Abstract
Attention facilitates the gating of information from the sending brain area to the receiving areas, with this being achieved by dynamical changes in effective connectivity, which refers to the directional influences between cortical areas. To probe the effective connectivity and cortical excitability modulated by covertly shifted attention, transcranial magnetic stimulation (TMS) was used to directly perturb the right retinotopic visual cortex with respect to attended and unattended locations, and the impact of this was tracked from the stimulated area to other areas by concurrent use of electroencephalography (EEG). TMS to the contralateral visual hemisphere led to a stronger evoked potential than stimulation to the ipsilateral hemisphere. Moreover, stronger beta- and gamma-band effective connectivities assessed as time-delayed phase synchronizations between stimulated areas and other areas were observed when TMS was delivered to the contralateral hemisphere. These effects were more enhanced when they preceded more prominent alpha lateralization, which is known to be associated with attentional gating. Our results indicate that attention-regulated cortical feedforward effective connectivity can be probed by TMS-EEG with direct cortical stimulation, thereby bypassing thalamic gating. These results suggest that cortical gating of the feedforward input is achieved by regulating the effective connectivity in the phase dynamics between cortical areas.
Highlights
In our daily lives, we are bombarded with sensory inputs far beyond our information processing capacity
transcranial magnetic stimulation (TMS)-EEG has allowed demonstration of the dynamical properties of effective connectivity by showing how the propagation patterns of TMS evoked potentials could be used to differentiate between sleep and wakeful states[31], as well as the propagation of TMS-induced transient phase resetting of ongoing oscillations from visual to motor areas[35]
TMS was applied to the visual cortex of the ipsilateral or contralateral hemisphere with respect to the attention direction (Fig. 1b)
Summary
We are bombarded with sensory inputs far beyond our information processing capacity. Bestmann and colleagues tested this issue by direct cortical stimulation of the visual cortex to ensure that the stimulus bypassed the thalamic gating through the retinogeniculate pathway[11] They showed that spatial attention facilitates awareness of phosphenes induced by TMS, and their results may reflect an increase in cortical excitability in the visual cortex. In a study using a covert visual attention paradigm, Doesburg and colleagues showed that gamma-band synchronization between the contralateral occipital electrode and other electrodes increased during attention maintenance[23,28] Their results suggested that long-range gamma synchronization helps establish a transient network that promotes information transmission from modality-specific cortical areas to other cortical areas. We investigated how local cortical excitability and/or inter-areal connectivity changes when the preceding alpha power is low or high, by directly perturbing the ipsilateral or contralateral V1/ V2 with respect to the attention direction
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