Y P O C T O N Phosphenes O D Intensive Course in E - PowerPoint PPT Presentation

Y P O C T O N Phosphenes O D Intensive Course in E Transcranial Magnetic Stimulation S A E October 2016 L P

Y P Phosphene: definition O C • From Greek phōs ‘light’ + phainein ‘to show’ T • Brief visual percept “flash of light” O N • Not caused by phototransduction O • But interpreted as visual stimuli D E S A E L P Modified from Bear, Connors, Paradiso, 1996

Y P Phosphene: causes O C • Mechanical stimulation T O – Rubbing your eyes N – “Seeing stars” from a blow to the head O – Pituitary tumor encroaching on optic chiasm D • Electrical stimulation E – Transcranial alternating current stimulation (tACS) S A – Transcranial magnetic stimulation (TMS) E L P

Y P Characteristics of TMS phosphenes O C • Subjective experience T O • Retinotopically organized N • Simple geometric shapes O • Appear as light (in D darkness or eyes closed) E S • Appear as blurring or A scotoma (eyes open) E L P From Marg & Rudiak, 1994

Y P Locating Phosphene Hotspot O C • Find the inion T • Mark point 2cm dorsal and O N 2cm lateral • Orient coil with handle O pointing laterally D – Optimal current direction is E lateral to medial (in brain) S • Phosphene should be A Optimal current direction: E lateral to medial in brain reported in contralateral L visual field P

Y P Assess Phosphene Threshold O C • Follow same procedure as motor threshold T O – Begin subthrehsold (e.g., 30% MSO) N – Increase in steps of 10 until phosphene reported O – Decrease in steps of 1-2 until occurrence < 50% D – Count only unambiguous responses E (“yes” or “no”), redo “maybe” S A E L P

Y P Considerations O C • Can be easier if subject is blindfolded T O • Have subject focus on center of visual field N – Directing attention to a part of the visual field will O decrease threshold to relative to rest of visual D field E S A E L P

Y No significant correlation between P O motor and phosphene thresholds C T O Correlation (PT vs MT) 0.75 0.70 Phosphene Threshold (% MSO) N 0.65 0.60 0.55 O 0.50 0.45 D 0.40 0.35 r 28 =0.29, p>0.1 0.30 r 16 =0.27, p>0.2 E 0.25 0.25 0.35 0.45 0.55 0.65 0.75 S Motor Threshold (% of MSO) From Gerwig et al., 2003, J Neurol Sci From Fried et al., 2011, PLoS1 A E L P

Y P Neural basis of phosphene awareness O C T O N O D E S A E L P From Taylor et al., 2010, Human Brain Mapping