Phosphene induction and motor cortex excitability: neuronavigated transcranial magmetic stimulation (TMS) study
Abstract
The aim of the study was to investigate the relationship between excitability of motor and visual cortex. Using neuronavigated single-pulse (SP) and paired-pulse (PP) transcranial magnetic stimulation (TMS, Magstim Rapid) over right visual cortex the phosphene thresholds were measured in 11 subjects.
Standard methodology was used to identify the motor threshold (MT). In all subjects the phosphenes were induced by both SP (median = 48%, IQR = 44,5-52,0) and PP (medián = 44%, IQR=39,5-48,0) TMS.
The PP phosphene thresholds were lower than the SP thresholds (U = 28,0, p <= 0,05). We found the positive correlation between MT and SP phosphene threshold (r = 0,597, p <= 0,05) but not for MT and PP.
The distance of coil position from the brain surface did not correlate with MT, SP nor PP phosphene threshold. Our findings confirm the relationship between MT a phosphene threshold measured by the use of single-pulse technique over right occipital cortex with horizontal position of coil.
The propose methodology should be used in experiments where cortical excitability of visual cortex is measured. SP phosphene threshold is proposed as a potential standard for inter-individual comparison in visual TMS experiments in patients.