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Motor and phosphene thresholds: a transcranial magnetic stimulation correlation study
L M Stewart1, V Walsh, J C Rothwell
1Institute of Cognitive Neuroscience, 17 Queen Square, London WC1N 3AR, UK. l.stewart@ucl.ac.uk
Neuropsychologia
|February 13, 2001
Summary
Motor threshold is not a reliable indicator of visual cortex excitability. Visual phosphene thresholds are stable but more variable, suggesting they may be a better standard for transcranial magnetic stimulation (TMS) studies in the visual system.
Area of Science:
- Neuroscience
- Neurophysiology
- Visual System
Background:
- Motor threshold is a standard index for cortical sensitivity in transcranial magnetic stimulation (TMS).
- Its applicability to non-motor cortical areas, like the visual system, is uncertain.
- Phosphene threshold has been suggested as a potential alternative for visual system TMS studies.
Purpose of the Study:
- To evaluate the stability of visual phosphene thresholds.
- To determine if visual phosphene thresholds correlate with motor thresholds.
- To assess the suitability of motor thresholds as a general index of cortical excitability.
Main Methods:
- Single-pulse transcranial magnetic stimulation (TMS) was used.
- Visual phosphene thresholds and motor thresholds were measured in 15 participants.
- Measurements were repeated in 7 participants after one week.
Main Results:
- Visual phosphene thresholds demonstrated within-subject stability across sessions.
- Visual phosphene thresholds exhibited greater variability compared to motor thresholds.
- No significant correlation was found between visual phosphene thresholds and motor thresholds.
Conclusions:
- Motor thresholds are not a reliable indicator of visual cortex excitability.
- Motor thresholds may also be inappropriate for assessing excitability in other non-motor brain regions.
- Phosphene thresholds are proposed as a potential standard for visual TMS experiments to allow for inter-individual comparisons.