Slowing down alpha oscillations to enhance endogenous time perception with tACS

Time perception is one fundamental ability for human survival and everyday life, and it holds potential as a marker for psychopathology assessment and early intervention. Neural oscillations, particularly alpha oscillations, have been proposed as a key mechanism underlying the temporal organization of perception. However, there is limited causal evidence regarding how brain oscillations regulate timing processes and whether non-invasive brain stimulation can modulate the precision of timing by manipulating endogenous alpha rhythm. In this study, we investigated the causal relationship between alpha oscillations and time perception by employing tACS over occipital cortex, whereas participants performed a self-initiated sub-second timing task. tACS was delivered with different stimulation protocols at the individual alpha frequency (IAF), as well as the slightly slower and faster frequencies (IAF±2 Hz). Concurrently, EEG signals were recorded pre- and post-tACS during the tasks to provide direct electrophysiological evidence at various stages of the timing process and elucidate neural responses to tACS effects. The results demonstrated that IAF can predict individual timing precision. tACS with lower frequency (IAF-2Hz) significantly enhanced timing precision compared to tACS with IAF and IAF+2Hz which had no effect on timing behavior. Furthermore, slower tACS not only specifically modulated phase changes in alpha activity prior to timing initiation but also altered patterns of event-related desynchronization (ERD) in alpha activity during the timing process. These findings provide causal evidence for an association between alpha-dependent neural activity and internal time processing mechanisms, and suggested the potential applications aimed at enhancing the time perception in psychopathology clinics.