The role of delta phase for temporal predictions investigated with bilateral parietal tACS

Previous research has shown that temporal prediction processes are associated with phase resets of low-frequency delta oscillations in a network of parietal, sensory and frontal areas during non-rhythmic sensory stimulation. Transcranial alternating current stimulation (tACS) modulates perceptually relevant brain oscillations in a frequency and phase-specific manner, allowing the assessment of their functional qualities in certain cognitive functions like temporal prediction.

We addressed the relation between oscillatory activity and temporal prediction by using tACS to manipulate brain activity in a sinusoidal manner. This enables the investigation of the relevance of low-frequency oscillations' phase for temporal prediction.

Delta tACS was applied over the left and right parietal cortex in two separate unimodal and crossmodal temporal prediction experiments. Participants judged either the visual or the tactile reappearance of a uniformly moving visual stimulus, which shortly disappeared behind an occluder. tACS was applied with six different phase shifts relative to sensory stimulation in both experiments. Additionally, a computational model was developed and analysed to elucidate oscillation-based functional principles for the generation of temporal predictions.

Only in the unimodal experiment, the application of delta tACS resulted in a phase-dependent modulation of temporal prediction performance. By considering the effect of sustained tACS in the computational model, we demonstrate that the entrained dynamics can phase-specifically modulate temporal prediction accuracy.

Our results suggest that delta oscillatory phase contributes to unimodal temporal prediction. Crossmodal prediction may involve a broader brain network or cross-frequency interactions, extending beyond parietal delta phase and the scope of our current stimulation design.