No correlation between moving phosphene and motor thresholds: a transcranial magnetic stimulation study

Area of Science:

• Neuroscience
• Visual Perception
• Cortical Excitability

Background:

• Moving phosphenes, perceived during V5 stimulation via transcranial magnetic stimulation (TMS), are debated for their stability and utility as an index of V5 cortical excitability.
• Motor thresholds (MTs) are currently the standard for assessing global cortical excitability.
• Stationary phosphene thresholds (PTs) have shown promise as alternatives for primary visual cortex stimulation.

Purpose of the Study:

• To investigate the temporal stability of moving phosphenes.
• To determine if moving phosphene thresholds (PTs) correlate with motor thresholds (MTs).
• To assess the suitability of PTs as a measure of V5 cortical excitability.

Main Methods:

• Used paired-pulse TMS to measure stationary and moving phosphene thresholds (PTs).
• Applied single-pulse TMS to measure motor thresholds (MTs) in 11 subjects.
• Retested PTs in 9 subjects 5-7 days later to assess temporal stability.

Main Results:

• Both stationary and moving PTs demonstrated high temporal stability within subjects across sessions.
• Stationary and moving PTs exhibited a strong inter-correlation.
• No significant correlation was found between phosphene thresholds (PTs) and motor thresholds (MTs).

Conclusions:

• Moving phosphene thresholds are stable and reliable measures for assessing the excitability of the visual cortex (V5).
• Phosphene thresholds (PTs) and motor thresholds (MTs) are not interchangeable and do not generalize across different cortical areas.
• Recommends using specific measures: PTs for visual experiments and MTs for motor experiments.