Correlation between motor and phosphene thresholds: A transcranial magnetic stimulation study

Choi Deblieck, Benjamin Thompson, Marco Iacoboni, Allan D. Wu

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

Transcranial magnetic stimulation (TMS) has become a common tool for the brain mapping of a wide variety of cognitive functions. Because TMS over cortical regions of interest other than motor cortex often does not produce easily observable effects, the ability to calibrate TMS intensity for stimulation over nonmotor regions can be problematic. Previous studies reported no correlation between motor thresholds (MT) over the motor cortex and phosphene thresholds (PT) over the visual cortex. However, different thresholding methods, lighting, and eye-closure conditions were used to determine MT and PT. We investigated the correlation between resting MT (rMT), active MT (aMT), and PT in 27 dark-adapted healthy volunteers. All thresholds were measured with eyes-open in the dark and determined by gradually reducing stimulation intensity downward. All subjects had aMT and rMT; 21 subjects had measurable PT. rMT was 70.4% ± 9.8% (mean ± SD of maximum stimulator output); aMT was 61.1% ± 7.9%; PT was 82.2% ± 10.1%. A significant positive correlation was found between aMT and PT (r = 0.53; P = 0.014) with a trend toward correlation between rMT and PT (r = 0.43; P = 0.052). Our results suggest that sensitivity to TMS over visual and motor cortices may be correlated under similar thresholding procedures. They also provide a rationale for the use of easily obtained aMT to calibrate TMS intensities in brain mapping studies that employ TMS in cortical regions besides motor cortex.

Original languageEnglish (US)
Pages (from-to)662-670
Number of pages9
JournalHuman Brain Mapping
Volume29
Issue number6
DOIs
StatePublished - Jun 2008
Externally publishedYes

Keywords

  • Cortical excitability
  • Motor threshold (MT)
  • Phosphene threshold (PT)
  • Transcranial magnetic stimulation (TMS)

ASJC Scopus subject areas

  • Anatomy
  • Radiological and Ultrasound Technology
  • Radiology Nuclear Medicine and imaging
  • Neurology
  • Clinical Neurology

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