of matched controls (4 male & 1 female, 49±14 years old) was studied for comparison. All participants underwent an MRI battery including T1-3D (TE=3.2ms, 1x1x1 mm3) and Diffusion (60 dir., b=1500 s/mm2, RT=14s, TE=88ms, 2 mm thickness) sequences. In 3 independent sessions set a week apart, we assessed the short-term modulation of the following tACS conditions: (A) Right hemisphere frontal 30 Hz tACS to the Frontal Eye Field (FEF); (B) Contralesional occipito-parietal 10Hz tACS to the intraparietal sulcus (IPS) and (C) Sham tACS. Effects were estimated by changes in the surface of the 'seen' visual field in kinetic (binocular) and static (monocular) visual field perimetry (Octopus 900, Haag-Streit), prior vs. immediately following 20 minutes of tACS. Stroke lesions of each patient were delineated on the original 3DT1 sequences with MRIcron [6] then normalized to the MNI template using SPM [7]. For lesion mapping, the AAL [8] and Natbrainlab [9] templates were used respectively, to estimate the % of damaged grey/white matter structures. Additionally, white matter tractography (DSI studio) was used to assess disconnections of key white matter notably, the optic radiations (OR) and the superior longitudinal fasciculus (SLF) by estimating their Fractional anisotropy (FA).
Results:
Visual field perimetry at baseline showed higher accuracy for kinetic (~56%) compared with static (~41%) visual field assessments, suggesting the presence of blindsight phenomena in these patients. Group analyses failed at this stage of recruitment to reveal significant effects or differences between the tACS conditions on the surface of the 'seen' visual field surface (all comparisons p>0.05, Wilcoxon Rank). Regardless, detailed examination of response patterns suggested improvements to different degrees in individual patients (particularly for those following occipito-parietal tACS) compared to sham. Most importantly, gray matter MRI assessments showed lesion patterns encompassing mainly the superior, middle and inferior occipital gyri, the lingual gyrus and the calcarine fissure (Fig.1) Tractography analyses of the OR and SLF revealed partial disconnections and lower FA in HLH patients for the OR (p<0.02) but not the SLF (p>0.05) compared to healthy controls (Fig. 2).
Conclusions:
At the current stage of recruitment, our analysis attests of the large heterogeneity of lesion patterns, spared visual field surface, predicted E-fields and the tACS outcomes. The recruitment of further patients is compulsory to allow reliable assessments of lesion patterns and modulatory effects. Recovery patterns shown by individual patients argue in favor of an influence of the status of key white matter tracts, and particularly the optic radiations (OR). Heterogeneity suggests a need for treatment customization based on the presence or absence of blindsight phenomena as guided by MRI-based biophysically tACS current distribution models.
Brain Stimulation:
Non-Invasive Stimulation Methods Other 1
Modeling and Analysis Methods:
Methods Development
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
White Matter Anatomy, Fiber Pathways and Connectivity 2
Perception, Attention and Motor Behavior:
Attention: Visual
Perception: Visual
Keywords:
Perception
STRUCTURAL MRI
Tractography
Vision
White Matter
WHITE MATTER IMAGING - DTI, HARDI, DSI, ETC
1|2Indicates the priority used for review
Provide references using author date format
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