Distinct Alpha Networks Modulate Different Aspects of Perceptual Decision-Making.

Why do we sometimes perceive a faint stimulus but miss it at other times? One explanation is that conscious perception fluctuates with the brain's internal state, influencing how external stimuli are processed. Ongoing brain oscillations in the alpha band (8-13 Hz), thought to reflect neuronal excitability levels and play a role in functional inhibition, have been shown as a key contributor to such perceptual variability. Under high alpha conditions, faint stimuli are more likely to be missed. Some studies suggested alpha oscillations modulate perceptual criterion , shifting the threshold for interpreting sensory information; while others (including our prior work) suggested alpha modulates sensitivity , changing the precision of sensory encoding. Few studies observed modulations in both metrics, making these results appear mutually exclusive. Most studies have focused solely on overall alpha activity-whether within a region of interest or across the whole brain-and overlooked the coexistence of multiple distinct alpha networks, which fluctuate in terms of predominance and adapt to behavioural demands. Hence, it remained unclear whether different networks' contributions to perception vary with their momentary state. Here, aiming to characterize how different alpha networks influence perceptual decision-making, we analyzed magnetoencephalography (MEG) data recorded while participants performed a visual detection task with threshold-level stimuli. We found that while the visual alpha network modulates perceptual sensitivity, the sensorimotor alpha network modulates criterion in perceptual decision-making. These findings reconcile previous conflicting results and highlight the functional diversity of alpha networks in shaping perception.