Abstract
[Background]. Our brains have limited bioenergetic resources. Visual adaptation and attention are two distinct mechanisms employed to efficiently allocate limited neural resources: Adaptation selectively reduces, whereas covert attention selectively enhances neural responses. Psychophysical experiments have shown that both adaptation and covert exogenous (involuntary) attention modulate contrast sensitivity, and that after adaptation attention restores sensitivity. Transcranial magnetic stimulation (TMS) has shown brain state-dependent effects and revealed that early visual cortex plays a causal role in adaptation and exogenous attention– tested in independent studies. Here we studied the effect of TMS on both simultaneously, to investigate whether and how adaptation modulates the effects of exogenous attention in early visual cortex. [Methods]. Observers performed an orientation discrimination task under adaptation and non-adaptation conditions. After a valid, neutral, or invalid exogenous cue, two Gabor patches were presented at symmetrical locations in the left and right visual fields (at the observer’s phosphene location and its mirror location in the other hemifield). A response cue indicated the location of the stimulus to be discriminated. Double-pulse TMS was applied at the occipital pole at the corresponding location where one of two stimuli were presented. In target-stimulated trials, the response cue matched the stimulated region; in distractor-stimulated (control) trials, they mismatched. [Results]. In the non-adaptation condition, the typical effect of exogenous attention (response gain) observed in the distractor-stimulated condition was eliminated in the target-stimulated condition. But in the adaptation condition, the attention effect remained in both distractor-stimulated and target-stimulated conditions. [Conclusion]. Without adaptation, we replicated the response gain effect of exogenous attention and its elimination with occipital TMS. However, after adaptation, the same occipital TMS did not eliminate the effect of exogenous attention. This study reveals that in the adapted state, even with TMS to early visual cortex, exogenous attention still restores sensitivity.