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Marie-Helene Grosbras, Jason Lauder, Nienke Hoogenboom; Frontal Eye Field modulation of Parieto-Occipital visual processing; An online TMS EEG study. Journal of Vision 2009;9(8):760. doi: 10.1167/9.8.760.
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A single pulse of transcranial magnetic stimulation (TMS) applied over the frontal eye field (FEF) can facilitate the subsequent detection of near-threshold stimuli (Grosbras and Paus, 2003) or increase the excitability of other visual regions (Silvanto et al., 2005). How FEF TMS influences cortical processes remains elusive, however. Here we aim to combine electro-encephalography (EEG) and single pulse TMS to explore the timing of the modulation of EEG as well as potential changes in the oscillatory activity.
Five subjects viewed gratings briefly flashed in their lower left or right half visual field while we recorded EEG. In some trials we applied single-pulse TMS over the right FEF or a control site (vertex) at three latencies relative to visual onset: -100, 0 and 50ms. In some trials we applied TMS without any visual stimulation. We excluded from the analysis the 30ms during which TMS artifact occurred. We analyzed (1) Event-Related Potentials (2) Power in alpha, beta, lower gamma and upper gamma frequency bands during the 500ms before and after visual stimulus onset.
We observed higher P300 amplitude for FEF- than for vertex TMS.
When no visual stimulation was present we observed a decrease in alpha power after TMS, larger for FEF stimulation than vertex and for the right than the left hemisphere. No univoqual effect was observed in other frequency bands. When a visual stimulus was present, FEF TMS applied 50 ms after a left target specifically increased alpha synchronization.
The TMS-induced changes in evoked visual response occurred at the same time as effects of attention have been observed, and are similar to what Taylor and al. (2006) reported with FEF rTMS. The reduction in background alpha synchronization in visual cortex is reminiscent of desynchronization during attention orienting and in line with a role of FEF in top-down visual control.
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