Transient visual field defects induced by transcranial magnetic stimulation over human occipital pole

Sabine Kastner, Iris Demmer, Ulf Ziemann

Research output: Contribution to journalArticle

104 Scopus citations

Abstract

Transient visual field defects (VFDs) and phosphenes were induced in normal volunteers by means of transcranial magnetic stimulation (TMS) using a circular magnetic coil of 12.5 cm diameter placed with its lower rim 2-4 cm above the inion in the midline. Subjects had to detect small, bright dots presented randomly for 14 ms in one of 60 locations on a computer screen resulting in a plot of the central 9°of the visual field. In 8 of 17 subjects, transient VFDs were inducible at peak magnetic field strenghts of 1.1-1.4 T. In the central 1-3°, detection of targets was impaired in both the upper and lower visual field, whereas at 4-9°large parts of only the lower visual field were affected with a sharp cut-off along the horizontal meridian. Targets at 1°in the lower field were affected with lower TMS intensities than corresponding locations in the upper or peripheral locations in the lower field. Detection of central targets was affected at more caudal stimulation sites than detection of peripheral targets. Phosphenes were elicitable in 14 of 17 subjects at clearly lower field strengths of 0.6-1.0 T. Many subjects perceived chromatophosphenes. From a discussion of the literature on patients with VFDs and the known topography of the human visual system, it is concluded that the transient VFDs at 1-3°are probably due to stimulation of both striate cortex (V1) and extrastriate areas (V2/V3), while VFDs in the lower visual field at eccentricities 4-9°are due to stimulation of V2/V3 but not V1.

Original languageEnglish (US)
Pages (from-to)19-26
Number of pages8
JournalExperimental Brain Research
Volume118
Issue number1
DOIs
StatePublished - Feb 9 1998
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)

Keywords

  • Human
  • Phosphenes
  • Transcranial magnetic brain stimulation
  • Visual field defect
  • Visual system

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