Abstract
The measurement of the Critical Flicker Frequency threshold is used to study the visual temporal resolution in healthy subjects and in pathological conditions. To better understand the role played by different cortical areas in the Critical Flicker Frequency threshold perception we used continuous Theta Burst Stimulation (cTBS), an inhibitory plasticity-inducing protocol based on repetitive transcranial magnetic stimulation. The Critical Flicker Frequency threshold was measured in twelve healthy subjects before and after cTBS applied over different cortical areas in separate sessions. cTBS over the left inferior parietal lobule altered the Critical Flicker Frequency threshold, whereas cTBS over the left mediotemporal cortex, primary visual cortex and right inferior parietal lobule left the Critical Flicker Frequency threshold unchanged. No statistical difference was found when the red or blue lights were used. Our findings show that left inferior parietal lobule is causally involved in the conscious perception of Critical Flicker Frequency and that Critical Flicker Frequency threshold can be modulated by plasticity-inducing protocols.
Highlights
Visual temporal resolution processes in humans can be evaluated by measuring the Critical Flicker Frequency threshold (CFFt)[1,2], defined as the frequency at which a flickering light is perceived as a continuous light [3,4]
Other authors provided information on cortical areas involved in CFFt encoding by showing left inferior parietal lobule (IPL) activation [21], a cortical area known for its important role in visual awareness [22,23]
Main experiments: effects of continuous Theta Burst Stimulation (cTBS) on CFFt Repeated measures ANOVA showed a significant interaction of factors "cortical areas" and ‘‘time’’ for the ascending method-red light (F(6,66) = 4.92; p,0.01), descending method-red light (F(6,66) = 2.24; p = 0.04), ascending method-blue light (F(6,66) = 2.29; p = 0.04) and descending method-blue light (F(3.01,33.1) = 3.07; p = 0.04)
Summary
Visual temporal resolution processes in humans can be evaluated by measuring the Critical Flicker Frequency threshold (CFFt)[1,2], defined as the frequency at which a flickering light is perceived as a continuous light [3,4]. Activity of V1, dependent on the frequency of the visual stimulation during exposure to a flickering light, has been confirmed by studies in humans with positron emission tomography (PET) [18,19] and functional magnetic resonance imaging (fMRI) [20]. It is not clear whether the activity in V1 is associated with conscious perception of a flickering light or if merely reflects early stages of visual stimuli processing. Additional information on the contribution of different cortical areas to CFFt is needed to better understand the pathophysiological mechanisms of altered temporal processing of visual stimuli reported in several neurological disorders [10,28,29,30,31,32,33,34]
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