P27. Acute Impact of an Extremely Low Frequency Magnetic Stimulus on Human Neurophysiological Function - Magnetophosphene perception

Background: Magnetophosphenes are classified as colourless, flickering lights that are perceived with closed eyes in the dark, and upon exposure to a magnetic field (MF). Uncertainties exist involving the MF threshold for magnetophosphene perception. Methods: Forty subjects will be enrolled in this experiment aiming to provide a frequency-response curve of magnetophosphene perception under MF exposure. Subjects will sit in a whole head MF exposure device wearing a 64-channel MRI-compatible EEG cap. Subjects will be exposed to a MF with a frequency of 5-300 Hz, in the form of an increasing flux density ramp (increasing magnetic field flux density from 0-100 mT), until phosphene perception is achieved. A button press will indicate the threshold of magnetophosphene perception. Experimental outcomes will be compared using standard repeated within-subjects ANOVAs with a between-subject factor. Results: EEG data will be continuously recorded and a time series analysis in the time and frequency domains will be performed on the three occipital electrodes (O1, O2, Oz) for each frequency condition. The expected results will provide a frequency response curve for magnetophosphene perception upon exposure to a MF of frequencies ranging from 5-300 Hz. Discussion & Conclusion: We hypothesize that retinal rod cells are responsible for this phenomenon, however, it is possible that perception of coloured phosphenes at higher frequencies indicates cone activation. Interdisciplinary Reflection: This research is crucial in allowing for the refinement of international guidelines to protect workers and the public from MF adverse effects, and it will offer the potential for diagnostic and therapeutic applications

Magnetic Field Frequency-Response for Human Magnetophosphene Perception and Associated EEG Modulations

Background: Magnetophosphenes are among the most reliably reported effects resulting from magnetic induction. The frequency dependence of the perception threshold is crucial, as guideline agencies use this information to set exposure limits whose purpose is to protect public and workers. Objective:Establish the magnetophosphene perception thresholds throughout the extremely low frequency range (0-300 Hz) and evaluate the use of EEG as a biomarker. Hypothesis:Perception thresholds will be lowest at ~30 Hz. EEG occipital alpha power will decrease upon perception. Methods:60 participants were exposed to homogenous magnetic fields up to 300 Hz, and 70 mT. EEG alpha power was calculated during each exposure. Results:Magnetophosphene thresholds were found to be lowest (16.92 mTrms) at 35 Hz. Thresholds established at powerline frequencies. Magnetophosphene perception was not accompanied by a change in EEG activity. Conclusions:Magnetophosphenes frequency dependence is consistent with previous studies involving magnetic stimuli. Occipital EEG alpha power is not an appropriate biomarker of magnetophosphene perception

Regulation of Balance After Spinning: A Comparison Between Figure Skaters and Controls

Introduction: The purpose of the present study was to compare the balance performance of control subjects and varsity figure skaters after spinning on a turntable for 6 seconds. It was hypothesized figure skaters would demonstrate better balance control after spinning. Methods: 9 female figure skaters and 9 female control subjects stood as still as possible for 15 seconds on a Kistler force plate during both a control condition and after spinning for 6 seconds on a turntable. Balance performance was quantified by the percentage of total time the center of pressure (CoP) was within a 5mm radius of the center of their base of support (BoS). Results: In the control condition, figure skaters and control participants did not have significantly different balance ability. In the post-spin condition, figure skaters were significantly better at maintaining their CoP within a smaller area. Conclusions: These results are valuable from a training and coaching perspective because they suggest that balance performance after spinning can be improved with training