Silva, A. E. | bioRxiv Science

bioRxiv2019

Multi-session visual cortex transcranial random noise stimulation in adults with amblyopia

PurposeWe tested the hypothesis that five daily sessions of visual cortex transcranial random noise stimulation would improve contrast sensitivity, crowded and uncrowded visual acuity in adults with amblyopia. MethodsNineteen adults with amblyopia (44.2 {+/-} 14.9yrs, 10 female) were randomly allocated to active or sham tRNS of the visual cortex (active, n = 9; sham, n = 10). tRNS was delivered for 25 minutes across five consecutive days. Monocular contrast sensitivity, uncrowded and crowded visual acuity were measured before, during, 5 minutes and 30 minutes post stimulation on each day. ResultsActive tRNS significantly improved contrast sensitivity and uncrowded visual acuity for both amblyopic and fellow eyes whereas sham stimulation had no effect. An analysis of the day by day effects revealed large within session improvements on day 1 for the active group that waned across subsequent days. No long-lasting (multi-day) improvements were observed for contrast sensitivity, however a long-lasting improvement in amblyopic eye uncrowded visual acuity was observed for the active group. This improvement remained at 28 day follow up. However, between-group differences in baseline uncrowded visual acuity complicate the interpretation of this effect. No effect of tRNS was observed for amblyopic eye crowded visual acuity. ConclusionsIn agreement with previous non-invasive brain stimulation studies using different techniques, tRNS induced short-term contrast sensitivity improvements in adult amblyopic eyes, however, multiple sessions of tRNS did not lead to enhanced or long-lasting effects for the majority of outcome measures.

neuroscience↗

bioRxiv2019

Continuous theta burst TMS of area MT+ impairs attentive motiontracking.

Attentive motion tracking deficits, measured using multiple object tracking (MOT) tasks, have been identified in a number of visual and neurodevelopmental disorders such as amblyopia and autism. These deficits are often attributed to the abnormal development of high-level attentional networks. However, neuroimaging evidence from amblyopia suggests that reduced MOT performance can be explained by impaired function in motion sensitive area MT+ alone. To test the hypothesis that MT+ plays an important role in MOT, we assessed whether modulation of MT+ activity using continuous theta burst stimulation (cTBS) influenced MOT performance in participants with normal vision. An additional experiment involving numerosity judgements of MOT stimulus elements was conducted to control for non-specific effects of MT+ cTBS on psychophysical task performance. The MOT stimulus consisted of 4 target and 4 distractor dots and was presented at 10{degrees} eccentricity in the right or left hemifield. Functional MRI-guided cTBS was applied to left MT+. Participants (n = 13, age:27 {+/-} 3) attended separate active and sham cTBS sessions where the MOT task was completed before, 5 mins post and 30 mins post cTBS. Active cTBS significantly impaired MOT task accuracy relative to baseline for the right (stimulated) hemifield 5 mins (10 {+/-} 2% reduction; t12 = 1.95, p = 0.03) and 30 mins (14 {+/-} 3% reduction; t12 = 2.96, p = 0.01) post stimulation. No impairment occurred within the left (control) hemifield after active cTBS or for either hemifield after sham cTBS. Numerosity task performance was unaffected by cTBS. These results highlight the importance of lower-level motion processing for MOT and suggest that abnormal function of MT+ alone is sufficient to cause a deficit in MOT task performance.

neuroscience↗