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This Article Full Text Full Text (PDF) All Versions of this Article: 565/2/659    most recent jphysiol.2004.080184v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fierro, B. Articles by Pascual-Leone, A. Search for Related Content PubMed PubMed Citation Articles by Fierro, B. Articles by Pascual-Leone, A.

¹ Neurophysiological Unit, University of Palermo, Palermo, Italy
² Center for Non-Invasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA, USA

The aim of the present study was to explore further the effects of light deprivation (LD) on visual cortex excitability. Healthy subjects reporting reliable induction of phosphenes by occipital transcranial magnetic stimulation (TMS) underwent 60 min of complete LD. Phosphene threshold (PT) was measured before (T₀), after 45 min (T₁) and 60 min (T₂) of LD, and then every 10 min after light re-exposure until recovery to T₀ values. Repetitive TMS (rTMS) (at 1 or 10 Hz) was applied in separate sessions during the last 15 min of LD. PTs significantly decreased after 45 min of LD. rTMS differentially modified the effects of 60 min LD on PTs depending on stimulation frequency. One hertz rTMS did not change the decreasing of PT values as observed in baseline condition, but significantly prolonged the time to recover T₀ PT values after light re-exposure. By contrast, 10 Hz rTMS significantly increased PT and the time to recover T₀ PT values after light re-exposure was shortened. The results of this study show that the modulatory effects of different rTMS frequencies on visual cortex critically depend on the pre-existing excitability state of inhibitory and facilitatory circuits, and provide novel insights into the neurophysiological changes that take place in the visual cortex following functional visual deafferentation.

(Received 4 December 2004; accepted after revision 9 March 2005; first published online 10 March 2005)
Corresponding author F. Brighina: Neurophysiological Unit, University of Palermo, Via G. La Loggia, 1, 90128, Palermo, Italy. Email: fbrighina{at}neuro.unipa.it

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