Purchase this article with an account.
Francesca Perini, Luigi Cattaneo, Marisa Carrasco, Jens Schwarzbach; Occipital TMS facilitates and hinders visual perception via a contrast gain mechanism. Journal of Vision 2011;11(11):1200. doi: 10.1167/11.11.1200.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The effects of transcranial magnetic stimulation (TMS) can vary radically according to the state in which the brain is at the moment of stimulation. Two possible mechanisms by which single magnetic stimuli produce different effects according to the initial activation state of targeted neurons have been proposed: (i) TMS suppresses neural signals and (ii) TMS adds random neuronal activity. Here we explore these two hypotheses by investigating the psychophysical effects of TMS on early visual cortex under different conditions of contrast adaptation. We tested six participants in an orientation discrimination task, where neuronal activation of visual cortex before each trial was altered through adaptation either to a blank screen or to two flickering gratings. In half of the trials a single TMS pulse was delivered simultaneously with target. Adaptation decreased performance. The effect of TMS on performance depended on the state of adaptation: it increased contrast sensitivity after adaptation but reduced it in the absence of adaptation. Correspondingly, TMS had a differential effect on threshold according to adaptation: it increased thresholds without adaptation but decreased them after adaptation. Notably, TMS did not affect the asymptote in any condition. The fact that TMS changed thresholds but not asymptotes suggests that TMS acts at the input level of neuronal processing, i.e. at the synaptic level. Moreover, the finding that TMS had opposite effects on the two adaptation conditions, even at the same performance levels at threshold, contradicts the hypothesis of TMS state-dependency as a product of noise increase.
This PDF is available to Subscribers Only