Polarity-Dependent Misperception of Subjective Visual Vertical during and after Transcranial Direct Current Stimulation (tDCS)

Pathologic tilt of subjective visual vertical (SVV) frequently has adverse functional consequences for patients with stroke and vestibular disorders. Repetitive transcranial magnetic stimulation (rTMS) of the supramarginal gyrus can produce a transitory tilt on SVV in healthy subjects. However, the effect of transcranial direct current stimulation (tDCS) on SVV has never been systematically studied. We investigated whether bilateral tDCS over the temporal- parietal region could result in both online and offline SVV misperception in healthy subjects. In a randomized, sham-controlled, single-blind crossover pilot study, thirteen healthy subjects performed tests of SVV before, during and after the tDCS applied over the temporal- parietal region in three conditions used on different days: right anode/left cathode; right cathode/left anode; and sham. Subjects were blind to the tDCS conditions. Montage-specific current flow patterns were investigated using computational models. SVV was significantly displaced towards the anode during both active stimulation conditions when compared to sham condition. Immediately after both active conditions, there were rebound effects. Longer lasting after-effects towards the anode occurred only in the right cathode/left anode condition. Current flow models predicted the stimulation of temporal-parietal regions under the electrodes and deep clusters in the posterior limb of the internal capsule. The present findings indicate that tDCS over the temporal-parietal region can significantly alter human SVV perception. This tDCS approach may be a potential clinical tool for the treatment of SVV misperception in neurological patients

Clinical examination tools for lateropulsion or pusher syndrome following stroke: a systematic review of the literature.

International audienceOBJECTIVE: To examine the clinimetric properties and clinical applicability of published tools for 'quantifying' the degree of lateropulsion or pusher syndrome following stroke. DATA SOURCES: Search through electronic databases (MEDLINE, EMBASE, CINAHL, Science Citation Index) with the terms lateropulsion, pushing, pusher syndrome, validity, reliability, internal consistency, responsiveness, sensitivity, specificity, posture and stroke. Databases were searched from their inception to October 2008. REVIEW METHODS: Abstracts were selected by one author. A panel of experts then determined which should be included in this review. Five abstracts were reviewed and the panel agreed to omit one abstract because those authors did not write a full manuscript. The panel critiqued manuscripts according to predetermined criteria about clinical and clinimetric properties. RESULTS: Four manuscripts referencing three tools for examining lateropulsion were found. Validity and reliability data support the clinical use of the Scale for Contraversive Pushing, the Modified Scale for Contraversive Pushing and the Burke Lateropulsion Scale. The Scale for Contraversive Pushing has the most extensive testing of clinimetric properties. The other tools show promising preliminary evidence of clinical and research utility. More testing is needed with larger, more diverse samples. REVIEWERS' CONCLUSIONS: The Scale for Contraversive Pushing, the Modified Scale for Contraversive Pushing and the Burke Lateropulsion Scale are reliable and valid measures with good clinical applicability. Larger, more varied samples should be used to better delineate responsiveness and other clinimetric properties of these examination tools

Sensitivity analysis of vertical perception tDCS using Finite Element Analysis.

<p>Bilateral temporal-parietal region stimulation with 5cm diameter electrodes was modeled in “two subjects,” each using two different conductivity sets, “Standard” and “H1”. Electric field (V/m) and current density (A/m²) were predicted for 2mA of stimulation. Columns 1 and 2 demonstrate the relative electrode position with current streamlines, whose radii are proportional to the logarithm of current density. The magenta ring represents the location of the axial slice in the far right column. Simulations using standard conductivity values resulted in diffuse electric field throughout the parietal lobe, while H1 conductivity values resulted in more concentrated cortical stimulation. Across two head models and two conductivity sets, the most reliable cortical and subcortical regions of influence were under the electrodes.</p

Mean and standard error of SVV scores for tDCS conditions at different times.

<p>Before tDCS (T0 = Baseline), during tDCS (T1 = 0.5min: 30 seconds after the start of stimulation; T2 = 15min: 15 minutes after the beginning of stimulation); and after tDCS (T3 = 20min: immediately after; T4 = 35min: 15 minutes after the end of stimulation; T5 = 50min: 30 minutes after the stimulation).</p

Descriptive data of SVV for each time and condition, and comparisons between pairs of conditions for time-points of SVV assessment.

<p>Descriptive data of SVV for each time and condition, and comparisons between pairs of conditions for time-points of SVV assessment.</p

Comparisons between time-points of SVV assessment for the tDCS conditions.

<p>Comparisons between time-points of SVV assessment for the tDCS conditions.</p

“Bucket method” for measuring Subjective Visual Vertical.

<p>Note the exterior digital inclinometer (left) and interior line reference.</p